by Danica Tiu
Project Exploration President and Cofounder, Paul Sereno, unleashed a menagerie of ancient crocodiles, the likes of which have not roamed the earth for at least 100 million years. Preparing the crocs for their re-emergence from the depths of time, however, has been a project almost a decade in the making. We are joined today by a number of special guests from the University of Chicago Fossil Lab– Senior Fossil Preparator Bob Masek (BM), as well as Paleoartists Tyler Keillor (TK) and Erin Fitzgerald (EF). Each member of the Sereno lab has been involved with the crocs in a number of different capacities: fossil prep, molding, casting, and flesh reconstruction, to name a few.
TK: For me, one of the things that impressed me was looking at the skull of DogCroc, a beautiful, little white skull that you can hold in the palm of your hand. Bob worked on that. Bob, it was so fragile – was it really hard to work on?
BM: It’s hard to explain what it’s like looking at a specimen through a microscope and removing the matrix without a visual aid. But one of the challenges was making such small movements [to prepare the specimen]. What I mainly did for this project was prepare the fossils, which pretty much took place over the course of almost 10 years – about as long as I have been working with Paul. Paul gave me Araripesuchus (DogCroc) to work on. In the field, someone had lifted up the skull – pretty much separated the skull into two pieces – and pushed it back down like a pancake. Paul wrapped it in a jacket and brought it back here, and it was my job to open up the jacket and see if I could save the skull. So I guess I did, and that’s where the croc project started. Over the years, Paul has given us these skulls to work on, whether lab personnel or volunteers to start or students. I don’t think Paul knew that this would end up as a massive CrocWorld exhibit that long ago. It’s taken a very long time to get the specimens cleaned up and prepared, and then to have them move onto the reconstruction stage.
TK: When you see the actual specimen, it looks so perfectly clean and repaired that it is unbelievable to think that when Bob got it, they had no idea what it was. And I think that’s one of the coolest things – how beautiful these fossils turn out to be. When you are cleaning a fossil off, you never really know how great it’s going to look, and so many of these have really amazing sculpture and surface detail, really nice information. Very delicate stuff – it takes a long time to get it cleaned off.
EF: I think that a lot of getting an excellent specimen has to do with the preparator’s skill level. And not only that – a preparator needs to know what they are capable of and what their limits are when preparing a fossil. For instance, I did some work on BoarCroc’s nasal area, which I thought was fascinating. Under the microscope, it looks like a bunch of valleys, hills, and canyons, and it’s always fascinating to see what the bone looks like in the end. BoarCroc has sturdier bone than DogCroc though, and removing the matrix was much easier. I also did some work on the little DuckCroc body and skull, which I found tremendously frustrating specifically because the bone itself felt a lot like a pressed powder. I had a lot of trouble deciding how to solidify it and couldn’t figure out a strategy. I ended up turning to Bob for some advice, and he ended up finishing up the fossil and doing a beautiful job. Bob has more experience with fossils, and you can see that in the great skill with which he handles the fossils. A preparator needs to know when to hand over a specimen to someone with more experience – that is, you need to know when you are not capable of achieving something and recognizing when someone else can do a wonderful job with what you are struggling with.
EF: We all tend to use the same tools on every specimen, but it really depends on what that specimen allows you to continue using. Like for DuckCroc, we couldn’t even bring this larger tool – an air scribe, which we use very, very commonly – close to the fossil. We did a lot of pin vice needlework with it to get it clean.
TK: And by comparison, the PancakeCroc jaws were a lot denser, harder bone, so we could use the air scribe on those pretty safely without the bone just shattering and disappearing from the force of the tool. The bigger ones, luckily, were a little bit stronger and harder; the little crocodiles, like DuckCroc and DogCroc, their skulls were pretty small and delicate.
EF: Well, that’s hard to say. We reached a number of different stopping points over the years, and we have a lot of people – lab staff and students – work on the specimens.
BM: Though if you added up all of the hours spent on a single specimen, I’m sure you would get weeks of solid, continuous work.
