56-546: See text The Cymatoceratidae is a family of Mesozoic and early Cenozoic nautiloid cephalopods and the most abundant of their kind in the Cretaceous. They are characterized by ribbed, generally involute shells of varied forms - coiled such that the outer whorl envelops the previous one, as with Nautilus, and sutures that are variably sinuous. Cymatoceratids first appear in the Middle Jurassic, derived from
112-855: A better sense of smell. The following cladogram is based on the analysis by Hartman et al . (2019), which found flight likely evolved five separate times among paravian dinosaurs, two of those among Avialae (in Scansoriopterygids and other avialans). Archaeopteryx and "anchiornithids" were placed in Deinonychosauria, Avialae's sister group. † Archaeopterygidae † Unenlagiidae † Dromaeosauridae † Troodontidae † Scansoriopterygidae † Yandangornis † Bauxitornis † Balaur † Shenzhouraptor † Jixiangornis † Zhongornis † Sapeornis † Confuciusornithidae † Changchengornis † Chongmingia † Jinguofortis † Zhongjianornis Ornithothoraces In
168-483: A boom of dinosaurian evolution on land as the continents began to separate from each other (Nyasasaurus from 243 to 210 million years ago, approximately 235–30 ma, some of them separated into Sauropodomorphs, Theropods and Herrerasaurids), as well as the first pterosaurs . During the Late Triassic, some advanced cynodonts gave rise to the first Mammaliaformes . All this climatic change, however, resulted in
224-529: A coating. This contrasts with the earth's current flora, in which the dominant land plants in terms of number of species are angiosperms . The earliest members of the genus Ginkgo first appeared during the Middle Jurassic. This genus is represented today by a single species, Ginkgo biloba . Modern conifer groups began to radiate during the Jurassic. Bennettitales , an extinct group of gymnosperms with foliage superficially resembling that of cycads gained
280-600: A decline in diversity of sauropods, stegosaurs, and other high-browsing groups, with sauropods particularly scarce in North America. Some island-hopping dinosaurs, such as Eustreptospondylus , evolved to cope with the coastal shallows and small islands of ancient Europe. Other dinosaurs rose up to fill the empty space that the Jurassic-Cretaceous extinction left behind, such as Carcharodontosaurus and Spinosaurus . Seasons came back into effect and
336-477: A few million years before the Triassic–Jurassic extinction event. Sea levels began to rise during the Jurassic, probably caused by an increase in seafloor spreading . The formation of new crust beneath the surface displaced ocean waters by as much as 200 m (656 ft) above today's sea level, flooding coastal areas. Furthermore, Pangaea began to rift into smaller divisions, creating new shoreline around
392-424: A global distribution during the Late Triassic, and represented one of the most common groups of Mesozoic seed plants. Flowering plants radiated during the early Cretaceous, first in the tropics , but the even temperature gradient allowed them to spread toward the poles throughout the period. By the end of the Cretaceous, angiosperms dominated tree floras in many areas, although some evidence suggests that biomass
448-671: A large die-out known as the Triassic–Jurassic extinction event, in which many archosaurs (excluding pterosaurs, dinosaurs and crocodylomorphs ), most synapsids , and almost all large amphibians became extinct, as well as 34% of marine life, in the Earth's fourth mass extinction event. The cause is debatable; flood basalt eruptions at the Central Atlantic magmatic province is cited as one possible cause. The Jurassic ranges from 200 million years to 145 million years ago and features three major epochs: The Early Jurassic,
504-568: A minority of studies have suggested that it might have been a deinonychosaur instead. Several older (but non flight-capable) possible avialans are known from the late Jurassic Tiaojishan Formation of China , dated to about 160 million years ago. Most researchers define Avialae as branch-based clade, though definitions vary. Many authors have used a definition similar to "all theropods closer to birds than to Deinonychus ." A nearly identical definition, "the theropod group that includes all taxa closer to Passer than to Dromaeosaurus ",
560-435: A variety of niches, beginning in the mid-Triassic 4 million to 6 million years after the extinction, and not fully proliferated until 30 million years after the extinction. Animal life was then dominated by various archosaurs: dinosaurs , pterosaurs, and aquatic reptiles such as ichthyosaurs, plesiosaurs, and mosasaurs . The climatic changes of the late Jurassic and Cretaceous favored further adaptive radiation. The Jurassic
616-637: Is an avialan, and not a member of Aves. Gauthier's proposals have been adopted by many researchers in the field of paleontology and bird evolution, though the exact definitions applied have been inconsistent. Avialae, initially proposed to replace the traditional fossil content of Aves, is sometimes used synonymously with the vernacular term "bird" by these researchers. † Anchiornis † Archaeopteryx † Rahonavis † Jixiangornis † Jeholornis [REDACTED] † Sapeornis † Confuciusornis [REDACTED] † Chongmingia Ornithothoraces [REDACTED] The earliest known avialans come from
