Earlier this week I reported on the discovery of a new, 190 million year old sauropodomorph dinosaur
Brian: How was the skeleton discovered, and when did you realize it was a new kind of dinosaur?
Mark: Seitaad was discovered by Joe Pachak, a local historian, sculptor and petroglyph expert from Bluff, Utah. Joe was hiking the Navajo Sandstone on Comb Ridge in the four corners region of Utah, came across the bones, and alerted both the BLM and the Utah Museum of Natural History. We received photographs in February of 2005 showing a skeleton in the side of a cliff. When we recognized the rocks in the photos as likely Navajo, we got really excited. So little is known of the Navajo Sandstone fauna that we suspected anything we might find would be significant and probably new. When we first excavated the skeleton we mistakenly thought we had a pterosaur, with the eroded ischium being the lower jaw. As we started to prep the blocks we recognized we had it 180° backwards and were leaning toward it being a theropod. As we prepped down to shoulders and arms we knew we had a “prosauropod.” Joe Sertich and I borrowed the scant materials from this group that were previously found in the Navajo Sandstone of Arizona (from Museum of Northern Arizona and the UCMP at Berkeley) and saw right away that we had something new. After comparing our specimen to all other known basal sauropodomorphs, we confirmed that we had something new to science.
Brian: The head, neck, and tail of Seitaad were missing. What could have happened to them?
Mark: As we completed the preparation we were able to determine that Seitaad was deposited literally standing on its head in a nearly vertical position. The skeleton was preserved with just the backbone emerging from the cliff wall. Every other bone (head, neck, pelvis, femora, and tail) would have been eroded away when the modern canyon formed. The sand immediately surrounding the fossil are consistent with dune collapse deposits and are laterally equivalent dune foresets. Similar isolated collapse deposits are repeated above in the cliff wall. Rapid burial by rare sedimentary event is the likely scenario in which the skeleton was preserved. It wasn’t until a year ago when we CT scanned the block at the University of Utah Hospital that we realized that Seitaad was missing a single toe and the fibula. Seitaad was probably recently dead and complete when it was buried and was held together by soft tissues.
Brian: For most of the public, the process by which dinosaurs are named is mysterious. How did Seitaad ruessi get its unusual name?
Mark: We wanted a unique name for the skeleton in a local dialect and settled on the rich traditions of the Navajo language. We found a Navajo (Diné) creation legend about Seit’aad, a sand-desert monster that swallowed its victims in sand dunes. The fossilized skeleton of Seitaad was "swallowed" by a sand dune, so it seemed appropriate. The suffix ruessi is derived from Everett Ruess, a famous young philosopher poet, artist, historian, explorer and lover of the red rock country of southern Utah (where he was last seen in 1934). We wanted to honor Everett Ruess for his love of the region, its people, and for his free-spirited and adventurous lifestyle.
Brian: As described in the paper, Seitaad is a sauropodomorph dinosaur. How did it and its extinct relatives relate to the later, long-necked sauropod dinosaurs?
Mark: Seitaad is a basal member of the clade Sauropodomorpha. Many of these basal forms have in the past formed a clade that we knew as “prosauropods.” Recent work has suggested that “prosauropods” do not form a group of their own, an idea we will further be able to test as we find more animals like Seitaad. The phylogenetic analyses we ran suggests Seitaad is a close relative of the “prosauropods” Plateosaurus from Germany and Riojasaurus and Adeopapposaurus from Argentina. Either way, Seitaad is now the best known, early sauropodomorph from western North America and is closely related to the animals we think of when we say “prosauropod.”
The last survivors of the sauropodomorphs the long-necked sauropods probably evolved large body size as super food processing strategy and or to deter predators. Seitaad represents the standard run of the mill basal sauropodomorph in terms of size. Interestingly, large true sauropods had evolved in other parts of the world by the time Seitaad was living in Utah.
Brian: What kind of environment did Seitaad live in? What other creatures did it live alongside?
Mark: Seitaad lived in a vast white desert. The backdrop would have been crescent shaped barchan dunes of white sand stretching as far as the eye could see. There were wetter areas with vegetation and interdunal ponds between some of the dunes. Most of the vegetation would have been plants like horsetails and ferns. According to work by David Loope, monsoonal rains from the summer northeasterlies would have produced periodic dune slumps and collapses. Not a very hospitable environment!
From fossils we know that there was a protomammal tritylodont living in the Navajo along with one or two crocodylomorphs. We have a single specimen of the small theropod dinosaur Segisaurus halli along with trackway evidence of a 20 feet long theropod probably similar to Dilophosaurus. Other than that, we know from tracks that there was a small ornithopod and can presume that pterosaurs flew in the skies above. Seitaad was by far the largest herbivore in the area, a fact confirmed by trackway evidence.
Brian: And, to conclude on a more personal note, what inspired you to pursue paleontology as a career?
Mark: Like most kids I always loved dinosaurs. I got into science in college as a chemistry major and really took a liking to solving research problems. I was lucky enough to land a summer research internship looking for fossils in the Eocene of Wyoming and immediately switched to geology and paleontology. During graduate school, I started to see both sedimentology and paleontology as a way to travel back in time and see the past. I am personally fascinated in past worlds and what the animals that lived in them were like.
For more on this new discovery, see Mark's interview with Andy Farke at the Open Source Paleontologist and his guest post at Dave Hone's Archosaur Musings.