A model of shell assembly that makes predictions for the as-yet unestablished history of the turtle stem group is built on by integrating novel data for Eunotosaurus africanus, which is congruent with molecular-based divergence estimates for the lineage, and remains viable whether turtles originated inside or outside crown Diapsida.
Phylogenetic analysis indicates that Anzu is most closely related to Caenagnathus collinsi, a taxon that is definitively known only from a mandible from the Campanian Dinosaur Park Formation of Alberta, and the problematic oviraptorosaurs Microvenator and Gigantoraptor are recovered as basal caenagnaths, as has previously been suggested.
This work provides the first explicitly justified minimum and soft maximum age constraints on 22 clades of turtles following best practice protocols and generates novel age-of-origination estimates for clades within crown Testudines.
A novel molecular dataset, the presence versus absence of specific microRNAs, is applied to the problem of the phylogenetic position of turtles and the root of the reptilian tree, and it is found that this dataset unambiguously supports a turtle + lepidosaur group.
This work reanalysed a recent dataset that allied turtles with the lizard–tuatara clade and found that the inclusion of the stem turtle Proganochelys quenstedti and the ‘parareptile’ Eunotosaurus africanus results in a single overriding morphological signal, with turtles outside Diapsida.
The adaptations related to fossoriality likely facilitated movement of stem turtles into aquatic environments early in the groups' evolutionary history, and this ecology may have played an important role in stem turtles surviving the Permian/Triassic extinction event.
Taphonomic evidence reveals that basal paracryptodires, including C. victa, preferred slow moving or ponded water environments, and the riverine habitat preference of baenodds must therefore be derived.
The phylogenetic analysis clearly reveals that Plesiobaena in the traditional sense is a paraphyletic assemblage relative to the clade formed by Gamerabaena sonsalla and Palatobaena spp.
The baenid topology reveals a demonstrably homoplastic trend towards the reduction of the temporal emargination and unique thickening of the posterior portion of the parietals that corresponds with the K/T boundary and is hypothesized to have provided limited protection from increasingly effective mammalian predators.
This work suggests that ecological filtering due to the temporary loss of significant plant cover across the K-Pg boundary selected against any flying dinosaurs committed to arboreal ecologies, resulting in a predominantly non-arboreal post-extinction neornithine avifauna.