A crew from Eagle Creek Homes excavating a road through a future housing development found the remains in Byron Township near Grand Rapids Aug. 31. They then notified the University of Michigan and plan to donate the remains to the university.
The female mastodon is a somewhat unusual finding, said Daniel Fisher, director of the U-M Museum of Paleontology: skeletons from male mastodons tend to be found more frequently. Fisher has a theory about why this might be.
"Males, by their lifestyle, tended to be solitary, whereas females tended to live in matriarchal family groups," said Fisher, also the Claude W. Hibbard Collegiate Professor of Paleontology. "It may have been easier to ambush and surprise a solitary individual than it was to ambush and surprise a group."
The Byron Township skeleton is the third such finding in three years. Fisher uncovered a mammoth in a farmer's field in Chelsea in 2015, and his crew was also called in to uncover a mastodon in Michigan's thumb region at the Fowler Center for Outdoor Learning in 2016.
Mammoths were slightly larger than mastodons, though the two lived at the same time in Michigan. Both the 2015 mammoth and 2016 mastodon were donated to the University of Michigan as well.
Mammoths and mastodons have been found across the lower half of the lower peninsula of Michigan, but not in the northern half in the peninsula, and not in the Upper Peninsula. Fisher thinks this is because glaciers had receded earlier in the southern half of the Lower Peninsula, giving time for vegetation to move in and provide a food source for the herbivores.
Fisher says each skeleton he is able to study provides more information about the interval of time when mastodons and mammoths inhabited this region. From an individual skeleton, Fisher can learn about that mastodon's life history: its individual reproductive history, its growth history, its health status, its age and its sex.
"To understand the history of the extinction process, we need specimens that are males, that are females, that are more advanced in life and that are younger," Fisher said. "And then there's the dimension of geological time: We need specimens long before extinction, and then later in their history, just before extinction."
Knowing a mastodon's life history information can give Fisher clues about what the environment and climate were at the time of the animal's life, as well as what its diet was.
"Each find gives us information on that one individual. It's like one data point to solve one of the big problems about this time," Fisher said. "To really address all the questions I'm interested in, I need data on 30 or 50 specimens, and right now, I only have data on 10 or 12 or 15."