More than half a century after its discovery, the enigmatic "Tully Monster" has found classification by a team of researchers who say that they have finally figured out what it is, and where it fits in the tree of life: as a 307-million year-old vertebrate, it was related to the modern lamprey.
The strange fossils were first discovered in 1958 by amateur fossil collector Francis Tully near a mine in Illinois, and since then the remains of this creature have only been found in the Mazon Creek region of the same state. The strange dimensions and physique of the Tully monster, or Tullimonstrum gregarium, have puzzled scientists since its first discovery.
They appear to have been soft-bodied and tubular aquatic creatures, ranging in size from 6 to 12 inches. Their eyes projected out of a bar-distantly resembling that of a hammerhead shark. On one end they had a tail fin, and on the other their long, narrow snouts tapered off into a simultaneously toothy and claw-like apparatus. They once swam in the temperate coastal waters of a Carboniferous-era sea, among worms, jellyfish and sea cucumbers.
In a research report published today, a team of researchers from the Field Museum, Yale University, Argonne National Laboratory and the American Museum of Natural History led by paleontologist Victoria McCoy, outlined their findings after an exhaustive process of digitizing and making an extensive database of fossil images.
"The Tully monster is very weird looking[,] but we found it is related to modern lamprey," McCoy said. "It shows us how evolution can take something very familiar and make it very weird without changing what we know about the tree of life."
The researchers examined more than 1,200 extant specimens of Tully monsters. Using cutting-edge X-ray technology, including scanning electron microscopes (SEM) and synchrotron imaging, the team scrutinized the morphology of the Tully monster in particular. Through this process, the team was able to outline new evidence for anatomical structures like gill pouches, multiple rows of teeth and a notochord (a backbone made out of similar material to cartilage).
The data was collated in order to construct a phylogenetic tree, which in turn established that the Tully monster can be classified as a vertebrate - ultimately related to the jawless lamprey, though they bear very little resemblance to each other. Previous attempts at classifying the mystifying creature placed it as a relative of worms, mollusks, arthropods, or conodonts - the category of microfossils that are thought to be distant ancestors of modern fish.
The discovery is extraordinary, since up to this point even the most basic classification of the Tully monster was unknown.
The Tully monster became the state fossil of Illinois in 1989, two years after the death of Francis Tully.
These findings were published in the March 16 edition of the journal Nature.
