An extinction event (also known as a mass extinction or biotic crisis ) is a widespread and rapid decrease in the biodiversity on Earth . Such an event is identified by a sharp fall in the diversity and abundance of multicellular organisms . It occurs when the rate of extinction increases with respect to the background extinction rate and the rate of speciation . Estimates of the number of major mass extinctions in the last 540 million years range from as few as five to more than twenty. These differences stem from disagreement as to what constitutes a "major" extinction event, and the data chosen to measure past diversity.
205-514: The Cretaceous–Paleogene ( K–Pg ) extinction event , also known as the K–T extinction , was the mass extinction of three-quarters of the plant and animal species on Earth approximately 66 million years ago. The event caused the extinction of all non-avian dinosaurs . Most other tetrapods weighing more than 25 kg (55 lb) also became extinct, with the exception of some ectothermic species such as sea turtles and crocodilians . It marked
410-737: A divergent to convergent plate boundary. The Alpine Orogeny developed in response to the collision between the African and Eurasian plates during the closing of the Neotethys Ocean and the opening of the Central Atlantic Ocean. The result was a series of arcuate mountain ranges, from the Tell - Rif - Betic cordillera in the western Mediterranean through the Alps , Carpathians , Apennines , Dinarides and Hellenides to
615-531: A paraphyletic group) by therapsids occurred around the Kungurian / Roadian transition, which is often called Olson's extinction (which may be a slow decline over 20 Ma rather than a dramatic, brief event). Another point of view put forward in the Escalation hypothesis predicts that species in ecological niches with more organism-to-organism conflict will be less likely to survive extinctions. This
820-401: A "collection" (such as a time interval) to assess the relative diversity of that collection. Every time a new species (or other taxon ) enters the sample, it brings over all other fossils belonging to that species in the collection (its " share " of the collection). For example, a skewed collection with half its fossils from one species will immediately reach a sample share of 50% if that species
1025-425: A Phanerozoic phenomenon, with merely the observable extinction rates appearing low before large complex organisms with hard body parts arose. Extinction occurs at an uneven rate. Based on the fossil record , the background rate of extinctions on Earth is about two to five taxonomic families of marine animals every million years. The Oxygen Catastrophe, which occurred around 2.45 billion years ago in
1230-664: A backdrop of decreasing extinction rates through time. Four of these peaks were statistically significant: the Ashgillian ( end-Ordovician ), Late Permian , Norian ( end-Triassic ), and Maastrichtian (end-Cretaceous). The remaining peak was a broad interval of high extinction smeared over the later half of the Devonian , with its apex in the Frasnian stage. Through the 1980s, Raup and Sepkoski continued to elaborate and build upon their extinction and origination data, defining
1435-409: A considerable period of time after a mass extinction, and which were reduced to only a few species, are likely to have experienced a rebound effect called the " push of the past ". Darwin was firmly of the opinion that biotic interactions, such as competition for food and space – the 'struggle for existence' – were of considerably greater importance in promoting evolution and extinction than changes in
1640-464: A diverse group of large predatory marine reptiles, also became extinct. Fossil evidence indicates that squamates generally suffered very heavy losses in the K–Pg event, only recovering 10 million years after it. The extinction of Cretaceous lizards and snakes may have led to the evolution of modern groups such as iguanas, monitor lizards, and boas. The diversification of crown group snakes has been linked to
1845-409: A few species of ground and water fowl, which radiated into all modern species of birds. Among other groups, teleost fish and perhaps lizards also radiated. The K–Pg extinction event was severe, global, rapid, and selective, eliminating a vast number of species. Based on marine fossils, it is estimated that 75% or more of all species became extinct. The event appears to have affected all continents at
2050-474: A general trend of decreasing extinction rates during the Phanerozoic , but as more stringent statistical tests have been applied to the accumulating data, it has been established that in the current, Phanerozoic Eon, multicellular animal life has experienced at least five major and many minor mass extinctions. The "Big Five" cannot be so clearly defined, but rather appear to represent the largest (or some of
2255-424: A high-resolution biodiversity curve (the "Sepkoski curve") and successive evolutionary faunas with their own patterns of diversification and extinction. Though these interpretations formed a strong basis for subsequent studies of mass extinctions, Raup and Sepkoski also proposed a more controversial idea in 1984: a 26-million-year periodic pattern to mass extinctions. Two teams of astronomers linked this to
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#17327662933182460-425: A hypothetical brown dwarf in the distant reaches of the solar system, inventing the " Nemesis hypothesis " which has been strongly disputed by other astronomers. Around the same time, Sepkoski began to devise a compendium of marine animal genera , which would allow researchers to explore extinction at a finer taxonomic resolution. He began to publish preliminary results of this in-progress study as early as 1986, in
2665-470: A lack of consensus on Late Triassic chronology For much of the 20th century, the study of mass extinctions was hampered by insufficient data. Mass extinctions, though acknowledged, were considered mysterious exceptions to the prevailing gradualistic view of prehistory, where slow evolutionary trends define faunal changes. The first breakthrough was published in 1980 by a team led by Luis Alvarez , who discovered trace metal evidence for an asteroid impact at
2870-524: A lingering impact winter which halted photosynthesis in plants and plankton . The impact hypothesis, also known as the Alvarez hypothesis , was bolstered by the discovery of the 180 km (112 mi) Chicxulub crater in the Gulf of Mexico 's Yucatán Peninsula in the early 1990s, which provided conclusive evidence that the K–Pg boundary clay represented debris from an asteroid impact . The fact that
3075-440: A long-term stress is compounded by a short-term shock. Over the course of the Phanerozoic , individual taxa appear to have become less likely to suffer extinction, which may reflect more robust food webs, as well as fewer extinction-prone species, and other factors such as continental distribution. However, even after accounting for sampling bias, there does appear to be a gradual decrease in extinction and origination rates during
3280-399: A new wave of studies into the dynamics of mass extinctions. These papers utilized the compendium to track origination rates (the rate that new species appear or speciate ) parallel to extinction rates in the context of geological stages or substages. A review and re-analysis of Sepkoski's data by Bambach (2006) identified 18 distinct mass extinction intervals, including 4 large extinctions in
3485-813: A paper which identified 29 extinction intervals of note. By 1992, he also updated his 1982 family compendium, finding minimal changes to the diversity curve despite a decade of new data. In 1996, Sepkoski published another paper which tracked marine genera extinction (in terms of net diversity loss) by stage, similar to his previous work on family extinctions. The paper filtered its sample in three ways: all genera (the entire unfiltered sample size), multiple-interval genera (only those found in more than one stage), and "well-preserved" genera (excluding those from groups with poor or understudied fossil records). Diversity trends in marine animal families were also revised based on his 1992 update. Revived interest in mass extinctions led many other authors to re-evaluate geological events in
3690-531: A period in the earliest part of the Cenozoic of decreased acanthomorph diversity, although acanthomorphs diversified rapidly after the extinction. Teleost fish diversified explosively after the mass extinction, filling the niches left vacant by the extinction. Groups appearing in the Paleocene and Eocene epochs include billfish, tunas, eels, and flatfish. There is limited evidence for extinction of amphibians at
3895-417: A planktonic strategy of reproduction (numerous eggs and planktonic larvae), which would have been devastated by the K–Pg extinction event. Additional research has shown that subsequent to this elimination of ammonoids from the global biota, nautiloids began an evolutionary radiation into shell shapes and complexities theretofore known only from ammonoids. Approximately 35% of echinoderm genera became extinct at
4100-552: A proliferation of aquatic ferns from the genus Azolla , resulting in the sequestering of large amounts of CO 2 from the atmosphere by the plants. From this time until about 34 Ma, there was a slow cooling trend known as the Middle-Late Eocene Cooling. As temperatures dropped at high latitudes the presence of cold water diatoms suggests sea ice was able to form in winter in the Arctic Ocean, and by
4305-489: A range of different species provide definitive evidence for the persistence of archaic birds to within 300,000 years of the K–Pg boundary. The absence of these birds in the Paleogene is evidence that a mass extinction of archaic birds took place there. The most successful and dominant group of avialans , enantiornithes , were wiped out. Only a small fraction of ground and water-dwelling Cretaceous bird species survived
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#17327662933184510-531: A rapid surge of diversification in the early Paleogene, as survivors of the Cretaceous–Paleogene extinction event took advantage of empty ecological niches left behind by the extinction of the non-avian dinosaurs, pterosaurs, marine reptiles, and primitive fish groups. Mammals continued to diversify from relatively small, simple forms into a highly diverse group ranging from small-bodied forms to very large ones, radiating into multiple orders and colonizing
4715-523: A result of cooling temperatures in the early Paleocene . Approximately 46% of diatom species survived the transition from the Cretaceous to the Upper Paleocene, a significant turnover in species but not a catastrophic extinction. The occurrence of planktonic foraminifera across the K–Pg boundary has been studied since the 1930s. Research spurred by the possibility of an impact event at
4920-921: A result, rather than a cause, of the plate tectonic forces that led to the propagation of rifting from the Central to the North Atlantic. Mountain building continued along the North America Cordillera in response to subduction of the Farallon plate beneath the North American Plate. Along the central section of the North American margin, crustal shortening of the Cretaceous to Paleocene Sevier Orogen lessened and deformation moved eastward. The decreasing dip of
5125-439: A result, they are likely to cause the climate to oscillate between cooling and warming, but with an overall trend towards warming as the carbon dioxide they emit can stay in the atmosphere for hundreds of years. Paleogene The Paleogene Period ( IPA : / ˈ p eɪ l i . ə dʒ iː n , - l i . oʊ -, ˈ p æ l i -/ PAY -lee-ə-jeen, -lee-oh-, PAL -ee- ; also spelled Palaeogene or Palæogene )
