Richard Collins: Riddle of Tully monster’s identity remains

Have researchers at University College Cork confirmed the true identity of the mysterious ‘Tully monster’?, asks Richard Collins

Richard Collins: Riddle of Tully monster’s identity remains

Have researchers at University College Cork confirmed the true identity of the mysterious ‘Tully monster’?, asks Richard Collins

IN the mid 19th century, rich fossil beds were discovered at the Mazon River Creek in Illinois. Finds made there were so important that the site is now a National Historic Landmark. In 1955, amateur collector Francis Tully came upon a strange-looking fossil in strata laid down 309m years ago.

The place had been a shallow muddy estuary when the creature was alive. Bone fossilises fairly well but soft tissues don’t. The bodies of creatures dying in the Creek, however, were buried in silt. Bacteria in the silt released carbon dioxide. This combined with iron in the water to form nodules entombing and preserving the remains.

Tully submitted a specimen for identification. Tullimonstrum gregarium (‘Tully’s sociable monster’) proved new to Science. Nothing quite like it had been found previously nor had similar fossils been discovered elsewhere.

The ‘monster’, although impressive, was not in the Lough Ness league, the largest specimen found being only 35cm long. Resembling a science-fiction comic-book creation, it was sausage-shaped, with a long snake-like neck and eyes out on stalks. There may have been fins located towards its tail. The jaws seemed to have rows of sharp teeth with which it probably seized small creatures. No evidence of bone shell or chitin, the material of which the hard parts of insects are composed, was found.

Scientists couldn’t agree as to the monster’s classification. “It has been serially attributed to almost every bilaterian group, including arthropods molluscs and ‘worms’ of every sort,” one expert wrote.

After decades of argument, two main theories are in contention. Some of its features suggest that the creature had gills and, possibly, a notochord, the cartilage forerunner of backbones.

“The Tully monster is a vertebrate,” proclaimed an article appearing in Nature in 2016. Based on an analysis of 1,200 specimens, lead author Victoria McCoy of Yale University placed the creature “on the stem lineage to lampreys”. Also granules, “melanosomes” in the eyes, were arranged like those of vertebrates.

Other experts disagreed; a paper appearing in the journal Palaeontology in 2017 was entitled ‘The Tully Monster is not a vertebrate’. Lauren Sallan, of the University of Pennsylvania, pointed to features which don’t fit the vertebrate theory. Notochords are not exclusive to vertebrates and what was assumed to be the monster’s one extended in front of the eyes, an unlikely feature.

Enter UCC palaeontologists Chris Rogers and Maria McNamara. Using a particle accelerator at Stanford University, they compared grains, taken from the fossilised eyes of the monster, with those of today’s animals. The eyes of invertebrates such as octopus and squid, they found, “also contain melanosomes partitioned by shape and size in a similar way to Tully’s eyes”. Also, the monster’s eyes contained a different type of copper to that found in vertebrates.

Rogers and McNamara, however, are less dogmatic in their claims than previous researchers have been. “While our work adds weight to the idea that Tully is not a vertebrate, it doesn’t clearly identify it as an invertebrate either,” they conclude.

The riddle of the Tully monster’s identity remains.

Rogers, C. et al. Synchroton-X-ray absorption spectroscopy of melanosomes in vertebrates and cephalopods: implications for the affinity of Tullimonstrum. Proceedings B. Royal Society. 2019.

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