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Yuornis
Yuornis is a genus of Late Cretaceous Enantiornithine bird from Henan, China. It contains one species, Yuornis junchangi.

Yuanchuavis
Yuanchuavis is a genus of Pengornithid in the group Enantiornithes. Its type and only species, Y. kompsosoura, was found fossilized with a fan of highly graduated rectrices.

See Also: Yuanchuavis

 * Enantiornitheans

Ypupiara
Ypupiara is a genus of unenlagiinae theropod.

Yanjisuchus
Yanjisuchus is an extinct genus of paralligatorid neosuchian known from the Early Cretaceous Longjing Formation of Guizhou, China. It contains a single species, Y. longshanensis.

Yamatosaurus
Yamatosaurus is a genus of basal hadrosaurid from the Late Cretaceous Kita-Ama Formation of Japan. The genus contains a single species, Yamatosaurus izanagii.

Yakemys
Yakemys is an extinct genus of macrobaenid turtles from the Late Jurassic-Early Cretaceous (Tithonian-Valanginian?) lower Phu Kradung Formation of Thailand. It is monotypic, containing a single species, Yakemys multiporcata. Its genus name is derived from ยักษ์ (yak), meaning "giant" in Thai, and its species name from Latin "multi" (multiple) and "porca" (ridge).

Discovery: Yakemys
Yakemys hails from fossil turtle site Ban Huai Yang (บ้านห้วยยาง) of Northeast Thailand, which, although expected to be within the later Phra Wihan Formation based on its geographic location, is thought to instead belong to the Phu Kradung Formation based on sedimentology. The recovered holotype of Yakemys multiporcata SM KS39 (housed in the Sirindhorn Museum) consists of a very partial shell, and the paratype PRC 151

Xenodens
Xenodens ("strange tooth") is an extinct genus of marine lizard belonging to the mosasaur family. It currently contains a single species, X. calminechari (From Arabic کالمنشار, meaning "like a saw"), which is known from Late Maastrichtian phosphate deposits in the Ouled Abdoun Basin, Morocco. Its closest known relative is believed to be the durophagous Carinodens.

Estimated to have measured around 1.6 m in length, both the genus and type species are named for the mosasaur's short and flattened blade-like teeth that collectively form a set of saw-like jaws. This is a feature that has never been seen in any other tetrapod but converge with the jaws of modern dogfish sharks and piranhas. Based on the feeding behavior of these animals, paleontologists believe that Xenodus used its highly specialized dentition for a broad diet on cephalopods, crustaceans, fish, and scavenged marine reptiles.

See Also: Xenodens

 * Mosasaurs

Vinitasaura
Vinitasaura is an extinct genus of lepidosauromorph from the Late Triassic of Virginia. It contains a single species, Vinitasaura lizae, which is based on a complete jaw and jaw fragment from the Carnian-age Vinita Formation of the Richmond Basin. Vinitasaura lived alongside several other lepidosauromorphs, including the sphenodontian Micromenodon and an undescribed pleurodont taxon. The Vinita Formation has the oldest lepidosauromorph assemblage found in North America, shedding light on the early diversification and dispersal of this reptile group.

See Also: Vinitasaura

 * Lepidosauromorphs
 * 2021 in paleontology

Vectiraptor
Vectiraptor is a genus of dromaeosaurid dinosaur from the Barremian age Wessex Formation of the United Kingdom. The type and only species is V. greeni, known from associated dorsal vertebrae and a partial sacrum.

Ulughbegsaurus
Ulughbegsaurus (meaning "Ulugh Beg's lizard") is a genus of carcharodontosaurian theropod dinosaur from the Late Cretaceous of Uzbekistan. The type species is Ulughbegsaurus uzbekistanensis.

See Also: Ulughbegsaurus

 * Carcharodontosauria
 * 2021 in paleontology

Ueekenkcoracias
Ueekenkcoracias is a genus of primobucconid coraciiform from the Huitrera Formation of Patagonia.<ref name="degrangeetal2021"/ A relatively large member of the stem-Coracii, Ueekenkcoracias possessed a robust femur and stout tibiotarsus, with a strongly projected facies articularis medialis.

