Randall B. Irmis joined the Utah Museum of Natural History as curator of paleontology at the beginning of this year with a freshly-minted doctorate! This week, his identification of a new dinosaur species, Tawa hallae, was published in the journal Science. This discovery was made by a team that includes scientists from the American Museum of Natural History, the Field Museum, the State University of New York in Stony brook, and the University of Texas.I talked with Randy earlier this week about his work and how a paleontologist discovers something new that is also over 200 million years old!
RBI: Well, most of my work has focused on the early Mesozoic Era (250-180 million years ago), and particularly during the Late Triassic (235-201 m.y.a.). For my Ph.D. dissertation, I investigated the origin and rise of early dinosaurs. I’m particularly interested in why dinosaurs became so successful, whereas other contemporaneous groups fell by the wayside. I also want to know how terrestrial ecosystems during this time responded to global climate change, similar to changes we are seeing today.
JF: Tell us about the new species of dinosaur that is part of your research publication?
RBI: This week we announced the publication of a new species of early carnivorous dinosaur called Tawa hallae, discovered in northern New Mexico at a place called Ghost Ranch. “Tawa” is the Hopi name for the Pueblo sun god, and is a reference to the rich Native American heritage in the area where the fossils were discovered, as well as to New Mexico itself, whose state symbol is a Puebloan representation of the sun. The species name “hallae” is for Ruth Hall, the woman who founded the paleontology museum at Ghost Ranch.
Tawa was found in rocks called the Chinle Formation, and is approximately 213 million years old. This places it in a time period called the Late Triassic, when all the continents were together as a super continent called Pangaea. During this time, North America was near the equator and had a warm and seasonal climate.
JF: What makes Tawa special to science?
RBI: The fossils are really complete and well-preserved; we have pretty much every bone in the body. The new species fills a gap in the evolutionary tree between the earliest carnivorous dinosaurs Herrerasaurus and Eoraptor (from Argentina), and later Triassic carnivorous dinosaurs like Coelophysis (also found at Ghost Ranch, New Mexico).
Using data from Tawa and other species, we were able to determine that the first dinosaurs evolved in South America, and then spread across Pangaea. In fact, the three species of carnivorous dinosaurs we find at Ghost Ranch each represent separate emigration events from the southern continents. This indicates that early dinosaurs were able to freely move across Pangaea without interference from physical barriers such as mountain ranges.
What’s really interesting is that some other dinosaur groups, namely ornithischians and sauropodomorphs, never made it to North America during the Triassic. This got us wondering – why didn’t these two groups arrive in North America when it is clear that early dinosaurs could freely move around? We think it has to do with climate – areas near the equator during the Triassic weren’t hospitable to the ornithischian and sauropodomorph dinosaurs, but the carnivorous dinosaurs could tolerate it.
JF: What drew you to conducting fieldwork in Ghost Ranch?
RBI: Ghost Ranch is world famous for the discovery of many skeletons of the Triassic dinosaur Coelophysis bauri, in addition to other lesser-known paleontological discoveries in the Late Triassic rocks there. It has always been a mecca for Triassic paleontologists. In fact, some of the very first Triassic vertebrate fossils to be described from the western U.S. were discovered in the vicinity of Ghost Ranch in the 1870s.
All of us on the research team had been to Ghost Ranch as paleontological tourists, but our field research there really was a result of serendipitous events starting in 2004. During the fall of that year, Sterling Nesbitt and I attended the Annual Meeting of the Society of Vertebrate Paleontology in Denver, Colorado. At that meeting, Alex Downs from the Ruth Hall Museum of Paleontology, showed us some early dinosaur bones from a new site, called the Hayden Quarry, that he was excavating at Ghost Ranch. We got excited, because they looked to be a new species.
We agreed to work with Alex on scientifically describing the new material, and the next spring we went to Ghost Ranch to do this work. When we got there, we were amazed at how many early dinosaur specimens had been excavated from the site – it was a treasure trove! Sterling and I spent only an afternoon at the site and we discovered half a dozen dinosaur bones. This was unprecedented for Triassic rocks in North America. No one else had ever found a site of this age where early dinosaur specimens were so numerous. So, we resolved to return the next summer, to begin large scale excavations.
During our first season of excavation, we were fortunate to discover several nearly complete skeletons, which ultimately gave us a complete picture of this new species. It has taken three years of lab work to remove these bones from the rock that encases them.
