Meet Gnathovorax: the most primitive herrerasaur/dinosaur

Pacheco et al. 2019
introduce Gnathovorax cabreirai (Figs. 1), a new herrerasaurid (Fig. 2) based on “an exquisite specimen” (Fig. 3)

Figure 1. Gnathovorax compared to Herrerasaurus, PVL 4597 and Decuriasuchus.

Figure 1. Gnathovorax compared to Herrerasaurus, PVL 4597 and Decuriasuchus. Phylogenetic miniaturization occurred at the genesis of bipedalism in PVL 4597.

Unfortunately,
taxon exclusion prevented Pacheco et al. from understanding and appreciating the micro-evolution now documented at the base of the Dinosauria (Fig. 1) based on the large reptile tree (LRT, 1594 taxa). The authors omitted basal bipedal crocs, like Pseudhesperosuchus (Fig. 4), the basalmost archosaur PVL 4597 (Fig. 1) and the basal poposaur, Decuriasuchus (Fig. 1).

Figure 2. Cladogram from Pacheco et al. 2019. Colors added over the nodes to show where taxa nest in the LRT.

Figure 2. Cladogram from Pacheco et al. 2019. Colors added over the nodes to show where taxa nest in the LRT where Ornithischia and Sauropodomorpha are derived from basal Phytodinosauria.

Lacking pertinent taxa
also prevents Pacheco et al. (Fig. 2) from recovering the clade Phytodinosauria, which splits from basal Theropoda in the LRT.

Figure 3. Gnathovorax in situ from Pacheco et al. 2019. Green bones belong to other taxa.

Figure 3. Gnathovorax in situ from Pacheco et al. 2019. Green bones belong to other taxa.

Between Euparkeria (Fig. 4) and Dinosauria
are several transitional taxa not listed by Pacheco et al. The phylogenetic miniaturization at the base of the Archosauria is a common phenomenon at the origin of major vertebrate clades.

Figure 2. The origin of dinosaurs to scale. Gray arrows show the direction of evolution. This image includes Decuriasuchus, Turfanosuchus, Gracilisuchus, Lewisuchus, Pseudhesperosuchus, Trialestes, Herrerasaurus, Tawa and Eoraptor.

Figure 4 The origin of dinosaurs to scale. Gray arrows show the direction of evolution. This image includes Decuriasuchus, Turfanosuchus, Gracilisuchus,  Pseudhesperosuchus, Herrerasaurus, Tawa and Eoraptor.The LRT is here for researchers to use
as a taxon checklist to make sure they are including all pertinent taxa in their smaller, more focused studies. Just because you’re a traditional paleontologist does not mean you have to omit non-traditional taxa.


References
Pacheco C, Müller RT, Langer M, Pretto FA, Kerber L and Dias da Silva S 2019. Gnathovorax cabreirai: a new early dinosaur and the origin and initial radiation of predatory dinosaurs. PeerJ 7:e7963 http://doi.org/10.7717/peerj.7963

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