5330-523: A separate event from the P–T extinction; if so, it would be larger than some of the "Big Five" extinction events. The End Cretaceous extinction, or the K–Pg extinction (formerly K–T extinction) occurred at the Cretaceous ( Maastrichtian ) – Paleogene ( Danian ) transition. The event was formerly called the Cretaceous-Tertiary or K–T extinction or K–T boundary; it is now officially named
5535-451: A small phylum of marine invertebrates, survived the K–Pg extinction event and diversified during the early Paleocene. The numbers bivalve genera exhibited significant diminution after the K–Pg boundary. Entire groups of bivalves, including rudists (reef-building clams) and inoceramids (giant relatives of modern scallops ), became extinct at the K–Pg boundary, with the gradual extinction of most inoceramid bivalves beginning well before
5740-508: A species' true extinction must occur after its last fossil, and that origination must occur before its first fossil. Thus, species which appear to die out just prior to an abrupt extinction event may instead be a victim of the event, despite an apparent gradual decline looking at the fossil record alone. A model by Foote (2007) found that many geological stages had artificially inflated extinction rates due to Signor-Lipps "backsmearing" from later stages with extinction events. Other biases include
5945-483: A study published in 2018, from about 56 to 48 Ma, annual air temperatures over land and at mid-latitude averaged about 23–29 °C (± 4.7 °C). For comparison, this was 10 to 15 °C higher than the current annual mean temperatures in these areas. This rapid rise in global temperatures and intense greenhouse conditions were due to a sudden increase in levels of atmospheric carbon dioxide (CO 2 ) and other greenhouse gases . An accompanying rise in humidity
6150-586: A time interval, and sampling time intervals in sequence, can together be combined into equations to predict extinction and origination with less bias. In subsequent papers, Alroy continued to refine his equations to improve lingering issues with precision and unusual samples. McGhee et al. (2013), a paper which primarily focused on ecological effects of mass extinctions, also published new estimates of extinction severity based on Alroy's methods. Many extinctions were significantly more impactful under these new estimates, though some were less prominent. Stanley (2016)
6355-661: Is a geologic period and system that spans 43 million years from the end of the Cretaceous Period 66 Ma (million years ago) to the beginning of the Neogene Period 23.03 Ma. It is the first period of the Cenozoic Era , the tenth period of the Phanerozoic and is divided into the Paleocene , Eocene , and Oligocene epochs. The earlier term Tertiary Period was used to define the time now covered by
Cretaceous–Paleogene extinction event - Misplaced Pages Continue
6560-401: Is also the largest known extinction event for insects . The highly successful marine arthropod, the trilobite , became extinct. The evidence regarding plants is less clear, but new taxa became dominant after the extinction. The "Great Dying" had enormous evolutionary significance: on land, it ended the primacy of early synapsids . The recovery of vertebrates took 30 million years, but
6765-502: Is associated with the Cretaceous–Paleogene extinction event. The boundary is defined as the rusty colored base of a 50 cm thick clay , which would have been deposited over only a few days. Similar layers are seen in marine and continental deposits worldwide. These layers include the iridium anomaly, microtektites , nickel -rich spinel crystals and shocked quartz , all indicators of a major extraterrestrial impact. The remains of
6970-447: Is because the very traits that keep a species numerous and viable under fairly static conditions become a burden once population levels fall among competing organisms during the dynamics of an extinction event. Furthermore, many groups that survive mass extinctions do not recover in numbers or diversity, and many of these go into long-term decline, and these are often referred to as " Dead Clades Walking ". However, clades that survive for
7175-473: Is clearly marked at the species level. Statistical analysis of marine losses at this time suggests that the decrease in diversity was caused more by a sharp increase in extinctions than by a decrease in speciation . Major spatial differences existed in calcareous nannoplankton diversity patterns; in the Southern Hemisphere, the extinction was less severe and recovery occurred much faster than in
7380-535: Is estimated that 75% or more of all species on Earth vanished. However, the extinction also provided evolutionary opportunities: in its wake, many groups underwent remarkable adaptive radiation —sudden and prolific divergence into new forms and species within the disrupted and emptied ecological niches. Mammals in particular diversified in the Paleogene , evolving new forms such as horses , whales , bats , and primates . The surviving group of dinosaurs were avians,
7585-474: Is influenced by a lack of fossil records, rather than extinctions. Ostracods , a class of small crustaceans that were prevalent in the upper Maastrichtian, left fossil deposits in a variety of locations. A review of these fossils shows that ostracod diversity was lower in the Paleocene than any other time in the Cenozoic . Current research cannot ascertain whether the extinctions occurred prior to, or during,
7790-522: Is more common in asteroids than in the Earth's crust . As originally proposed in 1980 by a team of scientists led by Luis Alvarez and his son Walter , it is now generally thought that the K–Pg extinction was caused by the impact of a massive asteroid 10 to 15 km (6 to 9 mi) wide, 66 million years ago causing the Chicxulub crater , which devastated the global environment, mainly through
7995-493: Is no evidence that late Maastrichtian non-avian dinosaurs could burrow, swim, or dive, which suggests they were unable to shelter themselves from the worst parts of any environmental stress that occurred at the K–Pg boundary. It is possible that small dinosaurs (other than birds) did survive, but they would have been deprived of food, as herbivorous dinosaurs would have found plant material scarce and carnivores would have quickly found prey in short supply. The growing consensus about
8200-448: Is postulated that some early monotremes, marsupials, and placentals were semiaquatic or burrowing, as there are multiple mammalian lineages with such habits today. Any burrowing or semiaquatic mammal would have had additional protection from K–Pg boundary environmental stresses. After the K–Pg extinction, mammals evolved to fill the niches left vacant by the dinosaurs. Some research indicates that mammals did not explosively diversify across
8405-454: Is reflected in an increase in kaolinite in sediments, which forms by chemical weathering in hot, humid conditions. Tropical and subtropical forests flourished and extended into polar regions. Water vapour (a greenhouse gas) associated with these forests also contributed to the greenhouse conditions. The initial rise in global temperatures was related to the intrusion of magmatic sills into organic-rich sediments during volcanic activity in
Cretaceous–Paleogene extinction event - Misplaced Pages Continue
8610-496: Is speculated to have ushered in the Phanerozoic. In May 2020, studies suggested that the causes of the mass extinction were global warming , related to volcanism , and anoxia , and not, as considered earlier, cooling and glaciation . However, this is at odds with numerous previous studies, which have indicated global cooling as the primary driver. Most recently, the deposition of volcanic ash has been suggested to be
8815-464: Is strong evidence supporting periodicity in a variety of records, and additional evidence in the form of coincident periodic variation in nonbiological geochemical variables such as Strontium isotopes, flood basalts, anoxic events, orogenies, and evaporite deposition. One explanation for this proposed cycle is carbon storage and release by oceanic crust, which exchanges carbon between the atmosphere and mantle. Mass extinctions are thought to result when
9020-451: Is the " Pull of the recent ", the fact that the fossil record (and thus known diversity) generally improves closer to the modern day. This means that biodiversity and abundance for older geological periods may be underestimated from raw data alone. Alroy (2010) attempted to circumvent sample size-related biases in diversity estimates using a method he called " shareholder quorum subsampling" (SQS). In this method, fossils are sampled from
9225-423: Is the first to be sampled. This continues, adding up the sample shares until a "coverage" or " quorum " is reached, referring to a pre-set desired sum of share percentages. At that point, the number of species in the sample are counted. A collection with more species is expected to reach a sample quorum with more species, thus accurately comparing the relative diversity change between two collections without relying on
9430-470: Is thought that ammonites were the principal food of mosasaurs , a group of giant marine reptiles that became extinct at the boundary. The K–Pg extinction had a profound effect on the evolution of life on Earth . The elimination of dominant Cretaceous groups allowed other organisms to take their place, causing a remarkable amount of species diversification during the Paleogene Period. After
9635-521: Is thought that body sizes of placental mammalian survivors evolutionarily increased first, allowing them to fill niches after the extinctions, with brain sizes increasing later in the Eocene . Plant fossils illustrate the reduction in plant species across the K–Pg boundary. There is overwhelming evidence of global disruption of plant communities at the K–Pg boundary. Extinctions are seen both in studies of fossil pollen, and fossil leaves. In North America,
9840-597: The Bering Straits between North America and Eurasia allowing the movement of land animals between the two continents. The PETM was followed by the less severe Eocene Thermal Maximum 2 (c. 53.69 Ma), and the Eocene Thermal Maximum 3 (c. 53 Ma). The early Eocene warm conditions were brought to an end by the Azolla event . This change of climate at about 48.5 Ma, is believed to have been caused by
10045-584: The Cambrian . These fit Sepkoski's definition of extinction, as short substages with large diversity loss and overall high extinction rates relative to their surroundings. Bambach et al. (2004) considered each of the "Big Five" extinction intervals to have a different pattern in the relationship between origination and extinction trends. Moreover, background extinction rates were broadly variable and could be separated into more severe and less severe time intervals. Background extinctions were least severe relative to
10250-458: The Cambrian explosion , five further major mass extinctions have significantly exceeded the background extinction rate. The most recent and best-known, the Cretaceous–Paleogene extinction event , which occurred approximately 66 Ma (million years ago), was a large-scale mass extinction of animal and plant species in a geologically short period of time. In addition to the five major Phanerozoic mass extinctions, there are numerous lesser ones, and
10455-873: The Canadian Arctic Archipelago , Svalbard and northern Greenland resulting in the Eureka Orogeny . From c. 47 Ma, the eastern margin of Greenland was cut by the Reykjanes Ridge (the northeastern branch of the Mid-Atlantic Ridge) propagating northwards and splitting off the Jan Mayen microcontinent . After c. 33 Ma seafloor spreading in Labrador Sea and Baffin Bay gradually ceased and seafloor spreading focused along
