Extinct genus of reptiles
Ignotosaurus is an extinct genus of silesaurid dinosauriform known from the Late Triassic (Carnian) Cancha de Bochas Member of the Ischigualasto Formation in the Ischigualasto-Villa Unión Basin in northwestern Argentina. It was therefore contemporary with early dinosaurs such as "Herrerasaurus," and lived in the same place.
Etymology.
The name, meaning 'unknown lizard' from the Latin 'ignotus' 'unknown' and the Greek " 'lizard', is quite apt as there is only one specimen known and this specimen is only known from the right ilium. This ilium is approximately long, but it is difficult to say accurately how large "Ignotosaurus" was.
Description.
The ilium is slender, and its blade has an extremely thin central portion (only thick), hence the specific name 'fragilis'. It has the saddle-shaped lateral profile of most silesaurids, and is longer than it is deep. The acetabulum has a back wall created by a ventral flange and this closes a socket as it is in contact with the ischium and pubis. The supraacetabular crest is laterally oriented and forms part of the articulation for the femur. A ridge rises from the dorsal edge of this crest and joins the preacetabular process, as in the close relative "Silesaurus". The preacteabular process is flattened anteroposteriorly and is angled at 90° to the iliac blade, pointing anterolaterally - these are the diagnostic features of this species. The end of the process has a rugose growth, but it is less extensive than that of "Silesaurus". The postacetabular process is long and has a brevis fossa present on the ventral side. It has a thick rectangular cross-section and a rugose area at the end. The pubic peduncle is long and stout, with a prominent dorsal margin.
"Ignotosaurus" is thought to be most closely related to "Silesaurus, Sacisaurus" and "Eucoelophysis," but as only one of the three characteristic features for silesaurids is preserved this is not certain (the other features are on the femur and tibia, which are not preserved).
It is thought that the Ischigualasto Formation at this time was a river basin habitat with abundant vegetation. As "Ignotosaurus" was probably a herbivore, like other silesaurids, it would probably have flourished here, competing for food with rhynchosaurs, cynodonts and possibly some early dinosaurs.
References.
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