109-648: Eufalconimorphae is a proposed clade of birds , consisting of passerines , parrots , falcons , caracaras , and forest falcons (but not other raptors ). It has whole-genome DNA support. This clade was defined in the PhyloCode by George Sangster and colleagues in 2022 as "the least inclusive crown clade containing Falco subbuteo and Passer domesticus ". Eufalconimorphae birds are characterized by their strong and hooked beaks, sharp talons, and powerful wings. They have excellent eyesight, which allows them to spot their prey from great distances. The Eufalconimorphae
218-788: A better sense of smell. A third stage of bird evolution starting with Ornithothoraces (the "bird-chested" avialans) can be associated with the refining of aerodynamics and flight capabilities, and the loss or co-ossification of several skeletal features. Particularly significant are the development of an enlarged, keeled sternum and the alula , and the loss of grasping hands. † Anchiornis † Archaeopteryx † Xiaotingia † Rahonavis † Jeholornis † Jixiangornis † Balaur † Zhongjianornis † Sapeornis † Confuciusornithiformes † Protopteryx † Pengornis Ornithothoraces † Enantiornithes Cretaceous%E2%80%93Paleogene extinction event The Cretaceous–Paleogene ( K–Pg ) extinction event , also known as
327-473: A definition similar to "all theropods closer to birds than to Deinonychus ", with Troodon being sometimes added as a second external specifier in case it is closer to birds than to Deinonychus . Avialae is also occasionally defined as an apomorphy-based clade (that is, one based on physical characteristics). Jacques Gauthier , who named Avialae in 1986, re-defined it in 2001 as all dinosaurs that possessed feathered wings used in flapping flight , and
436-465: 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
545-413: 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
654-442: A group called Paraves . Some basal members of Deinonychosauria, such as Microraptor , have features which may have enabled them to glide or fly. The most basal deinonychosaurs were very small. This evidence raises the possibility that the ancestor of all paravians may have been arboreal , have been able to glide, or both. Unlike Archaeopteryx and the non-avialan feathered dinosaurs, who primarily ate meat, studies suggest that
763-528: 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
872-534: 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
981-419: 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
1090-490: 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
1199-527: 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
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#17327728374441308-406: A sister group, the order Crocodilia , contain the only living representatives of the reptile clade Archosauria . During the late 1990s, Aves was most commonly defined phylogenetically as all descendants of the most recent common ancestor of modern birds and Archaeopteryx lithographica . However, an earlier definition proposed by Jacques Gauthier gained wide currency in the 21st century, and
1417-454: 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
1526-717: A time, sometimes for years, and rarely for life. Other species have breeding systems that are polygynous (one male with many females) or, rarely, polyandrous (one female with many males). Birds produce offspring by laying eggs which are fertilised through sexual reproduction . They are usually laid in a nest and incubated by the parents. Most birds have an extended period of parental care after hatching. Many species of birds are economically important as food for human consumption and raw material in manufacturing, with domesticated and undomesticated birds being important sources of eggs, meat, and feathers. Songbirds , parrots, and other species are popular as pets. Guano (bird excrement)
1635-413: Is a stub . You can help Misplaced Pages by expanding it . Bird Birds are a group of warm-blooded vertebrates constituting the class Aves ( Latin: [ˈaveːs] ), characterised by feathers , toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart , and a strong yet lightweight skeleton . Birds live worldwide and range in size from
1744-476: 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
1853-537: 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,
1962-429: Is harvested for use as a fertiliser. Birds figure throughout human culture. About 120 to 130 species have become extinct due to human activity since the 17th century, and hundreds more before then. Human activity threatens about 1,200 bird species with extinction, though efforts are underway to protect them. Recreational birdwatching is an important part of the ecotourism industry. The first classification of birds
2071-475: 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,
2180-526: 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
2289-494: 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
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#17327728374442398-503: Is not considered a direct ancestor of birds, though it is possibly closely related to the true ancestor. Over 40% of key traits found in modern birds evolved during the 60 million year transition from the earliest bird-line archosaurs to the first maniraptoromorphs , i.e. the first dinosaurs closer to living birds than to Tyrannosaurus rex . The loss of osteoderms otherwise common in archosaurs and acquisition of primitive feathers might have occurred early during this phase. After
2507-490: Is noted to produce aerodynamic force during the upstroke of flight to help create a vertical flight pattern. See below cladogram showing Eufalconimorphae's relationship within Australaves: Cariamiformes (seriemas) [REDACTED] Falconiformes (falcons) [REDACTED] Psittaciformes (parrots) [REDACTED] Passeriformes (songbirds) [REDACTED] This bird-related article
2616-451: 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
