Silesaurid

Silesauridae is an extinct family of Triassic dinosauriforms. It is most commonly considered to be a clade of non-dinosaur dinosauriforms, and the sister group of dinosaurs. Some studies have instead suggested that most or all silesaurids comprised an early diverging clade or a paraphyletic grade within ornithischian dinosaurs. Silesaurids have a consistent general body plan, with a fairly long neck and legs and possibly quadrupedal habits, but most silesaurids are heavily fragmentary nonetheless. Furthermore, they occupied a variety of ecological niches, with early silesaurids (such as '' Lewisuchus'') being carnivorous and later taxa (such as ''Kwanasaurus'') having adaptations for specialized herbivory. As indicated by the contents of referred coprolites, ''Silesaurus'' may have been insectivorous, feeding selectively on small beetles and other arthropods.

Classification

Silesauridae is typically considered the sister group to Dinosauria. The group was named in 2010 by Max C. Langer ''et al''. They defined it as a branch-based clade of all archosaurs closer to '' Silesaurus opolensis'' than to either '' Heterodontosaurus tucki'' or ''Marasuchus lilloensis''. At around the same time, Sterling J. Nesbitt ''et al''. (2010) independently named Silesauridae as a node-based clade consisting of '' Lewisuchus'', ''Silesaurus'', their last common ancestor and all their descendants. Currently, both definitions encompass the same group of animals. Nesbitt ''et al.'' noted that the earlier definition by Langer ''et al.'' did not include a diagnosis, and so was not sufficient to create a ranked family-level name according to the ICZN. Therefore, the family Silesauridae is attributed to Nesbitt ''et al.'' (2010) while the clade Silesauridae is attributed to Langer ''et al.'' (2010).

Phylogenetic studies originally recovered Silesauridae as a clade sister to Dinosauria, including a variety of Triassic taxa related to ''Silesaurus''. Sometimes the genera are recovered as successive sister taxa to dinosaurs rather than a clade, but often a group is recovered as possibly quadrupedal herbivorous taxa.

A large phylogenetic analysis of early dinosaurs and dinosauromorphs carried out by Matthew Baron, David Norman and Paul Barrett (2017) and published in the journal ''Nature'' recovered Silesauridae as a monophyletic sister group to Dinosauria. The study also recovered the taxon '' Agnosphitys'' within the clade Silesauridae, close to '' Lewisuchus'' and its synonymous taxon '' Pseudolagosuchus''. A 2022 study by Norman and colleagues instead found silesaurs to be a paraphyletic group on the branch leading to traditional Ornithischia. The cladogram below is based on their study. This topology is almost identical to the one recovered by Müller & Garcia (2020) in their first iteration of the same dataset. When found as a grade of ornithischians, '' Amanasaurus'', ''Ignotosaurus'' and ''Silesaurus'' have still been recovered as a clade, which makes them the only members of Silesauridae under those results.

The inclusion of ''Pisanosaurus'' by some studies would mean that, according to ICZN rules, the name of the family should be the older name, Pisanosauridae, which was erected by Rodolfo Casamiquela in 1967.

While Sulcimentisauria is used for all ornithischians by some authors, the original intention of the clade was as a subdivision within Silesauridae, the new use being significantly different from its original application. A solution to this could be to restrict Sulcimentisauria to only apply to a subclade of Silesauridae, where it would no longer be applied along the ornithischian stem as a clade.

Martz & Small, 2019

Müller & Garcia, 2023

References

External links

Silesauridae
in the Paleobiology Database

{{Taxonbar, from=Q941361

Prehistoric reptile families
Anisian first appearances
Rhaetian extinctions