Data from: Large neotheropods from the Upper Triassic of North America and the early evolution of large theropod body sizes

Large body sizes among non-avian theropod dinosaurs is a major feature in
the evolution of this clade, with theropods reaching greater sizes than
any other terrestrial carnivores. However, the early evolution of large
body sizes among theropods is obscured by an incomplete fossil record,
with the largest Triassic theropods represented by only a few individuals
of uncertain ontogenetic stage. Here, I describe two neotheropod specimens
from the Upper Triassic Bull Canyon Formation of New Mexico and place them
in a broader comparative context of early theropod anatomy. These
specimens possess morphologies indicative of ontogenetic immaturity (e.g.,
absence of femoral bone scars, lack of co-ossification between the
astragalus and calcaneum), and phylogenetic analyses recover these
specimens as early-diverging neotheropods in a polytomy with other early
neotheropods at the base of the clade. Ancestral state reconstruction for
body size suggests that the ancestral theropod condition was small (~240
mm femur length), but the ancestral neotheropod was larger (~300–340 mm
femur length), with coelophysoids experiencing secondary body size
reduction, although this is highly dependent on the phylogenetic position
of a few key taxa. Theropods evolved large body sizes before the
Triassic-Jurassic extinction, as hypothesized in most other ancestral
state reconstructions of theropod body sizes, but remained rare relative
to smaller theropods until the Jurassic.