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 decades puzzled over the Tully monster’s place on the tree of life, but mostly thought of it as a spineless invertebrate, maybe some ancient version of worm, arthropod, or mollusk. Instead, the study shows that it was an ancient cousin to lampreys, which were among the first animals with backbones to evolve.

http://news.nationalgeographic.com/2016/03/160316-tully-monster-vertebrate-fossil-animal-paleontology-science/