Stones and Bones: A conversation with paleontologist Dr. David Varricchio about Dinosaur Site Interpretation Dave spends some time in the collection at the Paleontological Center in Hohhot surrounded by fossils found in Inner Mongolia. A clutch of dinosaur eggs has been taken off the shelf for closer study.

"A little rockier than most paleontologists, but not as rocky as real geologists," is how Dr. David Varricchio describes the way in which he straddles the fields of paleontology and geology.

Dave grew up in Allentown, PA., the youngest of five children. "When I was a kid I didn't really know anything about geology. I think I didn't know what geology was until maybe high school when my folks got me a book about the history of life. I remember I liked it a lot."

Despite the book - and other key moments in his childhood, (a family trip to Badlands National Park in South Dakota; a 9th grade field trip to collect trilobites and brachiopods; hours spent with neighbors' kids prospecting for fossils and arrowheads and ending up with a collection of very interesting metamorphic rocks) Dave's plans to become a paleontologist formed late.

When it came time to go to college, Dave headed to Cornell College in New York, and found himself in the Engineering School. He quickly discovered that "working with machines and dials and meters to read" didn't appeal to him "at all," and graduated with a degree in geology. After college he headed south for a Masters in geology at the University of Georgia, then continued west to Montana. As a doctoral student under the tutelage of Jack Horner, Dave began to explore questions about dinosaur biology.

Dave cut his paleontological teeth on a complex bone bed known as "Jack's Birthday Site," a diverse site that preserves nine species of dinosaurs, along with crocodiles, turtles, fish, pterosaurs and even birds. In order to interpret the site, Dave had to combine paleontology and geology - it is a combination he continues to apply in his research on Troodons, dinosaur nesting and dinosaur egg-laying behavior.

Dave's interests in egg laying, Troodons and troodontids (small theropod dinosaurs close to the ancestors of birds) were at the heart of his decision to participate in the 2001 Chinese American Dinosaur Expedition to Inner Mongolia, where he is currently at work mapping the team's most recent discovery.

Dave is a veteran of Sereno expeditions to Morocco (1995), Argentina (1996) and Niger (1997), and more than a dozen years of fieldwork in the Western United States, particularly the Two Medicine Formation. When Dave isn't doing fieldwork he is teaching at Montana State University.

I spoke with Dave Varricchio during a lunch break in May, 2001, at Base Camp 1 about his interests in paleontology, and the ways in which geology and paleontology are combined to interpret a dinosaur site.

What appeals you to about paleonotology?
I have - I think I have always had - a basic interest in animals and other living things. But most of all I think I like the physicalness of paleontology. There are physical objects involved - things you can touch, hold, feel. Things like bones and rocks are the things you are really working with on a daily basis. I like the mystery of it too. I like trying to figure out the mystery of a discovery. I think that's why I like taphonomy so much - the mystery of it - and the fact that it is a combination of paleontology and geology.

What is taphonomy?
If you come to a dinosaur site - any site - the question is, "How did that animal get there? Why is it in these rocks?" It is a geological question and a biological question - understanding both contribute to solving the mystery of that site. Taphonomy is the study of the burial process - of how things get fossilized. Taphonomy tries to look at everything that happens to what is now a fossil from the time it dies until it is discovered. "From death to discovery," people say. To be able to reconstruct the events that led to the creation of the locality you have to study the rocks that surround the fossils. Interpretation of nesting behavior is a taphonomic question. You have to look at how eggs are arranged and analyze the geometry of the eggs vs. the sediments they're found in.

How can you look at rocks and know what the environment was like millions of years ago?
Rocks are formed by geologic processes. The processes that go on today - deposition, erosion, rivers flooding, lakes drying up - are the same as they were millions of years ago. Characteristics of modern environments, what channels look like at the bottom of a river, say, or mud cracks that form during a dry season - those are things you can observe and describe.

Personally I don't spend a lot of time walking around and studying modern environments. I use mostly sedimentologists' descriptions about environmental characteristics.

Every once in a while I get to see a modern version of what I see in the field. For instance, in Great Falls [Montana] one time the Missouri River was really low and you could see these great sand waves at the bottom of the river channel. Normally to see the bottom of a river channel you'd have to be scuba diving. It was really neat for me to see it because the big waves geologically translate into crossbedding - something I see a lot of in the field.

What are some of the challenges in interpreting a dinosaur site?
I think you have to know anatomy - otherwise, you find bones and you say, "Oh, great, here are some bones." Knowing anatomy let's you say, "there's a skeleton here," or "this is articulated, I wonder if this femur leads to a tibia." So the anatomy is important. But to tell the story of the site - of how that animal came to be there - you need to understand something about the rocks, too.

