Buriolestes

Description

Although Buriolestes superficially resembles predatory theropod dinosaurs, with jaws lined by finely serrated and slightly curved teeth well-adapted to a carnivorous diet, possibly preying on small vertebrates and soft invertebrates, it is in fact an early member of the otherwise-herbivorous Sauropodomorpha, the group that gave rise to the giant sauropods. Characteristically sauropodomorph traits seen in Buriolestes include a downturned jaw tip and a long deltopectoral crest on the humerus. However, Buriolestes also lacks a small head and enlarged nostrils, which are typical among sauropodomorphs, and the medial condyle on the end of its tibia projects backwards, a distinctive feature (autapomorphy) unique to this animal.

In Buriolestes, the shaft of the pubis is straight, in contrast to later sauropodomorphs, where it has been modified into an expanded "apron", theropods, where it forms a "boot," and all ornithischians, where it is reversed and is parallel to the ischium. Additional traits differentiate Buriolestes from both later and contemporary sauropodomorphs: the front expansion (preacetabular ala) of the ilium is relatively tall, the outer edges of the pubis are bevelled, the trochanter of the femur forms a shelf, and the metatarsal of the fifth digit on the foot is relatively long.

Skeletally mature specimens of Buriolestes exhibit intraspecific variation through size disparity, with one robust individual weighing over 15.4 kg (34 lb) and others weighing between 6.4–7.2 kg (14–16 lb). This robust specimen is collected from the Piche site, which makes it the first Buriolestes specimen outside the type locality.

In 2022, Aureliano and colleagues performed a mirco-computed tomography scan on the postcranial skeletons of some of the earliest saurischian dinosaurs that lived during the late Carnian including Gnathovorax with sauropodomorphs Pampadromaeus and Buriolestes, which showed that the invasive air sac system was absent and that their bones were not pneumatised. These results indicate that pneumatisation in archosaur groups (pterosaurs, theropods and sauropodomorphs) are not homologous, but are traits that independently evolved at least 3 times.

Classification

A phylogenetic analysis conducted in 2016 affirmed the sauropodomorph affinities of Buriolestes. Part of the phylogenetic tree from the study is shown below.

Five variants of phylogenetic analyses published earlier were used along with the description of the new specimens in 2018. One of these analyses, based on Langer et al. (2017) placed Buriolestes in a clade of early sauropodomorphs, alongside Eoraptor, Panphagia, Pampadromaeus, and Saturnalia. Another analysis, which used the dataset of Buriolestes' original description with the added parameter of implied weighting, placed it as the sister taxon to Eoraptor, with the Buriolestes+Eoraptor clade sister to a clade connecting Panphagia and Pampadromaeus. The other three analyses, which also corresponded to the original description's dataset, agreed with that study's placement of Buriolestes as the single most basal sauropodomorph.

Paleoecology

The shape of the teeth of Buriolestes suggest that it was a carnivore which fed on small vertebrates and invertebrates, which provides evidence that sauropodomorphs - and likely all saurischians and dinosaurs as a whole - were ancestrally carnivorous, and that sauropodomorphs, ornithischians, and various groups of theropods independently became herbivorous.

The co-occurrence of Buriolestes and Ixalerpeton parallels the simultaneous presence of dinosaurs and non-dinosaur dinosauromorphs at other sites (such as the Ischigualasto and Chinle Formations), suggesting that, after their initial evolutionary radiation, dinosaurs did not rapidly replace their dinosauromorph precursors.