Science Moab talks with Brian Davis, a paleontologist who teaches anatomy at a medical school. Brian is an associate professor at the University of Louisville School of Medicine in Louisville, Kentucky, and he works on early mammals—mostly teeth, jaws, and parts of skulls. His most recent work on mammal fossils is based in Cisco, Utah.
Science Moab: You are exploring in the Brushy Basin Member of the Morrison Formation, which is prolific for its preservation of amazing fossils—most notably, the large dinosaur bones. When you come across a fossil, how do you know if it’s a mammal?
Davis: Our record of mammals is still pretty poor, partly because they’re not easy to find during the age of dinosaurs, especially in the Late Jurassic. Mammal fossils are all very small, and fossilization is a really rough process—it is not kind to animals that are really little and delicate. So we tend to see robust, heavy parts of animals surviving best. The bigger you are, the heavier and harder your skeleton is, the more likely you are to turn up as a fossil.
When we find mammals, it’s usually the hardest parts of the skeleton—teeth. So teeth and jaws make up the majority of what we find. Occasionally, you get lucky and find a bit of skull or a couple pieces articulated here and there, but it’s really rare. Part of the reason we don’t know much about early mammals is that their fossils are exceedingly rare and also hard to find. You have to specifically look for mammal fossils to locate them. Many early discoveries were accidental.
Science Moab: How did you happen upon the Cisco quarry of mammal remains?
Davis: At Cisco, I was wandering up drainages, following occasional bits of turtle shell or weathered dinosaur bone, hoping to find a fossil-rich horizon. I climbed a hill, following some bits of fossil sticking out of the top, and on the crumbly mudstone surface was a teeny little piece of bone—about half the size of my pinky finger. That was the first piece from this locality.
When we cleaned the surface and dug around, we found other bone ends sticking out of the rock, but it turned out to be a very different microhabitat and collection environment than I expected. I was expecting an accumulation—a lens of small bones washed into one spot—but it appeared to be a quiet, backwater, ephemeral pond, perhaps a seasonal water source. The animals that died there were preserved in place. We tend to find somewhat more complete fossils of small animals that haven’t been transported, which is important. Fossil transport tends to break apart fragile remains—the kind I’m most interested in.
Science Moab: You began exploring the Cisco area in 2015 because of its Brushy Basin outcrops and similarity to discoveries just across the border in Fruita, Colorado. (The area south of Fruita at the base of Colorado National Monument is famous for small, complete, and exquisite mammal fossils.) Have you compared the Cisco fossils to the Fruita finds?
Davis: The little spot I found near Cisco seems to represent a microhabitat very similar to that of Fruita. The record is still pretty incomplete, and the animals from that era are very different from anything living today. But if the Cisco area has the same kind of microhabitat as Fruita, we’d expect some overlap, and that appears to be happening so far.
Science Moab: What stage is the excavation or exploration of the Cisco quarry?
Davis: There doesn’t seem to be an obvious productive horizon at Cisco. The bone seems to be everywhere, which is both great and frustrating. Any patch of exposed rock on the hilltop could be as productive as any other, making it hard to focus efforts. Essentially, we are working our way over the surface of the hill—pushing in one direction, then turning and going in another.
How much rock remains? It could stop producing fossils next summer, or keep going for 20 more years—it’s hard to know because there isn’t a clear fossil bed we’re following. But it’s fairly easy work since we’re exploring the top of this hill. It’s possible that nearby hills could be equally or even more productive. I may have spent 10 years on the least productive hill in the area—you just never know.
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