{{Short description|Extinct genus of reptiles}} {{Automatic taxobox | fossil_range = {{fossil range|Albian|Turonian}} | image = Priosphenodon skeleton.png | image_upright = 1.2 | image_caption = Reconstructed skeleton of ''P. avelasi'' | taxon = Priosphenodon | authority = Apesteguia & Novas 2003<ref name="Apesteguia and Novas 2003"/> | subdivision_ranks = Species | subdivision = * †''P. avelasi'' {{small|Apestiguia & Novas 2003<ref name="Apesteguia and Novas 2003"/>}} * †''P. minimus'' {{small|Apestiguia & Carballido 2014}} }}
'''''Priosphenodon''''' is an extinct, large herbivorous eilenodontine rhynchocephalian known from the mid-Cretaceous (Albian-Turonian) of Argentina.<ref name="Apesteguia and Novas 2003">{{cite journal |last1=Apesteguía |first1=Sebastián |last2=Novas |first2=Fernando E. |title=Large Cretaceous sphenodontian from Patagonia provides insight into lepidosaur evolution in Gondwana |journal=Nature |date=9 October 2003 |volume=425 |issue=6958 |pages=609–612 |doi=10.1038/nature01995 |pmid=14534584 |bibcode=2003Natur.425..609A |s2cid=4425130 }}</ref><ref name=":0">{{cite journal |last1=Apesteguia |first1=Sebastian |last2=Carballido |first2=Jose L. |date=March 2014 |title=A new eilenodontine (Lepidosauria, Sphenodontidae) from the Lower Cretaceous of central Patagonia |journal=Journal of Vertebrate Paleontology |volume=34 |issue=2 |pages=303–317 |doi=10.1080/02724634.2013.803974 |bibcode=2014JVPal..34..303A |s2cid=130381621 |hdl-access=free |hdl=11336/6524}}</ref> It is one of the largest known sphenodontians.
== Taxonomy == The type species of ''Priosphenodon'', ''P. avelasi'', was described in 2003 from the Late Cretaceous (Cenomanian-Turonian) aged Candeleros Formation of Argentina.<ref name="Apesteguia and Novas 2003" /> In 2014, a second smaller species, ''P. minimus'' was described from the same formation, though from an earlier unit suggested to be Early Cretaceous (Albian) in age.<ref name=":0" /> Other authors have disputed the use of the genus ''Priosphenodon'', with some authors treating ''P. avelasi'' and ''P. minimus'' as members of the previously named genus ''Kaikaifilusaurus'' instead.<ref>{{Cite journal |last1=Agnolín |first1=Federico L. |last2=Aranciaga Rolando |first2=A. Mauro |last3=Chimento |first3=Nicolás R. |last4=Novas |first4=Fernando E. |date=2023-10-12 |title=New small reptile remains from the Late Cretaceous of Patagonia increase morphological diversity of sphenodontids (Lepidosauria) |journal=Proceedings of the Geologists' Association |volume=135 |pages=36–44 |language=en |doi=10.1016/j.pgeola.2023.09.007}}</ref>
== Description == left|thumb|Skulls of ''P. avelasi'' corresponding to different ontogenetic stagesleft|thumb|Illustration of the skull of ''P. avelasi'' in lateral view thumb|Skeleton With some individuals reaching over {{Convert|1|m|ft}} in total length, ''Priosphenodon avelasi'' is the largest known terrestrial sphenodontian.<ref name="Apesteguia and Novas 2003" /> The skull is around {{Convert|15|cm|in}} long.<ref name=":0" /> The front of the upper jaw has a large beak-like structure,<ref name="Apesteguia and Novas 2003" /> unlike the beak of the living tuatara, which is formed from fused teeth, the beak of ''Priosphenodon'' is entirely composed of bone, similar to those of the unrelated (but also herbivorous) rhynchosaurs, unlike rhynchosaurs however, it has been suggested that ''Priosphenodon'' lacked a cornified rhamphotheca due to the smoothness of the bone surface.