Rhynchosaurs were a group of Triassic

Triassic

The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...

 diapsid

Diapsid

Diapsids are a group of reptiles that developed two holes in each side of their skulls, about 300 million years ago during the late Carboniferous period. Living diapsids are extremely diverse, and include all crocodiles, lizards, snakes, and tuatara...

 reptile

Reptile

Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...

s related to the archosaurs.

Description

Rhynchosaurs were herbivores, and at times abundant (in some fossil localities accounting for 40 to 60% of specimens found), with stocky bodies and a powerful beak. Early primitive forms like Mesosuchus

Mesosuchus

Mesosuchus is an extinct genus of basal rhynchosaur from middle Triassic deposits of Eastern Cape, South Africa. It is known from the holotype SAM 5882, a partial skeleton, and from the paratypes SAM 6046, SAM 6536, SAM 7416 and SAM 7701 from the Aliwal North Euparkeria site...

and Howesia

Howesia

Howesia is an extinct genus of basal rhynchosaur from early or middle Triassic deposits of Eastern Cape, South Africa. It is known from the holotype SAM 5884, a partial skeleton with palate and partial lower jaws and from two paratypes, SAM 5885 and SAM 5886...

were more typically lizard-like in build, and had skulls rather similar to the early diapsid Youngina

Youngina

Youngina is an extinct genus of diapsid reptile from the Late Permian Beaufort Group of the Karoo Red Beds of South Africa. This, and a few related forms, make up the family Younginidae, within the Order Eosuchia...

, except for the beak and a few other features.

In later and more advanced genera the skull is short, broad, and triangular, becoming much wider than long in the most advanced forms like Hyperodapedon

Hyperodapedon

Hyperodapedon is a genus of rhynchosaur from the late Triassic period . The type species of Scaphonyx , Scaphonyx fischeri that once thought to be a dinosaur, is now known to be based on dubious material and therefore should be a nomen dubium...

(= Scaphonyx), with a deep cheek region, and the premaxilla

Premaxilla

The incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....

 extending outwards and downwards to form the upper beak. The broad skull would have accommodated powerful jaw muscles. The lower jaw was also deep, and when the mouth was closed it clamped firmly into the maxilla

Maxilla

The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...

 (upper jaw), like the blade of a penknife

Penknife

A penknife, or pen knife, is a small folding pocket knife, originally used for cutting or sharpening a quill to make a pen nib. Originally, penknives did not necessarily have folding blades, but resembled a scalpel or wood knife by having a short, fixed blade at the end of a long handle...

 closing into its handle. This scissors-like action would have enabled rhynchosaurs to cut up tough plant material.

The teeth were unusual, those in the maxilla and palate modified into broad tooth plates. The hind feet were equipped with massive claws, presumably for digging up roots and tuber

Tuber

Tubers are various types of modified plant structures that are enlarged to store nutrients. They are used by plants to survive the winter or dry months and provide energy and nutrients for regrowth during the next growing season and they are a means of asexual reproduction...

s by backwards scratching of the hind limbs.

Like many animals of this time they had a worldwide distribution, being found across Pangea. These abundant animals died out suddenly at the end of the Carnian

Carnian

The Carnian is the lowermost stage of the Upper Triassic series . It lasted from about 228.7 till 216.5 million years ago . The Carnian is preceded by the Ladinian and is followed by the Norian...

 (Middle of the Late Triassic period), perhaps as a result of the extinction of the Dicroidium

Dicroidium

Dicroidium is an extinct genus of fork-leaved seed ferns that were distributed over Gondwana during the Triassic . Their fossils are known from South Africa, Australia, New Zealand, South America and Antarctica...

flora on which they may have fed.

