Basal bipedal crocs reviewed, with a focus on Barberenasuchus

Leardi, Yáñezc and Pol 2020 bring us
their thoughts on new and previously discovered South American crocodylomorphs. In the large reptile tree (LRT, 1737+ taxa; subset Fig. x) only Crocodylomorpha + Dinosauria comprise the Archosauria. The Poposauria (= Turfanosuchus and kin;  Fig. 1) is the proximal outgroup.

Figure 1. The origin of dinosaurs in the LRT to scale. Gray arrows show the direction of evolution. This image includes Decuriasuchus, Turfanosuchus, Gracilisuchus, Lewisuchus, Pseudhesperosuchus, Trialestes, Herrerasaurus, Tawa and Eoraptor.  Note the phylogenetic miniaturization at the origin of Archosauria (Crocs + Dinos).

Figure 1. The origin of dinosaurs in the LRT to scale. Gray arrows show the direction of evolution. This image includes Decuriasuchus, Turfanosuchus, Gracilisuchus, Lewisuchus, Pseudhesperosuchus, Trialestes, Herrerasaurus, Tawa and Eoraptor.  Note the phylogenetic miniaturization at the origin of Archosauria (Crocs + Dinos).

From the Leardi, Yáñezc and Pol Abstract
“Crocodylomorpha is a clade that has its origins during the Late Triassic and attained a global distribution early in their radiation.In this contribution we review the crocodylomorph Triassic record in South America by analyzing three units that have yielded fossils of the clade: the Santa María Supersequence in Brazil; and, the Ischigualasto and Los Colorados formations in Argentina.”

Good start!

Figure 3. Barberenasuchus to scale with sister taxa, Herrerasaurus, Eoraptor, Lewisuchus and Trialestes and Junggarsuchus, but without the autapomorphies of its sister Herrerasaurus. At present Barberenasuchus is the basalmost dinosaur. Note the difference in the nasal between the dinosaurs and protodinosaurs.

Figure 1. Barberenasuchus to scale with sister taxa, Herrerasaurus, Eoraptor, Lewisuchus and Trialestes and Junggarsuchus, but without the autapomorphies of its sister Herrerasaurus. At present Barberenasuchus is the basalmost dinosaur. Note the difference in the nasal between the dinosaurs and protodinosaurs.

Continuing from the abstract
“Our review does not support previous assignments of the taxon Barberenasuchus (Fig. 1) from the Santa María Supersequence as a non-crocodyliform crocodylomorph, as it displays traits that are absent in all known crocodylomorphs and are present in other earlier branching archosaurs.”

The LRT agrees, but what Barberenasuchus isn’t isn’t the same as what it is (Fig. 2). Adding taxa gradually and ultimately nests all taxa.

Figure 2. Subset of the LRT focusing on the Phytodinosauria.

Figure 2. Subset of the LRT focusing on the Phytodinosauria.

More specifically,
the LRT nests Barbarenasuchus with Eodromaeus (Fig. 3) within the base of the Phytodinosauria (Fig. 2). Only Buriolestes is more primitive in this plant-eating clade of the Dinosauria.

Figure 1. Eodromaeus reconstructed. We will look at this taxon in more detail tomorrow.

Figure 1. Eodromaeus reconstructed. We will look at this taxon in more detail tomorrow. Note the relatively small head of this plant eater.

Continuing from the abstract
“The Los Colorados Formation has a diverse crocodylomorph record being represented by a non-crocodyliform crocodylomorph (Psedhesperosuchus [Fig 1]) and two crocodyliforms (Hemiprotosuchus and Coloradisuchus).”

We looked at these two yesterday.

In the LRT, the Triassic is a little too early
for crocodyliforms. Adding taxa moves Hemiprotosuchus to the base of the Aetosauria. Coloradisuchus nests among basal bipedal crocodylomorpha, as we learned earlier. These are indeed found in the Triassic.

Continuing from the abstract
“Here we present a putative new non-crocodyliform crocodylomorph taxon from Los Colorados Formation. When compared with other crocodylomorph bearing formations around Pangea, the Ischigualasto Formation bears similarities with the crocodylomorphs assemblages of North America due to the presence of early branching crocodylomorphs (Trialestes) including “large-bodied” taxa. The Los Colorados Formation reveals a transitional composition corresponding to Norian and Early Jurassic assemblages of Pangea, as it shares the presence of basal crocodyliforms (i.e., protosuchids) typical of Early Jurassic units (e.g., Upper Elliot) and basal non-crocodyliform crocodylomorphs, widely present in Norian assemblages.”

Still waiting for data on this unnamed taxon. Meanwhile, let’s get back to Barberenasuchus (Figs. 1, 2).

Figure x. Subset of the LRT focusing on Euarchosauriformes and Crocodylomorpha.

Figure x. Subset of the LRT focusing on Euarchosauriformes and Crocodylomorpha.

When you add taxa, as done in the LRT,
Barberenasuchus brasiliensis (Mattar 1987, Middle Triassic) nests as a basal phytodinosaur. Barberenasuchus has shorter teeth and a larger orbit that more primitive carnivorous taxa. The skull is more gracile and smaller in size, as in other basal phytodinosoaurs.

Traditionally, and according to Wikipedia
“Barberenasuchus is an extinct genus of an archosauriform. Its phylogenetic position within Archosauriformes is uncertain; the author of its description classified it as a sphenosuchid crocodylomorph, while Kischlat (2000) considered it to be a rauisuchian. Irmis, Nesbitt and Sues (2013) stated that they “could not find any crocodylomorph character states preserved in the holotype specimen”.

Adding taxa makes the position of all taxa, including Barberenasuchus, in the LRT ever more certain.


References
Irmis RB, Nesbitt SJ and Sues H-D 2013.Early Crocodylomorpha. In Nesbitt SJ. Desojo JB and Irmis RB (eds.). Anatomy, phylogeny and palaeobiology of early archosaurs and their kin. The Geological Society of London. pp. 275–302. doi:10.1144/SP379.24
Kischlat E-E 2000.
 Tecodôncios: a aurora dos arcossáurios no Triássico. In Holz, M.; De Ros, L.F. (eds.). Paleontologia do Rio Grande do Sul. Porto Alegre: CIGO/UFRGS. pp. 273–316.
Leardi JM, Yáñezc I and Pol  D 2020. South American Crocodylomorphs (Archosauria; Crocodylomorpha): A review of the early fossil record in the continent and its relevance on understanding the origins of the clade. Journal of South American Earth Sciences. https://doi.org/10.1016/j.jsames.2020.102780
Mattar LCB 1987. Descrição osteólogica do crânio e segunda vértebrata cervical de Barberenasuchus brasiliensis Mattar, 1987 (Reptilia, Thecodontia) do Mesotriássico do Rio Grande do Sul, Brasil. Anais, Academia Brasileira de Ciências, 61: 319–333.

wiki/Eodromaeus
wiki/Barberenasuchus

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.