Scientists used archaeological remains of 311 rats from across eastern North America between the 1500s and early 1900s to show how newly-arrived brown rats outcompeted the more-established black rats. Along with establishing a timeline, the researchers analyzed the isotopes of carbon and nitrogen in the rodents’ bones and determined that the victorious brown rats preferred to eat more animal protein than black rats.

Why this is cool: Some of the rat remains came from seven shipwrecks. Scientists were able to date precisely when these shipwrecked rats were en route to America. While archaeologists frequently dig up rat remains, radiocarbon dating isn’t precise enough to give dates of organic remains for this period of history. And worse, brown rats have a pesky habit of burrowing into the ground, so they could have contaminated archaeological sites after the fact.

What the experts say: Which rats win out and why is an important question not just for historians and ecologists but also for scientists studying disease. “In some ways you could say that brown rats saved us from the plague,” says Johannes Krause, an archaeogeneticist at the Max Planck Institute for Evolutionary Anthropology. Black rats were the notorious reservoir of the Black Death, but were outcompeted when brown rats arrived on the scene from Asia in the 1700s, and the plague outbreaks largely ended. And yet, brown rats carry diseases of their own, so it’s important to track how these populations evolve over time. –Allison Parshall