Taxonomy

Genera
Genus	Species	Age	Location	Unit	Notes	Images
Ammorhynchus Ammorhynchus Ammorhynchus is an extinct genus of hyperodapedontid rhynchosaur from middle Triassic deposits of Navajo County, Arizona. It is known from the holotype MSM 02-153/P4585, a nearly complete left maxilla and from three paratypes from the same locality...	A. navajoi	Anisian Anisian In the geologic timescale, the Anisian is the lower stage or earliest age of the Middle Triassic series or epoch and lasted from 245 million years ago until 237 million years ago, approximately...	Arizona	Moenkopi Formation Moenkopi Formation The Moenkopi is a geological formation that is spread across the U.S. states of New Mexico, northern Arizona, Nevada, southeastern California, eastern Utah and western Colorado. This unit is considered to be a group in Arizona. Part of the Colorado Plateau and Basin and Range, this formation was...
Bentonyx Bentonyx Bentonyx is an extinct genus of rhynchosaur from the middle Triassic epoch of Devon in England. Its fossil, a well preserved skull, BRSUG 27200, was discovered in Otter Sandstone Formation and was first assigned to Rhynchosaurus spenceri, that is known from 25 specimens...	B. sidensis	Anisian Anisian In the geologic timescale, the Anisian is the lower stage or earliest age of the Middle Triassic series or epoch and lasted from 245 million years ago until 237 million years ago, approximately...	Kingdom of England	Otter Sandstone Formation
Fodonyx Fodonyx Fodonyx is an extinct genus of rhynchosaur from the middle Triassic epoch of Devon in England. Its fossils were discovered in Otter Sandstone Formation and were first assigned to Rhynchosaurus spenceri...	F. spenceri	Anisian Anisian In the geologic timescale, the Anisian is the lower stage or earliest age of the Middle Triassic series or epoch and lasted from 245 million years ago until 237 million years ago, approximately...	Kingdom of England	Otter Sandstone Formation
Howesia Howesia Howesia is an extinct genus of basal rhynchosaur from early or middle Triassic deposits of Eastern Cape, South Africa. It is known from the holotype SAM 5884, a partial skeleton with palate and partial lower jaws and from two paratypes, SAM 5885 and SAM 5886...	H. browni	late Olenekian Olenekian In the geologic timescale, the Olenekian is an age in the Early Triassic epoch or a stage in the Lower Triassic series. It spans the time between 249.7 ± 0.7 Ma and 245 ± 0.7 Ma . The Olenekian follows the Induan and is followed by the Anisian.The Olenekian saw the deposition of a large part of the...  - Anisian Anisian In the geologic timescale, the Anisian is the lower stage or earliest age of the Middle Triassic series or epoch and lasted from 245 million years ago until 237 million years ago, approximately...	South Africa	Burgersdorp Formation
Hyperodapedon Hyperodapedon Hyperodapedon is a genus of rhynchosaur from the late Triassic period . The type species of Scaphonyx , Scaphonyx fischeri that once thought to be a dinosaur, is now known to be based on dubious material and therefore should be a nomen dubium...	H. gordoni	Carnian Carnian The Carnian is the lowermost stage of the Upper Triassic series . It lasted from about 228.7 till 216.5 million years ago . The Carnian is preceded by the Ladinian and is followed by the Norian...	Kingdom of Scotland	Lossiemouth Sandstone Formation	Five valid species are known, the most of any rhynchosaur.
	H. huenei	Carnian Carnian The Carnian is the lowermost stage of the Upper Triassic series . It lasted from about 228.7 till 216.5 million years ago . The Carnian is preceded by the Ladinian and is followed by the Norian...	Brazil	Santa Maria Formation Santa Maria Formation The Santa Maria Formation is a sedimentary rock formation found in Rio Grande do Sul, Brazil. It has a late Ladinian – early Carnian age , and is notable for its fossils of early dinosaurs, including the herrerasaur Staurikosaurus, the basal saurischian Teyuwasu, and the basal sauropodomorph...