2725-516: Is synonymous to Avifilopluma. † Scansoriopterygidae † Eosinopteryx † Jinfengopteryx † Aurornis † Dromaeosauridae † Troodontidae Avialae Based on fossil and biological evidence, most scientists accept that birds are a specialised subgroup of theropod dinosaurs and, more specifically, members of Maniraptora , a group of theropods which includes dromaeosaurids and oviraptorosaurs , among others. As scientists have discovered more theropods closely related to birds,
2834-472: 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
2943-526: 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,
3052-480: Is used by many scientists including adherents to the PhyloCode . Gauthier defined Aves to include only the crown group of the set of modern birds. This was done by excluding most groups known only from fossils , and assigning them, instead, to the broader group Avialae, on the principle that a clade based on extant species should be limited to those extant species and their closest extinct relatives. Gauthier and de Queiroz identified four different definitions for
3161-448: 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
3270-629: 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
3379-669: The Tiaojishan Formation of China, which has been dated to the late Jurassic period ( Oxfordian stage), about 160 million years ago. The avialan species from this time period include Anchiornis huxleyi , Xiaotingia zhengi , and Aurornis xui . The well-known probable early avialan, Archaeopteryx , dates from slightly later Jurassic rocks (about 155 million years old) from Germany . Many of these early avialans shared unusual anatomical features that may be ancestral to modern birds but were later lost during bird evolution. These features include enlarged claws on
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3488-458: 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
3597-575: The only known living dinosaurs . Likewise, birds are considered reptiles in the modern cladistic sense of the term, and their closest living relatives are the crocodilians . Birds are descendants of the primitive avialans (whose members include Archaeopteryx ) which first appeared during the Late Jurassic . According to recent estimates, modern birds ( Neornithes ) evolved in the Late Cretaceous and diversified dramatically around
3706-451: 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 ,
3815-433: The 5.5 cm (2.2 in) bee hummingbird to the 2.8 m (9 ft 2 in) common ostrich . There are over 11,000 living species and they are split into 44 orders . More than half are passerine or "perching" birds. Birds have wings whose development varies according to species; the only known groups without wings are the extinct moa and elephant birds . Wings, which are modified forelimbs , gave birds
3924-606: 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
4033-492: 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
4142-606: 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
4251-548: 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 ,
4360-506: 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
4469-538: 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
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4578-672: 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
4687-445: 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
4796-421: 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
4905-506: 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
5014-521: 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
5123-412: 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
5232-493: 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
5341-555: 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
5450-418: 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
5559-532: 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
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#17327728374445668-663: 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
5777-496: 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
5886-601: 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
5995-541: 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
6104-417: 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
6213-604: 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
6322-447: 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
6431-480: The ability to fly, although further evolution has led to the loss of flight in some birds , including ratites , penguins , and diverse endemic island species. The digestive and respiratory systems of birds are also uniquely adapted for flight. Some bird species of aquatic environments, particularly seabirds and some waterbirds , have further evolved for swimming. The study of birds is called ornithology . Birds are feathered theropod dinosaurs and constitute
6540-548: 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
6649-428: The appearance of Maniraptoromorpha, the next 40 million years marked a continuous reduction of body size and the accumulation of neotenic (juvenile-like) characteristics. Hypercarnivory became increasingly less common while braincases enlarged and forelimbs became longer. The integument evolved into complex, pennaceous feathers . The oldest known paravian (and probably the earliest avialan) fossils come from
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#17327728374446758-609: 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
6867-402: 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
6976-509: The birds that descended from them. Despite being currently one of the most widely used, the crown-group definition of Aves has been criticised by some researchers. Lee and Spencer (1997) argued that, contrary to what Gauthier defended, this definition would not increase the stability of the clade and the exact content of Aves will always be uncertain because any defined clade (either crown or not) will have few synapomorphies distinguishing it from its closest relatives. Their alternative definition
7085-402: 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
7194-495: 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