<ref>{{Cite journal |last=Cavasin |first=Sol A. |last2=Cerda |first2=Ignacio A. |last3=Apesteguía |first3=Sebastián |date=March 2026 |title=BONE MICROSTRUCTURE OF THE BEAK-LIKE STRUCTURE IN THE HERBIVOROUS SPHENODONTIAN PRIOSPHENODON AVELASI (LEPIDOSAURIA) |url=https://linkinghub.elsevier.com/retrieve/pii/S0195667126000522 |journal=Cretaceous Research |language=en |article-number=106363 |doi=10.1016/j.cretres.2026.106363|url-access=subscription }}</ref> The teeth are densely packed with a cone-in-cone structure, and have prismatic enamel structure similar to those of mammals and the lizard ''Uromastyx,'' which was likely an adaptation to wear resistance in the absence of tooth replacement.<ref name=":1">{{cite journal |last1=LeBlanc |first1=Aaron R. H. |last2=Apesteguía |first2=Sebastián |last3=Larsson |first3=Hans C. E. |last4=Caldwell |first4=Michael W. |date=4 May 2020 |title=Unique Tooth Morphology and Prismatic Enamel in Late Cretaceous Sphenodontians from Argentina |journal=Current Biology |volume=30 |issue=9 |pages=1755–1761.e2 |doi=10.1016/j.cub.2020.02.071 |pmid=32220319 |s2cid=214659416 |doi-access=free|bibcode=2020CBio...30E1755L |hdl=11336/168855 |hdl-access=free }}</ref> There is a large elongate tooth row on the palatine bones on the roof of the mouth that runs parallel to the maxillary tooth row.<ref name="Apesteguia and Novas 2003" /> The ungual phalanges are square in shape, and are expanded towards their distal ends, a condition unlike those known in other lepidosaurs, which typically have pointed ungual phalanges.<ref name="Apesteguia and Novas 2003" />
''Priosphenodon avelasi'' exhibited variable but generally slow growth rates, with a probably sexually mature individual confirmed to be at least 13 years old by bone histology was still growing and only around 40% maximum size at the time of death.<ref>{{Cite journal |last1=Cavasín |first1=Sol |last2=Cerda |first2=Ignacio |last3=Apesteguia |first3=Sebastian |date=2024 |title=Bone microstructure of Priosphenodon avelasi (Rhynchocephalia: Sphenodontia): paleobiological implications |url=https://www.app.pan.pl/article/item/app010712023.html |journal=Acta Palaeontologica Polonica |volume=69 |doi=10.4202/app.01071.2023|doi-access=free }}</ref>
''Priosphenodon minimus'' differs from ''P. avelasi'' by having a proportionally shorter skull in addition to a considerably smaller body size, among a variety of differences in the arrangement and shape of the skull bones.<ref name=":0" />
== Ecology == thumb|Life restoration of ''P. avelasi''During feeding the dentary teeth of ''Priosphenodon'' slotted between the maxillary and palatine tooth rows, which in turn with backward and forward (propalinal) motion of the jaw, served to shred plant material. The Candeleros Formation is suggested to have been deposited in an arid environment. Remains of ''P. avelasi'' are the most abundant of any terrestrial vertebrate at the sites it is found, and the lack of other herbivores found at the localities suggests that it may have been the only resident herbivore.<ref name=":1" />
==References== {{Reflist}}
{{Sphenodontia}} {{Taxonbar|from=Q21368826}}
Category:Prehistoric lepidosaurs Category:Prehistoric reptile genera Category:Cenomanian life Category:Turonian life Category:Late Cretaceous reptiles of South America Category:Cretaceous Argentina Category:Fossils of Argentina Category:Candeleros Formation Category:Cerro Barcino Formation Category:Fossil taxa described in 2003 Category:Rhynchocephalia