	H. huxleyi	Carnian Carnian The Carnian is the lowermost stage of the Upper Triassic series . It lasted from about 228.7 till 216.5 million years ago . The Carnian is preceded by the Ladinian and is followed by the Norian...	India	Lower Maleri Formation Lower Maleri Formation The Lower Maleri Formation is a sedimentary rock formation found in Andhra Pradesh, India. It is the lowermost member of the Pranhita–Godavari Basin. It is of late Carnian to early Norian age , and is notable for its fossils of early dinosaurs, including the basal saurischian ...
	H. mariensis	Carnian Carnian The Carnian is the lowermost stage of the Upper Triassic series . It lasted from about 228.7 till 216.5 million years ago . The Carnian is preceded by the Ladinian and is followed by the Norian...	Brazil  Argentina	Santa Maria Formation Santa Maria Formation The Santa Maria Formation is a sedimentary rock formation found in Rio Grande do Sul, Brazil. It has a late Ladinian – early Carnian age , and is notable for its fossils of early dinosaurs, including the herrerasaur Staurikosaurus, the basal saurischian Teyuwasu, and the basal sauropodomorph... Ischigualasto Formation
	H. sanjuanensis	Carnian Carnian The Carnian is the lowermost stage of the Upper Triassic series . It lasted from about 228.7 till 216.5 million years ago . The Carnian is preceded by the Ladinian and is followed by the Norian...	Argentina  Brazil	Ischigualasto Formation Santa Maria Formation Santa Maria Formation The Santa Maria Formation is a sedimentary rock formation found in Rio Grande do Sul, Brazil. It has a late Ladinian – early Carnian age , and is notable for its fossils of early dinosaurs, including the herrerasaur Staurikosaurus, the basal saurischian Teyuwasu, and the basal sauropodomorph...
Isalorhynchus Isalorhynchus Isalorhynchus is an extinct genus of hyperodapedontine rhynchosaur from the late Triassic period of Toliara Province, southwestern Madagascar. It is known from the holotype MDE-R18, a nearly complete maxilla and from other specimens from the same locality, Malio River area. It was found in the...	I. genovefae	Carnian Carnian The Carnian is the lowermost stage of the Upper Triassic series . It lasted from about 228.7 till 216.5 million years ago . The Carnian is preceded by the Ladinian and is followed by the Norian...	Madagascar	Makay Formation (Isalo II)
Mesodapedon Mesodapedon Mesodapedon is an extinct genus of hyperodapedontid rhynchosaur from middle Triassic deposits of India. It is known from the holotype ISIR-300 and from the paratype ISIR-301 from the Yerrapalli Formation. It was first named by Sankar Chatterjee in 1980 and the type species is Mesodapedon kuttyi...	M. kuttyi	Anisian Anisian In the geologic timescale, the Anisian is the lower stage or earliest age of the Middle Triassic series or epoch and lasted from 245 million years ago until 237 million years ago, approximately...	India	Yerrapalli Formation
Mesosuchus Mesosuchus Mesosuchus is an extinct genus of basal rhynchosaur from middle Triassic deposits of Eastern Cape, South Africa. It is known from the holotype SAM 5882, a partial skeleton, and from the paratypes SAM 6046, SAM 6536, SAM 7416 and SAM 7701 from the Aliwal North Euparkeria site...	M. browni	Anisian Anisian In the geologic timescale, the Anisian is the lower stage or earliest age of the Middle Triassic series or epoch and lasted from 245 million years ago until 237 million years ago, approximately...	South Africa	Burgersdorp Formation
Otischalkia Otischalkia Otischalkia is an extinct genus of rhynchosaur from late Triassic deposits of Howard County, Texas. It is known from the holotype TMM 31025-263, left humerus and from the referred specimens TMM 31025-262, TMM 31025-266, TMM 31025-264, TMM 31185-92 and TMM 31185-93...	O. elderae	late Carnian Carnian The Carnian is the lowermost stage of the Upper Triassic series . It lasted from about 228.7 till 216.5 million years ago . The Carnian is preceded by the Ladinian and is followed by the Norian...	Republic of Texas	Dockum Group Dockum Group The Dockum is a Late Triassic geologic group found primarily on the Llano Estacado of western Texas and eastern New Mexico with minor exposures in southwestern Kansas, eastern Colorado, and Oklahoma panhandle. The Dockum reaches a maximum thickness of slightly over 650 m but is usually much...