Etymology: Ueekenkcoracias
The generic name of Ueekenkcoracias is derived from the native Tehuelche word ueekenk, meaning "outsider" in reference to its unusual presence in South America, and the genus name Coracias. The specific epithet honors Claudia Patricia Tambussi, who majorly contributed to paleornithology, particularly in South America.

Description: Ueekenkcoracias
The holotype specimen of Ueekenkcoracias consists of an incomplete right leg, preserved as a part and counterpart.

Trullidens
Trullidens is an extinct genus of sphenodontian from the Late Triassic Ischigualasto Formation of Argentina. The type species is Trullidens purgatorii.

Triamyxa
Triamyxa is an extinct genus of myxophagan beetle in the monotypic family Triamyxidae that is from the Late Triassic, approximately 230 million years ago in the Carnian faunal stage of what is now the Keuper Claystone of Poland. The type species is T. coprolithica and it was identified from specimens found in the coprolite of the dinosauriform Silesaurus opolensis. Because Triamyxa specimens were found inside coprolites, this may offer a new method of finding insect fossils aside from amber.

The specimens were preserved in 3D, with their legs and antennae intact and Triamyxa was likely consumed on by accident by Silesaurus while eating other animals, likely larger insects, and the specimens were likely not chewed much, which explains why one Triamyxa specimen was intact and the rest were fragmentary and Triamyxa was also probably present in the environment in large numbers.

Tlatolophus
Tlatlolophus is a genus of hadrosaur.

Tika giacchinoi
'Tika'' is an extinct genus of sphenodontian from the Late Cretaceous Candeleros Formation of Argentina. The type species is Tika giacchinoi.

Thapunngaka
Thapunngaka (Spear Mouth in Wanamara) is a genus pterosaur recovered from Queensland, found in the marine Toolebuc Formation. Native to the Early Cretceous, it was an an Anhanguerid.

Terropterus
Terropterus is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of the single and type species, T. xiushanensis, have been discovered in deposits of the Early Silurian period (Llandovery epoch) in China. Some fossils of Terropterus have not been assigned to any species as they differ slightly from T. xiushanensis, but too little material is known to determine whether these fossils represent another species of Terropterus or only an ontogenetic stage (a different developmental stage of the same animal throughout its life) of T. xiushanensis.

Terropterus is classified in the family Mixopteridae together with Mixopterus and Lanarkopterus, being the oldest known mixopterid to date and the only one found in the paleocontinent Gondwana and not in Laurussia, another paleocontinent. This genus differs from Mixopterus and Lanarkopterus mainly in the morphology of its appendages (limbs) and forms a group with Lanarkopterus within Mixopteridae, both being the sister group (closest relative) of each genera.

See Also: Terropterus

 * List of eurypterid genera
 * Timeline of eurypterid research
 * 2021 in paleontology
 * Diploperculata

Taytalura
Taytalura is an extinct genus of lepidosauromorph reptile from the Late Triassic of Argentina. It contains a single species, Taytalura alcoberi, which is based on a well-preserved skull from the late Carnian Ischigualasto Formation. Although Taytalura did not belong to any group of modern lepidosaurs, micro-CT scanning reveals features of the skull previously only seen in sphenodontians (tuatara and kin). This suggests that the ancestral condition of the skull in lepidosaurs was more similar to sphenodontians than to squamates (lizards and kin).

See Also: Taytalura

 * 2021 in paleontology

Tamarro
Tamarro (named after a mythological creature in local culture) is a genus of troodontid theropod from the Late Cretaceous of Spain. The genus contains a single species, Tamarro insperatus.

Tamarro (named after a mythological creature in local culture) is a genus of troodontid theropod from the Late Cretaceous of Spain. The genus contains a single species, Tamarro insperatus.

