Rhynchosaur

Rhynchosaurs Temporal range:
life restoration of Hyperodapedon
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Archosauromorpha
Clade:	Crocopoda
Order:	†Rhynchosauria Osborn, 1903

Rhynchosaurs were a group of Triassic diapsid reptiles related to the archosaurs.

Description

Illustration of the ventral surface of a tooth plate of Hyperodapedon.

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 and Howesia were more typically lizard-like in build, and had skulls rather similar to the early diapsid Youngina, 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 (= Scaphonyx), with a deep cheek region, and the premaxilla 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 (upper jaw), like the blade of a penknife 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 tubers 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 (Middle of the Late Triassic period), perhaps as a result of the extinction of the Dicroidium flora on which they may have fed.

Classification

Taxonomy

Genera
Genus	Species	Age	Location	Unit	Notes	Images
Ammorhynchus	A. navajoi	Anisian	Arizona	Moenkopi Formation		Hyperodapedon huxleyi (=Paradapedon) Mesosuchus browni Skull of Rhynchosaurus articeps
Bentonyx	B. sidensis	Anisian	England	Otter Sandstone Formation
Fodonyx	F. spenceri	Anisian	England	Otter Sandstone Formation
Howesia	H. browni	late Olenekian - Anisian	South Africa	Burgersdorp Formation
Hyperodapedon	H. gordoni	Carnian	Scotland	Lossiemouth Sandstone Formation	Five valid species are known, the most of any rhynchosaur.
	H. huenei	Carnian	Brazil	Santa Maria Formation
	H. huxleyi	Carnian	India	Maleri Formation
	H. mariensis	Carnian	Brazil Argentina	Santa Maria Formation Ischigualasto Formation
	H. sanjuanensis	Carnian	Argentina Brazil	Ischigualasto Formation Santa Maria Formation
Isalorhynchus	I. genovefae	Carnian	Madagascar	Makay Formation (Isalo II)
Mesodapedon	M. kuttyi	Anisian	India	Yerrapalli Formation
Mesosuchus	M. browni	Anisian	South Africa	Burgersdorp Formation
Otischalkia	O. elderae	late Carnian	Texas	Dockum Group
Rhynchosaurus	R. articeps	Anisian - Ladinian	England	Tarporley Siltstone Formation
	R. brodiei	Anisian - Ladinian	England	Bromsgrove Sandstone Formation
Stenaulorhynchus	S. stockleyi	Anisian	Tanzania	Manda Formation
Supradapedon	S. stockleyi	Middle - Late Triassic	Tanzania	Tunduru district
Teyumbaita	T. sulcognathus	early Norian	Brazil	Caturrita Formation	T. sulcognathus is the only Norian rhynchosaur.

Phylogeny

Cladogram based on Langer et al. (2000):

Hyperodapedontinae	"Scaphonyx" sulcognathus Hyperodapedon H. huenei H. mariensis H. sanjuanensis H. gordoni H. huxleyi

Cladogram based on Hone and Benton (2008):

Rhynchosauria	Mesosuchus Howesia Rhynchosauridae Stenaulorhynchus Rhynchosaurus R. articeps R. brodiei Fodonyx Ammorhynchus Hyperodapedontinae Mariante rhynchosaur Teyumbaita Hyperodapedon

Cladogram based on Langer et al. (2010):

Rhynchosauria	Mesosuchus Howesia Rhynchosauridae Rhynchosaurus Hyperodapedontidae Mariante rhynchosaur Stenaulorhynchus Bentonyx Fodonyx Hyperodapedontinae Isalorhynchus Teyumbaita Hyperodapedon

See also

• Paleorrota

External links

• Dinosaurs of Rio grande do Sul.

References

• Benton, M. J. (2000), Vertebrate Paleontology, 2nd ed. Blackwell Science Ltd
• Carroll, R. L. (1988), Vertebrate Paleontology and Evolution, W.H. Freeman & Co.
• Dilkes, D. W. 1998. The Early Triassic rhynchosaur Mesosuchus browni and the interrelationships of basal archosauromorph reptiles. Philosophical Transactions of the Royal Society of London: Biological Sciences, 353:501-541.