|Scientists examining some of the footprints on Brennan's land|
How can a set of footprints survive for 11,000 years? Fisher explained the process to the Chicago Tribune back in 1992. Basically, a male mastodon (scientists could tell it was a male because of the prints' size and depth) walked across what at the time was a pond whose bottom contained sand covered by a mud-type substance called marl. When the mastodon stepped down, his weight pressed his foot deep into the sand at the bottom of the pond. When the mastodon raised his foot, suction forced marl into the cavity, essentially preventing the footprint from disintegrating in the sand. As years passed, the pond filled with soil that covered the marl-filled footprints, which eventually ended up two or three feet below the surface, hidden to the world---until Brennan decided to create a pond on his property.
The footprints are remarkably well preserved, and reveal so much information about the mastodon's trek that researchers can tell where he stumbled on a log and then righted himself. Because the footprints were too fragile to dig up, Fisher made casts of them; then, he and his team reburied the trail to preserve it, though they marked the prints' locations so that researchers could find them for future study.
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If you're interested in seeing some of the casts, you can check them out at U of M's Museum of Natural History in Ann Arbor.
Many people confuse mastodons with mammoths; both animals looked similar, and both lived in Michigan. So what's the difference? Here's a pic showing models of the two side-by-side:
|The mammoth is on the left, the mastodon is on the right.|
Mammoths were larger than mastodons and had longer trunks; mammoths' tusks also curved more than did mastodons' tusks. Evidence from fossilized teeth reveals that mammoths ate primarily grass, while mastodons ate leaves and branches from trees. A fun fact: Although mastodons might have looked more like elephants than did mammoths, it's actually mammoths that are more closely related to today's elephant species.