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#1732790969153672-537: Is thought that a large meteor smashed into earth 66 million years ago, creating the Chicxulub Crater in an event known as the K-Pg Extinction (formerly K-T), the fifth and most recent mass extinction event, in which 75% of life became extinct, including all non-avian dinosaurs. Compared to the vigorous convergent plate mountain-building of the late Paleozoic, Mesozoic tectonic deformation
728-669: The Cenozoic . The era began in the wake of the Permian–Triassic extinction event , the largest mass extinction in Earth's history, and ended with the Cretaceous–Paleogene extinction event , another mass extinction whose victims included the non-avian dinosaurs , pterosaurs , mosasaurs , and plesiosaurs . The Mesozoic was a time of significant tectonic, climatic, and evolutionary activity. The supercontinent Pangaea began to break apart into separate landmasses. The climate of
784-704: The Greek prefix meso- ( μεσο- 'between') and zōon ( ζῷον 'animal, living being'). In this way, the Mesozoic is comparable to the Cenozoic ( lit. ' new life ' ) and Paleozoic ('old life') eras as well as the Proterozoic ('earlier life') Eon. The Mesozoic Era was originally described as the "secondary" era, following the "primary" ( Paleozoic ), and preceding the Tertiary . Following
840-711: The Indian subcontinent , which collided with the Asian plate during the Cenozoic, giving rise to the Himalayas . The Triassic was generally dry, a trend that began in the late Carboniferous , and highly seasonal, especially in the interior of Pangaea. Low sea levels may have also exacerbated temperature extremes. With its high specific heat capacity , water acts as a temperature-stabilizing heat reservoir, and land areas near large bodies of water—especially oceans—experience less variation in temperature. Because much of Pangaea's land
896-561: The Permian Period allowed for the radiation of many new lifeforms. In particular, the extinction of the large herbivorous pareiasaurs and carnivorous gorgonopsians left those ecological niches empty. Some were filled by the surviving cynodonts and dicynodonts , the latter of which subsequently became extinct. Recent research indicates that it took much longer for the reestablishment of complex ecosystems with high biodiversity, complex food webs, and specialized animals in
952-726: 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 and Aurornis xui . Xiaotingia zhengi used to be considered a member, but was later classified within the clade Dromaeosauridae . The well-known 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
1008-516: The Triassic , Jurassic and Cretaceous Periods . It is characterized by the dominance of gymnosperms such as cycads , ginkgoaceae and araucarian conifers, and of archosaurian reptiles such as the dinosaurs ; a hot greenhouse climate; and the tectonic break-up of Pangaea . The Mesozoic is the middle of the three eras since complex life evolved : the Paleozoic , the Mesozoic, and
1064-426: The birds , and their closest relatives. It is usually defined as all theropod dinosaurs more closely related to birds (Aves) than to deinonychosaurs , though alternative definitions are occasionally used (see below). Archaeopteryx lithographica , from the late Jurassic Period Solnhofen Formation of Germany , is usually considered the earliest known avialan which may have had the capability of powered flight;
1120-458: The Atlantic seaway, which has grown continually larger until today. The further separation of the continents gave opportunity for the diversification of new dinosaurs. The Cretaceous is the longest period of the Mesozoic, but has only two epochs: Early and Late Cretaceous. The Early Cretaceous spans from 145 to 100 million years ago. The Early Cretaceous saw the expansion of seaways and
1176-778: The Cretaceous–Paleogene extinction event. Approximately 50% of all genera became extinct, including all of the non- avian dinosaurs. The Triassic ranges roughly from 252 million to 201 million years ago, preceding the Jurassic Period. The period is bracketed between the Permian–Triassic extinction event and the Triassic–Jurassic extinction event , two of the " big five ", and it is divided into three major epochs: Early, Middle, and Late Triassic. The Early Triassic, about 252 to 247 million years ago,
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#17327909691531232-545: The Jurassic, having evolved from a branch of theropod dinosaurs, then true toothless birds appeared in the Cretaceous. The first mammals also appeared during the Mesozoic, but would remain small—less than 15 kg (33 lb)—until the Cenozoic. Flowering plants appeared in the Early Cretaceous and would rapidly diversify through the end of the era, replacing conifers and other gymnosperms ( sensu lato ), such as ginkgoales , cycads and bennettitales as
