Rhynchosaur

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Rhynchosaurs
Temporal range: Anisian–Carnian
Hyperodapedon BW2.jpg
life restoration of Hyperodapedon
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Archosauromorpha
Order: Rhynchosauria
Osborn, 1903

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

Description[edit]

Staurikosaurus and rhynchosaur.

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. 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 were 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 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 humeri from early-mid Norian Bull Canyon Formation in New Mexico, which they interpreted as bones of rhynchosaurs belonging to the species Otischalkia elderae; thus, the fossils might indicate that rhynchosaurs survived until the Norian.[1]

Classification[edit]

Taxonomy[edit]

Genera
Genus Species Age Location Unit Notes Images

Ammorhynchus

A. navajoi

Anisian

 USA (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

Lower 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

Noteosuchus

N. colletti

early Induan

 South Africa

Katberg Formation

Otischalkia

O. elderae

late Carnian

 USA (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[edit]

Skull of a rhynchosaur, in Educational Museum Gama D'Eça.
Illustration of the ventral surface of a tooth plate of Hyperodapedon.

Traditionally, the Rhynchosauria included a single family, named Rhynchosauridae. Hyperodapedontidae, which was named by Lydekker (1885), was considered its junior synonym. All rhynchosaurs, apart from the three Early and Middle Triassic monospecific genera, Mesosuchus, Howesia and Noteosuchus, were included in this family.[2] According to Dilkes (1998), Noteosuchus colletti is most probably a junior synonym of Mesosuchus browni.[3] Langer et al. (2000) noted that the family Hyperodapedontidae was erected by Lydekker to include Hyperodapedon gordoni and H. huxleyi, clearly excluding Rhynchosaurus articeps, which was the only other rhynchosaur known at that time. Thus, they defined it as the stem-based taxon that includes all rhynchosaurs more closely related to Hyperodapedon than to Rhynchosaurus. Using this definition, Rhynchosauridae must include all rhynchosaurs more closely related to Rhynchosaurus than to Hyperodapedon (or a smaller group), as a family can't be included in another family.[4]

The cladogram below follows Langer et al. (2000) definitions.[5]

Rhynchosauria

Mesosuchus browni




Howesia browni




Stenaulorhynchus stockleyi



Rhynchosauridae

Rhynchosaurus articeps



Rhynchosaurus brodiei



Hyperodapedontidae

Fodonyx spenceri


Hyperodapedontinae

Ammorhynchus navajoi




Mariante rhynchosaur



Teyumbaita sulcognathus



Hyperodapedon huenei



Hyperodapedon huxleyi



Hyperodapedon gordoni



Hyperodapedon mariensis



Hyperodapedon sanjuanensis









The cladogram below is based mostly on Langer et al. (2010). The relations between species of Hyperodapedon follow Langer et al. (2000),[4] as Langer et al. (2010) performed a genus-level phylogenetic analysis.[6]

Rhynchosauria

Mesosuchus browni




Howesia browni




Rhynchosaurus spp.


Hyperodapedontidae


Mariante rhynchosaur



Stenaulorhynchus stockleyi




Bentonyx sidensis




Fodonyx spenceri


Hyperodapedontinae

Isalorhynchus genovefae




Teyumbaita sulcognathus




Hyperodapedon huenei




Hyperodapedon mariensis



Hyperodapedon sanjuanensis




Hyperodapedon gordoni



Hyperodapedon huxleyi












See also[edit]

References[edit]

  1. ^ Justin A. Spielmann, Spencer G. Lucas and Adrian P. Hunt (2013). "The first Norian (Revueltian) rhynchosaur: Bull Canyon Formation, New Mexico, U.S.A.". New Mexico Museum of Natural History and Science Bulletin 61: 562–566. 
  2. ^ Benton, M. J. (1985). "Classification and phylogeny of the diapsid reptiles". Zoological Journal of the Linnean Society 84 (2): 97–164. doi:10.1111/j.1096-3642.1985.tb01796.x. 
  3. ^ David M. Dilkes (1998). "The Early Triassic rhynchosaur Mesosuchus browni and the interrelationships of basal archosauromorph reptiles". Philosophical Transactions of the Royal Society of London, Series B 353: 501–541. doi:10.1098/rstb.1998.0225. 
  4. ^ a b 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. doi:10.1111/1475-4983.00143. 
  5. ^ 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. 
  6. ^ 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. 

External links[edit]