A New “Lady” in Town, Part I: Why Priscilla the mastodon isn’t a mammoth at all

“It’s the biggest gosh darn mastodon I ever saw! Wowzah!

Yes, that’s a direct quote.

It wouldn’t be a lie to say it’s hard to surprise our esteemed Dr. Bob Bakker, Curator of Paleontology. (That would be me.) But Priscilla did it.

“It’s H-U-G-E ! You could fit a Diplodocus torso inside this rib cage!”

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I was standing under the capacious hips of our new cast Mammut americanum, better known as “the American Mastodon.” The stupendous backbone and legs were being hoisted up on cables so the Black Hills Institute staff could attach the head. Mind you, we at HMNS are no strangers to the mastodon — we’ve had a fine cast of a bull on display in our old hall. Big, formidable.

But Priscilla is way off the scale — in life, twice as heavy as the average bull Mammut. And far more massive than our new Columbian mammoth who will co-star in the new fossil hall.

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I’m getting ahead of myself, so let’s back up for a second.

What exactly is a mastodon? And how’s it different from a mammoth (because it is, you know)?

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North America has two fossil mammoths. The famous woolly mammoth, star of the Ice Age movies, lived in the far north, close to the glaciers. The Columbian mammoths were taller and even heavier and stayed further south, away from the frigid realms. For two million years, Columbian mammoth clans and mastodon were neighbors. They’re found together in many Texas Ice Age sites, at the famous La Brea Tar Pits, and scores of other excavations from Florida to Oregon as well.

Sure, from a distance, the mammoth and mastodon do seem similar. Both have big bodies, bulgy bellies, straight legs, short necks and compact skulls with a hole in the forehead where the long trunk attached in life. The tusks are long and curved and there is just one well developed pair in the upper jaw. (Mastodons might have tiny tusk vestiges in the lower jaw too.)

When they were alive, both would run with long strides with their weight supported by wide five-toed paws embedded in thick, cushiony pads. Both would move their limbs in that unusual gait employed by modern elephants — right fore and hind swung back together and forward together, while the left fore and hind went forward when the right limbs went back. And vice versa.

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But the mastodon clan and the mammoth clan separated some 25 million years ago. The short skulls, long upper tusks and well-developed trunks are mostly evolved in parallel from an ancestor who had long jaws and four long tusks — two in the upper jaw, two in the lower.

All mammoths really are genuine elephants, very close kin of the Asian elephant you see in zoos — that’s why scientists trying to clone a woolly mammoth from frozen specimens in Siberia hope to use the egg from a female Asian elephant.

All mammoths have elephant-style molars. Each tooth crown is a gigantic vegetable processor, with many vertical plates of enamel set in a mass of dentine and cement. (Clever system.) As the uppers and lowers grind against each other, the cement and dentine wear away faster than the enamel. So, the enamel ridges stick up a bit more, guaranteeing that the tooth still has multi-edged cutting/chopping/mincing action until the tooth is totally worn out.

Now look into the mouth of our American mastodon and you’ll see the outstanding difference. The teeth are much smaller and simpler and have nothing like the food-processing power of a mammoth’s grinder. Each mastodon tooth is like a human molar or a pig molar. There are four or six main cusps in two rows, one inside and one outside. The total volume of one molar is one-twentieth that of a mammoth of the same body size. And when the enamel outer covering wore away in a mastodon, there were no vertical ridges of enamel left to cut and chop.

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Clearly mastodons had to be more persnickety about their food choices than did the mammoths. Fossil stomach contents show that mammoths had an elephant-like diet: rushes, sedges, grass, branches, clumps of broad-leafed tree leaves. Stomach remnants and food bits caught between molars tell us that mastodons sought out soft bark from birch trees, soft branches, soft leaves, fallen fruit and nuts with just a wee bit of grass as a garnish.

After analyzing the dental differences, you’d predict that mastodons stayed in wetter, more wooded environments, rich in bushes and young trees. Mammoths would, on the contrary, penetrate far across the open meadows, grasslands and even deserts.

The census of fossil sites confirm your prediction.

Mastodon remains are abundant in bogs and swamps and sandbars from rivers flowing though forests. Mammoths, on the other hand, left many skeletons in sand dunes and rivers that flowed through open terrain. Occasionally both do occur in one spot, but usually one or the other dominates.

Stay tuned for Part II, where you’ll get to know Priscilla like you’ve never known a mastodon before.