Tacuadactylus
Tacuadactylus is a genus of ctenochasmatid pterosaur from the Late Jurassic of Uruguay. It was recovered from rocks in the Batoví Member of the Tacuarembó Formation. The type species is T.luciae.

See Also: Tacuadactylus

 * 2021 in paleontology

Syntomiprosopus
Syntomiprosopus (meaning "short face") is an extinct genus of archosauriform, possibly a crocodylomorph from the Late Triassic period of Arizona. The type and only known species is S. sucherorum. Syntomiprosopus was unusually short-snouted, comparable to the Late Cretaceous notosuchian Simosuchus, and is regarded as an example of convergent evolution between Triassic stem-archosaurs and Cretaceous archosaurs.

Discovery and naming: Syntomiprosopus
Fossils of Syntomiprosopus were discovered at a locality in the Downs' Quarry located in eastern Arizona, just above the "Placerias Quarry" and just below the principal horizon of the Downs' Quarry. The fossils were recovered during joint excavations by the North Carolina Museum of Natural Sciences (NCSM) and Appalachian State University (ASU) between 2013–2015 as part of a series of excavations that had begun in 2010. The quarry is part of the expansive Late Triassic Chinle Formation, and has been radiometrically dated to have been deposited at a maximum age of approximately 219.39 ± 0.16 million years old.

The holotype specimen (NCSM 29059–29060) consists of two associated pieces of a complete right mandible, along with the paratypes NCSM 26729 (an articular complex from the rear of the left jaw), NCSM 26730 (the front of a left mandible), NCSM 27677 (the middle portion of a left mandible), NCSM 27678 (another left articular complex) and NCSM 29061 (a right articular complex). These belong to at least two, but possibly up to four individuals. Part of the back of a skull and braincase (NCSM 27679) found associated with the jaw material may also belong to Syntomiprosopus, as well as some sacral vertebrae (NCSM 27991 and NCSM 27992), but they cannot be definitively referred to Syntomiprosopus on anatomical grounds. However, because there are no other similarly sized vertebrates in the fossil bed that it can be referred to, has identical preservation, and that it does not match any previously known animal from the Downs' Quarry, Heckert and colleagues were confident in referring the skull to Syntomiprosopus.

Heckert and colleagues named Syntomiprosopus from the Greek prefix syntomi- ("short") and prosopus ("face") to refer to its characteristically short jaws. The specific name sucherorum is in honour of Scott ("Major") and Karen Sucher, who had voluntarily spent 22 years supporting and aiding Heckert and his colleagues, including participating in the excavations at Downs' Quarry that discovered the remains of Syntomiprosopus.

Description: Syntomiprosopus
Syntomiprosopus'' is only known by bones of the lower jaw and potentially part of the braincase. However, the lower jaw is distinct amongst Late Triassic reptiles, being short and almost as broad as they are long, meeting with a U-shaped curve at their tips. The lower jaw is robust, approximately 2.5x as long as high, and is twice as deep at its end as the tips. They have a coarse and roughly textured surface with irregularly placed pits and grooves without any clear pattern.

Syntomiprosopus has very few teeth, with the smallest specimen having only eight active tooth positions and the largest specimen only four. The teeth are divided into a set 2—4 front teeth that are procumbent (angled forwards), a large canine-like (caniniform) tooth, followed by up to 3 small postcanine teeth, the smallest set in the toothrow. In larger specimens, the tooth sockets for these postcanines are resorbed into the jaw bone, and the teeth are lost. The teeth themselves are asymmetrical, with a flat outer surface and bulbous inner surface, and appear to have large denticles (serrations) along their edges.

Classification: Syntomiprosopus
Syntomiprosopus'' is evidenced to be an archosauriform, based on the presence of the mandibular fenestra and serrated teeth. However, no characteristics are identifiable in the lower jaw to identify its affinities beyond Archosauriformes. Notably, the rugose mandibular symphysis, large caniniform tooth, short prearticular, and the angular that is well exposed on the internal side of the jaw are all characteristics variably found in crocodylomorphs, although the first two traits are also found elsewhere in archosauriforms.

