سحلية منقارية

Rhynchosaurs Temporal range: Olenekian-Norian 250–205.6 Ma PreЄ Є O S D C P T J K Pg N
Life restoration of Hyperodapedon
التصنيف العلمي
أصنوفة غير معروفة (أصلحها):	Rhynchosauria
Subgroups
†Colobops? †Eohyosaurus †Howesia †Mesosuchus †Noteosuchus †Rhynchosauridae †Eifelosaurus †Rhynchosaurus †Hyperodapedontidae †Bentonyx †Fodonyx †Langeronyx †Hyperodapedontinae †Stenaulorhynchinae †Ammorhynchus †Brasinorhynchus †Elorhynchus †Mesodapedon †Stenaulorhynchus

Rhynchosaurs are a group of extinct herbivorous Triassic archosauromorph reptiles, belonging to the order Rhynchosauria. Members of the group are distinguished by their triangular skulls and elongated, beak like premaxillary bones. Rhynchosaurs first appeared in the Middle Triassic or possibly the Early Triassic, before becoming abundant and globally distributed during the Carnian stage of the Late Triassic.

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 Description

Models of Staurikosaurus and a 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. Rhynchosaur teeth had an unique condition known as ankylothecodonty, similar to the acrodonty of modern tuataras and some lizards but differing in the presence of deep roots.

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. Similar to elephants they had a fixed number of teeth where those further back in the jaws replaced those who were worn out as the animal grew in size and the teeth was worn out because of a diet of very tough plants. In the end they probably starved to death.

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.

 Classification

 Taxonomy

Genera
Genus	Species	Age	Location	Unit	Notes
Ammorhynchus	A. navajoi	Anisian	الولايات المتحدة (Arizona)	Moenkopi Formation
Beesiiwo	B. cooowuse	Carnian	الولايات المتحدة (Wyoming)	Popo Agie Formation
Brasinorhynchus	B. mariantensis	Ladinian	البرازيل	Santa Maria Formation	Previously known as the "Mariante Rhynchosaur".
Bentonyx	B. sidensis	late Anisian	المملكة المتحدة (England)	Otter Sandstone Formation
Eohyosaurus	E. wolvaardti	early Anisian	جنوب أفريقيا	Burgersdorp Formation
Fodonyx	F. spenceri	late Anisian	المملكة المتحدة (England)	Otter Sandstone Formation
Howesia	H. browni	early Anisian	جنوب أفريقيا	Burgersdorp Formation
Hyperodapedon	H. gordoni	Carnian	المملكة المتحدة (Scotland)	Lossiemouth Sandstone Formation	Six valid species has been named, the most of any rhynchosaur.
	H. huenei	Carnian	البرازيل	Santa Maria Formation
	H. huxleyi	Carnian	الهند	Lower Maleri Formation
	H. mariensis	Carnian	البرازيل الأرجنتين	Santa Maria Formation Ischigualasto Formation
	H. sanjuanensis	Carnian	الأرجنتين البرازيل	Ischigualasto Formation Santa Maria Formation
	H. tikiensis	Carnian	الهند	Tiki Formation
Isalorhynchus	I. genovefae	Carnian	مدغشقر	Makay Formation (Isalo II)
Mesodapedon	M. kuttyi	Anisian	الهند	Yerrapalli Formation
Langeronyx	L. brodiei	Anisian	المملكة المتحدة (England)	Bromsgrove Sandstone Formation
Mesosuchus	M. browni	early Anisian	جنوب أفريقيا	Burgersdorp Formation
Noteosuchus	N. colletti	early Induan	جنوب أفريقيا	Katberg Formation	The earliest known species, and the only Early Triassic representative.
Oryctorhynchus	O. bairdi	latest Carnian?-earliest Norian?	كندا (Nova Scotia)	Wolfville Formation
Rhynchosaurus	R. articeps	Anisian	المملكة المتحدة (England)	Tarporley Siltstone Formation
Stenaulorhynchus	S. stockleyi	late Anisian	تنزانيا	Manda Formation
Supradapedon	S. stockleyi	Middle - Late Triassic	تنزانيا	Tunduru district
Teyumbaita	T. sulcognathus	early Norian	البرازيل	Caturrita Formation	The latest surviving species, and the only Norian rhynchosaur.

Hyperodapedon huxleyi (=Paradapedon)

Mesosuchus browni

Skull of Rhynchosaurus articeps

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 Phylogeny

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. Hyperodapedontidae named by Lydekker (1885) was considered its junior synonym. 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.

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).

The cladogram below is based on Schultz et al. (2016) which is the most genera inclusive rhynchosaur phylogenetic analysis to date, 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.

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.

 References

 Bibliography

• 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.

 External links

• Dinosaurs of Rio Grande do Sul, Brasil.
• Information related to Rhynchosauria from Wikispecies.