Scleromochlus

File:Scleromochlus lithograph.jpg of the holotype]]

Its fossils have been found in the Carnian Lossiemouth Sandstone of Scotland. The holotype was discovered around 1900 and is listed as specimen BMNH R3556, a partial skeleton preserved as an impression in sandstone, with portions of the skull and tail missing.

Arthur Smith Woodward named and described Scleromochlus taylori in 1907.

Scleromochlus taylori was about {{convert|181|mm}} long, with long hind legs; it may have been capable of four-legged and two-legged locomotion. Studies about its gait suggest that it engaged in kangaroo- or springhare-like plantigrade hopping;{{Cite journal |last1=Sereno |first1=Paul C. |author-link1=Paul Sereno |last2=Arcucci |first2=Andrea B. |date=1994 |title=Dinosaurian precursors from the Middle Triassic of Argentina: Marasuchus lilloensis, gen. nov. |url=https://www.tandfonline.com/doi/abs/10.1080/02724634.1994.10011538 |url-access=subscription |journal=Journal of Vertebrate Paleontology |volume=14 |issue=1 |pages=53–73 |doi=10.1080/02724634.1994.10011538 |issn=0272-4634}}{{cite journal | last1=Benton | first1=Michael J. | author-link=Michael J. Benton | title=Scleromochlus taylori and the origin of dinosaurs and pterosaurs| pages= 1423–1446 | year=1999 | volume=354 |pmc=1692658 | journal=Philosophical Transactions of the Royal Society B: Biological Sciences | doi = 10.1098/rstb.1999.0489 | jstor=57034 | issue=1388 }}{{cite book |last=Witton |first=Mark P. |author-link=Mark P. Witton |title=Pterosaurs: Natural History, Evolution, Anatomy |date=2013 |publisher=Princeton University Press |isbn=9780691150611}} however, a 2020 reassessment of Scleromochlus by Bennett suggested that it was a "sprawling quadrupedal hopper analogous to frogs."{{cite journal |last=Bennett |first=S. Christopher |year=2020 |title=Reassessment of the Triassic archosauriform Scleromochlus taylori: neither runner nor biped, but hopper |journal=PeerJ |volume=8 |pages=e8418 |doi=10.7717/peerj.8418|pmid=32117608 |pmc=7035874 |issn=2167-8359|doi-access=free}} If Scleromochlus is indeed related to pterosaurs, this may offer insight as to how the latter evolved, since early pterosaurs also show adaptations for saltatorial locomotion.{{cite journal |last=Witton |first=Mark P. |date=2015 |title=Were early pterosaurs inept terrestrial locomotors? |journal=PeerJ |volume=3 |pages=e1018 |doi=10.7717/peerj.1018|pmid=26157605 |pmc=4476129 |issn=2167-8359 |doi-access=free }}

File:Scleromochlus taylori.jpg

File:Scleromochlus skeletal.png

File:Scleromochlus restoration.jpg

A lightly built cursorial animal, its phylogenetic position has been debated; as different analyses have found it to be either the basal-most ornithodiran, the sister-taxon to Pterosauria, or a basal member of Avemetatarsalia that lies outside of Ornithodira. In the phylogenetic analyses conducted by Nesbitt et al. (2017) Scleromochlus was recovered either as a basal member of Dinosauromorpha or as a non-aphanosaurian, non-pterosaur basal avemetatarsalian. However, the authors stressed that scoring Scleromochlus was challenging given the small size and poor preservation of the fossils, and stated that it could not be scored for many of the important characters that optimize near the base of Avemetatarsalia.{{cite journal |first1=S.J. |last1=Nesbitt |first2=R.J. |last2=Butler |first3=M.D. |last3=Ezcurra |first4=P.M. |last4=Barrett |first5=M.R. |last5=Stocker |first6=K.D. |last6=Angielczyk |first7=R.M.H. |last7=Smith |first8=C.A. |last8=Sidor |first9=G. |last9=Niedźwiedzki |first10=A.G. |last10=Sennikov |first11=A.J. |last11=Charig |year=2017 |title=The earliest bird-line archosaurs and the assembly of the dinosaur body plan |journal=Nature |volume=544 |issue=7651 |pages=484–487 |doi=10.1038/nature22037 |url-access=subscription |url=https://www.nature.com/articles/nature22037 |pmid=28405026|bibcode=2017Natur.544..484N |hdl=11336/49585 |hdl-access=free }}

In 2020, Bennett interpreted Scleromochlus as possessing certain characteristics, including osteoderms and a crurotarsal morphology of the ankle, which suggested that Scleromochlus was not closely related to ornithodirans. Instead, he argued for a position of Scleromochlus among the Doswelliidae or elsewhere among basal members of the Archosauriformes.

