Rhynchosaur

Taxobox
name = Rhynchosaurs
fossil_range = Early - Late Triassic

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image_width = 250px
image_caption = life restoration of "Hyperodapedon"
regnum = Animalia
phylum = Chordata
classis = Sauropsida
subclassis = Diapsida
infraclassis = Archosauromorpha
ordo = Rhynchosauria
ordo_authority = Osborn, 1903
familia = Rhynchosauridae
familia_authority = Huxley, 1859
subdivision_ranks = Genera
subdivision = "Mesosuchus"
"Fodonyx"
"Howesia"
"Stenaulorhynchys"
"Rhynchosaurus"
"Otischalia"
"Isalorhynchus"
"Hyperodapedon"
"Paradapeton"

Rhynchosaurs were a group of unusual Triassic diapsid reptiles related to the archosaurs. They 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 "Younginia", 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 "Dicrodium" flora on which they may have fed.

ee also

*Paleorrota

External links

* [http://www.royalsul.com.br/paleo/galeria.asp 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. "", 353:501-541.