A New Nose for Herrerasaurus

A new nose for Herrerasaurus

Figure 1. A new nose for Herrerasaurus, courtesy of DGS (digital graphic segregation, see below) and Digimorph. The original restoration of the premaxilla (lower right) represents a crack in the maxilla. Click for more info on Herrerasaurus.

The original reconstruction of the Herrerasaurus (Reig 1963) rostrum (Fig. 1)  included a very large post-narial process of the premaxilla, which wasn’t there. That “suture” was a crack in the maxilla.

The skull of Herrerasaurus

Figure 1. The skull of Herrerasaurus with color overlays delineating select bones. Note the post-narial expansion of the nasal and the reduced post-narial process of the premaxilla. An enlarged post-narial premaxilla does not appear until Daemonosaurus at the base of the Phytodinosauria.

What Drew My Attention
No dinosaur sister taxa had such a large post-narial process of the premaxilla. Not until Daemonosaurus, at the base of the Phytodinosauria, does the post-narial process of the premaxilla expand in dinosaurs and then not so much. Moreover, there’s no overlapping of the premaxilla by the nasal in dinos. These two bones meet each other evenly. Also the maxilla commonly overlaps the premaxilla in dinosaurs and this was not reproduced in the original reconstruction.

DGS and Digimorph
To determine the actual sutures, Digital Graphic Segregation turned out to be useful. Digimorph also features Herrerasaurus and it’s worth a look in various views (yaw works nicely), including comparing the left and right sides for confirmation.

Cladistic Analysis
I would not have focused on the nasal if it wasn’t so different from that of other dinosaurs and so similar to the outgroup taxon, a non-dinosaur and a fellow basal archosaur, Gracilisuchus (Romer 1972, Fig. 2.) Trialestes (Reig 1963) nests between these two, but the nasal area in question is missing in the one and only specimen. Note the many shared traits of Gracilisuchus and Herrerasaurus.

Gracilisuchus nose

Figure 2. Gracilisuchus, a basal archosaur with a very similar nasal bone - and overall a good match overlooked by all prior workers as a sister taxon to Herrerasaurus. Even here the premaxilla does not underlap the nasal. Click for more data.

No Substitute for First-Hand Examination?
This plesiomorphic nose detail on Herrerasaurus had been overlooked by all prior workers who published on this specimen. They’ve held the specimen in their hand. Having never seen the fossil except in photos, here’s my contribution.

It’s been said time and again “there’s no substitute for first-hand observation,” but here’s the exception, joining a long list of others (Vancleaveapterosaur wing shapes, etc.) frequently blogged here at PterosaurHeresies.com.

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
Novas FE 1994. New information on the systematics and postcranial skeleton of Herrerasaurus ischigualastensis (Theropoda: Herrerasauridae) from the Ischigualasto.
Reig OA 1963. La presencia de dinosaurios saurisquios en los “Estratos de Ischigualasto” (Mesotriásico Superior) de las provincias de San Juan y La Rioja (República Argentina). Ameghiniana 3: 3-20.
Romer AS 1972. The Chañares (Argentina) Triassic reptile fauna. An early ornithosuchid pseudosuchian, Gracilisuchus stipanicicorum, gen. et sp. nov. Breviora 389:1-24.
Sereno PC and Novas FE 1993. The skull and neck of the basal theropod Herrerasaurusischigualastensis. Journal of Vertebrate Paleontology 13: 451-476. doi:10.1080/02724634.1994.10011525.

wiki/Herrerasaurus
wiki/Sanjuansaurus

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2 thoughts on “A New Nose for Herrerasaurus

    • Two points brought out by Mickey Mortimer’s blog. The lack of antorbital fossa in Herrerasaurus. I agree, there’s not much of a depression there, but sister taxa all around have an antorbital fossa. Is this an autapomorphy? If so, the vestige of that fossa is still present, not well marked, but still present. Point two, something about a tiny crack misinterpreted as a suture? Perhaps so. There are two sides to the Herrerasaurus skull, both obviously will show similar morphologies. I have the CT-scan as well from Digimorph and will present both sides in a few days. Unfortunately there is much more to the reinterpretation of the Herrerasaurus skull that was not considered by MM, but should have been. I encourage MM to post a refutation of the rest of the image that takes into account all the changes I proposed and to support the original interpretation with imagery and phylogeny. I am pleased that this interpretation was tested. Let’s test it again. There’s lots of evidence to look at. The most unfortunate aspect of this reply is the tone imparted, unbecoming of a scientist. Words like “complete nonsense,” are always uncalled for and seem to reflect some sort of fight or flight instinct, rather than a joining together to find the right answer.

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