The Woolly Mammoth (Mammuthus primigenius) and the American Mastodon (Mammut americanum) both roamed the North American wilderness until roughly 10,000 years BCE (although a few remarkable “dwarf mammoths” managed to hold out for a good while longer). But what exactly is it that sets them apart? (And yes, there were several other species of both Mammoth and Mastodon, but for simplicity’s sake, we’ll focus on the two most famous.)

Let’s start with a quick look at their family tree. The group of land mammals scientifically known as “proboscideans” contains living elephants and their ancient kin. In its heyday, this was a pretty diverse lot. Twenty-first century elephants are far more closely akin to mammoths than the relatively-primitive mastodons.

Want proof? Check out their teeth. Just like today’s tuskers, Mammoths tended to live in wide open plains, as demonstrated by their very elephant-like molars, each of which looked like a bony cheese-grater and was built to grind up tough grasses. Conversely, the word “Mastodon” literally means “nipple tooth." This is because the grooves in their chompers reminded some 18th Century paleontologists of human breasts. High-crowned teeth like this are better suited for mashing leaves and twigs, and, appropriately, Mastodon remains are usually found in forested environments. You can see the animals’ jaws compared side-by-side in this clip at the 0:26-mark:

Furthermore, as expert Daniel Fisher explained in the video above, Mammoths have curved tusks and high shoulders while Mastodons have straighter tusks and lower shoulders.

Thanks to a handful of frozen carcasses, genetic analyses have long-since confirmed the link between Mammoths and elephants. In fact, Mammuthus DNA has been so broadly studied that a Mammoth Genome Project is in the works.

Mastodons have had their admirers as well, including Thomas Jefferson himself, who actually stored a collection of their bones in the White House—though he did mistakenly believe that they were gigantic carnivores.