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#173276629331810660-901: The Izu-Bonin-Mariana and Tonga-Kermadec arcs. Subduction of the Farallon Plate beneath the American plates continued from the Late Cretaceous. The Kula-Farallon spreading ridge lay to its north until the Eocene (c. 55 Ma), when the northern section of the plate split forming the Vancouver/Juan de Fuca Plate . In the Oligocene (c. 28 Ma), the first segment of the Pacific–Farallon spreading ridge entered
10865-538: The Paleoproterozoic , is plausible as the first-ever major extinction event. It was perhaps also the worst-ever, in some sense, but with the Earth's ecology just before that time so poorly understood, and the concept of prokaryote genera so different from genera of complex life, that it would be difficult to meaningfully compare it to any of the "Big Five" even if Paleoproterozoic life were better known. Since
11070-627: The San Juan River in Colorado, indicate that the animal lived during the Cenozoic, approximately 64.5 Ma (about 1 million years after the K–Pg extinction event). If their existence past the K–Pg boundary can be confirmed, these hadrosaurids would be considered a dead clade walking . The scientific consensus is that these fossils were eroded from their original locations and then re-buried in much later sediments (also known as reworked fossils ). Most paleontologists regard birds as
11275-783: The Tasmanian Passage in the Eocene and deep ocean routes opening from the mid Oligocene. Rifting between the Antarctic Peninsula and the southern tip of South America formed the Drake Passage and opened the Southern Ocean also during this time, completing the breakup of Gondwana. The opening of these passages and the creation of the Southern Ocean established the Antarctic Circumpolar Current . Glaciers began to build across
11480-636: The Taurides in the east. From the Late Cretaceous into the early Paleocene, Africa began to converge with Eurasia. The irregular outlines of the continental margins, including the Adriatic promontory (Adria) that extended north from the African Plate, led to the development of several short subduction zones, rather than one long system. In the western Mediterranean, the European Plate
11685-423: The air and marine ecosystems by the Eocene . Birds , the only surviving group of dinosaurs, quickly diversified from the very few neognath and paleognath clades that survived the extinction event, also radiating into multiple orders, colonizing different ecosystems and achieving an extreme level of morphological diversity. Percomorph fish, the most diverse group of vertebrates today, first appeared near
11890-589: The biosphere rather than the total diversity and abundance of life. For this reason, well-documented extinction events are confined to the Phanerozoic eon – with the sole exception of the Oxygen Catastrophe in the Proterozoic – since before the Phanerozoic, all living organisms were either microbial, or if multicellular then soft-bodied. Perhaps due to the absence of a robust microbial fossil record, mass extinctions might only seem to be mainly
12095-455: The molluscan class Cephalopoda became extinct at the K–Pg boundary. These included the ecologically significant belemnoids , as well as the ammonoids , a group of highly diverse, numerous, and widely distributed shelled cephalopods. The extinction of belemnites enabled surviving cephalopod clades to fill their niches. Ammonite genera became extinct at or near the K–Pg boundary; there was a smaller and slower extinction of ammonite genera prior to
12300-448: The photic zone ) areas of the ocean were less impacted by the K–Pg boundary. Colonial coral species rely upon symbiosis with photosynthetic algae , which collapsed due to the events surrounding the K–Pg boundary, but the use of data from coral fossils to support K–Pg extinction and subsequent Paleocene recovery, must be weighed against the changes that occurred in coral ecosystems through the K–Pg boundary. Most species of brachiopods ,
12505-648: The trench leading to the development of the Dinarides, Hellenides and Tauride mountain chains as the passive margin sediments of Adria were scrapped off onto the Eurasia crust during subduction. The Zagros mountain belt stretches for c. 2000 km from the eastern border of Iraq to the Makran coast in southern Iran . It formed as a result of the convergence and collision of the Arabian and Eurasian plates as
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#173276629331812710-459: The Antarctica continent that now lay isolated in the south polar region and surrounded by cold ocean waters. These changes contributed to the fall in global temperatures and the beginning of icehouse conditions. Extensional stresses from the subduction zone along the northern Neotethys resulted in rifting between Africa and Arabia, forming the Gulf of Aden in the late Eocene. To the west, in
12915-725: The Central Andes were dominated by the subduction of oceanic crust and the Southern Andes were impacted by the subduction of the Farallon-East Antarctic ocean ridge. The Caribbean Plate is largely composed of oceanic crust of the Caribbean Large Igneous Province that formed during the Late Cretaceous. During the Late Cretaceous to Paleocene, subduction of Atlantic crust was established along its northern margin, whilst to
13120-541: The Cretaceous. Along with the aforementioned mosasaurs, plesiosaurs , represented by the families Elasmosauridae and Polycotylidae , became extinct during the event. The ichthyosaurs had disappeared from fossil record tens of millions of years prior to the K-Pg extinction event. Ten families of crocodilians or their close relatives are represented in the Maastrichtian fossil records, of which five died out prior to
13325-417: The Cretaceous–Paleogene (or K–Pg) extinction event. About 17% of all families, 50% of all genera and 75% of all species became extinct. In the seas all the ammonites , plesiosaurs and mosasaurs disappeared and the percentage of sessile animals was reduced to about 33%. All non-avian dinosaurs became extinct during that time. The boundary event was severe with a significant amount of variability in
13530-438: The Eocene ants became dominant and diverse, with larger colonies. Butterflies diversified as well, perhaps to take the place of leaf-eating insects wiped out by the extinction. The advanced mound-building termites, Termitidae , also appear to have risen in importance. There are fossil records of jawed fishes across the K–Pg boundary, which provide good evidence of extinction patterns of these classes of marine vertebrates. While
13735-667: The Eocene-Oligocene boundary and the present day Late Cenozoic ice age began. The Paleogene began with the brief but intense " impact winter " caused by the Chicxulub impact , which was followed by an abrupt period of warming. After temperatures stabilised, the steady cooling and drying of the Late Cretaceous-Early Paleogene Cool Interval that had spanned the last two ages of the Late Cretaceous continued, with only
13940-610: The Farallon Plate beneath the western edge of South America continued from the Mesozoic. Over the Paleogene, changes in plate motion and episodes of regional slab shallowing and steepening resulted in variations in the magnitude of crustal shortening and amounts of magmatism along the length of the Andes . In the Northern Andes, an oceanic plateau with volcanic arc was accreted during the latest Cretaceous and Paleocene, whilst
14145-527: The Greenland and northwest European margins and is associated with the proto-Icelandic mantle plume , which rose beneath the Greenland lithosphere at c. 65 Ma. There were two main phases of volcanic activity with peaks at c. 60 Ma and c. 55 Ma. Magmatism in the British and Northwest Atlantic volcanic provinces occurred mainly in the early Palaeocene, the latter associated with an increased spreading rate in
14350-603: The Hell Creek Formation shows a minimum of 75% of turtle species survived. Following the extinction event, turtle diversity exceeded pre-extinction levels in the Danian of North America, although in South America it remained diminished. European turtles likewise recovered rapidly following the mass extinction. The rhynchocephalians which were a globally distributed and diverse group of lepidosaurians during
14555-416: The Himalayas in India through Myanmar ( West Burma block ) Sumatra , Java to West Sulawesi . During the Late Cretaceous to Paleogene, the northward movement of the Indian Plate led to the highly oblique subduction of the Neotethys along the edge of the West Burma block and the development of a major north-south transform fault along the margin of Southeast Asia to the south. Between c. 60 and 50 Ma,
14760-677: The India-Eurasia collision continued, movement of material away from the collision zone was accommodated along, and extended, the already existing major strike slip systems of the region. During the Paleocene, seafloor spreading along the Mid-Atlantic Ridge propagated from the Central Atlantic northwards between North America and Greenland in the Labrador Sea (c. 62 Ma) and Baffin Bay (c. 57 Ma), and, by
14965-546: The Jurassic and continued to diversify throughout the Cretaceous. They are currently the most successful and diverse group of living reptiles, with more than 10,000 extant species. The only major group of terrestrial lizards to go extinct at the end of the Cretaceous were the polyglyphanodontians , a diverse group of mainly herbivorous lizards known predominantly from the Northern Hemisphere. The mosasaurs ,
15170-505: The K-Pg boundary known as the Main Fossiliferous Layer (MFL) containing a thanatocoenosis of disarticulated vertebrate fossils, which was likely also caused by a catastrophic flood from the impact. The K–Pg boundary represents one of the most dramatic turnovers in the fossil record for various calcareous nanoplankton that formed the calcium deposits for which the Cretaceous is named. The turnover in this group
15375-664: The K–Pg boundary resulted in numerous publications detailing planktonic foraminiferal extinction at the boundary; there is ongoing debate between groups which think the evidence indicates substantial extinction of these species at the K–Pg boundary, and those who think the evidence supports a gradual extinction through the boundary. There is strong evidence that local conditions heavily influenced diversity changes in planktonic foraminifera. Low and mid-latitude communities of planktonic foraminifera experienced high extinction rates, while high latitude faunas were relatively unaffected. Numerous species of benthic foraminifera became extinct during
15580-534: The K–Pg boundary subsequently becoming extinct in the Miocene . The gharial-like choristodere genus Champsosaurus ' palatal teeth suggest that there were dietary changes among the various species across the K–Pg event. More than 80% of Cretaceous turtle species passed through the K–Pg boundary. All six turtle families in existence at the end of the Cretaceous survived into the Paleogene and are represented by living species. Analysis of turtle survivorship in
15785-444: The K–Pg boundary, although taxa that thrived in low-latitude, shallow-water environments during the late Cretaceous had the highest extinction rate. Mid-latitude, deep-water echinoderms were much less affected at the K–Pg boundary. The pattern of extinction points to habitat loss, specifically the drowning of carbonate platforms , the shallow-water reefs in existence at that time, by the extinction event. Atelostomatans were affected by
