They aren't certain, but underwater archaeologists say they may have discovered a boulder with a prehistoric carving in Lake Michigan's Grand Traverse Bay.
The granite rock has markings that resemble a mastodon — an elephant-like creature that once inhabited parts of North America — with what could be a spear in its side, say divers who have seen it.
They came across the boulder at a depth of about 40 feet while searching for shipwrecks in June, said Mark Holley, a scientist with the Grand Traverse Bay Underwater Preserve Council.
"When you see it in the water, you're tempted to say this is absolutely real," Holley said Tuesday during a news conference with photos of the boulder on display. "But that's what we need the experts to come in and verify."
Specialists shown pictures of the boulder have asked for more evidence before confirming the markings are an ancient petroglyph, said Holley, an underwater archaeologist who teaches at Northwestern Michigan College in Traverse City.
"They want to actually see it," he said. Unfortunately, he added, "Experts in petroglyphs generally don't dive, so we're running into a little bit of a stumbling block there."
Among those withholding judgment is Daniel Fisher, curator of the University of Michigan Museum of Paleontology, who has studied human interactions with mastodons. He has examined a couple of the photos and is waiting for more.
"The difficulty I saw was that the features of what's interpreted as an engraving were so subtle, and they're not the only thing on the boulder," Fisher said in a phone interview.
Also, he said, mastodons are not known to have ranged into northern Michigan, although fossil remains have been found in the southern part of the state. They became extinct about 10,000 years ago.
It's possible that ancient peoples familiar with the beasts migrated north, Fisher added.
"It's conceivable" that the image on the rock is a petroglyph, he said. "I'm intrigued enough to take another look."
The boulder is within the 32-mile-long bay, Holley said, but the exact loction will be kept secret to prevent vandalism or theft.
Students of Holley's and divers with the preservation council found the boulder on the flat, sandy lake floor, which is strewn with algae and zebra mussels.
It was part of a row of stones of varying sizes that might have marked the shoreline 6,000 to 10,000 years ago, Holley said.
Some — although not the boulder — were arranged in a circle. That could indicate human manipulation although it's unclear, said Rob Houston, a geology instructor at the college who has inspected the site.
The boulder with the markings is 3.5 to 4 feet high and about 5 feet long. Photos show a surface with numerous fissures. Some may be natural while others appear of human origin, but those forming what could be the petroglyph stood out, Holley said.
Viewed together, they suggest the outlines of a mastodon-like back, hump, head, trunk, tusk, triangular shaped ear and parts of legs, he said.
"We couldn't believe what we were looking at," said Greg MacMaster, president of the underwater preserve council.
Michigan has only two confirmed petroglyphs, said John Halsey, the state archaeologist. They include sandstone carvings in the Thumb area known as the Sanilac Petroglyphs, and images in an isolated rock in the northern Lower Peninsula. Ancient rock paintings have been found in the Upper Peninsula.
The Grand Traverse Bay group plans further research and consultations with outside specialists.
"We want to get them involved with this project so that we can categorically prove it," Holley said.