An Anisian Triassic Silesaurid was Very Large

A large-bodied silesaurid from the Lifua Member of the Manda beds (Middle Triassic) of Tanzania and its implications for body-size evolution in Dinosauromorpha

Authors:

Barrett et al

Abstract:

Many dinosaur lineages were characterised by wide ranges of body-size, ranging from taxa that were < 1 m in length to the largest of all terrestrial vertebrates. On the other hand, the closest relatives of dinosaurs, the non-dinosaurian dinosauromorphs, such as Marasuchus and lagerpetids, were small-bodied animals with little variation in body-size. Here, we describe a partial femur of an unexpectedly large-bodied silesaurid (non-dinosaurian dinosauriform) from the Lifua Member of the Manda beds (?late Anisian) from southwestern Tanzania. This specimen (NHMUK R16303) is estimated to have had a femoral length of approximately 345 mm, which exceeds that of many Triassic and Lower Jurassic dinosaurs, and is either a large individual of the contemporary Asilisaurus kongwe or represents a new and otherwise unknown silesaurid taxon. In either case, it shows that body-size increases were more prevalent among early dinosauromorphs than realised previously. Moreover, silesaurid size increase occurred in parallel with that in early dinosaurs, alongside the convergent acquisition of other features related to locomotion and herbivory. However, Late Triassic faunas including large-bodied sauropodomorph and theropod dinosaurs lack similarly-sized non-dinosaurian dinosauromorphs, whereas the Lifua Member fauna includes both a large silesaurid and the early ?dinosaur Nyasasaurus, which overlapped in size.