15990-419: The K–Pg boundary, despite the ecological niches made available by the extinction of dinosaurs. Several mammalian orders have been interpreted as diversifying immediately after the K–Pg boundary, including Chiroptera ( bats ) and Cetartiodactyla (a diverse group that today includes whales and dolphins and even-toed ungulates ), although recent research concludes that only marsupial orders diversified soon after
16195-490: The K–Pg boundary. A study of fossil vertebrates across the K–Pg boundary in Montana concluded that no species of amphibian became extinct. Yet there are several species of Maastrichtian amphibian, not included as part of this study, which are unknown from the Paleocene. These include the frog Theatonius lancensis and the albanerpetontid Albanerpeton galaktion ; therefore, some amphibians do seem to have become extinct at
16400-502: The K–Pg boundary. Deposit feeders were the most common bivalves in the catastrophe's aftermath. Abundance was not a factor that affected whether a bivalve taxon went extinct, according to evidence from North America. Veneroid bivalves developed deeper burrowing habitats as the recovery from the crisis ensued. Except for nautiloids (represented by the modern order Nautilida ) and coleoids (which had already diverged into modern octopodes , squids , and cuttlefish ) all other species of
16605-519: The K–Pg boundary. Five families have both Maastrichtian and Paleocene fossil representatives. All of the surviving families of crocodyliforms inhabited freshwater and terrestrial environments—except for the Dyrosauridae , which lived in freshwater and marine locations. Approximately 50% of crocodyliform representatives survived across the K–Pg boundary, the only apparent trend being that no large crocodiles survived. Crocodyliform survivability across
16810-408: The K–Pg boundary. However, morphological diversification rates among eutherians after the extinction event were thrice those of before it. Also significant, within the mammalian genera, new species were approximately 9.1% larger after the K–Pg boundary. After about 700,000 years, some mammals had reached 50 kilos (110 pounds), a 100-fold increase over the weight of those which survived the extinction. It
17015-552: The K–Pg boundary. Long-term survival past the boundary was assured as a result of filling ecological niches left empty by extinction of non-avian dinosaurs. Based on molecular sequencing and fossil dating, many species of birds (the Neoaves group in particular) appeared to radiate after the K–Pg boundary. The open niche space and relative scarcity of predators following the K-Pg extinction allowed for adaptive radiation of various avian groups. Ratites , for example, rapidly diversified in
17220-416: The K–Pg event. Scientists agree that all non-avian dinosaurs became extinct at the K–Pg boundary. The dinosaur fossil record has been interpreted to show both a decline in diversity and no decline in diversity during the last few million years of the Cretaceous, and it may be that the quality of the dinosaur fossil record is simply not good enough to permit researchers to distinguish between the options. There
17425-528: The K–Pg extinction event as marine environments were. Among the terrestrial clade Notosuchia , only the family Sebecidae survived; the exact reasons for this pattern are not known. Sebecids were large terrestrial predators, are known from the Eocene of Europe, and would survive in South America into the Miocene. Tethysuchians radiated explosively after the extinction event. Two families of pterosaurs, Azhdarchidae and Nyctosauridae , were definitely present in
17630-661: The K–Pg extinction event, although they suffered losses. In particular, metatherians largely disappeared from North America, and the Asian deltatheroidans became extinct (aside from the lineage leading to Gurbanodelta ). In the Hell Creek beds of North America, at least half of the ten known multituberculate species and all eleven metatherians species are not found above the boundary. Multituberculates in Europe and North America survived relatively unscathed and quickly bounced back in
17835-494: The K–Pg extinction event, biodiversity required substantial time to recover, despite the existence of abundant vacant ecological niches . Evidence from the Salamanca Formation suggests that biotic recovery was more rapid in the Southern Hemisphere than in the Northern Hemisphere. Despite the massive loss of life inferred to have occurred during the extinction, and a number of geologic formations worldwide that span
18040-427: The Labrador Sea, whilst northeast Atlantic magmatism occurred mainly during the early Eocene and is associated with a change in the spreading direction in the Labrador Sea and the northward drift of Greenland. The locations of the magmatism coincide with the intersection of propagating the rifts and large-scale, pre-existing lithospheric structures, which acted as channels to the surface for the magma . The arrival of
18245-773: The Late Devonian extinction interval ( Givetian , Frasnian, and Famennian stages) to be statistically significant. Regardless, later studies have affirmed the strong ecological impacts of the Kellwasser and Hangenberg Events. The End Permian extinction or the "Great Dying" occurred at the Permian – Triassic transition. It was the Phanerozoic Eon's largest extinction: 53% of marine families died, 84% of marine genera, about 81% of all marine species and an estimated 70% of terrestrial vertebrate species. This
18450-600: The Lilliput effect. Insect damage to the fossilized leaves of flowering plants from fourteen sites in North America was used as a proxy for insect diversity across the K–Pg boundary and analyzed to determine the rate of extinction. Researchers found that Cretaceous sites, prior to the extinction event, had rich plant and insect-feeding diversity. During the early Paleocene, flora were relatively diverse with little predation from insects, even 1.7 million years after
18655-539: The Maastrichtian age, 28 shark families and 13 batoid families thrived, of which 25 and 9, respectively, survived the K–T boundary event. Forty-seven of all neoselachian genera cross the K–T boundary, with 85% being sharks. Batoids display with 15%, a comparably low survival rate. Among elasmobranchs, those species that inhabited higher latitudes and lived pelagic lifestyles were more likely to survive, whereas epibenthic lifestyles and durophagy were strongly associated with
18860-415: The Maastrichtian, and they likely became extinct at the K–Pg boundary. Several other pterosaur lineages may have been present during the Maastrichtian, such as the ornithocheirids , pteranodontids , a possible tapejarid , a possible thalassodromid and a basal toothed taxon of uncertain affinities, though they are represented by fragmentary remains that are difficult to assign to any given group. While this
19065-580: The Neotethys Ocean closed and is composed sediments scrapped from the descending Arabian Plate. From the Late Cretaceous, a volcanic arc developed on the Eurasia margin as the Neotethys crust was subducted beneath it. A separate intra-oceanic subduction zone in the Neotethys resulted in the obuction of ocean crust onto the Arabian margin in the Late Cretaceous to Paleocene, with break-off of
19270-607: The Neotethys Ocean lying between it and southern Eurasia. Debate about the amount of deformation seen in the geological record in the India–Eurasia collision zone versus the size of Greater India, the timing and nature of the collision relative to the decrease in plate velocity, and explanations for the unusually high velocity of the Indian plate have led to several models for Greater India: 1) A Late Cretaceous to early Paleocene subduction zone may have lain between India and Eurasia in
19475-534: The Neotethys, dividing the region into two plates, subduction was followed by collision of India with Eurasia in the middle Eocene. In this model Greater India would have been less than 900 km wide; 2) Greater India may have formed a single plate, several thousand kilometres wide, with the Tethyan Himalaya microcontinent separated from the Indian continent by an oceanic basin . The microcontinent collided with southern Eurasia c. 58 Ma (late Paleocene), whilst
19680-608: The North American subduction zone near Baja California leading to major strike-slip movements and the formation of the San Andreas Fault . At the Paleogene-Neogene boundary, spreading ceased between the Pacific and Farallon plates and the Farallon Plate split again forming the present date Nazca and Cocos plates. The Kula Plate lay between Pacific Plate and North America. To the north and northwest it
19885-504: The North Atlantic Igneous Province, between about 56 and 54 Ma, which rapidly released large amounts of greenhouse gases into the atmosphere. This warming led to melting of frozen methane hydrates on continental slopes adding further greenhouses gases. It also reduced the rate of burial of organic matter as higher temperatures accelerated the rate of bacterial decomposition which released CO 2 back into
20090-601: The Northern Hemisphere. Following the extinction, survivor communities dominated for several hundred thousand years. The North Pacific acted as a diversity hotspot from which later nannoplankton communities radiated as they replaced survivor faunas across the globe. The K–Pg boundary record of dinoflagellates is not so well understood, mainly because only microbial cysts provide a fossil record, and not all dinoflagellate species have cyst-forming stages, which likely causes diversity to be underestimated. Recent studies indicate that there were no major shifts in dinoflagellates through
20295-485: The Oligocene. The Paleogene is divided into three series / epochs : the Paleocene, Eocene, and Oligocene. These stratigraphic units can be defined globally or regionally. For global stratigraphic correlation, the International Commission on Stratigraphy (ICS) ratify global stages based on a Global Boundary Stratotype Section and Point (GSSP) from a single formation (a stratotype ) identifying
20500-650: The Pacific Plate moved north. At c. 47 Ma, movement of the hotspot ceased and the Pacific Plate motion changed from northward to northwestward in response to the onset of subduction along its western margin. This resulted in a 60 degree bend in the seamount chain. Other seamount chains related to hotspots in the South Pacific show a similar change in orientation at this time. Slow seafloor spreading continued between Australia and East Antarctica. Shallow water channels probably developed south of Tasmania opening
20705-560: The Pacific, Farallon, Kula and Izanagi plates. The central Pacific Plate grew by seafloor spreading as the other three plates were subducted and broken up. In the southern Pacific, seafloor spreading continued from the Late Cretaceous across the Pacific–Antarctic, Pacific-Farallon and Farallon–Antarctic mid ocean ridges. The Izanagi-Pacific spreading ridge lay nearly parallel to the East Asian subduction zone and between 60–50 Ma
20910-445: The Paleocene, but Asian forms were devastated, never again to represent a significant component of mammalian fauna. A recent study indicates that metatherians suffered the heaviest losses at the K–Pg event, followed by multituberculates, while eutherians recovered the quickest. K–Pg boundary mammalian species were generally small, comparable in size to rats ; this small size would have helped them find shelter in protected environments. It
