By Brian Switek
This time last year, two teams of paleontologists announced that they had finally solved one of the most inscrutable mysteries in the history of life on Earth. The Tully Monster – a flat, bug-eyed, nozzle-nosed animal truly worthy of the title Monster – went from a 300 million year old Rorsarch test to a vertebrate, a strange lamprey rather than a pincer-faced invertebrate. Fossil fans sent up a cheer as the unusual critter was welcomed into the fold. But now a different group of researchers has once again raised uncertainty about what, exactly, the Tully Monster is.
Paleontologist Lauren Sallen and colleagues write that the idea Tullimonstrum was a nightmarishly aberrant fish runs into “biological, functional, and taphonomic” challenges. In their view, the Tully Monster is no vertebrate but something more akin to a mollusk, arthropod, or some strange chordate. Disagreement is no surprise when you’re dealing with a species that looks like the star of an early Roger Corman film.
One of the pro-vertebrate studies, published by Thomas Clements and collaborators, concluded that the Tully Monster is one of our family based on its eye. The shape as the eye, as well as two organelles inside it, appeared to align the Tully Monster with vertebrates more than other animals. Sallen and coauthors regard these same characteristics as equivocal, possibly having more to do with convergence than true relationships.
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