1288-465: The Late Cretaceous declined for poorly understood reasons, though this might be due to tendencies of the fossil record, as their diversity seems to be much higher than previously thought. Birds became increasingly common and diversified into a variety of enantiornithe and ornithurine forms. Though mostly small, marine hesperornithes became relatively large and flightless, adapted to life in
1344-539: The Late Jurassic to the Tertiary Oligocene. The only other to cross a period boundary is Paracymatoceras which lived during both the Late Jurassic and Early Cretaceous. The others are restricted to a simple period, sometimes to a single epoch. Mesozoic The Mesozoic Era is the era of Earth's geological history , lasting from about 252 to 66 million years ago , comprising
1400-779: The Lower Jurassic Cenoceras ( Nautilidae ) and extend as far as the Oligocene . Ten cymatoceratid genera are described in the Treatise Part K, 1964. First to appear was the large, tightly involute, rapidly expanding Procymatoceras from the Middle Jurassic , followed by the Middle and Upper Jurassic Cymatonautilus which has a wide umbilicus and subquadrate whorl section. Procymatoceras and Cymatonautilus are followed by Cymatoceras and
1456-469: The Mesozoic was varied, alternating between warming and cooling periods. Overall, however, the Earth was hotter than it is today. Dinosaurs first appeared in the Mid-Triassic, and became the dominant terrestrial vertebrates in the Late Triassic or Early Jurassic, occupying this position for about 150 or 135 million years until their demise at the end of the Cretaceous. Archaic birds appeared in
1512-498: The Middle Jurassic, and the Late Jurassic. The Early Jurassic spans from 200 to 175 million years ago. The climate was tropical and much more humid than the Triassic, as a result of the large seas appearing between the land masses. In the oceans, plesiosaurs , ichthyosaurs and ammonites were abundant. On land, dinosaurs and other archosaurs staked their claim as the dominant race, with theropods such as Dilophosaurus at
1568-628: The Paleozoic, the Mesozoic extended roughly 186 million years, from 251.902 to 66 million years ago when the Cenozoic Era began. This time frame is separated into three geologic periods . From oldest to youngest: The lower boundary of the Mesozoic is set by the Permian–Triassic extinction event , during which it has been estimated that up to 90-96% of marine species became extinct although those approximations have been brought into question with some paleontologists estimating
1624-474: The Tethys Ocean. Temperatures continued to increase, then began to stabilize. Humidity also increased with the proximity of water, and deserts retreated. The climate of the Cretaceous is less certain and more widely disputed. Probably, higher levels of carbon dioxide in the atmosphere are thought to have almost eliminated the north–south temperature gradient : temperatures were about the same across
1680-540: The actual numbers as low as 81%. It is also known as the "Great Dying" because it is considered the largest mass extinction in the Earth's history. The upper boundary of the Mesozoic is set at the Cretaceous–Paleogene extinction event (or K–Pg extinction event ), which may have been caused by an asteroid impactor that created Chicxulub Crater on the Yucatán Peninsula . Towards the Late Cretaceous, large volcanic eruptions are also believed to have contributed to
1736-521: The beginnings of the breakup of Pangaea and the opening of the Tethys Ocean . Ecosystems had recovered from the Permian extinction. Algae, sponge, corals, and crustaceans all had recovered, and new aquatic reptiles evolved, such as ichthyosaurs and nothosaurs . On land, pine forests flourished, as did groups of insects such as mosquitoes and fruit flies. Reptiles began to get bigger and bigger, and
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1792-526: The birds that descended from them. The clade Avialae was given a formal phylogenetic definition in the PhyloCode by Juan Benito and colleagues in 2022 as "the largest clade containing Vultur gryphus , but not Dromaeosaurus albertensis and Saurornithoides mongoliensis ". This definition ensures that both dromaeosaurids and troodontids are excluded from Avialae . Gauthier and de Queiroz (page 34) identified four conflicting ways of defining
1848-431: The current level (about 21%) throughout the Mesozoic, some concluding they were lower in the Triassic and part of the Jurassic but higher in the Cretaceous, and some concluding they were higher throughout most or all of the Triassic, Jurassic and Cretaceous. The dominant land plant species of the time were gymnosperms , which are vascular, cone-bearing, non-flowering plants such as conifers that produce seeds without
1904-404: The dawn of the Mesozoic, ocean plankton communities transitioned from ones dominated by green archaeplastidans to ones dominated by endosymbiotic algae with red-algal-derived plastids. This transition is speculated to have been caused by an increasing paucity of many trace metals in the Mesozoic ocean. Avialae Avialae ("bird wings") is a clade containing the only living dinosaurs ,
