Palacrodon
| Palacrodon Temporal range:Triassic,
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|---|---|
Scientific classification
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Diapsida |
| Clade: | Neodiapsida |
| Genus: | †Palacrodon Broom, 1906 |
| Type species | |
| †Palacrodon browni | |
| Other species | |
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| Synonyms | |
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P. browni:
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Palacrodonis an extinctgenusofTriassicreptile with a widespread distribution. It was initially described from teeth collected inEarly Triassicdeposits inSouth Africa,and later reported from the Early Triassic ofAntarctica[1][2]and theLate TriassicofArizona.[3]Although previously considered an earlyrhynchocephalian,it is currently considered to be a non-saurianneodiapsid.[2]
History
[edit]The type specimen ofPalacrodon browniwas described from the Early TriassicCynognathus Assemblage Zoneof South Africa byRobert Broom,who classified it inRhynchocephalia.[4]Malan (1963) questioned the rhynchocephalian placement ofPalacrodon,viewing it as either a lizard or procolophonid.[5]A skull collected from the lower part ofFremouw Formationof Antarctica was namedFremouwsaurus geludensby Gow (1992),[6]but that taxon was synonymized withPalacrodonby Gow (1999).[1]Gow also described new material of the genus from South Africa and concluded thatPalacrodonitself was not a member of Rhynchocephalia due to its lack of aquadratojugaland the presence of alacrimal.[6][1]A later study of the Antarctic specimen showed that much more of the skeleton was present than just the skull.[2]
In 2018, new tooth and jaw material was described from theAdamanian-ageBlue Mesa Memberof theChinle Formationin Arizona. This extends the stratigraphic range of the form into theNorianstage of the Late Triassic.[3]In 2024, these specimens were determined to belong to a distinct species and was namedP. parkeri.The two species are distinguished by their teeth.P. brownihas a pair of parallel ridges on the underside of itstooth crownbetween its outer and inner edges, gaps beneath where two teeth contact each other, andforaminain the jaw beneath each tooth, whileP. parkerilacks these features. In tetrapods, thepulp cavityof teeth typically matches the shape of the tooth's surface, and the ridges ofP. browniare unique amongst tetrapods. The function of these ridges is unclear, but it is hypothesised that they may have provided extra surface area for a soft-tissue attachment to the jaw bone, asPalacrodonhasacrodontdentition and so its teeth lack roots.[7]A 2022 paper re-evaluating the Fremouw specimen found it to be closely related toSauriawithin theNeodiapsida,and suggested that it may have beenarborealbased on the elongatedphalangesof the hands.[2]
References
[edit]- ^abcGow, C. (1999)."The Triassic reptilePalacrodon browniBroom, synonymy and a new specimen ".Palaeontologia Africana.35:21–23.
- ^abcdJenkins, Kelsey M.; Meyer, Dalton L.; Lewis, Patrick J.; Choiniere, Jonah N.; Bhullar, Bhart-Anjan S. (2022)."Re-description of the early Triassic diapsidPalacrodonfrom the lower Fremouw formation of Antarctica ".Journal of Anatomy.241(6): 1441–1458.doi:10.1111/joa.13770.PMC9644968.PMID36168715.
- ^abKligman, Ben T.; Marsh, Adam D.; Parker, William G. (2018)."First records of diapsidPalacrodonfrom the Norian, Late Triassic Chinle Formation of Arizona, and their biogeographic implications ".Acta Palaeontologica Polonica.63(1): 117–127.doi:10.4202/app.00426.2017.S2CID56558390.
- ^Broom, R. (1905)."On a new South African Triassic rhynchocephalian".Transactions of the South African Philosophical Society.16:379–380.doi:10.1080/21560382.1905.9526075.
- ^Malan, M. E. (1963-05-01)."The dentitions of the South African rhynchocephalia and their bearing on the origin of the Rhynosaurs".South African Journal of Science.59(5): 214–220.hdl:10520/AJA00382353_2356.
- ^abGow, C. (1992)."An enigmatic new reptile from the Lower Triassic Fremouw Formation of Antarctica"(PDF).Palaeontologia Africana.29:21–23.
- ^Jenkins, K. M.; Bell, C. J.; Hancox, P. J.; Lewis, P. J. (2024). "A new species ofPalacrodonand a unique form of tooth attachment in reptiles ".Journal of Vertebrate Paleontology.e2328658.doi:10.1080/02724634.2024.2328658.
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