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Rhynchosaurs are a group of extinct herbivorous Triassic Archosauromorpha , belonging to the order Rhynchosauria. Members of the group are distinguished by their triangular skulls and elongated, beak like Premaxilla. Rhynchosaurs first appeared in the Early Triassic, reaching their broadest abundance and a global distribution during the Carnian stage of the Late Triassic.
The teeth were unusual; those in the maxilla and palate were modified into broad tooth plates. The hind feet were equipped with massive claws, presumably for digging up roots and by backwards scratching of the hind limbs. They had a fixed number of teeth, and similar to , those that were further back in the jaws replaced teeth that were worn out as the animal grew in size and the teeth were worn out because of a diet of very tough plants. In the end, they likely starved to death. Ancient herbivore's diet weakened teeth and lead to eventual starvation, suggests study
Like many animals of this time, they had a worldwide distribution, being found across Pangea. These abundant animals might have died out suddenly at the end of the Carnian (Middle of the Late Triassic period), perhaps as a result of the extinction of the Dicroidium flora on which they may have fed. On the other hand, Spielmann, Lucas and Hunt (2013) described three distal ends of Humerus from early-mid Norian Bull Canyon Formation in New Mexico, which they interpreted as bones of rhynchosaurs belonging to the species Otischalkia; thus, the fossils might indicate that rhynchosaurs survived until the Norian. These fossils were later reinterpreted as belonging to Malerisaurinae Azendohsauridae.
| Ammorhynchus | A. navajoi | Anisian | ([[Arizona]])
| Moenkopi Formation A stenaulorhynchine. | |
| Beesiiwo | B. cooowuse | Carnian | ([[Wyoming]])
| Popo Agie Formation A hyperodapedontine previously referred to Hyperodapedon. | |
| Brasinorhynchus | B. mariantensis | Ladinian | Santa Maria Formation | A stenaulorhynchine, previously known as the "Mariante Rhynchosaur". | |
| Bentonyx | B. sidensis | late Anisian | ([[England]])
| Otter Sandstone Formation A basal hyperodapedontid. | |
| Elorhynchus | E. carrolli | late Ladinian? - earliest Carnian? | Chañares Formation ( Tarjadia Assemblage Zone) | A stenaulorhynchine. | |
| Eohyosaurus | E. wolvaardti | early Anisian | Burgersdorp Formation ( Cynognathus Assemblage Zone) A basal (non-rhynchosaurid) rhynchosaur. | ||
| Fodonyx | F. spenceri | late Anisian | (England)
| Otter Sandstone Formation A basal hyperodapedontid. | |
| Howesia | H. browni | early Anisian | Burgersdorp Formation ( Cynognathus Assemblage Zone) A basal (non-rhynchosaurid) rhynchosaur. | ||
| Hyperodapedon | H. gordoni | Carnian | ([[Scotland]])
| Lossiemouth Sandstone Formation| rowspan="6" | A hyperodapedontine, one of the most abundant and speciose rhynchosaur genera. Six valid species has been named, the most of any rhynchosaur. |
| H. huenei | Carnian | Santa Maria Formation | |||
| H. huxleyi | Carnian | Lower Maleri Formation | |||
| H. mariensis | Carnian | Santa Maria Formation Ischigualasto Formation | |||
| H. sanjuanensis | Carnian | Ischigualasto Formation Santa Maria Formation | |||
| H. tikiensis | Carnian | Tiki Formation | |||
| Isalorhynchus | I. genovefae | Carnian | Makay Formation (Isalo II)A hyperodapedontine occasionally referred to Hyperodapedon. | ||
| Mesodapedon | M. kuttyi | Anisian | Yerrapalli Formation A stenaulorhynchine. | ||
| Langeronyx | L. brodiei | Anisian | (England)
| Bromsgrove Sandstone FormationA basal hyperodapedontid. | |
| Mesosuchus | M. browni | early Anisian | Burgersdorp Formation ( Cynognathus Assemblage Zone) A basal (non-rhynchosaurid) rhynchosaur. | ||
| Noteosuchus | N. colletti | early Induan | Katberg Formation ( Lystrosaurus Assemblage Zone) | A basal (non-rhynchosaurid) rhynchosaur. The earliest known species of rhynchosaur, and the only known Early Triassic representative. | |
| Oryctorhynchus | O. bairdi | latest Carnian?-earliest Norian? | ([[Nova Scotia]])
| Wolfville FormationA hyperodapedontine previously referred to Hyperodapedon. | |
| Rhynchosaurus | R. articeps | Anisian | (England)
| Tarporley Siltstone FormationA basal rhynchosaurid. | |
| Stenaulorhynchus | S. stockleyi | late Anisian | Manda FormationA stenaulorhynchine. | ||
| Supradapedon | S. stockleyi | Middle Triassic/" itemprop="url" title="Wiki: Late Triassic"><span itemprop="name">Middle Triassic">Late Triassic">Middle Triassic - [[Late Triassic | Tunduru districtA hyperodapedontine previously referred to Hyperodapedon. | ||
| Teyumbaita | T. sulcognathus | late Carnian - early Norian | Caturrita Formation Ischigualasto Formation | The latest surviving species, and the only rhynchosaur known with confidence to have survived into the Norian stage. | |
Within Hyperodapedontidae, which is now a subgroup of Rhynchosauridae, two subfamilies have been named. Stenaulorhynchinae named by Kuhn (1933) is defined sensu Langer and Schultz (2000) to include all species more closely related to Stenaulorhynchus than to Hyperodapedon. Hyperodapedontinae named by Chatterjee (1969) was redefined by Langer et al. (2000) to include "all rhynchosaurs closer to Hyperodapedon than to "Rhynchosaurus" spenceri" (now Fodonyx).
The cladogram below is based on Schultz et al. (2016) which is the most genera inclusive rhynchosaur phylogenetic analysis to date, with the position of Noteosuchus taken from other recent analyses (since it was removed in Schultz et al. (2016)), all in consensus with one another.Ezcurra MD. (2016) The phylogenetic relationships of basal archosauromorphs, with an emphasis on the systematics of proterosuchian archosauriforms. PeerJ, 4:e1778 [2]
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