1960-636: The definition of Avialae. Troodon had long been considered a close relative of the dromaeosaurids in the larger group Deinonychosauria, though some contemporary studies found it and other troodontids more closely related to modern birds, and so it has been specifically excluded from Avialae in more recent studies. Avialae is also occasionally defined as an apomorphy-based clade (that is, one based on derived characteristics that were not present among lineage predecessors). Jacques Gauthier , who named Avialae in 1986, re-defined it in 2001 as all dinosaurs that possessed feathered wings used in flapping flight , and
2016-457: The dominant group of plants. The phrase "Age of Reptiles" was introduced by the 19th century paleontologist Gideon Mantell who viewed it as dominated by diapsids such as Iguanodon , Megalosaurus , Plesiosaurus , and Pterodactylus . The current name was proposed in 1840 by the British geologist John Phillips (1800–1874). "Mesozoic" literally means 'middle life', deriving from
2072-605: The dramatic rifting of the supercontinent Pangaea, which gradually split into a northern continent, Laurasia , and a southern continent, Gondwana . This created the passive continental margin that characterizes most of the Atlantic coastline (such as along the U.S. East Coast ) today. By the end of the era, the continents had rifted into nearly their present forms, though not their present positions. Laurasia became North America and Eurasia , while Gondwana split into South America , Africa , Australia , Antarctica and
2128-467: The fern prairies, chased by many new predators such as Allosaurus . Conifer forests made up a large portion of the forests. In the oceans, plesiosaurs were quite common, and ichthyosaurs flourished. This epoch was the peak of the reptiles. The Late Jurassic spans from 163 to 145 million years ago. During this epoch, the first avialans , such as Archaeopteryx , evolved from small coelurosaurian dinosaurs. The increase in sea levels opened up
2184-467: The first crocodilians and dinosaurs evolved, which sparked competition with the large amphibians that had previously ruled the freshwater world, respectively mammal-like reptiles on land. Following the bloom of the Middle Triassic, the Late Triassic, from 237 to 201 million years ago, featured frequent heat spells and moderate precipitation (10–20 inches per year). The recent warming led to
2240-487: The food web. In the oceans, mosasaurs ruled, filling the role of the ichthyosaurs, which, after declining, had disappeared in the Cenomanian-Turonian boundary event . Though pliosaurs had gone extinct in the same event, long-necked plesiosaurs such as Elasmosaurus continued to thrive. Flowering plants, possibly appearing as far back as the Triassic, became truly dominant for the first time. Pterosaurs in
2296-432: The fossil record. The Late Cretaceous spans from 100 to 66 million years ago. The Late Cretaceous featured a cooling trend that would continue in the Cenozoic Era. Eventually, tropics were restricted to the equator and areas beyond the tropic lines experienced extreme seasonal changes in weather. Dinosaurs still thrived, as new taxa such as Tyrannosaurus , Ankylosaurus , Triceratops and hadrosaurs dominated
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2352-437: The latter were lost independently in a number of avialan groups, including modern birds (Aves). While the earliest forms, such as Archaeopteryx and Shenzhouraptor , retained the long bony tails of their ancestors, the tails of more advanced avialans were shortened with the advent of the pygostyle bone in the group Pygostylia . In the late Cretaceous, around 95 million years ago, the ancestor of all modern birds also evolved
2408-459: The open sea. Metatherians and primitive eutherian also became common and even produced large and specialised genera such as Didelphodon and Schowalteria . Still, the dominant mammals were multituberculates, cimolodonts in the north and gondwanatheres in the south. At the end of the Cretaceous, the Deccan traps and other volcanic eruptions were poisoning the atmosphere. As this continued, it
2464-437: The planet, and about 10° C higher than today. The circulation of oxygen to the deep ocean may also have been disrupted, preventing the decomposition of large volumes of organic matter, which was eventually deposited as " black shale ". Different studies have come to different conclusions about the amount of oxygen in the atmosphere during different parts of the Mesozoic, with some concluding oxygen levels were lower than
2520-641: The poles got seasonally colder, but some dinosaurs still inhabited the polar forests year round, such as Leaellynasaura and Muttaburrasaurus . The poles were too cold for crocodiles, and became the last stronghold for large amphibians such as Koolasuchus . Pterosaurs got larger as genera such as Tapejara and Ornithocheirus evolved. Mammals continued to expand their range: eutriconodonts produced fairly large, wolverine -like predators such as Repenomamus and Gobiconodon , early therians began to expand into metatherians and eutherians , and cimolodont multituberculates went on to become common in
