Tully monster debate reignited

A group of paleobiologists are refuting claims made last year about the classification of the ‘Tully monster’.

The researchers have said that two papers released last year, stating that this scientific oddity was a fish, are flawed. The Tully Monster has been known to scientists since the 1950s, when the fossils were found in Mazon Creek fossil beds in Illinois.

Lauren Sallan, an assistant professor from the University of Pennsylvania, said: “This animal doesn't fit easy classification because it's so weird. It has eyes that are on stalks, this pincer at the end of a long proboscis and there's even disagreement about which way is up. But the last thing that the Tully monster could be is a fish."

The studies published last year concluded that the Tully monster was a vertebrate for different reasons. A group of researchers, after studying more than 1,000 specimens, determined the existence of a notochord, a type of primitive backbone. In addition to this they claimed the Tully monster contained other internal organ structures such as gill sacs that identified it as a fish.

In the second of the published papers, scientists discovered structures called melanosomes – that produce and store melanin – in Tully’s eyes. It was these structures which suggested to the authors there was a very strong case to consider the Tully Monster a vertebrate.

Sallan argued however, that complex eye structures could also be seen in arthropods and cephalopods. She said: “Eyes have evolved dozens of times; it’s not too much of a leap to imagine Tully monsters could have evolved an eye that resembled a vertebrate eye.”

Authors from both papers have responded to the points put forward by Sallan in Palaeontology. Dr Victoria McCoy now situated at the University of Leicester, and co-author of the Nature paper first mentioned by Sallan, said: “In general, I'm excited to see that other scientists are being inspired by our previous paper to do more research on the Tully Monster. It is only by extensive scientific discussion and debate that we will ever reach a scientific consensus about the affinities of the Tully Monster.”

She said: “However, I disagree with the general approach of this group: they did not do any new specimen analyses or in fact contribute any new data to the question of the affinity of the Tully Monster, which makes their conclusions less than convincing.”

The accuracy of the researchers’ conclusions was also questioned by Thomas Clements, also from the University of Leicester and lead author of the second paper, also published in Nature. He said: “A fundamental problem is that because Sallan thinks that we didn’t find many of the characters that Sallan considers vital for Tully to be a vertebrate, such as optic capsules, then it simply can’t be one, which misrepresents our study: we did not investigate or look for these characters in Tully.”

He continued: “All Sallan et al do in their paper is articulate how to test our hypothesis and not present any actual new data to strengthen their argument. We are well aware of this test; articulating the test in itself does not constitute a refutation.”