Scleromochlus (from , 'hard' and , 'lever') is an extinct genus of small Pterosauromorpha from the Triassic Lossiemouth Sandstone of Scotland. The genus contains the type and only species Scleromochlus taylori, named by Arthur Smith Woodward in 1907.
Discovery
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.
Description
Scleromochlus taylori was about 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;
however, a 2020 reassessment of
Scleromochlus by Bennett suggested that it was a "sprawling quadrupedal hopper analogous to frogs."
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.
Classification
A lightly built
cursorial animal, its
phylogeny position has been debated; as different analyses have found it to be either the basal-most
, 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-
, 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.
In 2020, Bennett interpreted Scleromochlus as possessing certain characteristics, including 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