21115-542: The Paleogene Period and subsequent Neogene Period; despite no longer being recognized as a formal stratigraphic term , "Tertiary" still sometimes remains in informal use. Paleogene is often abbreviated "Pg", although the United States Geological Survey uses the abbreviation " Pe " for the Paleogene on the Survey's geologic maps. Much of the world's modern vertebrate diversity originated in
21320-514: The Paleogene, and lasted from 33.9 Ma to 23.03 Ma. It is divided into two stages: the Rupelian 33.9 Ma to 27.82 Ma; and, Chattian 27.82 - 23.03 Ma. The GSSP for the base of the Oligocene is at Massignano , near Ancona , Italy . The extinction the hantkeninid planktonic foraminifera is the key marker for the Eocene-Oligocene boundary, which was a time of climate cooling that led to widespread changes in fauna and flora. The final stages of
21525-430: The Phanerozoic. This may represent the fact that groups with higher turnover rates are more likely to become extinct by chance; or it may be an artefact of taxonomy: families tend to become more speciose, therefore less prone to extinction, over time; and larger taxonomic groups (by definition) appear earlier in geological time. It has also been suggested that the oceans have gradually become more hospitable to life over
21730-569: The Sun, oscillations in the galactic plane, or passage through the Milky Way's spiral arms. However, other authors have concluded that the data on marine mass extinctions do not fit with the idea that mass extinctions are periodic, or that ecosystems gradually build up to a point at which a mass extinction is inevitable. Many of the proposed correlations have been argued to be spurious or lacking statistical significance. Others have argued that there
21935-546: The adaptations of many dinosaurs to cold environments. Whether the extinction occurred gradually or suddenly has been debated, as both views have support from the fossil record. A highly informative sequence of dinosaur-bearing rocks from the K–Pg boundary is found in western North America, particularly the late Maastrichtian-age Hell Creek Formation of Montana . Comparison with the older Judith River Formation (Montana) and Dinosaur Park Formation ( Alberta ), which both date from approximately 75 Ma, provides information on
22140-605: The atmosphere, causing longer-term effects on the climate and food chain . In October 2019, researchers asserted that the event rapidly acidified the oceans and produced long-lasting effects on the climate, detailing the mechanisms of the mass extinction. Other causal or contributing factors to the extinction may have been the Deccan Traps and other volcanic eruptions, climate change , and sea level change. However, in January 2020, scientists reported that climate-modeling of
22345-490: The base of the Eocene is at Dababiya, near Luxor , Egypt and is marked by the start of a significant variation in global carbon isotope ratios, produced by a major period of global warming. The change in climate was due to a rapid release of frozen methane clathrates from seafloor sediments at the beginning of the Paleocene-Eocene thermal maximum (PETM). The Oligocene is the third and youngest series/epoch of
22550-400: The biases inherent to sample size. Alroy also elaborated on three-timer algorithms, which are meant to counteract biases in estimates of extinction and origination rates. A given taxon is a "three-timer" if it can be found before, after, and within a given time interval, and a "two-timer" if it overlaps with a time interval on one side. Counting "three-timers" and "two-timers" on either end of
22755-399: The biotic recovery in the aftermath of the K-Pg extinction event. Pan-Gekkotans weathered the extinction event well, with multiple lineages likely surviving. ∆ Ca values indicate that prior to the mass extinction, marine reptiles at the top of food webs were feeding on only one source of calcium, suggesting their populations exhibited heightened vulnerability to extinctions at the terminus of
22960-401: The boundary associated with a late Cretaceous marine regression, and a small, gradual reduction in ammonite diversity occurred throughout the very late Cretaceous. Researchers have pointed out that the reproductive strategy of the surviving nautiloids, which rely upon few and larger eggs, played a role in outsurviving their ammonoid counterparts through the extinction event. The ammonoids utilized
23165-491: The boundary interval. Ostracods that were heavily sexually selected were more vulnerable to extinction, and ostracod sexual dimorphism was significantly rarer following the mass extinction. Among decapods , extinction patterns were highly heterogeneous and cannot be neatly attributed to any particular factor. Decapods that inhabited the Western Interior Seaway were especially hard-hit, while other regions of
23370-496: The boundary layer. There were blooms of the taxa Thoracosphaera operculata and Braarudosphaera bigelowii at the boundary. Radiolaria have left a geological record since at least the Ordovician times, and their mineral fossil skeletons can be tracked across the K–Pg boundary. There is no evidence of mass extinction of these organisms, and there is support for high productivity of these species in southern high latitudes as
23575-449: The boundary may have resulted from their aquatic niche and ability to burrow, which reduced susceptibility to negative environmental effects at the boundary. Jouve and colleagues suggested in 2008 that juvenile marine crocodyliforms lived in freshwater environments as do modern marine crocodile juveniles, which would have helped them survive where other marine reptiles became extinct; freshwater environments were not so strongly affected by
23780-779: The boundary, only a few fossil sites contain direct evidence of the mass mortality that occurred exactly at the K-Pg boundary. These include the Tanis site of the Hell Creek Formation in North Dakota , USA, which contains a high number of well-preserved fossils that appear to have buried in a catastrophic flood event that was likely caused by the impact. Another important site is the Hornerstown Formation in New Jersey , USA, which has prominent layer at
23985-416: The boundary. The relatively low levels of extinction seen among amphibians probably reflect the low extinction rates seen in freshwater animals. Following the mass extinction, frogs radiated substantially, with 88% of modern anuran diversity being traced back to three lineages of frogs that evolved after the cataclysm. The choristoderes (a group of semi-aquatic diapsids of uncertain position) survived across
24190-678: The breakup of Pangaea occurred during the Paleogene as Atlantic Ocean rifting and seafloor spreading extended northwards, separating the North America and Eurasian plates, and Australia and South America rifted from Antarctica , opening the Southern Ocean . Africa and India collided with Eurasia forming the Alpine-Himalayan mountain chains and the western margin of the Pacific Plate changed from
24395-627: The brief interruption of the Latest Danian Event (c. 62.2 Ma) when global temperatures rose. There is no evidence for ice sheets at the poles during the Paleocene. The relatively cool conditions were brought to an end by the Thanetian Thermal Event, and the beginning of the PETM. This was one of the warmest times of the Phanerozoic eon, during which global mean surface temperatures increased to 31.6 °C. According to
24600-486: The changes in dinosaur populations over the last 10 million years of the Cretaceous. These fossil beds are geographically limited, covering only part of one continent. The middle–late Campanian formations show a greater diversity of dinosaurs than any other single group of rocks. The late Maastrichtian rocks contain the largest members of several major clades: Tyrannosaurus , Ankylosaurus , Pachycephalosaurus , Triceratops , and Torosaurus , which suggests food
24805-436: The circumstances of food chain disruption previously mentioned, non-avian dinosaurs died out, while some crocodiles survived. In this context, the survival of other endothermic animals, such as some birds and mammals, could be due, among other reasons, to their smaller needs for food, related to their small size at the extinction epoch. Prolonged cold is unlikely to have been a reason for the extinction of non-avian dinosaurs given
25010-406: The cold circumpolar current. Dense polar waters sank into the deep oceans and moved northwards, reducing global ocean temperatures. This cooling may have occurred over less than 100,000 years and resulted in a widespread extinction in marine life. By the Eocene-Oligocene boundary, sediments deposited in the ocean from glaciers indicate the presence of an ice sheet in western Antarctica that extended to
25215-662: The collision of the Tethyan (Tibetan) Himalayas , the leading edge of Greater India, with the Lhasa Terrane of Tibet (southern Eurasian margin), along the Indus-Yarling-Zangbo suture zone . To the south of this zone, the Himalaya are composed of metasedimentary rocks scraped off the now subducted Indian continental crust and mantle lithosphere as the collision progressed. Palaeomagnetic data place
25420-413: The context of their effects on life. A 1995 paper by Michael Benton tracked extinction and origination rates among both marine and continental (freshwater & terrestrial) families, identifying 22 extinction intervals and no periodic pattern. Overview books by O.H. Walliser (1996) and A. Hallam and P.B. Wignall (1997) summarized the new extinction research of the previous two decades. One chapter in
25625-430: The cooler oceans also reduced moisture in the atmosphere and increased aridity. By the early Oligocene, the North American and Eurasian tropical and subtropical forests were replaced by dry woodlands and widespread grasslands. The Early Oligocene Glacial Maximum lasted for about 200,000 years, and the global mean surface temperature continued to decrease gradually during the Rupelian . A drop in global sea levels during
25830-478: The correlation of extinction and origination rates to diversity. High diversity leads to a persistent increase in extinction rate; low diversity to a persistent increase in origination rate. These presumably ecologically controlled relationships likely amplify smaller perturbations (asteroid impacts, etc.) to produce the global effects observed. A good theory for a particular mass extinction should: It may be necessary to consider combinations of causes. For example,
26035-702: The crater are found at Chicxulub on the Yucatan Peninsula in Mexico . The extinction of the non-avian dinosaurs , ammonites and dramatic changes in marine plankton and many other groups of organisms, are also used for correlation purposes. The Eocene is the second series/epoch of the Paleogene, and lasted from 56.0 Ma to 33.9 Ma. It is divided into four stages: the Ypresian 56.0 Ma to 47.8 Ma; Lutetian 47.8 Ma to 41.2 Ma; Bartonian 41.2 Ma to 37.71 Ma; and, Priabonian 37.71 Ma to 33.9 Ma. The GSSP for
26240-422: The data suggests massive devastation and mass extinction of plants at the K–Pg boundary sections, although there were substantial megafloral changes before the boundary. In North America, approximately 57% of plant species became extinct. In high southern hemisphere latitudes, such as New Zealand and Antarctica, the mass die-off of flora caused no significant turnover in species, but dramatic and short-term changes in
26445-496: The deep-sea realm was able to remain seemingly unaffected, there was an equal loss between the open marine apex predators and the durophagous demersal feeders on the continental shelf. Within cartilaginous fish , approximately 7 out of the 41 families of neoselachians (modern sharks , skates, and rays) disappeared after this event and batoids (skates and rays) lost nearly all the identifiable species, while more than 90% of teleost fish (bony fish) families survived. In