7303-498: 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
7412-450: 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
7521-780: 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
7630-418: 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
7739-487: 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
7848-438: 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
7957-423: 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
8066-498: 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
8175-665: The earliest members of Aves, is removed from this group, becoming a non-avian dinosaur instead. These proposals have been adopted by many researchers in the field of palaeontology and bird evolution , though the exact definitions applied have been inconsistent. Avialae, initially proposed to replace the traditional fossil content of Aves, is often used synonymously with the vernacular term "bird" by these researchers. † Coelurus † Ornitholestes † Ornithomimosauria † Alvarezsauridae † Oviraptorosauria Paraves Most researchers define Avialae as branch-based clade, though definitions vary. Many authors have used
8284-643: 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
8393-422: 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
8502-630: 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
8611-642: 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
8720-527: 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
8829-405: 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
8938-422: 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
9047-409: 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
9156-490: 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
9265-449: 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
9374-586: 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
9483-471: 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
9592-473: 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
9701-451: The first avialans were omnivores . The Late Jurassic Archaeopteryx is well known as one of the first transitional fossils to be found, and it provided support for the theory of evolution in the late 19th century. Archaeopteryx was the first fossil to display both clearly traditional reptilian characteristics—teeth, clawed fingers, and a long, lizard-like tail—as well as wings with flight feathers similar to those of modern birds. It
9810-467: 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
9919-414: 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
10028-493: 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,
10137-412: 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,
10246-444: 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
10355-426: 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
10464-402: The outermost half) can be seen in the evolution of maniraptoromorphs, and this process culminated in the appearance of the pygostyle , an ossification of fused tail vertebrae. In the late Cretaceous, about 100 million years ago, the ancestors of all modern birds evolved a more open pelvis, allowing them to lay larger eggs compared to body size. Around 95 million years ago, they evolved
10573-536: The previously clear distinction between non-birds and birds has become blurred. By the 2000s, discoveries in the Liaoning Province of northeast China, which demonstrated many small theropod feathered dinosaurs , contributed to this ambiguity. The consensus view in contemporary palaeontology is that the flying theropods, or avialans , are the closest relatives of the deinonychosaurs , which include dromaeosaurids and troodontids . Together, these form
10682-489: 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
10791-494: 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
10900-452: The same biological name "Aves", which is a problem. The authors proposed to reserve the term Aves only for the crown group consisting of the last common ancestor of all living birds and all of its descendants, which corresponds to meaning number 4 below. They assigned other names to the other groups. Lizards & snakes Turtles Crocodiles Birds Under the fourth definition Archaeopteryx , traditionally considered one of
11009-531: 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
11118-493: The second toe which may have been held clear of the ground in life, and long feathers or "hind wings" covering the hind limbs and feet, which may have been used in aerial maneuvering. Avialans diversified into a wide variety of forms during the Cretaceous period. Many groups retained primitive characteristics , such as clawed wings and teeth, though the latter were lost independently in a number of avialan groups, including modern birds (Aves). Increasingly stiff tails (especially
11227-600: The time of the Cretaceous–Paleogene extinction event 66 million years ago, which killed off the pterosaurs and all non- ornithuran dinosaurs. Many social species preserve knowledge across generations ( culture ). Birds are social, communicating with visual signals, calls, and songs , and participating in such behaviour as cooperative breeding and hunting, flocking , and mobbing of predators. The vast majority of bird species are socially (but not necessarily sexually) monogamous , usually for one breeding season at
11336-597: 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
11445-466: Was developed by Francis Willughby and John Ray in their 1676 volume Ornithologiae . Carl Linnaeus modified that work in 1758 to devise the taxonomic classification system currently in use. Birds are categorised as the biological class Aves in Linnaean taxonomy . Phylogenetic taxonomy places Aves in the clade Theropoda as an infraclass or a subclass, more recently a subclass. Aves and
11554-527: 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
11663-480: 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
11772-614: 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
11881-428: 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
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