The braincase and back of the skull, if correctly referred to Syntomiprosopus, may further indicate affinities to early crocodylomorphs. Crocodylomorph characteristics of this skull include a sagittal crest along the midline (formed by fused, raised parietal bones), the rear edge of the parietals diverge at almost 90° from the midline of the skull, a contact between the laterosphenoid and parabasisphenoid of the braincase, and a possible contact between the prootic bone of the middle ear and quadrate bone on the external surface of the skull.

However, the partial skull also lacks characteristics found in more derived crocodylomorphs (such as deep hollow on the underside of the basioccipital, or on the parabasisphenoid)) and preserves features lost in more derived crocodylomorphs (such as the entrances for the internal carotid arteries being placed high on the skull and modifications to the middle ear). This combination of traits indicate that if Syntomiprosopus is indeed a crocodylomorph, it must be a relatively basal early-diverging species, less derived than Sphenosuchus.

Paleobiology: Syntomiprosopus
The smaller specimen of Syntomiprosopus preserves more open tooth sockets, four in front, a canine-like tooth, and three postcanine teeth behind. The larger specimen only preserves the three front teeth and the caniniform, with the remaining tooth sockets behind being either fully or partially resorbed into the jaw bone. This suggests that Syntomiprosopus lost these teeth as it matured, losing close to half of its dentition. Some archosaurs are known to decrease their tooth counts as they mature (e.g. tyrannosaurids and possibly modern crocodylians), however, only Limusaurus shows a similarly drastic loss in teeth between juveniles and adults (whereby juveniles have sharp, pointed teeth that are lost for a beak in adults).

Palaeocology: Syntomiprosopus
The only other fossils recovered from the same layers as Syntomiprosopus are of indeterminate phytosaurs. However, the layers immediately below and above contain fossils of the herbivorous armoured aetosaurs Desmatosuchus, Calyptosuchus and Tecovasuchus, as well as a dicynodont (likely Placerias) and an unidentified allokotosaur.

See Also: Syntomiprosopus

 * Archosauriforms
 * Crocodylomorphs
 * 2021 in paleontology

Sumpalla
Sumpalla is an ophthalmosaurid ichthyosaur from the Late Jurassic Vaca Muerta Formation of Argentina. It contains a single species, S. argentina.

Stegouros
Stegouros is an ankylosaur.

Stauromatodon
Stauromatodon is an extinct genus of diapsid reptile, possibly related to Saurosphargidae, from the Middle Triassic Erfurt Formation of Germany. It contains a single species, Stauromatodon mohli.

Spicomellus
Spicomellus is an ankylosaurian dinosaur.

Sphenofontis
Sphenofontis is an extinct genus of sphenodontian reptile known from the Late Jurassic of Germany, with a single known species. S. veiserae It is known from a single nearly complete and articulated sub-adult specimen (SNSB-BSPG 1993 XVIII), found in the late Kimmeridgian aged Torleite Formation in Brunn quarry in Bavaria, Southern Germany. It is thought to be a close relative of the living tuatara (Sphenodon puncatus).

Sinomacrops
Sinomacrops is a genus of extinct anurognathid pterosaur from the Middle to Late Jurassic periods of what is now the Daohugou Beds of the Tiaojishan Formation in Mutoudeng, Qinglong County of the Hebei province. The remains of Sinomacrops date back around 164 and 158 million years ago. The type and only known species is Sinomacrops bondei

Sinocephale
Sinocephale is a genus of pachycephalosaurid dinosaur that lived in Inner Mongolia, China during the Cretaceous period. The type and only species S. bexelli, was originally named as a species of the genus Troodon in 1953, and later transferred to the genus Stegoceras. After decades of being considered dubious, it was re-evaluated in 2021 and recognized as a valid taxon, being given a unique generic name.

See Also: Sinocephale

 * Pachycephalosaurs
 * 1953 in paleontology
 * 2021 in paleontology

Silutitan
Silutitan is a genus of euhelopodid sauropod dinosaur from China.