JF: What does it mean to be classified as “a new species”?
RBI: As paleontologists, we typically only have bones to look at when trying to distinguish different species. We look for anatomical characters on the bones – bumps, ridges, depressions, and other small features – that tell us if a specimen is distinct or not. If a fossil specimen has a unique character or unique combination of anatomical characters preserved on the bones, these tells us it is a new species not known to science.
But we have to be careful – we compare the bones to all other known species first to make sure that some other species don’t already have these anatomical characters on the bones. This requires a lot of time and effort – particularly visiting museums across the world to look at their fossil collections.
JF: That sounds like fun work! How do you work with artists to come up with a rendering of what the dinosaur may have looked like?
RBI: A good paleoartist has an excellent knowledge of anatomy, and there is a constant dialogue between the artist and scientists as work progresses. We provide images of the bones, our skeletal reconstruction, notes on anatomy, things like that to the artist to give them an idea of what the skeleton looked like.
The artist then uses their knowledge of anatomy of living relatives of the dinosaur -- like, birds, for example -- to flesh out the skeleton and bring the animal to life. As the artist works, they’ll provide sketches and preliminary renderings that us as scientists can comment on and make suggestions. Jorge Gonzalez was our paleoartist, and he did an amazing job!
JF: How do you know that this is what this species looked like?
RBI: Some of it we know based on the skeleton, whereas other parts are scientifically informed inferences. For example, the general body and head shape is clear from the complete skeletons we have. But we don’t know for sure what color Tawa was, or what it was covered in. You’ll notice that Jorge’s reconstruction of Tawa is covered in a downy plumage of “protofeathers.”
Although we only have the bones of Tawa, we know from fantastic discoveries of fossils with soft tissue preservation from China that a wide variety of dinosaurs had these protofeathers. So, we thought it was a reasonable inference that Tawa would have had a similar covering.
Color really is up to the artist – but even here we can make some guesses. For example, carnivores today generally aren’t a garish bright color, because they don’t want their potential prey to spot them prematurely. So it’s a reasonable guess that as a carnivore, Tawa also had a subdued color scheme.
JF: How can the public see the fossils?
RBI: We’ll have original fossils of Tawa, along with fossils of other creatures from the same time, on display in the Utah Museum of Natural History lobby for the next few months – so I encourage you all to come down and see them! I’ll also be doing a special presentation in the museum from Noon to 4 p.m. on Saturday, December 12th.
JF: You participate in several Scientist in the Spotlight events like this at the Museum. What will people see when they come Saturday?
RBI: I’ll have a variety of original dinosaur fossils available for people to see up close. We also demonstrate how specimens are removed in the lab from their rocky tombs, and show what it’s like to excavate dinosaurs in the field.
JF: How does this new research, and your work in general, contribute to the overall work of the Museum and the University of Utah?
RBI: UMNH has a long tradition of dinosaur research, and is currently one of the only museums in the world to have an active research program in all three periods of the Age of Dinosaurs. In recent years, we’ve been particularly strong in studying the latter two geologic periods of the Age of Dinosaurs, the Jurassic and Cretaceous. My research gives us expertise and active research in the Triassic, at the beginning of the dinosaur age.
JF: What are you working on next?
RBI: I have a variety of Triassic and early dinosaur research projects in the works right now. Several of these should be published in the coming year. Look for a major announcement about the earliest relatives of dinosaurs in early 2010! I’m also involved in the long-term Kaiparowits Basin Project, which aims to understand terrestrial ecosystems from the end of the Age of Dinosaurs, during the Late Cretaceous (80-70 m.y.a.) in Grand Staircase-Escalante National Monument of southern Utah. We have discovered a variety of new dinosaur species, some of which we hope will be announced in the next year.
JF: One last question: How did you end up as a paleontologist, anyway?
RBI: I always wanted to be a paleontologist since my childhood love affair with dinosaurs. As I got older, my interests broadened to geology and evolutionary biology, but I never lost sight of the goal of becoming a paleontologist. In college, I majored in Geology with an emphasis in Paleontology, and got involved in several undergraduate research projects. This propelled me into the field, and I was lucky enough to be accepted into the Ph.D. program at University of California, Berkeley. The rest, as they say, is history!
To see photos and the paleoartist's rendition of Tawa hallae, visit umnh.utah.edu/dinos
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