TK: And that’s not including molding. Most of the specimens were molded so that casts could be made of all the fossils. In some cases, like with the larger, more fragile DuckCroc skeleton and skull, we weren’t sure if the specimen would survive the molding process, so we didn’t put it through. Paul ended up sending it off to be CT scanned so that we would have a record of the data that, if we needed to at some point, could be prototyped into a cast or replica of the fossil without us having stressed the fossil by doing a silicone mold of it. But for the other fossils, after they were totally cleaned, we could move onto the molding process. Which had its own difficulties because these skulls, being so fully prepared, all the cavities in the skull – where the brain case is, behind the eyes – was totally cleaned out and the molds had to be pretty complicated to fill out all the deep undercuts of the skull. Sometimes, the rubber would seep through cavities and become wider on the inside than the little opening you would have to pull it out through. We then had to factor in not destroying the skull when the mold was taken apart. It was a tricky process; we experience this a lot with the skulls we have to mold, but it was especially true with these crocodiles.
BM: And this real soft bone, when it breaks, doesn’t leave straight edges to glue back. It sort of just fractures and falls apart; it’s thin as paper. So when it breaks, a lot of times, it’s irreparable. Also, every time someone picks up a specimen to study it, things will continue breaking off. That’s just part of the process – you just try to get as much information out of the fossil as possible.
So is the general procedure to first prepare the fossil, then create a mold and cast of the specimen, and finally create a flesh model?
TK: Actually, sometimes there’s an intermediate stage after the fossils themselves are cast. Sometimes, before going on to a life reconstruction, we’ll do a fossil reconstruction. For example, PancakeCroc jaws are almost really complete. There’s just a little section in the front that had to be restored so that the jaws could fit together better and really show what the jaw looked like. So after the fossils had been molded and cast, the casts were glued together and a couple of small clay reconstructions were added to help connect the dots. We then end up with the fossil as it existed and a slightly more complete duplicate that can be exhibited and really illustrate what the jaw really looked like. This is true for some of the other fossils too, like BoarCroc, which had a couple of small pieces missing from the back of the skull. These reconstructed fossils are exhibit copies – not research copies – and this is what we sculpt on top of.
BM: That brings us to reproduction, which is Tyler’s and Erin’s area of expertise.
All right, Bob, thank you for your time. Tyler and Erin, how did you begin reconstructing these crocodiles?
TK: This was a little different than some of our recent projects because we were working with crocodiles, so we’ve got living crocodiles to look at and guide us in reconstruction. Crocodiles have very specific, distinctive parts of the soft anatomy, and for the most part, we were doing bust portraits – heads. The head of a crocodile is pretty bony. There’s not a lot of meat, but there are ear flaps that move, sets of eyelids, and the nostrils – these are all really distinctive features. There are also very distinctive details on the skin that lines the teeth area, and some crocodiles have distinctive little bumps full of nerve endings that help them detect ripples in the water to find prey. Most of these fossil crocodiles are pretty different from anything that’s alive today, though, so we had to expand on and extrapolate from what is alive today to help us flesh out these ancient things. We also had a lot of guidance from Paul – we also had to take into consideration whether he was interpreting whether these animals had more terrestrial or aquatic lifestyles. These different lifestyles influenced how the finished models look.
What, then, are the different features of terrestrial and aquatic crocodiles? And how did these features manifest themselves in the models?
TK: With the exception of DogCroc, we don’t really have full, complete skeletons to look at, so we’re looking at the range of living and fossil crocodiles to inform us about what the range of possibilities were in lifestyles. The speculation involved is really about the lifestyle, and to say with any certainty that a croc was purely terrestrial or purely aquatic is very difficult. Although, just in the case of PancakeCroc, we are pretty sure that the croc was mainly aquatic. Evidence alone from the jaw shows that the animal appears to be very long. The joint between the left and the right jaw at the front of the chin is not big or strong, and the joint at the back where the jaw attaches to the back of the skull doesn’t look like there was a lot of room for attachment with huge muscles – it doesn’t look like a big, powerful jaw. Given the fact that it’s so slender and long, you don’t envision it running around and eating things on land. It seems much more adapted to lurking in the water and just snapping up fish and whatever swims by. So even in a jaw, there is evidence that can help guide you toward what this thing might look like.