However, in 2022, Foffa and colleagues reconstructed a complete skeleton using microcomputed tomographic scans of the seven specimens found to date. This enabled a new phylogenetic analysis to be undertaken, which strongly supported the hypothesis that Scleromochlus was a member of the Pterosauromorpha – either as a genus of the Lagerpetidae family (shown to be a part of Pterosauromorpha in 2020{{cite journal |last1=Ezcurra |first1=Martín D |author-link1=Martin Ezcurra |last2=Nesbitt |first2=Sterling J. |last3=Bronzati |first3=Mario |last4=Dalla Vecchia |first4=Fabio Marco |last5=Agnolin |first5=Federico L. |last6=Benson |first6=Roger B. J. |last7=Brissón Egli |first7=Federico |last8=Cabreira |first8=Sergio F. |last9=Evers |first9=Serjoscha W. |last10=Gentil |first10=Adriel R. |last11=Irmis |first11=Randall B. |last12=Martinelli |first12=Agustín G. |last13=Novas |first13=Fernando E. |last14=Roberto da Silva |first14=Lúcio |last15=Smith |first15=Nathan D. |last16=Stocker |first16=Michelle R. |last17=Turner |first17=Alan H. |last18=Langer |first18=Max C. |date=2020 |title=Enigmatic dinosaur precursors bridge the gap to the origin of Pterosauria |url=https://www.nature.com/articles/s41586-020-3011-4 |url-access= |journal=Nature |volume=588 |issue=7838 |pages=445–449 |doi=10.1038/s41586-020-3011-4 |issn=1476-4687 |access-date=6 October 2022|hdl=11336/134853 |hdl-access=free }}) or as the sister group to pterosaurs and lagerpetids. Previous alternative classifications were demonstrated to have been based on misinterpretations of incomplete or ambiguous anatomical features found in the fossil record.{{cite journal |last1=Foffa |first1=Davide |last2=Dunne |first2=Emma M. |last3=Nesbitt |first3=Sterling J. |author-link3=Sterling Nesbitt |last4=Butler |first4=Richard J. |author-link4=Richard J. Butler |last5=Fraser |first5=Nicholas C. |author-link5=Nicholas Fraser |last6=Brusatte |first6=Stephen L. |author-link6=Stephen L. Brusatte |last7=Farnsworth |first7=Alexander |last8=Lunt |first8=Daniel J. |last9=Valdes |first9=Paul J. |last10=Walsh |first10=Stig |last11=Barrett |first11=Paul M. |date=2022 |title=Scleromochlus and the early evolution of Pterosauromorpha |url=https://www.nature.com/articles/s41586-022-05284-x |url-access=subscription |journal=Nature |volume=610 |issue=7931 |pages=313–318 |doi=10.1038/s41586-022-05284-x|hdl=20.500.11820/3134b3f1-41e0-47bb-9688-a5e5b0b64492 |hdl-access=free }}{{cite web |last=Gill |first=Victoria |date=6 October 2022 |title=Scottish fossil revealed to be pterodactyl ancestor |url=https://www.bbc.co.uk/news/science-environment-63146271 |website=BBC News |publisher=BBC |access-date=6 October 2022}} Foffa et al. followed up with a more extensive redescription of Scleromochlus fossils in 2023.{{Cite journal |last=Foffa |first=Davide |last2=Nesbitt |first2=Sterling J. |last3=Butler |first3=Richard J. |last4=Brusatte |first4=Stephen L. |last5=Walsh |first5=Stig |last6=Fraser |first6=Nicholas C. |last7=Barrett |first7=Paul M. |date=2024 |title=The osteology of the Late Triassic reptile Scleromochlus taylori from μCT data |url=https://anatomypubs.onlinelibrary.wiley.com/doi/full/10.1002/ar.25335 |journal=The Anatomical Record |language=en |volume=307 |issue=4 |pages=1113–1146 |doi=10.1002/ar.25335 |issn=1932-8494}}

{{Reflist|colwidth=20em}}

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{{Avemetatarsalia|state=autocollapse}}

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Category:Pterosauromorpha

Category:Triassic archosaurs

Category:Carnian genera

Category:Late Triassic reptiles of Europe

Category:Triassic Scotland

Category:Fossils of Scotland

Category:Fossil taxa described in 1907

Category:Taxa named by Arthur Smith Woodward

Category:Prehistoric reptile genera