Scientists Finally Know What Kind of Monster a Tully Monster Was

The enigmatic creature—Illinois’ official state fossil—is a vertebrate, putting it on our branch of the massive tree of life.

More than 60 years after its discovery, Illinois’ bizarre state fossil—a soft-bodied “monster” that swam in rivers more than 300 million years ago—has been identified as a vertebrate. That puts the strange creature among the earliest in the group that eventually branched into today’s vertebrates, including fish, birds, reptiles—and us.

The surreal-looking creature, dubbed Tullimonstrum gregarium or the Tully monster, defies easy description.

“It looks like an alien,” says Victoria McCoy of the University of Leicester, who authored the study while at Yale.

McCoy’s analysis of more than a thousand Tully monster fossils, published Wednesday in Nature, reveals that the Tully monster was a vertebrate and had a primitive spinal cord.

The announcement comes as a shock to paleontologists, who for

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