It might have happened to you at one time or another: A project you were working on got delayed—or, even worse, canceled completely—because historical or archaeological artifacts were discovered at the site. Ideally, an archaeological survey takes place long before work begins, but every so often something is uncovered during excavation or construction.
Frustrating as it is, delaying a project can sometimes save things that would otherwise be lost forever. The things in question might be buried in the dirt, or they might even be the dirt itself. As this article from the Economist discusses, tracks in the mud (now fossilized) found in Italy’s Dolomite mountains are shedding new light on the dinosaurs and how and when they evolved.
Scientists have long focused on what killed them; the prevailing theory is that a meteor landed in what is now Mexico about 66 million years ago, and the resulting climate disruptions killed three-quarters or so of all the species then living, including most of the dinosaurs. Less well understood is what happened a couple hundred million years before that, around the time that the dinosaurs appeared and gained prominence. It’s now believed that an earlier mass extinction took place between 234 million and 232 million years ago. “This extinction emptied both the land and the oceans,” according to the article, “leaving a blank canvas for evolution to work on.”
Fossilized bones from this period are rare, though, and have been found in relatively few places. This is where the tracks come in. The Dolomites contain lots of them, and the region’s particular geology makes it a good source of information: “The Dolomites’ rocks were formed at a time when the sea’s level, relative to the land, was going up and down like a yo-yo. This was partly because of rises and falls in the sea itself, and partly because of the land rising and falling in response to tectonic shifts. Such transgressions and regressions mean that marine and terrestrial sediments are interleaved in these mountains, and the marine sediments provided the information needed.” The alternating layers of sediment make it possible to date the layers fairly precisely, as does radiocarbon dating of volcanic ash in some of the layers.
Over a period of several million years, the tracks show, dinosaurs went from almost nonexistent to 40% of the total track-making population to 90%. Other clues, including the amount of volcanic ash in the rock layers, have fueled new theories about what might have caused the mass extinction that allowed them to flourish and has even raised questions about whether the meteor in Mexico was the main cause of the dinosaurs’ eventual demise or whether it was a red herring; volcanic eruptions in other parts of the world may have been equally responsible.