26650-458: The difficulty in assessing taxa with high turnover rates or restricted occurrences, which cannot be directly assessed due to a lack of fine-scale temporal resolution. Many paleontologists opt to assess diversity trends by randomized sampling and rarefaction of fossil abundances rather than raw temporal range data, in order to account for all of these biases. But that solution is influenced by biases related to sample size. One major bias in particular
26855-544: The disruption of the Chicxulub impact settled, a period of cool and dry conditions continued from the Late Cretaceous. At the Paleocene-Eocene boundary global temperatures rose rapidly with the onset of the Paleocene-Eocene Thermal Maximum (PETM). By the middle Eocene, temperatures began to drop again and by the late Eocene (c. 37 Ma) had decreased sufficiently for ice sheets to form in Antarctica. The global climate entered icehouse conditions at
27060-575: The early Mesozoic , had begun to decline by the mid-Cretaceous, although they remained successful in the Late Cretaceous of southern South America . They are represented today by a single species, the tuatara ( Sphenodon punctatus ) found in New Zealand . Outside of New Zealand, one rhynchocephalian is known to have crossed the K-Pg boundary, Kawasphenodon peligrensis , known from the earliest Paleocene (Danian) of Patagonia. The order Squamata comprising lizards and snakes first diversified during
27265-681: The early Eocene (c. 54 Ma), into the northeastern Atlantic between Greenland and Eurasia. Extension between North America and Eurasia, also in the early Eocene, led to the opening of the Eurasian Basin across the Arctic, which was linked to the Baffin Bay Ridge and Mid-Atlantic Ridge to the south via major strike slip faults. From the Eocene and into the early Oligocene, Greenland acted as an independent plate moving northwards and rotating anticlockwise. This led to compression across
27470-465: The early Oligocene, flood basalts erupted across Ethiopia , northeast Sudan and southwest Yemen as the Afar mantle plume began to impact the base of the African lithosphere. Rifting across the southern Red Sea began in the mid Oligocene, and across the central and northern Red Sea regions in the late Oligocene and early Miocene. Climatic conditions varied considerably during the Paleogene. After
27675-420: The early Paleocene provided the food source to support large benthic foraminiferal assemblages, which are mainly detritus-feeding. Ultimate recovery of the benthic populations occurred over several stages lasting several hundred thousand years into the early Paleocene. There is significant variation in the fossil record as to the extinction rate of marine invertebrates across the K–Pg boundary. The apparent rate
27880-624: The early Paleogene and are believed to have convergently developed flightlessness at least three to six times, often fulfilling the niche space for large herbivores once occupied by non-avian dinosaurs. Mammalian species began diversifying approximately 30 million years prior to the K–Pg boundary. Diversification of mammals stalled across the boundary. All major Late Cretaceous mammalian lineages, including monotremes (egg-laying mammals), multituberculates , metatherians (which includes modern marsupials), eutherians (which includes modern placentals), meridiolestidans , and gondwanatheres survived
28085-497: The effect of reducing the estimated severity of the six sampled mass extinction events. This effect was stronger for mass extinctions which occurred in periods with high rates of background extinction, like the Devonian. Because most diversity and biomass on Earth is microbial , and thus difficult to measure via fossils, extinction events placed on-record are those that affect the easily observed, biologically complex component of
28290-513: The end of the Cretaceous period. The Alvarez hypothesis for the end-Cretaceous extinction gave mass extinctions, and catastrophic explanations, newfound popular and scientific attention. Another landmark study came in 1982, when a paper written by David M. Raup and Jack Sepkoski was published in the journal Science . This paper, originating from a compendium of extinct marine animal families developed by Sepkoski, identified five peaks of marine family extinctions which stand out among
28495-578: The end of the Cretaceous and underwent sudden extinction after the Cretaceous–Paleogene extinction event. Alternatively, interpretation based on the fossil-bearing rocks along the Red Deer River in Alberta, Canada, supports the gradual extinction of non-avian dinosaurs; during the last 10 million years of the Cretaceous layers there, the number of dinosaur species seems to have decreased from about 45 to approximately 12. Other scientists have made
28700-537: The end of the Cretaceous but saw a very rapid radiation into their modern order and family-level diversity during the Paleogene, achieving a diverse array of morphologies. The Paleogene is marked by considerable changes in climate from the Paleocene–Eocene Thermal Maximum , through global cooling during the Eocene to the first appearance of permanent ice sheets in the Antarctic at the beginning of
28905-524: The end of the Cretaceous period, and with it the Mesozoic era, while heralding the beginning of the current era, the Cenozoic . In the geologic record , the K–Pg event is marked by a thin layer of sediment called the K–Pg boundary, Fatkito boundary or K–T boundary , which can be found throughout the world in marine and terrestrial rocks. The boundary clay shows unusually high levels of the metal iridium , which
29110-752: The end of the period of pressure. Their statistical analysis of marine extinction rates throughout the Phanerozoic suggested that neither long-term pressure alone nor a catastrophe alone was sufficient to cause a significant increase in the extinction rate. MacLeod (2001) summarized the relationship between mass extinctions and events that are most often cited as causes of mass extinctions, using data from Courtillot, Jaeger & Yang et al. (1996), Hallam (1992) and Grieve & Pesonen (1992): The most commonly suggested causes of mass extinctions are listed below. The formation of large igneous provinces by flood basalt events could have: Flood basalt events occur as pulses of activity punctuated by dormant periods. As
29315-405: The endothermy of dinosaurs (see dinosaur physiology ) helps to understand their full extinction in contrast with their close relatives, the crocodilians. Ectothermic ("cold-blooded") crocodiles have very limited needs for food (they can survive several months without eating), while endothermic ("warm-blooded") animals of similar size need much more food to sustain their faster metabolism. Thus, under
29520-462: The entire Phanerozoic. As data continued to accumulate, some authors began to re-evaluate Sepkoski's sample using methods meant to account for sampling biases . As early as 1982, a paper by Phillip W. Signor and Jere H. Lipps noted that the true sharpness of extinctions was diluted by the incompleteness of the fossil record. This phenomenon, later called the Signor-Lipps effect , notes that
29725-421: The event's severity, there was significant variability in the rate of extinction between and within different clades . Species that depended on photosynthesis declined or became extinct as atmospheric particles blocked sunlight and reduced the solar energy reaching the ground. This plant extinction caused a major reshuffling of the dominant plant groups. Omnivores , insectivores , and carrion -eaters survived
29930-407: The event, presumably because they depend on organic debris for nutrients, while biomass in the ocean is thought to have decreased. As the marine microbiota recovered, it is thought that increased speciation of benthic foraminifera resulted from the increase in food sources. In some areas, such as Texas, benthic foraminifera show no sign of any major extinction event, however. Phytoplankton recovery in
30135-481: The extinction event favored the asteroid impact and not volcanism . A wide range of terrestrial species perished in the K–Pg extinction, the best-known being the non-avian dinosaurs, along with many mammals, birds, lizards, insects , plants, and all the pterosaurs . In the oceans, the K–Pg extinction killed off plesiosaurs and mosasaurs and devastated teleost fish, sharks , mollusks (especially ammonites , which became extinct), and many species of plankton. It
30340-448: The extinction event is best represented by the marked discrepancy between the rich and relatively abundant late-Maastrichtian pollen record and the post-boundary fern spike. Polyploidy appears to have enhanced the ability of flowering plants to survive the extinction, probably because the additional copies of the genome such plants possessed allowed them to more readily adapt to the rapidly changing environmental conditions that followed
30545-583: The extinction event, perhaps because of the increased availability of their food sources. Neither strictly herbivorous nor strictly carnivorous mammals seem to have survived. Rather, the surviving mammals and birds fed on insects , worms , and snails , which in turn fed on detritus (dead plant and animal matter). In stream communities and lake ecosystems , few animal groups became extinct, including large forms like crocodyliforms and champsosaurs , because such communities rely less directly on food from living plants, and more on detritus washed in from
30750-468: The extinction event. Studies of the size of the ichnotaxon Naktodemasis bowni , produced by either cicada nymphs or beetle larvae, over the course of the K-Pg transition show that the Lilliput effect occurred in terrestrial invertebrates thanks to the extinction event. The extinction event produced major changes in Paleogene insect communities. Many groups of ants were present in the Cretaceous, but in
30955-472: The extinctions occurred simultaneously provides strong evidence that they were caused by the asteroid. A 2016 drilling project into the Chicxulub peak ring confirmed that the peak ring comprised granite ejected within minutes from deep in the earth, but contained hardly any gypsum , the usual sulfate-containing sea floor rock in the region: the gypsum would have vaporized and dispersed as an aerosol into
31160-556: The following section. The "Big Five" mass extinctions are bolded. Graphed but not discussed by Sepkoski (1996), considered continuous with the Late Devonian mass extinction At the time considered continuous with the end-Permian mass extinction Includes late Norian time slices Diversity loss of both pulses calculated together Pulses extend over adjacent time slices, calculated separately Considered ecologically significant, but not analyzed directly Excluded due to
31365-429: The former source lists over 60 geological events which could conceivably be considered global extinctions of varying sizes. These texts, and other widely circulated publications in the 1990s, helped to establish the popular image of mass extinctions as a "big five" alongside many smaller extinctions through prehistory. Though Sepkoski died in 1999, his marine genera compendium was formally published in 2002. This prompted
31570-464: The impact, giving rise to today's birds. The only bird group known for certain to have survived the K–Pg boundary is the Aves. Avians may have been able to survive the extinction as a result of their abilities to dive, swim, or seek shelter in water and marshlands. Many species of avians can build burrows, or nest in tree holes, or termite nests, all of which provided shelter from the environmental effects at
