Tullimonstrum

Tullimonstrum, also known as the Tully monster or sometimes Tully's monster, is an extinct kind of soft-bodied sea animal. It lived in shallow, warm coastal waters with muddy estuaries during the Pennsylvanian period, about 310 million years ago. Only one species, T. gregarium, is known. It should not be confused with the Telly Monster.

Examples of Tullimonstrum have been found only in rock layers laid down far from the old coastline (called the Essex biota). They come from the Mazon Creek fossil beds in Illinois, United States. Scientists have argued about its classification for a long time. Some ideas have compared it to molluscs, arthropods, conodonts, worms, tunicates, and vertebrates.

This creature had a body shaped mostly like a cigar, a triangular tail fin, two long stalked eyes, and a proboscis with a mouth-like part at its tip. From the fossils, it seems it was a nektonic meat-eater that swam and hunted in the ocean's water column. When Tullimonstrum was alive, Illinois had a mix of places, including muddy estuaries, seas, rivers, and lakes.

Description

Tullimonstrum probably grew up to 35 centimeters (14 in) long. The smallest ones were about 8 cm (3.1 in) long.

Tullimonstrum had a pair of vertical fins on its belly near the tail. Scientists find these fins hard to be sure about, because its soft body was not always well kept as a fossil. It usually had a long proboscis with up to eight small, sharp teeth on each "jaw". It may have used this to poke the muddy bottom for small creatures and food bits called detritus. It lived alongside many other soft-bodied organisms found in the Mazon Creek fossils from Grundy County, Illinois.

The fossil has no hard parts. This suggests the animal did not have bones, chitin or calcium carbonate. There is some evidence of inside structures that repeat along the body. Its head is hard to make out. A bar-shaped structure ends in two round organs linked to dark material. Scientists have identified this material as melanosomes, which hold the coloring melanin. Their shape and structure suggest a camera-type eye. Tullimonstrum also had structures that scientists think were gills, and possibly a notochord or a simple spinal cord.

History of discovery

Amateur collector Francis Tully found the first of these fossils in 1955. He found it in a fossil bed called the Mazon Creek formation. He took the strange creature to the Field Museum of Natural History. Paleontologists were not sure which phylum Tullimonstrum belonged to. The species, Tullimonstrum gregarium ("Tully's common monster"), was named later. Its genus name honors Tully. The species name, gregarium, means "common." This is because many of these fossils were found in the formation. The word monstrum ("monster") relates to the creature's strange look and unusual body plan.

The fossil is still "a puzzle." Scientists have compared it to a worm, a mollusc, an arthropod, a conodont, or a vertebrate. It seems to lack features of well-known modern groups. Some have suggested it may belong to a stem group of worms. It was also compared to ancient creatures from the Cambrian period, including a suggested link to Nectocaris pteryx and a general resemblance to Opabinia regalis. However, another researcher found the two were too morphologically different to be related.

Classification

Scientists have argued for a long time about what group Tullimonstrum belongs to. Some have suggested it may be a basal vertebrate, a member of the phylum Chordata. In 2016, McCoy et al. found it may be closely related to modern lampreys. This was based on cartilage structures called arcualia, a dorsal fin, an uneven caudal fin, keratinous teeth, a single nostril, and tectal cartilages. However, it also has features not found in Cyclostomes (lampreys and hagfishes). That same year, Clements et al. studied its eyes. They found a camera-like eye with melanosomes arranged in layers and a retinal pigmented epithelium (RPE). The dark pigment was identified as melanin, rather than ommochromes or pterins, which are used by many invertebrate groups.

In 2020, McCoy, Wiemann and colleagues used Raman spectroscopy to show that the material preserved with the animal came from chordate tissues. It did not come from chitin, a material found in arthropods that is based on polysaccharide. In 2022, Wiemann and colleagues repeated these results using Fourier-Transform Infrared spectroscopy. Similar signals have been found in carbonaceous remains of other animals. Other scientists disagree. In 2017, Sallan et al. pointed out that melanosome types vary even among vertebrates, and that hagfish lack them. They also noted that the notochord extends in front of the eyes. This is not seen in other vertebrates, though it is seen in lancelets. Rogers et al. (2019) found that certain squid (Loligo vulgaris) and cuttlefish (Sepia officinalis) do have two melanosome forms. So eye structure alone cannot rule out invertebrate relatives. Even if the eye looks similar to a vertebrate eye, Tullimonstrum might not be a vertebrate. Similar traits also appear in tunicates, lancelets, acorn worms, and the extinct vetulicolians. Mikami et al. (2023) scanned 153 specimens using a 3‑D scanner. They concluded that some traits used to support a vertebrate identity are not comparable to those of vertebrates. They suggested it could be a non-vertebrate chordate or a protostome.

Paleoecology

Tullimonstrum was probably a meat-eater. It swam freely in the open sea. Sometimes it was carried into shallow water near the shore, where it was preserved. It did not stay attached to a hard surface or live in the benthic environment.

The Mazon Creek fossils formed in an unusual way. When animals died, they were quickly buried in silty mud. Bacteria broke down the plant and animal remains. As they did, they made carbon dioxide in the sediments around them. This gas mixed with iron from the groundwater to form lumps of siderite around the remains. These lumps trapped the animal, slowed its decay, and kept an impression or carbon traces of its body. Because the animals were buried fast and the siderite formed fast, the Mazon Creek fossils are among the world's major Lagerstätten, which are places where many fossils are found together. Bodies were often folded and bent. The proboscis is rarely found whole, though some part of it is often preserved. Other fossils found alongside Tullimonstrum include the sea anemone Essexella, the malacostracan Belotelson, the eurypterid Adelophthalmus mazonensis, horseshoe crabs, the elasmobranch fish Bandringa, and the coleoid cephalopod Jeletzkya.

The dancing worms of Turkana

From 1966 to 1968, paleontologist Bryan Patterson played a joke. He said that strange animals might live in remote lakes in Kenya. The local name for them was "Ekurut Loedonkakini." These "dancing worms of Turkana" were said to be dangerous and to make a kind of milk. People there were even said to know about them, including school-age children.

Patterson had letters sent from Kenya under several made-up names to Eugene Richardson, a curator at the Field Museum. Patterson had once worked there as the museum's curator of vertebrate paleontology. A helper at the museum knew about the joke and kept it from going too far. A planned trip was cancelled after the joke was discovered in a friendly Christmas letter. Richardson later told the story. He published the original letters, poems, and changed photos in a book under the pen name E. Scumas Rory.

In culture

In 1989, Tullimonstrum gregarium was named the state fossil of Illinois. A picture of it appears on U-Haul rental trucks from the state.