Late Triassic first appearances

left|thumb|Skull of Xianshou, a [[euharamiyidan]] Allotheria (from Ancient Greek αλλός (allós), meaning "other", and θηρίον (theríon), meaning "beast") is an extinct clade of theriiform mammals known from the Mesozoic and early Cenozoic. Shared characteristics of the group are the presence of lower molariform teeth equipped with longitudinal rows of cusps and enlarged incisors. Typically, the canine teeth are also lost. Allotheria includes Multituberculata, Gondwanatheria (which may be part of Multituberculata, as the sister group to Cimolodonta), and probably Haramiyida, (sometimes only inclu

Ornithosuchidae is an extinct family of pseudosuchian archosaurs (distant relatives of modern crocodilians) from the Triassic period. Ornithosuchids were quadrupedal and facultatively bipedal (e.g. like chimpanzees), meaning that they had the ability to walk on two legs for short periods of time. They had distinctive, downturned snouts, unique, "crocodile-reversed" ankle bones, and several other features that distinguish them from other archosaurs. Ornithosuchids were geographically widespread during the Carnian and Norian stages of the Late Triassic with members known from Argentina, Brazil,

Pachycormiformes is an extinct order of marine ray-finned fish known from the Early Jurassic to the end of the Cretaceous. Depending on the treatment, it only includes a single family, Pachycormidae, or two families: the mostly filter-feeding Pachycormidae and the carnivorous Protosphyraenidae. They were characterized by having serrated pectoral fins (though more recent studies demonstrated that fin shape diversity in this group was high), reduced pelvic fins and a bony rostrum. Pachycormiformes are morphologically diverse, containing both tuna and swordfish-like carnivorous forms, as well as

Californosaurus ('California lizard') is an extinct genus of ichthyosaur, an extinct marine reptile, from the Lower Hosselkus Limestone (Carnian, Late Triassic) of California, and also the Muschelkalk (Ladinian, Middle Triassic) of Germany.

Morganucodonta ("Glamorgan teeth") is an extinct order of basal Mammaliaformes, a group including crown-group mammals (Mammalia) and their close relatives. Their remains have been found in Southern Africa, Western Europe, North America, India and China. The morganucodontans were probably insectivorous and nocturnal, though like eutriconodonts some species attained large sizes and were carnivorous. Nocturnality is believed to have evolved in the earliest mammals in the Triassic (called the nocturnal bottleneck) as a specialisation that allowed them to exploit a safer, night-time niche, while mo

Poposauridae is a family of large carnivorous archosaurs which lived alongside dinosaurs during the Late Triassic. They were around long. Poposaurids are known from fossil remains from North and South America. While originally believed to be theropod dinosaurs (they mirrored the theropods in a number of respects, such as features of the skull and bipedal locomotion), cladistic analysis has shown them to be more closely related to crocodiles.

Tritheledontidae, the tritheledontids or ictidosaurs, is an extinct family of small to medium-sized (about 10 to 20 cm long) cynodonts. They were highly mammal-like, specialized cynodonts, although they still retained a few reptile-like anatomical traits. Tritheledontids were mainly carnivorous or insectivorous, though some species may have developed omnivory. Their skeletons show that they had a close relationship to mammals. Tritheledontids or their closest relatives may have given rise to the mammaliaforms. The tritheledontids were one of the longest lived non-mammalian therapsid linea

Tritylodontidae ("three-knob teeth", named after the shape of their cheek teeth) is an extinct family of small to medium-sized, highly specialized mammal-like cynodonts, with several mammalian traits including erect limbs, endothermy, and some details of the skeleton. They were the last-known family of the non-mammaliaform synapsids, persisting into the Early Cretaceous.

Leptonectidae is a family of ichthyosaurs known from Late Triassic to Early Jurassic marine deposits in Europe. They were all small to medium-sized creatures, most noted for their very long, swordfish-like snouts, which could have been used like a weapon, slashing through schools of fish.

Protosuchia is a group of extinct Mesozoic crocodyliforms. They were small in size (~1 meter in length) and terrestrial. In phylogenetic terms, Protosuchia is considered an informal group because it is a grade of basal crocodyliforms, not a true clade.

Toretocnemus (meaning 'perforated tibia') is an extinct genus of ichthyosaurs that lived during the Carnian stage of the Upper Triassic in what is now North America. Two species are known, T. californicus and T. zitelli, first described in 1903 by John Campbell Merriam from fossils discovered in the Hosselkus Limestone, Shasta County. The second species was first seen by Merriam as belonging to a distinct genus, but in 1999 it was reclassified into the original taxon. Toretocnemus fossils are primarily known from California, although some specimens are also reported from Alaska and Mexico. Wit

Clevosaurus (meaning "Gloucester lizard") is an extinct genus of rhynchocephalian reptile from the Late Triassic and the Early Jurassic periods. Species of Clevosaurus were widespread across Pangaea, and have been found on all continents except Australia and Antarctica. Five species of Clevosaurus have been found in ancient fissure fill deposits in south-west England and Wales, alongside other sphenodontians, early mammals and dinosaurs. In regards to its Pangaean distribution, C. hadroprodon is the oldest record of a sphenodontian from Gondwana, though its affinity to Clevosaurus has been que

Ecteniniidae is an extinct family of probainognathian cynodonts from the Triassic of South America. They are notable for their large size, as well as for being among the first synapsids with specializations towards cursoriality.

Leptosuchomorpha is a clade of phytosaurs. It is a node-based taxon defined by Michelle R. Stocker in 2010 as the last common ancestor of Leptosuchus studeri and Pseudopalatus pristinus and all of its descendants. A new definition was proposed by Andrew S. Jones and Richard J. Butler in 2018 as the last common ancestor and all descendants of Smilosuchus lithodendrorum, Leptosuchus studeri, and Machaeroprosopus pristinus to reflect the new interrelationships of Phytosauria they recovered.

Henodontidae is an extinct family of superficially turtle-like placodonts belonging to the superfamily Cyamodontoidea. Fossils have been found in Germany and Spain.

Protosuchidae is a family of basal crocodyliform reptiles that lived from the Late Triassic to the Late Cretaceous. This family should not be confused with Protosuchia, which is an informal evolutionary grade of primitive crocodyliforms

Mystriosuchini, historically known as Pseudopalatinae, is an extinct tribe (formerly subfamily) of derived phytosaurs in the clade Leptosuchomorpha. As with all other phytosaurs, mystriosuchins lived during Late Triassic. The name is derived from the genus Mystriosuchus, and the clade was phylogenetically defined by Andrew S. Jones and Richard J. Butler in 2018 as the last common ancestor and all descendants of Mystriosuchus planirostris, Machaeroprosopus jablonskiae, and Machaeroprosopus buceros.

Desmatosuchinae is a major subfamily of aetosaurs within the clade Desmatosuchia. It is a stem-based taxon defined as all aetosaurs more closely related to Desmatosuchus than to Stagonolepis, Aetosaurus, or Paratypothorax.

Kuehneotheriidae is an extinct family of mammaliaforms traditionally placed within 'Symmetrodonta', though now generally considered more basal than true symmetrodonts. All members of Kuehneotheriidae which have been found so far are represented only by teeth, but these teeth have features which have led paleontologists to classify kuehneotheriids as very close relatives of the first true mammals. But fossil clades based solely on teeth often lead to difficulties (Ausktribosphenidae being a good example), and it is not possible to draw significant conclusions about mammalian evolution from Kueh

Placochelyidae is an extinct family of placodonts belonging to the superfamily Cyamodontoidea.