To say that paleontologists can’t make heads or tails of the Tully Monster would be untrue. The claw-tipped proboscis on the front end and the arrow-shaped rear fins at the posterior end can be easily identified in complete specimens. Beyond that, though, this 300 million year old invertebrate remains one of the most vexing fossil species ever found.
Tully Monsters first came to the attention of paleontologists in 1958. While looking for fossils among the mining pits of northeastern Illinois, collector Francis Tully stumbled across an assemblage of marine organisms unlike any found elsewhere in the area. Especially perplexing were six-inch, worm-like impressions found inside the numerous concretions that littered the pits. Soon other amateur fossil hunters began finding them, too, and these strange creatures got their popular name in honor of their discoverer.
When presented with some of these specimens by Tully, the professional paleontologists at Chicago’s Field Museum were puzzled. The Tully Monsters did not correspond to any other known animal. In his 1966 description of these fossils, Field Museum scientist Eugene Richardson gave the animal a proper scientific title – Tullimonstrum gregarium, honoring its discoverer, enigmatic nature, and the sheer number of individuals that had been discovered – but he refrained from giving it a precise place in the tree of life. “While this obscure but plentiful animal is being studied,” Richardson wrote, “I prefer not to assign it to a phylum.”
Richardson published a more complete description of the beasts three years later with colleague Ralph Gordon Johnson. They still were not certain what it was. “There is no compelling reason to assign Tullimonstrum to any of the known phyla,” they wrote, concluding that “It could be imagined as an aberrant member of one of several phyla but the critical evidence is not available.” Nevertheless, examination of scores of specimens allowed the paleontologists to flesh out the anatomy of the monster.
The chief difficulty with studying the Tully Monsters was the fact that all the specimens were only impressions of the soft-bodied animals. No exoskeletons, no chitin plates, and no hard parts were left behind. A few specimens that had begun to decay before they were buried allowed a blurry look at the organs of the Tully Monsters, but Johnson and Richardson were mostly restricted to studying the external anatomy.
As reconstructed by Richardson and Johnson, the Tully Monsters had segmented, semi-cylindrical bodies marked by three remarkable external traits. At the posterior end of the animal were two triangular tail fins arranged like the undulating side fins of squid. On the opposite end, however, Tully Monsters had two peculiar sensory organs. Sticking out of the animal’s head was a flexible schnozzle tipped in a minutely-spiked grasping claw, and further back on the head were two stalks with cup-like depressions. An exquisite specimen in which the mineral pyrite preserved the form of these organs showed that these flexible stalks probably supported the eyes. Slight variations seen among various specimens suggested that eye stalks could be angled forward or backward for different views.
Richardson and Johnson were also able to say a little about the prehistoric habitat of the Tully Monsters. The marine invertebrates lived in the warm coastal waters of a 300 million year old ocean. Fossils of jellyfish, annelid worms, and sea cucumbers were found in the same deposits, but larger creatures swam there, too. “A few [Tully monster specimens] terminate abruptly,” the scientists wrote, “a portion of the trunk having been torn away.” Ancient sharks seemed to be the most likely culprits, especially since the fish left behind fossil feces right alongside the invertebrate body fossils.
Over four decades later, we don’t know much more about the Tully Monsters. Merrill Foster, in his 1979 reassessment of the fossils, considered Tully Monsters to be related to the subgroup of molluscs that contains conches, whelks, and limpets. A more recent 2005 paper hinted that the Tully Monsters might instead be related to the Cambrian invertebrate Vetustovermis, itself a problematic fossil of uncertain affinities. As strange as they are though, there is something familiar about the Tully Monsters. Although separated by about 200 million years, the Tully Monsters show a general similarity to the nozzle-faced Cambrian creature Opabinia regalis. Both had stalked eyes, a flexible proboscis tipped with a grasping appendage, and moved by way of flexible fins on the sides of their bodies. (The fact that the proboscis of the Tully Monsters did not have a mouth or throat – and was probably used to move food to the mouth as in Opabinia – is another clue worth considering.) Might the Tully Monsters be some long-lived cousin of Opabinia, suggesting an as-yet-undiscovered trail of trunked invertebrates? Maybe, maybe not. As ever, we need more fossils.
There is one other aspect of the Tully Monster story worth visiting, though. The first time I came across an illustration of a Tully Monster, it was not in a book about paleontology. It was in a book about the legendary Loch Ness Monster.
As retold by Richard Ellis in Monsters of the Sea, the Tully Monster’s Loch Ness connection was most prominently promoted by self-styled monster hunter F.W. Holiday. After claiming to have spotted Nessie in 1962, Holiday became convinced that the lake monster was an enormous worm, and he organized a second photographic expedition to document the creature in 1965. The monster failed to appear, but soon afterward Holiday was visited by the University of Chicago biologist Roy Mackal. The Illiniois-based scientist carried with him a photograph of the recently-described Tully Monster, and Holiday took it as a miniature version of the mythical giant Loch Ness worm. The eye stalks looked like flippers, and the long proboscis could be mistaken for a neck with a small head at the end, leading Holiday to write “No-one knows whether the Orm of Loch Ness is a form of Tullimonstrum; but talking most unscientifically, I would bet my shirt that it is.”
The idea of plus-sized Tully Monsters sculling around Loch Ness is just as fanciful as thinking the lake contains a population of living plesiosaurs. Tully Monsters have only been found in the 300 million year old strata of Illinois. That’s quite a time gap, not to mention the disparity in size between the 6-inch invertebrates and the giant Scottish monster. Tully Monsters might fit the expected profiles on lake monsters, but there is no indication that they survive today, much less that have grown to gigantic size during the intervening epochs. In this case, though, the truth is just as wonderful as the fiction. Why invent monsters when they were so abundant during the prehistoric past?
Top Image: A restoration of the Tully Monster (Tullimonstrum gregarium) from Johnson and Richardson, 1969.
Richardson, E. (1966). Wormlike Fossil from the Pennsylvanian of Illinois Science, 151 (3706), 75-76 DOI: 10.1126/science.151.3706.75-a
Chen, J., Huang, D., & Bottjer, D. (2005). An Early Cambrian problematic fossil: Vetustovermis and its possible affinities Proceedings of the Royal Society B: Biological Sciences, 272 (1576), 2003-2007 DOI: 10.1098/rspb.2005.3159
Ralph Gordon Johnson, Eugene S. Richardson (1969). The Morphology and Affinities of Tullimonstrum. Fieldiana: Geology, 12 (8), 119-149