Quick, how long ago did mammals evolve?
Okay, not a fair question, because scientists have only recently discovered it was a lot further in the past than they had thought. How did they find out? Well, they found a ground hog in a 154-pound hunk of sandstone that had been hauled from Madagascar to New York in order to study the fish fossils it contained. Actually, they didn’t find the entire ground hog, only the fossilized skull. And even that didn’t have the lower jaw.
Okay, how much can they really figure out about a creature when all they have is a skull? Quite a lot, it turns out. Dubbed Vintana sertichi, the 5-inch skull indicated the live animal weighed about 20 pounds, which is about twice the size of a modern ground hog. To us humans, that doesn’t sound very big, but it’s heavier than our medium-small dog, and heavier than any house cat I’ve ever owned. In the world of the Mesozoic era mammals, that size makes it a super heavyweight. All the other mammals of the time were about the size of mice.
What else did this skull tell the scientists? Vintana had rodent-like incisors as well as molars that indicated a diet of roots, seeds and fruit. Large eyes meant it could see in low light, while the inner ear configuration indicated it could probably hear higher frequencies than humans can. Its large nasal cavity implied a keen sense of smell.
Keep in mind that in the Mesozoic era of 66 million years ago, the non-mammal neighborhood held dinosaurs (both meat- and plant-eaters), crocodiles, snakes, giant frogs, lizards, fish and a few bird species. It’s a wonder the big guys didn’t just step on the tiny mammals, probably without even realizing they’d done it. If they noticed mammals - even Vintana, at its ‘great’ size - they probably figured that tiny bite wasn’t worth the trouble of chomping on it.
But eventually, like the dinosaurs, all the Vintana sertichi died out and were gone. So it’s a good thing we aren’t descended from them, because we never would have come into being.