The tiny skull of an ancient fish, whose fossil was found in Siberia, may be a key in understanding the history of all jawed vertebrates, including humans.

According to Live Science, the Janusiscus schultzei fossil about two centimeters in length and dates back some 415 million years. It was originally classified as a "bony fish" and was unearthed in Siberia in the 1970s.

Authors of a study recently published in the journal Nature examined the J. schultzei's brain case and found evidence suggesting it was both bony and had cartilage.

"The results from our analysis help to turn this view on its head: the earliest jawed vertebrates would have looked somewhat more like bony fishes, at least externally, with large dermal plates covering their skulls," study co-author Sam Giles, of Oxford University's Department of Earth Sciences, said in a press release. "In fact, they would have had a mix of what are now viewed as cartilaginous- and bony fish-like features, supporting the idea that both groups became independently specialized later in their separate evolutionary histories."

Vertebrates are typically one or the other, but this specimen could be one of the oldest to have characteristics of both.

"This 415 million year-old fossil gives us an intriguing glimpse of the 'Age of Fishes', when modern groups of vertebrates were really beginning to take off in an evolutionary sense," study co-author Matt Friedman, an Oxford Department of Earth Sciences colleague of Giles', said in the release. "It tells us that the ancestral jawed vertebrate probably doesn't fit into our existing categories.

"This mix of features, some reminiscent of bony fishes and others cartilaginous fishes, suggests that humans may have just as many features that you might call 'primitive' as sharks."