March 20th

What Trace Fossils Tell Us

When we think about dinosaur remains, most of us usually imagine gigantic fossil bones. But body fossils are just one line of evidence in the search for the everyday reality of dinosaur lives. Dinosaur trace fossils, which comprise non-skeletal remains, tell us an enormous amount about our favorite extinct creatures–some would argue even more than corpses do.

Let’s start with dinosaur eggs. Fossilized eggs are somewhat taken for granted these days, but when Roy Chapman Andrews and company returned from Mongolia’s Gobi Desert with the first dinosaur eggs in the 1920s, they were a source of bewilderment. In those days, dinosaurs were still overgrown lizards–monstrous and dim-witted. Eggs, though previously hypothesized (and mis-identified), allowed dinosaurs to be seen as living animals, rather than primeval leviathans awaiting extinction.

If eggs were a sensation, complete dinosaur nests were even more illuminating. Half a century after Andrews, Jack Horner and Bob Makela–with the help of Marion Brandvold–described the first dinosaur nesting grounds in Montana. Not only did dinosaurs breed like modern animals, they were parents. This, along with many other factors, was another key development in the modern understanding of dinosaurs as caring, nurturing beings.

Dinosaur footprint / Wikimedia Commons

Dinosaur footprints have been known to science for much longer than eggs. In the 1800s, New England was the primary locale to find them. They were initially thought to come from remotely old birds, even from “Noah’s raven.” As the frequency of fossil footprint sites increased, and our understanding of Mesozoic life progressed, trackways revealed that dinosaurs weren’t as slow as we once thought, that they moved in herds as social animals, that they migrated.

Evidence for all these ideas is corroborated by another form of trace fossil–coprolites–fossilized dung. Excrement always draws giggles, but dinosaur waste is a valuable source of information that tells us about ancient ecosystems, what dinosaurs fed on, how their digestive systems operated, about the snails and beetles that relied on the dung for sustenance. Herbivorous dung is often trampled by the feet of the herd, while predatory dung is often undisturbed. Coprology is a fascinating, if peculiar, line of inquiry into dinosaur lives.

Other trace fossils, like gastroliths (the grinding stones that dinosaurs may have swallowed to help grind up plant material), and tooth scratches on bones continue to give us evidence about how the beings that left behind those mysterious skeletons thrived in a time long before our own.

We’ll talk about another interesting trace fossil and the dinosaur that created it tomorrow!

Until then, we want to hear about your favorite trace fossils! Share the stories of your favorite discoveries and photos of your favorite non-skeletal dinosaur fossils with us on Facebook and Twitter using the hashtag #TDIDinos.