2016-11-08 20:54:20
Trilobites: How a Mastodon’s Tooth Found in Michigan May Tell Us How It Died

20:54, November 08 202 0

Seth Colling, who teaches children with developmental disabilities at an outdoor learning center in Michigan, was walking along a creek looking for fish with his students in 2014 when they saw something odd sticking out from the water.

“It looked really strange,” Mr. Colling said. “I said to my student ‘Hey what is that?’”

As Mr. Colling and his students would find out, what they had discovered was a leg bone belonging to the most complete mastodon skeleton found in Michigan in more than 70 years. After a full excavation last month, paleontologists uncovered 75 bones, including ribs, a pelvis, shoulder bones and a skull with five gleaming molars that looked as if they were made of quartz.

The teeth may hold the keys to figuring out how the beast died some 13,000 years ago: Was it butchered by hungry prehistoric hunters; did it succumb to starvation in the harsh environment; or was it the loser in a mating-season death match?

Mastodons are ice age relatives of the elephant that once roamed across much of North America and went extinct 10,000 years ago. Like mammoths, they were herbivores, but unlike their grazing behemoth brethren, they had sharp, pointed teeth, which they used to eat twigs and shear trees.

Although the teachers and students at the Fowler Center for Outdoor Learning first found the bones at the site in 2014, it was not until this October that a large-scale excavation took place. A small army of schoolteachers, volunteers and researchers uncovered the beast’s skull as well as 70 percent of its skeleton. It is the most complete find in the state since the discovery of the Owosso mastodon in 1944.

“Not only was it complete, it was mostly undisturbed,” said Daniel Fisher, a paleontologist at the University of Michigan who helped excavate the Fowler Center Mastodon. “This is the way it was left for around 12,000 to 13,000 years.”

They found the bones buried in distinct piles, which Dr. Fisher has seen in other mammoth finds in Michigan. One clump contained the skull, and about nine feet away there was a pile that had a shoulder blade, some vertebrae, a rib and parts of the forelimbs and hindlimbs. They also found a third pile which contained a lower back vertebra, part of the pelvis, some more bones from the forelimbs and a lot of ribs.

“The pattern we see is not what you would expect under any natural or nonhuman scenario,” Dr. Fisher said. “If it’s a crime scene and you found a forelimb nestled to a pelvis you would say ‘Hmm, something happened here.’”

Dr. Fisher is not yet arguing that humans were involved in the mastodon’s death, but he said the findings pointed in that direction. The evidence that could potentially answer how the mastodon died lies within its mouth, he said.

Paleontologists can tell a lot from mastodon teeth. In this case the team uncovered the top portion of the skull, which included five molars. Based on the conditions of the molars, they concluded that the mastodon had been around 30 years old. But to solve the cold case they need to look beneath the surface.

Mastodon teeth grew layers incrementally in a way that roughly corresponded with the changing seasons. Using a microCT scan, researchers can examine the insides of a tooth to determine what time of year the mastodon died, according to Dr. Fisher.

If the analysis shows that the mastodon died in the winter, then its death was most likely because it starved or was sick. If it died in the spring or summer and was a male, then it most likely lost a battle with another male during mating season.

It is the deaths in autumn that humans most likely had a hand in, Dr. Fisher said. The mastodons that he has found in Michigan that have died in the fall all showed signs that they were butchered, he said.

“We don’t have an exception to that yet,” Dr. Fisher said. “It suggests that humans were on the scene and probably part of the cause of death.”

What most likely happened, he said, is that human hunters or scavengers butchered the carcass and submerged it in a pond for refrigeration. Last year he and his team identified a mammoth that they believe was processed this way; it is now on display at the University of Michigan Museum of Natural History.

Ross MacPhee, a curator at the American Museum of Natural History’s Department of Mammalogy, praised Dr. Fisher’s methods but said he did not think there was enough evidence to say whether humans were involved in the mastodon’s death. He said he was unsure whether the teeth would hold many answers.

“It’s an interesting argument, but whether or not the animal was actually hunted to me is unclear,” he said. “There are no arrowheads, no actual signs of butchery.”

For Mr. Colling, who found the tibia in 2014, just excavating the mastodon with his students was exciting enough.

“It was amazing that I got to do this,” he said. “When I was a kid I wanted to be a paleontologist, so it was like a childhood dream come true.”