What it is
A soft animal that was swimming about 308 million years ago. It has a banded body with a fin at the tail, and a long flexible snout, thin as a shoelace, ending in a claw with small teeth inside it. Its eyes sit on the two ends of a stiff bar that juts straight out sideways. It would sit in your palm.
Why it matters
Every specimen anyone has ever found came out of one coal pit in northern Illinois. And nobody can tell you what it is. In 2016 a team said it was a jawless fish. Other teams took that apart. In 2023, a team scanned 153 specimens in 3D and found a head built in segments, which no animal with a backbone has. There is no bone here and no shell. What survives is a stain and an outline, flattened.
How it was kept
Each Tully monster is sealed inside an ironstone nodule, a hard lump of rock that formed around the soft body as it rotted. Collectors crack the nodules open to find them, and the same nodules hold ferns, shrimp, jellyfish and many other soft things from the same swamps and shallow sea.
Read the sources
- The 'Tully monster' is a vertebrate · Nature (2016)
- The 'Tully monster' is not a vertebrate · Palaeontology (2017)
- Three-dimensional anatomy of the Tully monster · Palaeontology (2023)
- The Mazon Creek Lagerstätte: an ecosystem entombed within siderite concretions · Journal of the Geological Society (2018)
- Tully's mystery monster · National Geographic