Another Gracilisuchus (from Brinkman 1981)
It’s time to add another Gracilisuchus to the data matrix
This one (MCZ4118) has been known since Brinkman (1981) and is deemed worthy of inclusion due to its phylogenetic placement (between Gracilisuchus and Scleromochlus) and distinct morphology. You might remember earlier we looked at the hind limb specimen (PVL 4597) described by Lecuona and Desojo 2011 and found it nested a few nodes away from the holotype and therefore could not be congeneric.
Figure 1. The second Gracilisuchus described (Brinkman 1981) with a more juvenile looking skull despite sharing a similar size with the holotype (fig. 2). It nests between Gracilisuchus and Scleromochlus. It is not congeneric, but certainly a sister to Gracilisuchus.
Basal crocodylomorphs and basal archosaurs
This taxon is important in that it demonstrates the vertical quadrate atypical for crocs and more typical for dinos. It nests near the base of the Archosauria. It had a robust neck pretty much like that of Gracilisuchus (fig. 2) and tiny Scleromochlus, it’s other sister.
Figure 2. Gracilisuchus (Romer 1972). Click for more data.
What do the larger orbit and taller skull tell us?
This specimen had even larger eyes. The rounder rostral profile reminds one of the basal dinosaur/phytosaur/maybe ornithischian, Daemonosaurus, which was heading toward herbivory. Not sure if the same can be said here in the case of the Brinkman specimen or not.
The flatter skull is a trait shared by Gracilisuchus and Scleromochlus to the exclusion of this Brinkman (1981) specimen, which indicates it is an offshoot without any other short-rostrum relatives currently known.
As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.
Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.
References
Brinkman D 1981. The origin of the crocodiloid tarsi and the interrelationships of thecodontian archosaurs. Breviora 464: 1–23.
Lecuona A and Desojo J B 2011. Hind limb osteology of Gracilisuchus stipanicicorum (Archosauria: Pseudosuchia). Earth and Environmental Science Transactions of the Royal Society of Edinburgh 102 (2):105-128.
Romer AS 1972. The Chañares (Argentina) Triassic reptile fauna. An early ornithosuchid pseudosuchian, Gracilisuchus stipanicicorum, gen. et sp. nov. Breviora 389:1-24.
2013-03-16 15:56:06
Source: http://pterosaurheresies.wordpress.com/2013/03/11/another-gracilisuchus-from-brinkman-1981/
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