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.
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.
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.
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 (Vancleavea, pterosaur 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.
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.