Rhynchosaurus Rhynchosaurus Rhynchosaurus is a genus of rhynchosaur that lived during the Middle Triassic Period. It lived in Europe. It was related to the archosaurs, but not within that group. The species of Rhynchosaurus are R. articeps and R. brodiei. Michael Benton had named a third species, R...	R. articeps	Anisian Anisian In the geologic timescale, the Anisian is the lower stage or earliest age of the Middle Triassic series or epoch and lasted from 245 million years ago until 237 million years ago, approximately...  - Ladinian Ladinian The Ladinian is a stage and age in the Middle Triassic series or epoch. It spans the time between 237 ± 2 Ma and 228 ± 2 Ma...	Kingdom of England	Tarporley Siltstone Formation
	R. brodiei	Anisian Anisian In the geologic timescale, the Anisian is the lower stage or earliest age of the Middle Triassic series or epoch and lasted from 245 million years ago until 237 million years ago, approximately...  - Ladinian Ladinian The Ladinian is a stage and age in the Middle Triassic series or epoch. It spans the time between 237 ± 2 Ma and 228 ± 2 Ma...	Kingdom of England	Bromsgrove Sandstone Formation
Stenaulorhynchus Stenaulorhynchus Stenaulorhynchus is an extinct genus of hyperodapedontid rhynchosaur from Middle Triassic deposits of Tanganyika Territory, Tanzania. It was found in the Manda Formation. It was first named by Sidney Henry Haughton in 1932 and the type species is Stenaulorhynchus stockleyi.-Material:Many specimens...	S. stockleyi	Anisian Anisian In the geologic timescale, the Anisian is the lower stage or earliest age of the Middle Triassic series or epoch and lasted from 245 million years ago until 237 million years ago, approximately...	Tanzania	Manda Formation
Supradapedon Supradapedon Supradapedon is an extinct genus of hyperodapedontine rhynchosaur from mid-late Triassic deposits of Tanganyika Territory, Tanzania. It is known from the holotype SAM-11704. The holotype and only specimen of Supradapedon was first assigned to a species of Scaphonyx , Scaphonyx stockleyi...	S. stockleyi	Middle Middle Triassic In the geologic timescale, the Middle Triassic is the second of three epochs of the Triassic period or the middle of three series in which the Triassic system is divided. It spans the time between 245 ± 1.5 Ma and 228 ± 2 Ma...  - Late Triassic Late Triassic The Late Triassic is in the geologic timescale the third and final of three epochs of the Triassic period. The corresponding series is known as the Upper Triassic. In the past it was sometimes called the Keuper, after a German lithostratigraphic group that has a roughly corresponding age...	Tanzania	Tunduru district
Teyumbaita Teyumbaita Teyumbaita is an extinct genus of hyperodapedontine rhynchosaur from the Upper Triassic epoch of Paleorrota, Rio Grande do Sul, southern Brazil...	T. sulcognathus	early Norian Norian The Norian is a division of the Triassic geological period. It has the rank of an age or stage . The Norian lasted from 216.5 ± 2.0 to 203.6 ± 1.5 million years ago. It was preceded by the Carnian and succeeded by the Rhaetian.-Stratigraphic definitions:The Norian was named after the Noric Alps in...	Brazil	Caturrita Formation Caturrita Formation The Caturrita Formation is a rock formation found in Rio Grande do Sul, Brazil. Its sediments were deposited in the Paraná Basin. The formation has a late Carnian to early Norian age and forms part of the Santa Maria Supersequence in the upper section of the Rosário do Sul Group.-Etymology:The...	T. sulcognathus is the only Norian rhynchosaur.

Phylogeny

Cladogram

Cladogram

A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...

 based on Langer et al. (2000):
Cladogram

Cladogram

A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...

 based on Hone and Benton (2008):
Cladogram based on Langer et al. (2010):

External links

• Dinosaurs of Rio grande do Sul.