Tullimonstrum gregarium
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Tullimonstrum Temporal range: Middle Pennsylvanian |
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| Fossil of Tullimonstrum gregarium (part and counterpart) |
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| Scientific classification | |
| Kingdom: | Animalia |
| Clade: | Bilateria |
| Genus: |
†Tullimonstrum Richardson, 1966 |
| Type species | |
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Tullimonstrum gregarium Richardson, 1966 |
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Tullimonstrum, colloquially known as the Tully Monster, is an extinct genus of soft-bodied bilaterian that lived in shallow tropical coastal waters of muddy estuaries during the Pennsylvanian geological period, about 300 million years ago. A single species, T. gregarium, is known. Examples of Tullimonstrum have been found only in the Mazon Creek fossil beds of Illinois, United States. Its classification has been the subject of continual controversy, and interpretations of the fossil likened it to molluscs, arthropods, conodonts, worms, and even possibly vertebrates.
Tullimonstrum probably reached lengths of up to 35 centimetres (14 in); the smallest individuals are about 8 cm (3.1 in) long.
Tullimonstrum had a pair of fins like those of a cuttlefish, which were situated at the tail end of its body. The organism also possibly featured vertical, ventral fins (though the fidelity of preservation of fossils of its soft body makes this difficult to determine), and typically featured a long proboscis with up to eight small sharp teeth on each "jaw", with which it may have actively probed for small creatures and edible detritus in the muddy bottom. It was part of the ecological community represented in the unusually rich group of soft-bodied organisms found among the assemblage called the Mazon Creek fossils from their site in Grundy County, Illinois.
The absence of hard parts in the fossil implies that the animal did not possess organs composed of bone, chitin or calcium carbonate. There is evidence of serially repeated internal structures. Its head is poorly differentiated. A transverse bar-shaped structure, which was either dorsal or ventral, terminates in two round organs which are associated with dark material similar to the pigmentation often found in eyes. Their form and structure is suggestive of a camera-type construction.Tullimonstrum possessed structures which have been interpreted as gills, and a possible or rudimentary spinal cord.
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