31775-601: The impact. Beyond extinction impacts, the event also caused more general changes of flora such as giving rise to neotropical rainforest biomes like the Amazonia , replacing species composition and structure of local forests during ~6 million years of recovery to former levels of plant diversity . Extinction event In a landmark paper published in 1982, Jack Sepkoski and David M. Raup identified five particular geological intervals with excessive diversity loss. They were originally identified as outliers on
31980-412: The land, protecting them from extinction. Modern crocodilians can live as scavengers and survive for months without food, and their young are small, grow slowly, and feed largely on invertebrates and dead organisms for their first few years. These characteristics have been linked to crocodilian survival at the end of the Cretaceous. Similar, but more complex patterns have been found in the oceans. Extinction
32185-490: The landscape for centuries after the event. In the sediments below the K–Pg boundary the dominant plant remains are angiosperm pollen grains, but the boundary layer contains little pollen and is dominated by fern spores. More usual pollen levels gradually resume above the boundary layer. This is reminiscent of areas blighted by modern volcanic eruptions, where the recovery is led by ferns, which are later replaced by larger angiosperm plants. In North American terrestrial sequences,
32390-456: The large terrestrial vertebrate niches. The dinosaurs themselves had been beneficiaries of a previous mass extinction, the end-Triassic , which eliminated most of their chief rivals, the crurotarsans . Similarly, within Synapsida , the replacement of taxa that originated in the earliest, Pennsylvanian and Cisuralian evolutionary radiation (often still called " pelycosaurs ", though this is
32595-623: The largest) of a relatively smooth continuum of extinction events. All of the five in the Phanerozoic Eon were anciently preceded by the presumed far more extensive mass extinction of microbial life during the Great Oxidation Event (a.k.a. Oxygen Catastrophe) early in the Proterozoic Eon . At the end of the Ediacaran and just before the Cambrian explosion , yet another Proterozoic extinction event (of unknown magnitude)
32800-422: The last 500 million years, and thus less vulnerable to mass extinctions, but susceptibility to extinction at a taxonomic level does not appear to make mass extinctions more or less probable. There is still debate about the causes of all mass extinctions. In general, large extinctions may result when a biosphere under long-term stress undergoes a short-term shock. An underlying mechanism appears to be present in
33005-520: The late Eocene (c. 37 Ma) there is evidence of glaciation in Antarctica. Changes in deep ocean currents, as Australia and South America moved away from Antarctica opening the Drake and Tasmanian passages, were responsible for the drop in global temperatures. The warm waters of the South Atlantic, Indian and South Pacific oceans extended southward into the opening Southern Ocean and became part of
33210-535: The leading northeastern edge of Greater India collided with the West Burma block resulting in deformation and metamorphism . During the middle Eocene, north-dipping subduction resumed along the southern edge of Southeast Asia, from west Sumatra to West Sulawesi, as the Australian Plate drifted slowly northwards. Collision between India and the West Burma block was complete by the late Oligocene. As
33415-408: The likelihood of perishing during the extinction event. There is evidence of a mass extinction of bony fishes at a fossil site immediately above the K–Pg boundary layer on Seymour Island near Antarctica , apparently precipitated by the K–Pg extinction event; the marine and freshwater environments of fishes mitigated the environmental effects of the extinction event. The result was Patterson's Gap,
33620-492: The lower boundary of the stage. The Paleocene is the first series/epoch of the Paleogene and lasted from 66.0 Ma to 56.0 Ma. It is divided into three stages: the Danian 66.0 - 61.6 Ma; Selandian 61.6 - 59.2 Ma; and, Thanetian 59.2 - 56.0 Ma. The GSSP for the base of the Cenozoic, Paleogene and Paleocene is at Oued Djerfane, west of El Kef , Tunisia . It is marked by an iridium anomaly produced by an asteroid impact, and
33825-430: The marine aspect of the end-Cretaceous extinction appears to have been caused by several processes that partially overlapped in time and may have had different levels of significance in different parts of the world. Arens and West (2006) proposed a "press / pulse" model in which mass extinctions generally require two types of cause: long-term pressure on the eco-system ("press") and a sudden catastrophe ("pulse") towards
34030-599: The northeast Atlantic. By the late Oligocene, the plate boundary between North America and Eurasia was established along the Mid-Atlantic Ridge, with Greenland attached to the North American plate again, and the Jan Mayen microcontinent part of the Eurasian Plate, where its remains now lie to the east and possibly beneath the southeast of Iceland. The North Atlantic Igneous Province stretches across
34235-442: The number of flowering plants. However, phylogenetic evidence shows no mass angiosperm extinction. Due to the wholesale destruction of plants at the K–Pg boundary, there was a proliferation of saprotrophic organisms, such as fungi , that do not require photosynthesis and use nutrients from decaying vegetation. The dominance of fungal species lasted only a few years while the atmosphere cleared and plenty of organic matter to feed on
34440-622: The ocean. The development of the circumpolar current led to changes in the oceans, which in turn reduced atmospheric CO 2 further. Increasing upwellings of cold water stimulated the productivity of phytoplankton , and the cooler waters reduced the rate of bacterial decay of organic matter and promoted the growth of methane hydrates in marine sediments. This created a positive feedback cycle where global cooling reduced atmospheric CO 2 and this reduction in CO 2 lead to changes which further lowered global temperatures. The decrease in evaporation from
34645-423: The oceans. The (relatively) sudden climatic changes associated with the PETM resulted in the extinction of some groups of fauna and flora and the rise of others. For example, with the warming of the Arctic Ocean, around 70% of deep sea foraminifera species went extinct, whilst on land many modern mammals, including primates , appeared. Fluctuating sea levels meant, during low stands, a land bridge formed across
34850-426: The old, dominant group and makes way for the new one, a process known as adaptive radiation . For example, mammaliaformes ("almost mammals") and then mammals existed throughout the reign of the dinosaurs , but could not compete in the large terrestrial vertebrate niches that dinosaurs monopolized. The end-Cretaceous mass extinction removed the non-avian dinosaurs and made it possible for mammals to expand into
35055-400: The ongoing mass extinction caused by human activity is sometimes called the sixth mass extinction . Mass extinctions have sometimes accelerated the evolution of life on Earth . When dominance of particular ecological niches passes from one group of organisms to another, it is rarely because the newly dominant group is "superior" to the old but usually because an extinction event eliminates
35260-424: The only surviving dinosaurs (see Origin of birds ). It is thought that all non-avian theropods became extinct, including then-flourishing groups such as enantiornithines and hesperornithiforms . Several analyses of bird fossils show divergence of species prior to the K–Pg boundary, and that duck, chicken, and ratite bird relatives coexisted with non-avian dinosaurs. Large collections of bird fossils representing
35465-565: The origination rate in the middle Ordovician-early Silurian, late Carboniferous-Permian, and Jurassic-recent. This argues that the Late Ordovician, end-Permian, and end-Cretaceous extinctions were statistically significant outliers in biodiversity trends, while the Late Devonian and end-Triassic extinctions occurred in time periods which were already stressed by relatively high extinction and low origination. Computer models run by Foote (2005) determined that abrupt pulses of extinction fit
35670-686: The pattern of prehistoric biodiversity much better than a gradual and continuous background extinction rate with smooth peaks and troughs. This strongly supports the utility of rapid, frequent mass extinctions as a major driver of diversity changes. Pulsed origination events are also supported, though to a lesser degree which is largely dependent on pulsed extinctions. Similarly, Stanley (2007) used extinction and origination data to investigate turnover rates and extinction responses among different evolutionary faunas and taxonomic groups. In contrast to previous authors, his diversity simulations show support for an overall exponential rate of biodiversity growth through
35875-480: The physical environment. He expressed this in The Origin of Species : Various authors have suggested that extinction events occurred periodically, every 26 to 30 million years, or that diversity fluctuates episodically about every 62 million years. Various ideas, mostly regarding astronomical influences, attempt to explain the supposed pattern, including the presence of a hypothetical companion star to
36080-454: The present day Indian continent further south at the time of collision and decrease in plate velocity, indicating the presence of a large region to the north of India that has now been subducted beneath the Eurasian Plate or incorporated into the mountain belt. This region, known as Greater India, formed by extension along the northern margin of India during the opening of the Neotethys. The Tethyan Himalaya block lay along its northern edge, with
36285-399: The proto-Iceland plume has been considered the driving mechanism for rifting in the North Atlantic. However, that rifting and initial seafloor spreading occurred prior to the arrival of the plume, large scale magmatism occurred at a distance to rifting, and that rifting propagated towards, rather than away from the plume, has led to the suggestion the plume and associated magmatism may have been
36490-566: The rate of extinction between and among different clades . Mammals , descended from the synapsids , and birds , a side-branch of the theropod dinosaurs, emerged as the two predominant clades of terrestrial tetrapods. Despite the common presentation focusing only on these five events, no measure of extinction shows any definite line separating them from the many other Phanerozoic extinction events that appear only slightly lesser catastrophes; further, using different methods of calculating an extinction's impact can lead to other events featuring in
36695-421: The relative abundance of plant groups. European flora was also less affected, most likely due to its distance from the site of the Chicxulub impact. In northern Alaska and the Anadyr-Koryak region of Russia, the flora was minimally impacted. Another line of evidence of a major floral extinction is that the divergence rate of subviral pathogens of angiosperms sharply decreased, which indicates an enormous reduction in
36900-588: The rock exposure of Western Europe indicates that many of the minor events for which a biological explanation has been sought are most readily explained by sampling bias . Research completed after the seminal 1982 paper (Sepkoski and Raup) has concluded that a sixth mass extinction event due to human activities is currently under way: Extinction events can be tracked by several methods, including geological change, ecological impact, extinction vs. origination ( speciation ) rates, and most commonly diversity loss among taxonomic units. Most early papers used families as
