Rhynchocephalia ("beak-heads") is an order of lizard-like reptiles that includes only one living species, the tuatara of New Zealand, which is thought to have two subspecies the latter was recognised as a separate species from 1989 to 2009.
Carnassials are paired upper and lower teeth modified in such a way as to allow enlarged and often self-sharpening edges to pass by each other in a shearing manner. The modification arose separately in several groups of carnivorous mammals. Different pairs of teeth were involved in the separate modifications. In modern Carnivora, the carnassials are the modified fourth upper premolar and the first lower molar. These teeth are also referred to as sectorial teeth. Humans lack carnassial teeth.
Tillodontia is an extinct suborder of eutherian mammals known from the Early Paleocene to Late Eocene of China, the Late Paleocene to Middle Eocene of North America where they display their maximum species diversity, the Middle Eocene of Pakistan, and the Early Eocene of Europe. Leaving no descendants, they are most closely related to the pantodonts, another extinct group. The tillodonts were medium- to large-sized animals that probably feed on roots and tubers in temperate to subtropical habitats.
Asiatosuchus is an extinct genus of crocodyloid crocodilians that lived in Eurasia during the Paleogene. Many Paleogene crocodilians from Europe and Asia have been attributed to Asiatosuchus since the genus was named in 1940. These species have a generalized crocodilian morphology typified by flat, triangular skulls. The feature that traditionally united these species under the genus Asiatosuchus is a broad connection or symphysis between the two halves of the lower jaw. Recent studies of the evolutionary relationships of early crocodilians along with closer examinations of the morphology of fossil specimens suggest that only the first named species of Asiatosuchus, A. grangeri from the Eocene of Mongolia, belongs in the genus. Most species are now regarded as nomina dubia or "dubious names", meaning that their type specimens lack the unique anatomical features necessary to justify their classification as distinct species. Other species such as "A." germanicus and "A." depressifrons are still considered valid species, but they do not form an evolutionary grouping with A. grangeri that would warrant them being placed together in the genus Asiatosuchus.
Bergisuchus is an extinct genus of small sebecosuchian mesoeucrocodylian known primarily from the Eocene Messel Pit in Germany. Few fossils of Bergisuchus have been discovered, only a single incomplete snout, a few partial lower jaws and some teeth. Despite being fragmentary, the jaw bones are enough to indicate that Bergisuchus had a short, deep, narrow snout and serrated teeth, quite unlike the broad flat snouts of modern crocodylians.
Culebrasuchus is an extinct genus of caiman known from the Early to Middle Miocene (Hemingfordian) of the Panama Canal Zone of Panama. It contains a single species, Culebrasuchus mesoamericanus.
Barbaturex is an extinct genus of giant herbivorous iguanian lizards from the Eocene of Myanmar. It is represented by a single species, Barbaturex morrisoni, which is known from several partial dentaries and a fused pair of frontals, two bones that form part of the top of the skull. Based on the size of these bones, Barbaturex morrisoni is estimated to have been about 1 metre (3.3 ft) from snout to vent, and possibly up to 6 feet (1.8 m) including the tail. Barbaturex morrisoni was named after The Doors frontman Jim Morrison, a play on his epithet "The Lizard King". The genus's name is a portmanteau of the Latin words Barbatus and rex, meaning "bearded king", in reference to ridges along the mandible and the lizard's large size.
Urtinotherium is an extinct genus of indricothere hyracodontid mammals. It was a large animal that was closely related to Paraceratherium, and found in rocks dating from the Late Eocene to Early Oligocene period. The remains were first discovered in the Urtyn Obo region in Inner Mongolia, which the name Urtinotherium is based upon. Other referred specimens are from northern China.
Olbitherium is an extinct mammal of the order Perissodactyla from the early Eocene epoch of Shandong, China.
Pyrenasaurus is an extinct genus of lizard that includes only one species, the type species Pyrenasaurus evansae, which lived around the Pyrenees mountains during the Late Eocene. P. evansae was named in 2014 on the basis of three dentaries, one from the Phosphorites du Quercy in Quercy, France and two from the Sossís fossil locality in Catalonia, Spain. The paucity of known material makes its relationships uncertain; it is either a true skink in the family Scincidae or a close relative of skinks in the larger group Scincoidea. Pyrenasaurus is very small for a lizard, with a dentary length of only 3.4 millimetres (0.13 in). It also has very few teeth for a lizard, with only eleven tooth positions in the dentary. Other unusual anatomical features include the shortness straightness of the jaw, the lack of a Meckelian groove on the inside of the dentary, and the enlargement and lateral compression of the posterior-most dentary teeth. Pyrenasaurus may have been a fossorial or burrowing lizard because a short, straight dentary with few teeth is also present in numerous living fossorial lizards, having evolved independently in many lineages. However, the extremely small size of Pyrenasaurus may have inhibited its ability to burrow. The enlarged posterior teeth of Pyrenasaurus suggest it had a specialized diet, but what it was eating remains unknown because no living lizards have similar dentitions.
Indiagama is an extinct genus of agamid lizard known from the type species Indiagama gujarata from the early Eocene of India. Indiagama was named in 2013 on the basis of a single lower jaw from the Cambay Shale in Gujarat. The rectangular shape of its teeth distinguish it from all other agamids, living and extinct.
