From mammoths to giant jellyfish, meet the extinct animals that once called Wisconsin home

A recent study has led scientists to ponder whether it was just an asteroid's collision with Earth that killed off the dinosaurs 66 million years ago.

The study posited that volcanic eruptions may have already thrown the ecosystem into chaos and threatened the existence of many dinosaurs before the asteroid crashing into Earth delivered the final blow. The international team of researchers involved in the study claimed that the levels of sulfur from the eruptions may have triggered a global drop in temperatures around the world, creating conditions inhospitable to life.

All the excitement around the study got us thinking about the now-extinct species that once roamed the prehistoric world. We spoke with University of Wisconsin-Milwaukee assistant professor of paleontology Dr. Tory McCoy about the unique creatures that called modern-day Wisconsin home. She walked us through a chronological timeline of some of the most interesting species that used to live here.

Here's what we learned.

Prehistoric giant jellyfish could grow up to three feet wide

During the Cambrian period, between 509 and 485 million years ago, giant jellyfish roamed the waters near modern-day central Wisconsin. The creatures could be as wide as three feet in diameter.

Fossilized remains of the jellyfish were found at the Blackberry Hill exceptional fossil site in Marathon County in the late 1990s. An "exceptional fossil site" is a scientific term for a site that's able to preserve remains that typically don't preserve elsewhere, McCoy said. Jellyfish do not tend to preserve well, she continued, and very little remained of the giant jellyfish found at Blackberry Hill.

Still, thousands of fossilized impressions of the jellyfish were found at the site, and it is believed that the jellyfish, which were living in nearby waters, got stranded on the shore and buried under the sand during a storm or other intense weather event.

"Having this fossil site with at least hundreds of gigantic jellyfish really kind of revolutionized our idea of what jellyfish were doing back in ancient times, because not only is it rare to find (remains of) them, but they were so big ... that they were likely one of the major predators in this area," McCoy said.

Back in that time period, the major marine predators we have today, like sharks and whales, did not exist yet. In fact, it's possible that the giant jellyfish were the only large predators in their environment, McCoy said. However, this is not known for sure because their remains weren't found in the same place they lived.

It is also unknown whether the giant jellyfish are direct descendants of modern-day jellyfish or just close evolutionary cousins.

Ancient Milwaukee was home to coral reefs and trilobites

The Cambrian period was followed by the Ordovician period (485 to 443 million years ago) and the Silurian period (443 to 420 million years ago). During these periods, Wisconsin was covered by a "warm, shallow sea" that housed extensive coral reefs, especially where Milwaukee is today, McCoy explained.

The ancient reefs were comprised of now-extinct coral species called Rugosa and Tabulata coral, McCoy said. The type of coral that makes up today's reefs is called "Scleractinia coral," and it did not evolve until 250 to 200 million years ago, she continued.

"There were a lot of reefs in that time period across the world, but the one around Milwaukee was probably the best preserved in the fossil record," McCoy said. "The reef isn't just the coral, but it's all the animals living in it. So we have a really great record of all the different diversity of life that was there."

McCoy said ancient reef environments were very different from reef environments today, including when it came to the kinds of creatures that lived in them. One of these creatures was the trilobite, Wisconsin's state fossil.

Trilobites are "an extinct group of arthropods, animals with a hard shell and jointed legs," McCoy explained. Some trilobites were swimmers, but most crawled around on the sea floor. Trilobites were also among the first organisms to have "good vision and really good, complex eyes," McCoy said.

The giant nautilus was like an octopus with a hard, straight shell

Another unique creature that scientists believe lived among ancient Wisconsin's coral reefs was the giant nautilus, a tentacled relative of today's octopi and squid, but with a hard, straight shell. The species could grow up to 13 feet long, McCoy said. Like octopi and squid, the nautilus is a member of the cephalopod family, but it is the only member with a hard, external shell.

Unfortunately, giant nautilus have been poorly preserved in our area, McCoy said, so scientists have no official species name for the pointy-shelled creature. However, many researchers believe giant nautilus were major predators in ancient reefs, just as squid and octopi are in their environments today.

Other researchers, though, think the giant nautilus may have been a filter feeder, like today's whales, and may have eaten microscopic plankton. But, because the species' remains have been so poorly preserved, researchers don't know for sure what the giant nautilus' diet looked like.

"Because we don't have their tentacles preserved, we can't know," McCoy explained. "They would've had different types of tentacles for filter feeding versus predation."

Waukesha County was home to the Conodont Panderodus, a fish with fangs

Wisconsin's Silurian-era seas were also home to the Conodont Panderodus, a primitive fish.

The species had "an eel-like body and no paired fin, so they had a tail fin, but they didn't have the two pectoral fins that most fish use to swim," McCoy said. This ancient fish also had "huge, popped eyes" that stuck out of its head and "massive fangs" on either side of its mouth, she added.

Remains of the Conodont Panderodus were found at the Waukesha Biota site, located in modern-day Waukesha County.

"It wasn't very big, so it certainly wasn't the dominant predator of its time," McCoy said of the species. "But, it was thought to be a pretty effective small animal predator. These huge fangs and the huge eyes would have let it see prey very well and eat them effectively."

Mammoths and mastodons once roamed Wisconsin alongside humans

Because of destruction to the Earth's rock layers caused by glaciers during Wisconsin's Ice Age (which took place from about 70,000 years ago through 10,000 years ago), little was preserved in the state's fossil record from after the Devonian period (419 to 358 million years ago) until the Ice Age, McCoy said.

Mammoths and mastodons, roamed Wisconsin between about 20,000 to 12,000 years ago. Both species are ancient relatives of the modern-day elephant and likely interacted with humans. So, what differentiates them?

According to the National Park Service, "Mastodons were shorter and stockier than mammoths with shorter, straighter tusks. Mastodons were wood browsers and their molars have pointed cones specially adapted for eating woody browse. Mammoths were grazers, their molars have flat surfaces for eating grass."

The two species also thrived in different climates. Mammoths preferred a colder, tundra-like environment where they could find grass to eat, while mastodons needed a warmer environment with more plants and leaves, McCoy explained.

"We find both mammoths and mastodons in Wisconsin, and what this reflects is that, during the Ice Age, it wasn't uniformly cold and covered by glaciers," she said. "There were time periods where it was a little bit warmer and time periods where it was colder."

Both species would follow their preferred environment. When the glaciers moved further south into Wisconsin, the mammoths would also move further south. Similarly, in warmer periods, when the glaciers would retreat north, the mammoths would follow north, and the mastodons would come up to Wisconsin.

Additionally, unlike any other animal on this list, mammoths and mastodons may have gone extinct due, in part, to human activity. Mammoth remains have been found with butcher marks from human hunting, McCoy said, though "it's not proof that human over-hunting was what led to their extinction, but it did play a role."

USA TODAY reporter Eric Lagatta contributed to this report.