Secrets of an ancient monster finally revealed

“Tully monster” related to lampreys

Tully monster

Reconstruction of the extinct aquatic monster Tullimonstrum gregarian, which lived 300 million years ago in the carboniferous seas – Sean McMahon, Yale University

Since the discovery of the Tully monster in 1958, by Francis Tully an amateur fossil hunter, the nature and identity of the creature has been fiercely debated. Found in the Mazon Creek fossil beds in Illinois and dating to around 300 million years ago, Tullimonstrum gregarian exhibits characteristics that could be attributed to a plethora of taxonomic groups. The monster has been placed in groups as far ranging from snails to worms, but none have come up an agreed upon phylum, that is until now.

tully skelteton

Fossilized anatomical features of the Tully monster, which have been interpreted differently over the years (Clements et al. 2016)

The creature exhibits a few characteristics that seem typically vertebrate such as: bilateral symmetry, a tail fin with dorsal and ventral lobes, and a tripartite brain-like structure. A few of T. gregarian characteristics have been identified as almost entirely unique to this species such as: a proboscis and jaw most similar to a creature from the Cambrian, Opabinia, belonging to a an extinct arthropod group; and a transverse bar with spherical structures at the end, identified as eyes, and reminiscent of an insect-like hammerhead shark. A closer look into the eyes, using sophisticated techniques in fossil chemical mapping and analysis, revealed two structural melanosomes, which are characteristic of vertebrate eyes (for more information see Clements et al. 2016). Another recent discovery dealt with the correct assessment of the internal structure. The white line structure, pictured above in the fossil, had been previously identified as gut contents, but further analysis and repeated examinations of thousands of fossils show that this in fact is a notochord, a component universal to all chordate animals (vertebrates)(for more information see McCoy et al. 2016).

The position of this monster amongst the chordates was then examined. The notochord pointed downwards toward the tail is a characteristic typical of the lampreys. Also a recently found gut closely resembled that of the hagfish. Together these findings, along with other anatomical notes, indicated its position as most closely related to cyclostomes.

tully tree

Proposed phylogenetic position of Tullimonstrum, a divergence from the vertebrate group containing the lampreys and hagfishes (McCoy et al. 2016)

However, the anatomical structure of all cyclostomes (lamprey and hagfish) is remarkably similar. Therefore, the Tully monster must be an early divergent from modern day cyclostomes, and leads to the possibility of a vast array of diversity in early organisms of this lineage. This means there are many more spooky animal monsters out there, and some could be lurking near you.

The findings of these studies also indicate the potential classification of an aquatic ecology blogger, Sam, whose resemblance to the Tully monster is rather uncanny.





Learn more:

Clements, T., Dolocan, A., Martin, P., Purnell, M. A., Vinther, J., & Gabbott, S. E. (2016).        The eyes of Tullimonstrum reveal a vertebrate affinity. Nature, 532(7600), 500-503.

McCoy, V. E., Saupe, E. E., Lamsdell, J. C., Tarhan, L. G., McMahon, S., Lidgard, S., … & Vogt, S. (2016). The ‘Tully monster’is a vertebrate. Nature. 532(760), 496-499.

Jim Shelton, Yale Biologists Solve the Mystery of the Tully Monster – SciTech Daily –

Nicholas St. Fleur – Solving the Tully Monster’s Cold Case – New York Times –


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