Tully Monster Identity Mystery

Tullimonstrum gregarium, better known as the Tully Monster, was so bizarre that paleontologists still argue over what kind of animal it actually was. Scientists have found thousands of fossils, all from the Mazon Creek fossil beds in Illinois, yet the debate over whether it was closer to a vertebrate, an invertebrate, or something in between still has not fully ended. A 2016 pair of studies argued for a vertebrate connection, but later papers challenged that conclusion, and a 2023 study said its three-dimensional anatomy casts doubt on those supposed vertebrate traits.

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