Early sauropodomorph was an agile biped

[Pandora]

Walking with early dinosaurs: appendicular myology of the Late
Triassic sauropodomorph Thecodontosaurus antiquus

Abstract

Dinosaur evolution is marked by numerous independent shifts from
bipedality to quadrupedality. Sauropodomorpha is one of the lineages
that transitioned from small bipedal forms to graviportal quadrupeds,
with an array of intermediate postural strategies evolving in
non-sauropodan sauropodomorphs. This locomotor shift is reflected by
multiple modifications of the appendicular skeleton, coupled with a
drastic rearrangement of the limb musculature. Here, we describe the
osteological correlates of appendicular muscle attachment of the Late
Triassic sauropodomorph Thecodontosaurus antiquus from multiple
well-preserved specimens and provide the first complete forelimb and
hindlimb musculature reconstruction of an early-branching
sauropodomorph. Comparisons with other sauropodomorphs and early
dinosaurs reveal a unique combination of both plesiomorphic and
derived musculoskeletal features. The diversity of appendicular
osteological correlates among early dinosaurs and their relevance in
muscle reconstruction are discussed. In line with previous evidence,
aspects of the limb muscle arrangement, such as conspicuous correlates
of lower limb extensors and flexors and low moment arms of hip
extensors and flexors, suggest Thecodontosaurus was an agile biped.
This reconstruction helps to elucidate the timing of important
modifications of the appendicular musculature in the evolution of
sauropodomorphs which facilitated the transition to quadrupedalism and
contributed to their evolutionary success.

Open access:
https://royalsocietypublishing.org/doi/10.1098/rsos.211356

[John Harshman]

The conventional wisdom is that Herrerasaurus is a sauropodomorph and
also an agile biped. This paper mentions it only once, briefly, but it
seems that they don't think it's a sauropodomorph. Could have used a bit
more phylogenetic context to that analysis.