Biology:Rhynchosauria
Rhynchosaurs are a group of extinct herbivorous Triassic archosauromorph reptiles, belonging to the order Rhynchosauria.[1] Members of the group are distinguished by their triangular skulls and elongated, beak like premaxillary bones. Rhynchosaurs first appeared in the Early Triassic, reaching their broadest abundance and a global distribution during the Carnian stage of the Late Triassic.
Description
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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, 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 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 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.[2]
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. They had a fixed number of teeth, and similar to elephants, those that were further back in the jaws replaced teeth that were worn out as the animal grew in size and the teeth were worn out because of a diet of very tough plants. Rhynchosaur teeth were ankylothecodont, similar to the acrodonty of modern tuataras and some lizards but differing in the presence of deep roots.[2]
Evolution
Rhynchosaurs first appeared during the Induan, the first stage of the Triassic, appearing shortly after the end-Permian mass extinction, as part of a major diversification of reptiles during this period. Like many animals of this time, they had a worldwide distribution, being found across Pangea,[1] being especially common in the southern Gondwanan part of Pangaea, though with records also in Europe and North America.[3] Over their evolution, rhynchosaurs saw a progressive increase in their body size.[1] It has been suggested that rhynchosaurs went extinct at the end of the Carnian stage during the early Late Triassic as part of an end-Carnian extinction event. 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.[4] These fossils were later reinterpreted as belonging to malerisaurine azendohsaurids.[5]
Classification
Relationships with other reptiles
Historically, rhynchosaurs were considered to be closely related to Rhynchocephalia, the clade that includes the living tuatara and its extinct relatives.[6] Today however the two groups are considered to be unrelated, and rhynchosaurs are considered to be archosauromorphs, more closely related to modern crocodilians and birds than to rhynchocephalians and lizards, as members of the archosauromorph subclade Crocopoda.[7]
Cladogram of Archosauromorpha after Schoch et al. 2025:[7]
| Archosauromorpha |
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Phylogeny
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.[8] Hyperodapedontidae named by Lydekker (1885) was considered its junior synonym.[9] 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.[10]
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).[11]
The cladogram below is based on Schultz et al. (2016) which is the most genera inclusive rhynchosaur phylogenetic analysis to date,[11] 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.[8][12]
| Rhynchosauria |
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List of genera
| List of rhynchosaur genera | |||||
|---|---|---|---|---|---|
| Genus | Species | Age | Location | Unit | Notes |
|
A. navajoi |
Anisian |
|
A stenaulorhynchine | ||
|
B. cooowuse |
Carnian |
|
Popo Agie Formation |
A hyperodapedontine previously referred to Hyperodapedon | |
|
B. mariantensis |
Ladinian |
|
Santa Maria Formation |
A stenaulorhynchine, previously known as the "Mariante Rhynchosaur" | |
|
B. sidensis |
late Anisian |
|
A basal hyperodapedontid | ||
| E. triadicus | early Anisian |  Germany
|
Röt Formation | A basal rhynchosaurid | |
| Elorhynchus | E. carrolli | late Ladinian? - earliest Carnian? |  Argentina
|
Chañares Formation (Tarjadia Assemblage Zone) | A stenaulorhynchine |
|
E. wolvaardti |
early Anisian |
|
Burgersdorp Formation (Cynognathus Assemblage Zone) |
A basal (non-rhynchosaurid) rhynchosaur | |
|
F. spenceri |
late Anisian |
|
A basal hyperodapedontid | ||
|
H. browni |
early Anisian[8] |
|
Burgersdorp Formation (Cynognathus Assemblage Zone) |
A basal (non-rhynchosaurid) rhynchosaur | |
|
H. gordoni |
Carnian |
|
A hyperodapedontine, one of the most abundant and speciose rhynchosaur genera. Six valid species have been named, the most of any rhynchosaur. | ||
|
H. huenei |
Carnian |
|
Santa Maria Formation | ||
|
H. huxleyi |
Carnian |
|
Lower Maleri Formation | ||
|
H. mariensis |
Carnian |
|
Santa Maria Formation | ||
|
H. sanjuanensis |
Carnian |
|
Ischigualasto Formation | ||
|
H. tikiensis |
Carnian |
|
|||
|
I. genovefae |
Carnian |
|
Makay Formation (Isalo II) |
A hyperodapedontine occasionally referred to Hyperodapedon | |
|
Isodapedon |
I. varzealis |
Carnian |
|
Santa Maria Formation |
A hyperodapedontine |
|
L. brodiei |
Anisian |
|
Bromsgrove Sandstone Formation |
A basal hyperodapedontid | |
|
M. kuttyi |
Anisian |
|
A stenaulorhynchine | ||
|
M. browni |
early Anisian[8] |
|
Burgersdorp Formation (Cynognathus Assemblage Zone) |
A basal (non-rhynchosaurid) rhynchosaur | |
|
N. colletti |
early Induan |
|
Katberg Formation (Lystrosaurus Assemblage Zone) |
A basal (non-rhynchosaurid) rhynchosaur; the earliest known species of rhynchosaur, and the only known Early Triassic representative[8] | |
|
O. bairdi |
latest Carnian?-earliest Norian? |
|
Wolfville Formation |
A hyperodapedontine previously referred to Hyperodapedon | |
|
R. articeps |
Anisian |
|
Tarporley Siltstone Formation |
A basal rhynchosaurid | |
|
S. stockleyi |
late Anisian |
|
A stenaulorhynchine | ||
|
S. stockleyi |
|
Tunduru district |
A hyperodapedontine previously referred to Hyperodapedon | ||
|
T. sulcognathus |
late Carnian - early Norian |
|
The latest surviving species, and the only rhynchosaur known with confidence to have survived into the Norian stage | ||
References
- ↑ 1.0 1.1 1.2 Ezcurra, Martín D.; Montefeltro, Felipe; Butler, Richard J. (2016). "The Early Evolution of Rhynchosaurs" (in English). Frontiers in Ecology and Evolution 3. doi:10.3389/fevo.2015.00142. ISSN 2296-701X.