37105-422: The same assessment following their research. Several researchers support the existence of Paleocene non-avian dinosaurs . Evidence of this existence is based on the discovery of dinosaur remains in the Hell Creek Formation up to 1.3 m (4.3 ft) above and 40,000 years later than the K–Pg boundary. Pollen samples recovered near a fossilized hadrosaur femur recovered in the Ojo Alamo Sandstone at
37310-470: The same short time interval. To circumvent this issue, background rates of diversity change (extinction/origination) were estimated for stages or substages without mass extinctions, and then assumed to apply to subsequent stages with mass extinctions. For example, the Santonian and Campanian stages were each used to estimate diversity changes in the Maastrichtian prior to the K-Pg mass extinction. Subtracting background extinctions from extinction tallies had
37515-466: The same time. Non-avian dinosaurs , for example, are known from the Maastrichtian of North America, Europe , Asia, Africa , South America, and Antarctica , but are unknown from the Cenozoic anywhere in the world. Similarly, fossil pollen shows devastation of the plant communities in areas as far apart as New Mexico , Alaska , China , and New Zealand . Nevertheless, high latitudes appear to have been less strongly affected than low latitudes. Despite
37720-441: The southwest, an island arc collided with the northern Andes forming an east dipping subduction zone where Caribbean lithosphere was subducted beneath the South American margin. During the Eocene (c. 45 Ma), subduction of the Farallon Plate along the Central American subduction zone was (re)established. Subduction along the northern section of the Caribbean volcanic arc ceased as the Bahamas carbonate platform collided with Cuba and
37925-414: The spreading ridge began to be subducted. By c. 50 Ma, the Pacific Plate was no longer surrounded by spreading ridges, but had a subduction zone along its western edge. This changed the forces acting on the Pacific Plate and led to a major reorganisation of plate motions across the entire Pacific region. The resulting changes in stress between the Pacific and Philippine Sea plates initiated subduction along
38130-422: The subducted oceanic plate close to the Arabian margin occurring during the Eocene. Continental collision began during the Eocene c. 35 Ma and continued into the Oligocene to c. 26 Ma. The Indian continent rifted from Madagascar at c. 83 Ma and drifted rapidly (c. 18 cm/yr in the Paleocene) northwards towards the southern margin of Eurasia. A rapid decrease in velocity to c. 5 cm/yr in the early Eocene records
38335-421: The subducting Farallon Plate led to a flat-slab segment that increased friction between this and the base of the North American Plate. The resulting Laramide Orogeny , which began the development of the Rocky Mountains , was a broad zone of thick-skinned deformation , with faults extending to mid-crustal depths and the uplift of basement rocks that lay to the east of the Sevier belt, and more than 700km from
38540-602: The top five. Fossil records of older events are more difficult to interpret. This is because: It has been suggested that the apparent variations in marine biodiversity may actually be an artifact, with abundance estimates directly related to quantity of rock available for sampling from different time periods. However, statistical analysis shows that this can only account for 50% of the observed pattern, and other evidence such as fungal spikes (geologically rapid increase in fungal abundance) provides reassurance that most widely accepted extinction events are real. A quantification of
38745-482: The trench. With the Laramide uplift the Western Interior Seaway was divided and then retreated. During the mid to late Eocene (50–35 Ma), plate convergence rates decreased and the dip of the Farallon slab began to steepen. Uplift ceased and the region largely levelled by erosion . By the Oligocene, convergence gave way to extension, rifting and widespread volcanism across the Laramide belt. Ocean-continent convergence accommodated by east dipping subduction zone of
38950-505: The trigger for reductions in atmospheric carbon dioxide leading to the glaciation and anoxia observed in the geological record. The largest extinction was the Kellwasser Event ( Frasnian - Famennian , or F-F, 372 Ma), an extinction event at the end of the Frasnian, about midway through the Late Devonian. This extinction annihilated coral reefs and numerous tropical benthic (seabed-living) animals such as jawless fish, brachiopods , and trilobites . The other major extinction
39155-453: The unit of taxonomy, based on compendiums of marine animal families by Sepkoski (1982, 1992). Later papers by Sepkoski and other authors switched to genera , which are more precise than families and less prone to taxonomic bias or incomplete sampling relative to species. These are several major papers estimating loss or ecological impact from fifteen commonly-discussed extinction events. Different methods used by these papers are described in
39360-431: The vacant niches created the opportunity for archosaurs to become ascendant . In the seas, the percentage of animals that were sessile (unable to move about) dropped from 67% to 50%. The whole late Permian was a difficult time, at least for marine life, even before the P–T boundary extinction. More recent research has indicated that the End-Capitanian extinction event that preceded the "Great Dying" likely constitutes
39565-422: The velocity of the plate did not decrease until c. 50 Ma when subduction rates dropped as young, oceanic crust entered the subduction zone; 3) This model assigns older dates to parts of Greater India, which changes its paleogeographic position relative to Eurasia and creates a Greater India formed of extended continental crust 2000 - 3000 km wide. The Alpine-Himalayan Orogenic Belt in Southeast Asia extends from
39770-406: The western Mediterranean arc of the Tell, Rif, Betic and Apennine mountain chains. The rate of convergence was less than the subduction rate of the dense lithosphere of the western Mediterranean and roll-back of the subducting slab led to the arcuate structure of these mountain ranges. In the eastern Mediterranean, c. 35 Ma, the Anatolide-Tauride platform (northern part of Adria) began to enter
39975-536: The world's oceans were refugia that increased chances of survival into the Palaeocene. Among retroplumid crabs, the genus Costacopluma was a notable survivor. Approximately 60% of late-Cretaceous scleractinian coral genera failed to cross the K–Pg boundary into the Paleocene. Further analysis of the coral extinctions shows that approximately 98% of colonial species, ones that inhabit warm, shallow tropical waters, became extinct. The solitary corals, which generally do not form reefs and inhabit colder and deeper (below
40180-457: Was another paper which attempted to remove two common errors in previous estimates of extinction severity. The first error was the unjustified removal of "singletons", genera unique to only a single time slice. Their removal would mask the influence of groups with high turnover rates or lineages cut short early in their diversification. The second error was the difficulty in distinguishing background extinctions from brief mass extinction events within
40385-407: Was being subducted beneath the Aleutian trench . Spreading between the Kula and Pacific and Farallon plates ceased c. 40 Ma and the Kula Plate became part of the Pacific Plate. The Hawaiian-Emperor seamount chain formed above the Hawaiian hotspot . Originally thought to be stationary within the mantle, the hotspot is now considered to have drifted south during the Paleocene to early Eocene, as
40590-419: Was followed by a c.10 million year pause in the convergence of Africa and Eurasia, connected with the onset of the opening of the North Atlantic Ocean as Greenland rifted from the Eurasian Plate in the Palaeocene. Convergence rates between Africa and Eurasia increased again in the early Eocene and the remaining oceanic basins between Adria and Europe closed. Between about 40 and 30 Ma, subduction began along
40795-526: Was more severe among animals living in the water column than among animals living on or in the sea floor. Animals in the water column are almost entirely dependent on primary production from living phytoplankton , while animals on the ocean floor always or sometimes feed on detritus. Coccolithophorids and mollusks (including ammonites , rudists , freshwater snails , and mussels ), and those organisms whose food chain included these shell builders, became extinct or suffered heavy losses. For example, it
41000-475: Was occurring, modern birds were undergoing diversification; traditionally it was thought that they replaced archaic birds and pterosaur groups, possibly due to direct competition, or they simply filled empty niches, but there is no correlation between pterosaur and avian diversities that are conclusive to a competition hypothesis, and small pterosaurs were present in the Late Cretaceous. At least some niches previously held by birds were reclaimed by pterosaurs prior to
41205-545: Was plentiful immediately prior to the extinction. A study of 29 fossil sites in Catalan Pyrenees of Europe in 2010 supports the view that dinosaurs there had great diversity until the asteroid impact, with more than 100 living species. More recent research indicates that this figure is obscured by taphonomic biases and the sparsity of the continental fossil record. The results of this study, which were based on estimated real global biodiversity, showed that between 628 and 1,078 non-avian dinosaur species were alive at
41410-426: Was present. Once the atmosphere cleared photosynthetic organisms returned – initially ferns and other ground-level plants. In some regions, the Paleocene recovery of plants began with recolonizations by fern species, represented as a fern spike in the geologic record; this same pattern of fern recolonization was observed after the 1980 Mount St. Helens eruption . Just two species of fern appear to have dominated
41615-428: Was replaced by strike-slip movements as a transform fault, extending from the Mid-Atlantic Ridge, connected with the northern boundary of the Caribbean Plate. Subduction now focused along the southern Caribbean arc ( Lesser Antilles ). By the Oligocene, the intra-oceanic Central American volcanic arc began to collide with northwestern South American. At the beginning of the Paleogene, the Pacific Ocean consisted of
41820-401: Was subducted southwards beneath the African Plate, whilst in the eastern Mediterranean, Africa was subducted beneath Eurasia along a northward dipping subduction zone. Convergence between the Iberian and European plates led to the Pyrenean Orogeny and, as Adria pushed northwards the Alps and Carpathian orogens began to develop. The collision of Adria with Eurasia in the early Palaeocene
42025-448: Was the Hangenberg Event (Devonian-Carboniferous, or D-C, 359 Ma), which brought an end to the Devonian as a whole. This extinction wiped out the armored placoderm fish and nearly led to the extinction of the newly evolved ammonoids . These two closely spaced extinction events collectively eliminated about 19% of all families, 50% of all genera and at least 70% of all species. Sepkoski and Raup (1982) did not initially consider
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