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Great Mondays in (South Dakota) history

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Time for another Great Monday in South Dakota history. This series attempts to get you through Monday morning alive by taking you back through some of the most important Mondays in South Dakota’s own history.

For our second installment, we’re stomping the now-vanished South Dakota forests with an animal large and regal enough to put even the bison to shame.

Monday, May 15; 35,745,862 B.C., 2:10 p.m.

In the midday heat, you’re glad to have the shade of the tall trees arching above you. This subtropical forest in the middle of North America is your home; there’s plenty of tasty roots and shoots to eat, and the thick carpet of growth is difficult for predators to penetrate. Not that you need to worry about predators. At over eight feet tall at the shoulder, more than 16 feet long and weighing over three tons, you’re just too big for any upstart set of jaws to mess with.

But as you stop to sniff at a strange — and strangely familiar — scent lingering in the air, you know that today won’t be a quiet day, predators or no. As you come to a clearing in the forest, you find the source of the odd scent. Another male Megacerops, like you. Smaller, but by the look of him younger and faster. The only reason another male would dare encroach this far into your territory, this time of year, is to claim your breeding rights with the local females. He snorts a low warning at you, you snort one back. Instinct drives you both to what happens next.

A charge! Six tons of angry muscle and bone collide. Horns — a pair of long, blunt growths at the end of your snouts — clash as you both bellow low calls, trying to intimidate each other into fleeing. After hours of struggle, your size and experience finally wins out over the youngster’s chutzpah. With one last charge, you feint and twist your head left, sending your horns into his ribs. The wind knocked out of him, the younger male turns and flees. You have secured your territory this day, but there will always be more challengers, and you’re not getting any younger…

Our protagonist this week was a Megacerops, a genus of large mammals that lived in western South Dakota during the late Eocene epoch, between about 38 million and 34 million years ago. While they superficially resembled modern rhinoceros — thick hide, tall shoulders, pillar-like legs, snouts tipped with a pair of bony horns — recent research indicates they were more closely related to modern horses than to rhinos. They were also much larger than rhinos; the largest specimens approached the size of modern African Forest Elephants.

They were similar to rhinos, though, in that they seemed to live mostly solitary adult lives. This was likely a result of their environment. They lived at a time when the climate of South Dakota was warmer and the land was heavily forested. Large herds of animals, like bison, would not be suited to the time period’s topography.

“At 38 million years ago, South Dakota was still forested... It was also much wetter.” said Dr. Darrin Pagnac, a professor of Paleontology at the South Dakota School of Mines and Technology. “What goes hand in hand with that is changes to the animals. The animals that lived in the forest were big; they’re lumbering... Big herds can’t move around, so they’re solitary.”

Some evidence indicates Megacerops may have fought with each other. For example, one Megacerops fossil was found with shattered ribs. Other Megacerops would have been the only animals in the area large or strong enough to inflict such an injury.

Megacerops were members of a larger mammal family known as Brontotheriidae, now extinct. Brontotheres as a whole occupied similar ecological niches in their time as large solitary mammals like forest elephants, rhinos and tapirs do today. They thrived while the land was warm and wet and covered with abundant foliage. As the climate began to dry, and forests gave way to modern grassland, these majestic creatures disappeared forever.

“Over 20 million years, we’ll go from closed forest to spotty woodland… and it’s not until like four million years ago that we get anything resembling the prairie we’re familiar with today,” Pagnac said. “The more open we get, the animals get smaller and congregate in herds because now they can and there’s safety in numbers, and they get better at running.”

Next week, a new species of mammal arrives on the Great Plains. It walks on two legs, uses complex tools and is the deadliest predator North America has seen in millions of years. The humans are here.

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