Rhynchosaur

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

See text.

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

Brasinorhynchus

B. mariantensis

Ladinian

 Brazil

Santa Maria Formation

Previously known as the "Mariante Rhynchosaur".

Bentonyx

B. sidensis

late Anisian

 England

Otter Sandstone Formation

Eohyosaurus[2]

E. wolvaardti

early Anisian

 South Africa

Burgersdorp Formation

Fodonyx

F. spenceri

late Anisian

 England

Otter Sandstone Formation

Howesia

H. browni

early Anisian[2]

 South Africa

Burgersdorp Formation

Hyperodapedon

H. gordoni

Carnian

 Scotland

Lossiemouth Sandstone Formation

Six valid species has been named, 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

H. tikiensis

Carnian

 India

Tiki Formation

Isalorhynchus

I. genovefae

Carnian

 Madagascar

Makay Formation (Isalo II)

Mesodapedon

M. kuttyi

Anisian

 India

Yerrapalli Formation

Langeronyx

L. brodiei

Anisian

 England

Bromsgrove Sandstone Formation

Mesosuchus

M. browni

early Anisian[2]

 South Africa

Burgersdorp Formation

Noteosuchus

N. colletti

early Induan

 South Africa

Katberg Formation

The earliest known species, and the only Early Triassic representative.[2]

Otischalkia

O. elderae

late Carnian

 USA (Texas)

Dockum Group

A nomen dubium

Rhynchosaurus

R. articeps

Anisian

 England

Tarporley Siltstone Formation

Stenaulorhynchus

S. stockleyi

late Anisian

 Tanzania

Manda Formation

Supradapedon

S. stockleyi

Middle - Late Triassic

 Tanzania

Tunduru district

Teyumbaita

T. sulcognathus

early Norian

 Brazil

Caturrita Formation

The latest surviving species, and 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.

The Rhynchosauria included a single family, named Rhynchosauridae. All rhynchosaurs, apart from the four Early and Middle Triassic monospecific genera, Eohyosaurus, Mesosuchus, Howesia and Noteosuchus, are included in this family.[2] Hyperodapedontidae named by Lydekker (1885) was considered its junior synonym.[3] However, Langer et al. (2000) noted that 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.[4]

Within Hyperodapedontidae, which is now a subgroup of Rhynchosauridae, two subfamilies have been named. Stenaulorhynchinae named by Kuhn (1933) is defined sensu Langer and Schultz (2000) to include all species more closely related to Stenaulorhynchus than to Hyperodapedon. Hyperodapedontinae named by Chatterjee (1969) was redefined by Langer et al. (2000) to include "all rhynchosaurs closer to Hyperodapedon than to "Rhynchosaurus" spenceri" (now Fodonyx).[5]

The cladogram below is based on Schultz et al. (2016) which is the most genera inclusive rhynchosaur phylogenetic analysis to date,[5] with the position of Noteosuchus taken from other recent analyses (since it was removed in Schultz et al. (2016)), all in consensus with one another.[2][6]

Rhynchosauria 

Noteosuchus colletti




Mesosuchus browni




Howesia browni




Eohyosaurus wolvaardti


 Rhynchosauridae 

Rhynchosaurus articeps


 Hyperodapedontidae 
 Stenaulorhynchinae 

Ammorhynchus navajoi



Mesodapedon kuttyi




Brasinorhynchus mariantensis



Stenaulorhynchus stockleyi






Bentonyx sidensis



Langeronyx brodiei




Fodonyx spenceri


Hyperodapedontinae

Isalorhynchus genovefae




Teyumbaita sulcognathus



Hyperodapedon spp.












See also[edit]

  • Paleorrota

References[edit]

Notes
  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." (PDF). New Mexico Museum of Natural History and Science Bulletin 61: 562–566. 
  2. ^ a b c d e f Richard J. Butler, Martín D. Ezcurra, Felipe C. Montefeltro, Adun Samathi and Gabriela Sobral (2015). "A new species of basal rhynchosaur (Diapsida: Archosauromorpha) from the early Middle Triassic of South Africa, and the early evolution of Rhynchosauria". Zoological Journal of the Linnean Society 174 (3): 571–588. doi:10.1111/zoj.12246. 
  3. ^ 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. 
  4. ^ Max C. Langer & 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. ^ a b Cesar Leandro Schultz, Max Cardoso Langer and Felipe Chinaglia Montefeltro (2016). "A new rhynchosaur from south Brazil (Santa Maria Formation) and rhynchosaur diversity patterns across the Middle-Late Triassic boundary". Paläontologische Zeitschrift. in press. doi:10.1007/s12542-016-0307-7. 
  6. ^ Ezcurra MD. (2016) The phylogenetic relationships of basal archosauromorphs, with an emphasis on the systematics of proterosuchian archosauriforms. PeerJ, 4:e1778 [1]
Bibliography

External links[edit]

Triassic Period
Lower/Early Triassic Middle Triassic Upper/Late Triassic
Induan |Olenekian Anisian | Ladinian Carnian | Norian
Rhaetian