Jan 10, 2014 11:46 AM EST By Staff Reporter, UniversityHerald Reporter

Shark fossils in an Illinois coal mine? That's just the old news. Upon re-examining 310 million year old fossils of (now extinct) spoon-billed sharks known as badringas first discovered in a coal mine in Illinois in 1969, scientists determined that the specimens were actually all babies, Live Science reported. Further up a connecting river were teenaged samples and even further were the remnants of adults. The findings provide strong evidence that badringa sharks during this ancient time period spent different portions of their lives in different places, and that the Mazon Creek coal mine acted as a nursery of sorts.

"This is the first time we have eggs and fossilized hatchlings in the same place, proving it's a shark nursery," said study co-author Lauren Sallan, distinguishing her study from a similar finding in Germany, which found only eggs and not the hatchlings.

According to Mark Purnell, a paleobiologist not part of the study, the research presented "convincing evidence to support the hypothesis that these rocks preserve a shark nursery from 300 million years ago," or the oldest shark nursery ever discovered, according to Live Science.

Back in 1969 and until this study, scientists believed that different shark species lived in the various locations their fossils were discovered, from Mazon Creek, Il. to Ohio to Pennsylvania. Since the baby sharks didn't have full formed endoskeletons yet, only their tissues were preserved, fooling scientists into believing they were actually a different species from the specimens in other locations.

"When you account for the different preservation modes, there is nothing that distinguishes them at all," Sallan told the Los Angeles Times.

When badringa sharks were still alive, they spent most of their adult lives in freshwaters, but were born in an inlet of sea water, as the body of water in Mazon Creek once was. Though it's pretty typical of sharks to give birth in "nurseries," few distinguish their lives between salt water and freshwater, according to the LA Times.

Badringa's long bill vacuumed prey and tracked their kills by way of elctro-receptors. The sharks also had "these giant, needle-like spines on the top of its head and cheeks," likely as a defense against predators, according to Salan.

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