I am not a sedimentologist, but I spend a lot of time on expedition looking closely at the geology. Studying the geology has its own kind of challenges. You have to allow yourself enough time to see the details. The details of the rocks are important. If you're in a new place that's not familiar, your eye isn't trained to look at it and be able to note what you're seeing. Sometimes the details take a while to sink in. At the beginning you're trying to notice it all - anything from the sediment grain size, to color variations, to root traces, to bedding textures.

Is there anything about the fieldwork that frustrates you?
Trying to keep the nails in the site while I am mapping. Everyone always wants to take them out while they're working.

A good map will provide a record of what is there - even after you've excavated a site. You lay out a grid with nails, try to have it oriented north/south and then you have to sketch in the bones. The other thing - in addition to sketching the bones - is to take trends and plunges - measure the direction of the bones. The information you get might tell you if there had been water current strong enough to move the bones.

It's always nice to have a good map. The challenge comes in because I am mapping while people are digging bones up and removing them. And somehow the nails you hammer in for the grid are always getting dug up or kicked out.

Another thing that can be frustrating is wind. I don't mind cold, I don't mind heat, but it's really hard to map in the wind - all the pages flap around - and on you get grit in your eyes and ears. We had a couple of bad, windy days at this site while I was trying to map.

Are you describing the geology at the site the team is working on now?
Right. I am studying the geology to try to understand what event - or environmental situation - caused these animals to be buried where they are.

I have been doing a geologic section over the last few days. When you do a geological section you're trying to pin down the depositional environment - what kind of environment the dinosaur was buried and fossilized in. The sediments had to accumulate somewhere - but where were they accumulating?

So, are you trying to solve the mystery of the site while you're in the field?
Not really - I just want to record what's there. The job when you're in the field is to observe and describe what you see. In the field you don't have to come to a conclusion about what you are finding. Doing a geologic section is just an exercise in describing the rocks that are there. The real point is to observe and describe what you see.

The first day you approach the geology of the site, Day 1 - is in some ways just going around, mapping things, taking plunges and trends, data recording - getting to know the geology of the site. You have to generate the data before you can come to a conclusion.

You've been a team member on expeditions to Morocco, Niger, Argentina- as well as having done years of fieldwork in Montana and the Western United States. What kind of sites do you like to work best?
I like it when a site is complicated. When you dig up one animal that died in a riverbed, that's a pretty simple scenario. To me it's really cool when you have several individuals all at one locality, and they accumulated in a short period of time, on a single horizon. You've got all these possibilities and questions: How did the animals get here? Were they washed in by rain water or a flood? Did something draw them to that locality? Were they driven to that locality? There's more of a challenge to the work.Actually, the site we're working on now in the field is one of the most interesting I've had a chance to work on.

What makes this site stand out?
The site is really unusual. We haven't spent a lot of time at the site yet, but there were some interesting things that stand out as significant right away. It's a site that seems to have preserved a number of the same kind of dinosaur along the same time horizon. It's also unusual because that dinosaur is a theropod. More often it's herbivores that are many times the size of this dinosaur, such as duckbilled or horned dinosaurs, that are preserved at a single site in large numbers.

So what is answer? How did the dinosaurs at the site get preserved in such unusual positions?
We don't really have a conclusion yet. We're still doing a lot of talking about what we're finding. The conversation the team had after dinner the other night was really good. We were trying everything out, running through as many scenarios as we could come up with, trying to think of any studies that describe a site similar to the one we're working on.

There's some strong evidence in favor of a mass mortality, or sudden death. But we haven't finished excavating the site and the truth is, there are some things we just can't know in the field. For instance, we won't know things like what elements [bones] are represented, or missing entirely, which bones are articulated, and which are isolated or scattered about until the material is prepared back in the lab. That kind of data is significant and must be quantified. Quantifying stuff in the field is almost impossible because so many of the fossils are still encased in rock. The great thing is that in the field, it's not necessary to come to a definitive conclusion.

It sounds like you're saying that "finding the answer" isn't necessarily the most important thing. Is that true? I think most important is that we have good data and that we have a good description with as many details as possible. We might not know as much as we need to know to interpret the data correctly. The most important thing for us is to have a description.

Of course you want your interpretation to be right, but someone 10 or 20 or 100 years from now might know a lot more than we do now about sites like this. They may be able to come up with a better or more complete interpretation based on our observations. So it is critical to make careful observations. I think that's the fundamental aspect of what's happening with the research. After everything else, the description you do is what is going to live on and be useful to other people - even more than your conclusions.

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