Parringtonia Restored

In 1939 von Huene described some bits and pieces of a Middle Triassic archosaur and named it Parringtonia gracilis (Fig. 2). Recently Nesbitt and Butler (2012) reexamined the material and confirmed von Huene’s assessment that Parringtonia was close to Erpetosuchus, a bizarre crcocodylomorph with a broad triangular skull, tiny teeth set only at the front of its jaws and a deep antorbital fossa. The broad toothless cheeks were the most distinct trait, best appreciated in palatal view.

Erpetosuchus in several views.

Figure 1. Erpetosuchus in several views. Click for more info.

Nesbitt and Butler’s Assessment
Erpetosuchus and Parringtonia have been assigned to their own clade. According to Nesbitt and Butler (2012) “Erpetosuchidae can be assigned to the Archosauria based on the presence of palatal processes of the maxilla that are in contact along the midline (32-1), an antorbital fossa that is present on the posterodorsal portion of the maxilla (137-2) and a distinctly raised acromion process (220-1) of the scapula.” The problem is: where in the Archosauria do these two lie? Nesbitt and Butler (2012) confessed, “Our results illustrate the difficulties involved in accurately reconstructing the phylogenetic position of Erpetosuchidae within Archosauria.”

To their points, the palatal processes of the maxilla are not in contact along the midline in Scleromochlus, Herrerasaurus, Massospondylus and Lesothosaurus, but they are in contact in Sphenosuchus. The antorbital fossa and raised acrominon process are present  on all archosauriformes, including phytosaurs, not just archosaurs.

Parringtonia elements

Figure 2. Here I’ve reduced all the Parringtonia elements by half in an attempt to match similar bones in Erpetosuchus. The maxilla is deeper and has larger teeth set extending much further posteriorly, a plesiomorphic trait befitting its older age. The scapula is a close match, but  has a larger posterior process at the glenoid. The cervical and dorsal are proportionately more robust.  Where the maxilla of Erpetosuchus turns down anteriorly, the maxilla of Parringtonia curves up, more like Sphenosuchus.

Nesbitt and Butler (2012) did not attempt a reconstruction or restoration. Here (Fig. 2) the bones of Parringtonia are reduced by half and placed on the reconstruction of Erpetosuchus. Then here (Fig. 3) bones and teeth were restored with confidence decreasing with distance.

Nesbitt and Butler (2012) reported, “Erpetosuchidae differs from all other archosauriforms in 1) dentition present only in the anterior half of the maxilla, 2) mediolateral length of the posterior portion of the maxilla greater than the dorsoventral length and 3) tooth serrations absent.” Unfortunately, in the present reconstruction, Parringtonia does not agree with #1: (but does have a toothless posterior with only one more tooth position), and #3: one replacement tooth was found deep in the maxilla by CT scanning that did not appear to have serrations, but then, when do tooth serrations appear on teeth? Not sure how #2 scores elsewhere. They mention one other trait, “a deep anteroposteriorly oriented groove on the dorsal surface of the neural spines.”  

They also note the skeleton of Parringtonia was immature based on sutures in the vertebra.

Restoring the skull of Parringtonia

Figure 3. Restoring the skull of Parringtonia by extension and comparison with likely sister taxa, like Sphenosuchus and Erpetosuchus. Of course, the further away from the maxilla, the more risk and the less accurate the restoration is likely to be. The size of the teeth are apparent from the size of the tooth sockets, but note how few teeth Parringtonia had.

Altogether Parringtonia is a likely predecessor to Erpetosuchus, a taxon that nested in the large reptile tree between Sphenosuchus and Hesperosuchus. It demonstrates the reduction in tooth number and the lateral expansion of the poster maxilla taken to extremes in Erpetosuchus.

Once again, big teeth precede a specialized diet
With its small teeth set only in the front of the jaws, no doubt Erpetosuchus had a distinct diet. What sort of diet? Who knows? Parringtonia, on the other hand, had large teeth, judging by the sockets. As in Stenocybus and Daemonosaurus, large teeth – may  – have preceded small teeth in the transition to an herbivorous diet. IF…

I was tough on Sterling Nesbitt earlier. This time he nailed it. Congrats are in order.

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
Huene FV 1939. 
Ein kleiner Pseudosuchier und ein Saurischier aus den ostafrikanischen Mandaschichten. Neues Jahrbuch für Geologie und Paläeontologie, Beilage-Bände Abteilung B 81, 61–9.
Nesbitt SJ and Butler RJ 2012. Redescription of the archosaur Parringtonia gracilis from the Middle Triassic Manda beds of Tanzania, and the antiquity of Erpetosuchidae. Geological Magazine, Available on CJO doi:10.1017/S0016756812000362

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