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Rhynchosaurs
Temporal range: Anisian–Carnian
250px
life restoration of Hyperodapedon
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Infraclass: Archosauromorpha
Order: Rhynchosauria
Osborn, 1903

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

Description

File:Hyperodapedon huxleyi maxilla.jpg

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 generally small and 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 grew to medium to medium large size, up to two meters in length. The skull in these forms were 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

Flag of the United States.svg USA (Arizona)

Moenkopi Formation

Bentonyx

B. sidensis

Anisian

Template:Country data England

Otter Sandstone Formation

Fodonyx

F. spenceri

Anisian

Template:Country data England

Otter Sandstone Formation

Howesia

H. browni

late Olenekian - Anisian

Template:Country data South Africa

Burgersdorp Formation

Hyperodapedon

H. gordoni

Carnian

Template:Country data Scotland

Lossiemouth Sandstone Formation

Five valid species are known, the most of any rhynchosaur.

H. huenei

Carnian

Template:Country data Brazil

Santa Maria Formation

H. huxleyi

Carnian

Template:Country data India

Lower Maleri Formation

H. mariensis

Carnian

Template:Country data Brazil
Template:Country data Argentina

Santa Maria Formation
Ischigualasto Formation

H. sanjuanensis

Carnian

Template:Country data Argentina
Template:Country data Brazil

Ischigualasto Formation
Santa Maria Formation

Isalorhynchus

I. genovefae

Carnian

Template:Country data Madagascar

Makay Formation (Isalo II)

Mesodapedon

M. kuttyi

Anisian

Template:Country data India

Yerrapalli Formation

Mesosuchus

M. browni

Anisian

Template:Country data South Africa

Burgersdorp Formation

Otischalkia

O. elderae

late Carnian

Flag of the United States.svg USA (Texas)

Dockum Group

Rhynchosaurus

R. articeps

Anisian - Ladinian

Template:Country data England

Tarporley Siltstone Formation

R. brodiei

Anisian - Ladinian

Template:Country data England

Bromsgrove Sandstone Formation

Stenaulorhynchus

S. stockleyi

Anisian

Template:Country data Tanzania

Manda Formation

Supradapedon

S. stockleyi

Middle - Late Triassic

Template:Country data Tanzania

Tunduru district

Teyumbaita

T. sulcognathus

early Norian

Template:Country data Brazil

Caturrita Formation

T. sulcognathus is the only Norian rhynchosaur.

Phylogeny

Cladogram based on Langer et al. (2000):[1]

Hyperodapedontinae

"Scaphonyx" sulcognathus


Hyperodapedon

H. huenei




H. mariensis



H. sanjuanensis




H. gordoni



H. huxleyi






Cladogram based on Hone and Benton (2008):[2]

Rhynchosauria

Mesosuchus




Howesia


Rhynchosauridae

Stenaulorhynchus



Rhynchosaurus

R. articeps



R. brodiei





Fodonyx




Ammorhynchus


Hyperodapedontinae

Mariante rhynchosaur



Teyumbaita



Hyperodapedon









Cladogram based on Langer et al. (2010):[3]

Rhynchosauria

Mesosuchus




Howesia



Rhynchosauridae

Rhynchosaurus


Hyperodapedontidae


Mariante rhynchosaur



Stenaulorhynchus




Bentonyx




Fodonyx


Hyperodapedontinae

Isalorhynchus




Teyumbaita



Hyperodapedon









See also

External links

References

  1. ^ Max C. Langer and Cesar L. Schultz (2000). "A new species of the Late Triassic rhynchosaur Hyperodapedon from the Santa Maria Formation of south Brazil". Palaeontology. 43 (6): 633–652. 
  2. ^ David W. E. Hone and Michael J. Benton (2008). "A new genus of Rhynchosaur from the Middle Triassic of South-West England". Palaeontology. 51 (1): 95–115. doi:10.1111/j.1475-4983.2007.00739.x. 
  3. ^ Max C. Langer, Felipe C. Montefeltro, David E. Hone, Robin Whatley and Cesar L. Schultz (2010). "On Fodonyx spenceri and a new rhynchosaur from the Middle Triassic of Devon". Journal of Vertebrate Paleontology. 30 (6): 1884–1888. doi:10.1080/02724634.2010.521901. 



Template:Project Rhynchosauria Taxonomy

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