Suratagama is an extinct genus of agamid lizard known from the type species Suratagama neeraae from the early Eocene of India. It was named in 2013 on the basis of three isolated jaw bones from the Cambay Shale in Gujarat.
Pleurodontagama is an extinct genus of iguanian lizard from the Late Cretaceous of Mongolia. The type species, Pleurodontagama aenigmatodes, was named in 1984 on the basis of a mostly complete skull and isolated lower jaw from a fossil locality called Khermeen Tsav. It has a wide skull with a flat snout, large eye sockets, and small bumps on the surfaces of the bones. Pleurodontagama was initially classified in the family Priscagamidae, which is usually grouped in a large clade of iguanians called Acrodonta, members of which are characterized by an "acrodont" dentition in which the teeth grow from the margins of the jaws. However, Pleurodontagama is unusual in that it has a sub-pleurodont dentition, meaning that some of its teeth grow from the inner surfaces of the jaw. There is also evidence to suggest that its teeth may have been continuously replaced throughout life, as opposed to the permanent teeth of acrodontans. Pleurodontagama may have been a transitional form between the derived acrodont type and the pleurodont type inferred for the ancestors of Acrodonta.
Phrynosomimus is an extinct genus of iguanian lizard from the Late Cretaceous of Mongolia belonging to the extinct family Priscagamidae. The type species Phrynosomimus asper was named in 1996. Fossils have been found in the Barun Goyot and Djadochta formations and include several complete skulls. Phrynosomimus has a short, triangular skull with bony spikes projecting from the back, stemming from the squamosal and parietal bones. These spikes give it a similar appearance to the modern horned lizard Phrynosoma and inspire its name, which means "Phrynosoma mimic". Like other priscagamids it has an acrodont dentition, meaning that its teeth grow from the margins of the jaws rather than their inner surfaces, as is the case for the pleurodont dentitions of most lizards.
Gueragama is an extinct genus of iguanian lizard from the Late Cretaceous of Brazil. It belongs to a group of iguanians called Acrodonta, whose living members include chameleons and agamids and are currently restricted to the Old World. Gueragama is the only acrodont known from South America, providing evidence that the group once ranged across much of Gondwana and only became restricted to the Old World after the supercontinent broke apart. The type species, Gueragama sulamericana, was named in 2015 on the basis of an isolated lower jaw from the Turonian- to Campanian-age Goio-Erê Formation in the Bauru Basin, which was deposited in a desert environment. Unlike modern acrodontans, whose teeth implant on the margins of the jaws, Gueragama has teeth that implant along the inner surface of the lower jaw, a feature common in most non-acrodontan lizards and characteristic of the second major group of iguanians, Pleurodonta. The non-acrodont dentition of Gueragama is evidence of its basal position within Acrodonta, and is shared with the taxon of Late Cretaceous acrodontan relatives, the family Priscagamidae.
Bharatagama is an extinct genus of iguanian lizard from the Early Jurassic of India. It is one of the oldest known lizards and the oldest known iguanian. The type and only species is Bharatagama rebbanensis, named in 2002. Over one hundred fossils of Bharatagama have been found in the Kota Formation, which outcrops in the Pranhita–Godavari Basin and dates back to about 190 million years ago (Ma). Despite its abundance, Bharatagama is known only from isolated jaw bones mixed together in microvertebrate assemblages with equally fragmentary remains of fish, sphenodontians, dinosaurs, crocodylomorphs, and mammals. These fossils represent all stages of development, from hatchlings to adults. The total length of the skull in adult specimens is estimated to have been about 15 millimetres (0.59 in).
Acrodonta are a subclade of iguanian squamates consisting almost entirely of Old World taxa. Extant representation include the families Chamaeleonidae (chameleons) and Agamidae, with at least over 500 species described. A fossil genus, Gueragama, was found in Brazil, making it the only known American representative of the group.
Opisthodontia is a clade of extinct sphenodontian rhynchocephalians. They first appeared in the late Triassic and survived at least as late as the Paleocene. While most rhynchocephalians, such as the modern tuatara, were carnivores or insectivores, opisthodonts were herbivorous. Advanced opisthodonts of the subfamily Eilenodontinae were among the largest rhynchocephalians known. Opisthodontia is defined as all rhynchocephalians closer to Priosphenodon than to Sphenodon (tuatara).
Clevosaurs are an extinct group of rhynchocephalian reptiles from the Triassic and Jurassic periods.
Azygonyx was a small tillodont mammal, likely the size of a cat to raccoon, that lived in North America during the Paleocene and Eocene in the early part of the Cenozoic Era. The only fossils that have been recovered are from the Willwood and Fort Union Formations in the Bighorn Basin of Wyoming, United States, and date to the Clarkforkian to Wasatchian, about 56 to 50 million years ago. Fifty-six collections that have been recovered thus far include the remains of Azygonyx. Azygonyx survived the Paleocene Eocene Thermal Maximum along with other mammals like Phenacodus and Ectocion, both of which were ground-dwelling mammals. Azygonyx probably was a generalist terrestrial mammal that may have roamed around the ground, but was also capable of climbing trees.
