STL Science Center

STL Science Center

07 September 2011

Discovery and Completion of Herrerasaurus

In 1963 Osvaldo Reig named Herrerasaurus after the Andean goatherd, Victorino Herrera, who found the original fossils near the city of San Juan in an outcrop of rock in 1959 (Herrerasaurus has been out of the rocks as long as my parents!). Reig uncovered what he thought was another species, which was in the paper presented yesterday, called Ischisaurus. This is now thought to be a junior synonym, and juvenile specimen, of Herrerasaurus. Fernando Novas had the same thing happen to him in 1986 when he named a find, Frenguellisaurus ischigualastensis, which is also now thought to be a junior synonym to Herrerasaurus.

Reig contended that his find was a basal carnosaur at the time of his description and naming of the animal. Until the 1990's there was no real clear consensus on exactly what kind of dinosaur Herrerasaurus was. In the 1970's first Rodney Steel described Herrerasaurus as a prosauropod and then Peter Galton described it as an animal without classification beyond Saurischia. In later books and papers Herrerasaurus was placed with Staurikosaurus in a pre-ornithischian/saurischian split off area of evolution; basically at the ground level of the dinosaurian tree. Let's not forget that there have been those that also stated that Herrerasaurus wasn't even a dinosaur as well. Given the general consensus at the current time it's safe to disregard this last argument for the time being.

In 1988, however, the first complete skull of Herrerasaurus was uncovered and many papers were written subsequently that either supported the claim of basal theropod (Sereno and Novas 1992, Rauhut 2003, Bittencourt and Kellner, 2004 just to name a few) while others claimed that Herrerasaurus belonged to a "sister-group of Theropoda + Sauropodomorpha" (Bonaparte and Pumares 1995, Holtz 1995, Langer 2004 to name a few). There is newer literature available in both theories, and a short search will turn it up, I only chose a few for each to make for a quick reference, but the quoted section above is linked to an article that compiles a great deal of the previous research in discussing a new Herrerasaurid from northwest Argentina.

Lastly, but certainly not least, I asked a member of the expedition in 1988, Dr. Catherine Forster, if she would be so kind as to share with us a little bit of the experience of being a member of that expedition. I think that the narrative is fantastic as it is and so I won't change a thing, I'll just let the readers read:
We spent two seasons down in Argentina in the Ischigualasto Fm. and found quite  bit.  It was a  joint expedition between the Univ. de San Juan (Alfredo Monetta and his students Oscar  Alcober and Ricardo Martinez) and the Univ. of Chicago (Paul Sereno).  It was a lot of fun and I made many lasting friends- we were basically all very young graduate students and new  professors at the time.  Those two seasons turned up the nearly complete Hererrasaurus  skeleton with skull (found by Paul the first season) and the skeleton of Eoraptor (found by Ricardo the second season).  Herrerasaurus was a known dinosaur at that time, and Oscar and Ricardo had already found a really nice skeleton earlier in the first season (no skull but a great  body including hands).  The area, called the Valle de la Luna, is really beautiful, and chocked full of fossils.  Lots of small carnivorous and herbivorous cynodonts, rhynchosaurs, and various  "crocodile-relatives" such as rauisuchids. The second year geology student Ray Rogers came with us and found an ashfall tuff near the bottom of the formation, providing the first good date  for the Ischigualato.  That was a great discovery.  I remember many nights around a campfire or in the cook tent singing songs and trying to understand spanish.  Jose Bonaparte was there part of hte time the first season as well.  Some very cold nights as we were there in the austral winter- I use to wer my down jacket to bed to keep warm.  These were my first international expeditions so it was very exciting- plus very productive and a ton of fun.  I still have a red brush from those first expeditions to Argentina that I've used on all field work since then- my lucky  brush!

No comments:

Post a Comment