Science is Fun Fridays!
Francis Tully found this fossil in the Mazon Creek area of Illinois back in 1955. He took it to the Field Museum of Natural History, but paleontologists were stumped about what it was. It remains an ongoing debate to this day. A 2016 study determined it may be closely related to modern lampreys. They referred to the presence of a primitive stiffened support rod, called a notochord, and concluded it must be a vertebrate. McCoy et al studied again in 2020 and found that samples from the body contain the decay products of chordate tissues, as opposed to the chitin found in arthropods. But Mikami et al, in 2023, found segmentation extending to the preoptic region, which is very different from vertebrates. And so, the Tully monster is a genus of one. Phylum: Incertae sedis, or problematica. An enigma.