2576-542: 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. It is also thought that early avialans were either cranially akinetic or had otherwise limited cranial kinesis . Avialans diversified into a wide variety of forms during the Cretaceous Period . Many groups retained primitive characteristics , such as clawed wings and teeth, though
2632-734: The similar Paracymatoceras . Six genera are restricted to the Cretaceous ; Eucymatoceras and Heminautilus from the Lower Cretaceous; Anglonautilus from both the Lower and Upper Cretaceous; Deltocymatoceras , Epicymatoceras , and Syrionautilus . Neocymatoceras from the Oligocene is synonymous with Cymatoceras . Of the Cymatoceratidae, Cymatoceras has the longest temporal range, extending from
2688-409: The term "Aves", which is a problem since the same biological name is being used four different ways. They proposed a solution, number 4 below, which is to reserve the term Aves only for the crown group , the last common ancestor of all living birds and all of its descendants. Other definitions of Aves found in literature were reassigned to other clade names. Under the fourth definition Archaeopteryx
2744-506: The top of the food chain. The first true crocodiles evolved, pushing the large amphibians to near extinction. All-in-all, archosaurs rose to rule the world. Meanwhile, the first true mammals evolved, remaining relatively small, but spreading widely; the Jurassic Castorocauda , for example, had adaptations for swimming, digging and catching fish. Fruitafossor , from the late Jurassic Period about 150 million years ago,
2800-531: Was about the size of a chipmunk, and its teeth, forelimbs and back suggest that it dug open the nests of social insects (probably termites , as ants had not yet appeared) ; Volaticotherium was able to glide for short distances, such as modern flying squirrels . The first multituberculates such as Rugosodon evolved. The Middle Jurassic spans from 175 to 163 million years ago. During this epoch, dinosaurs flourished as huge herds of sauropods, such as Brachiosaurus and Diplodocus , filled
2856-928: Was comparatively mild. The sole major Mesozoic orogeny occurred in what is now the Arctic , creating the Innuitian orogeny , the Brooks Range , the Verkhoyansk and Cherskiy Ranges in Siberia, and the Khingan Mountains in Manchuria. This orogeny was related to the opening of the Arctic Ocean and suturing of the North China and Siberian cratons to Asia. In contrast, the era featured
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#17327909691532912-537: Was distant from its shores, temperatures fluctuated greatly, and the interior probably included expansive deserts . Abundant red beds and evaporites such as halite support these conclusions, but some evidence suggests the generally dry climate of the Triassic was punctuated by episodes of increased rainfall. The most important humid episodes were the Carnian Pluvial Event and one in the Rhaetian ,
2968-538: Was dominated by deserts in the interior of the Pangaea supercontinent. The Earth had just witnessed a massive die-off in which 95% of all life became extinct, and the most common vertebrate life on land were Lystrosaurus , labyrinthodonts , and Euparkeria along with many other creatures that managed to survive the Permian extinction. Temnospondyls reached peak diversity during the early Triassic. The Middle Triassic, from 247 to 237 million years ago, featured
3024-602: Was still dominated by cycads and ferns until after the Cretaceous–Paleogene extinction. Some plant species had distributions that were markedly different from succeeding periods; for example, the Schizeales , a fern order, were skewed to the Northern Hemisphere in the Mesozoic, but are now better represented in the Southern Hemisphere. The extinction of nearly all animal species at the end of
3080-485: Was the height of archosaur diversity, and the first birds and eutherian mammals also appeared. Some have argued that insects diversified in symbiosis with angiosperms, because insect anatomy , especially the mouth parts, seems particularly well-suited for flowering plants. However, all major insect mouth parts preceded angiosperms, and insect diversification actually slowed when they arrived, so their anatomy originally must have been suited for some other purpose. At
3136-441: Was used by Agnolín and Novas (2013) for their clade Averaptora , operating under the assumption that troodontids and birds were more closely related to each other than to dromaeosaurs. They also redefine Avialae as the smallest clade containing Archaeopteryx and modern birds. Additionally, beginning in the late 2000s and early 2010s, several groups of researchers began adding the genus Troodon as an additional specifier in
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