For BoarCroc, some of the evidence lay in the eyes. Its eyes are not strictly pointing upwards, as a stalking, aquatic crocodile’s would be, but actually point a little bit more toward the sides and the front, as you see in animals that are out and doing things on land. That skull also has fewer pressure receptors – evidence of an animal that is detecting ripples in water all the time as a mode of lifestyle. There are little hints that we get and they really play into imagining what the lifestyles were, what the flesh models look like, and some pretty accurate anatomical structures on the models.
EF: Some of the crocodiles, though, display terrestrial and aquatic characteristics. For BoarCroc, the snout with nasal openings toward the top of the skull is characteristic of aquatic crocodiles – it’s how they breathe as they sit and wait under the water. Then again, this crocodile has a weird, keratin “battering ram” at the front of its face. This feature is very uncharacteristic of aquatic crocodiles, which led Paul to speculate that perhaps this crocodile would use its snout to run into its prey and knock it down. This kind of behavior would suggest that’s okay for the nasal openings to be located on the top of the snout. DuckCroc also displays the same nasal openings on the top of the snout, but because its snout is so long and “Pinocchio”-like, DuckCroc’s snout suggests that the animal used its nose to dig. Of course, that also doesn’t mean that these animals don’t go into water either.
TK: The parts of the skeletons that we had for DuckCroc and the much more complete DogCrocs showed limb proportions that were longer than those of living crocodiles, which have an amphibious lifestyle, come out on land, and are also well-adapted for the water. They also don’t do some of their locomotion on land as elegantly as a purely terrestrial animal. By comparison, the DuckCroc has really long arms and hands and fingers; the DogCrocs also have long, straight limb bones with proportions that are longer than those of living crocodiles. So they seem to be specialized toward local locomotion – running, walking, etc. They probably could have done more on land than modern crocodiles. We ended up building a full-body, flexible body of DuckCroc, which helped Paul visualize the tail and correlate it to these galloping juvenile crocodiles alive today in Australia. These Australian crocodiles have a very interesting, bounding locomotion to get to the water, and when they hit the water, they hit with a swimming phase. Their bodies then undulate in two different directions – galloping and swimming. The flexible model let us play with the range of motion for DuckCroc, helping us to envision and depict locomotion for the documentary and future exhibits.
EF: Lifestyles and environment also help Tyler and I decide on what we would like the crocodiles to look like in terms of coloration and so on.
How does lifestyle and environment influence how a crocodile looks?
TK: We have no evidence of what these things look like at all, but we can look at the range of colors in modern crocodiles and alligators. There’s a pretty big range of spots, stripes, and colors, so we had a pretty wide palette to choose from for these prehistoric crocodiles. We didn’t really venture outside the realm of what you see today in nature, but we had a wide enough palette so that we could make each reconstructed species look distinctly different. So not only do the shapes and the features and the sizes of the sculpted heads look different, but the color looks different on each one as well. The first model we completed – BoarCroc – has a skull that is evocative of an alligator. Since we are creating things that are unlike any modern crocodiles or alligators, but are still immediately recognizable, I used an American alligator’s coloration as inspiration for paint job on BoarCroc. BoarCroc is very dark with a very light throat.
EF: For PancakeCroc, I used [Gharial Crocodiles] to decide how the animal may have looked. The two shared a lot of the same characteristics – weaker jaw joints, a longer body. When I was deciding to find a color palette for PancakeCroc, I referenced Paul’s idea that PancakeCroc hovered under the water and waited for a fish to swim into its mouth and then closed its jaws around its prey. This animal probably wasn’t very active – that is, not really hunting down its prey – so it probably had good camouflage to just hover on the surface of the water. I used Mugger Crocodiles as inspiration for PancakeCroc’s drab appearance, a coloration that the crocodile could use to camouflage itself under water. I also put a little green tint into some of the highlights, a kind of algae-stain on the crocodile’s skin.
TK: For RatCroc, Paul really liked the freckling and spotting on the crocodiles he saw in Australia. Erin used these Australian crocodiles as the launching point for RatCroc’s coloration. DogCroc was inspired by a juvenile South American Caiman, which are a little bit brighter when they are young and freshly hatched. DuckCroc was a combination of Cuban crocodiles, which are somewhat spotted along their flanks, and a little bit of a Dwarf Caiman, which has a bit of brown to it. We ended up with a pretty interesting range of looks for these crocs.
Visit Project Exploration’s web site for more information on the five ancient crocs.