- ↑ 2.0 2.1 Sethapanichsakul, Thitiwoot; Coram, Robert A.; Benton, Michael J. (2023). "Unique dentition of rhynchosaurs and their two‐phase success as herbivores in the Triassic". Palaeontology 66 (3). doi:10.1111/pala.12654. https://onlinelibrary.wiley.com/doi/10.1111/pala.12654.
- ↑ Sues, Hans-Dieter; Fitch, Adam J.; Whatley, Robin L. (2020-03-03). "A New Rhynchosaur (Reptilia, Archosauromorpha) from the Upper Triassic of Eastern North America" (in en). Journal of Vertebrate Paleontology 40 (2). doi:10.1080/02724634.2020.1771568. ISSN 0272-4634. https://www.tandfonline.com/doi/full/10.1080/02724634.2020.1771568.
- ↑ Justin A. Spielmann; Spencer G. Lucas; 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. https://www.researchgate.net/publication/280880846.
- ↑ Nesbitt, Sterling J.; Stocker, Michelle R.; Ezcurra, Martín D.; Fraser, Nicholas C.; Heckert, Andrew B.; Parker, William G.; Mueller, Bill; Sengupta, Saradee et al. (2022). Field, Daniel. ed. "Widespread azendohsaurids (Archosauromorpha, Allokotosauria) from the Late Triassic of western USA and India" (in en). Papers in Palaeontology 8 (1). doi:10.1002/spp2.1413. ISSN 2056-2799. https://www.researchgate.net/publication/356929019.
- ↑ "Phylogeny" In the Shadow of the Dinosaurs: Early Mesozoic Tetrapods. Cambridge University Press. 1994. p. 25. ISBN 0-521-45242-2.
- ↑ 7.0 7.1 Schoch, Rainer R.; Sues, Hans-Dieter; Sobral, Gabriela; Kurz, Cornelia; Gottmann-Quesada, Annalisa; Spiekman, Stephan N. F. (2025-12-31). "New data on the skull of Protorosaurus speneri (Reptilia: Archosauromorpha) and their phylogenetic significance" (in en). Journal of Systematic Palaeontology 23 (1). doi:10.1080/14772019.2025.2496744. ISSN 1477-2019. https://www.tandfonline.com/doi/full/10.1080/14772019.2025.2496744.
- ↑ 8.0 8.1 8.2 8.3 8.4 8.5 Richard J. Butler; Martín D. Ezcurra; Felipe C. Montefeltro; Adun Samathi; 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.
- ↑ 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.
- ↑ 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. Bibcode: 2000Palgy..43..633L.
- ↑ 11.0 11.1 Cesar Leandro Schultz; Max Cardoso Langer; 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 90 (3): 593–609. doi:10.1007/s12542-016-0307-7.
- ↑ Ezcurra MD. (2016) The phylogenetic relationships of basal archosauromorphs, with an emphasis on the systematics of proterosuchian archosauriforms. PeerJ, 4:e1778 [1]
- ↑ Fitch, A. J.; Haas, M.; C'Hair, W.; Ridgley, E.; Ridgley, B.; Oldman, D.; Reynolds, C.; Lovelace, D. M. (2023). "A New Rhynchosaur Taxon from the Popo Agie Formation, WY: Implications for a Northern Pangean Early-Late Triassic (Carnian) Fauna". Diversity 15 (4): 544. doi:10.3390/d15040544.
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
Data related to Rhynchosauria at Wikispecies
Template:Rhynchosauria Wikidata ☰ Q131768 entry
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