Tullimonstrum, colloquially known as the Tully monster or sometimes Tully's monster, is an extinct genus of soft-bodied bilaterian marine animal that lived in shallow tropical coastal waters of muddy estuaries during the Pennsylvanian, about 310 million years ago. A single species, T. gregarium, is known. Examples of Tullimonstrum have been found only in sediments deposited far from the palaeocoast (formally termed the Essex biota), in the Mazon Creek fossil beds of Illinois, United States.
Tullimonstrum had a pair of vertical, ventral fins (though the fidelity of preservation of fossils of its soft body makes this difficult to determine) situated at the tail end of its body, 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. Their form and structure is suggestive of a camera-type eye.
History of discovery
thumb|T. gregarium fossil (part and counterpart)|rightAmateur collector found the first of these fossils in 1955 in a fossil bed known as the Mazon Creek formation. He took the strange creature to the Field Museum of Natural History, but paleontologists were stumped as to which phylum Tullimonstrum belonged to. The species Tullimonstrum gregarium ("Tully's common monster"), as these fossils later were named, takes its genus name from Tully, The term monstrum ("monster") relates to the creature's outlandish appearance and strange body plan.
The fossil remains "a puzzle", and interpretations liken it to a worm, a mollusc, an arthropod, a conodont, or a vertebrate. Others pointed to a general resemblance between Tullimonstrum and Opabinia regalis, although Cave et al. notes that they were too morphologically dissimilar to be related.
Classification
The classification of Tullimonstrum has been an ongoing debate since the creature was first described, it also has many features not found in Cyclostomes (lampreys and hagfishes).
Clements et al. (2016)
Clements et al. (2016) examined the eye anatomy of Tullimonstrum, concluding that the camera-like eye, with preserved lenses and the presence of cylindrical and spheroid melanosomes arranged in distinct layers, was indicative of a stem-vertebrate affinity. These ocular pigments and their unique structure was interpreted to be a retinal pigmented epithelium (RPE), offering strong support that the bar organs were indeed eyes. In 2022, Wiemann and colleagues replicated these spectral signals in collaboration with independent laboratories using Fourier-Transform Infrared spectroscopy. Comparable tissue signatures have been detected in preserved carbonaceous remains of a diversity of other animals.
Arguments in favour of non-vertebrate affinities
Sallan et al. (2017)
In 2017 Sallan et al. rejected the identification of the Tully monster as a vertebrate. Firstly, they noted that even the presence of the two melanosome types is variable among vertebrates; hagfish lack them altogether, and extant sharks as well as extinct forms found in the Mazon Creek area, such as Bandringa, only have spheroid melanosomes. Additionally, the supposed notochord extends in front of the level of the eyes, which is not the case in any other vertebrate, although is seen in lancelets. Even if the structure was a notochord, the presence of notochords is not limited to vertebrates either.
Further criticism was drawn towards the identification of the blocks of the body variously as gill pouches and muscle blocks (myomeres), despite the lack of differentiation in the structure of these blocks. In vertebrates, myomeres are also thinner, and extend along the whole length of the body rather than stopping short of the head. Meanwhile, the gill pouches of lampreys are paired extensions rather than segmented structures, and are usually embedded in a complex gill skeleton, neither of which is the case in Tullimonstrum. On a plot of trace metal signatures in the eyes of Mazon Creek fossils, Tullimonstrum is clearly distinct from both vertebrates (which have a higher concentration of zinc) and the eyespots of the putative cephalopod Pohlsepia (however, no evidence of melanosomes were found in Pohlsepia) – although these signals are influenced by the fossilisation process. The authors state that Tullimonstrum was not a cephalopod (in the absence of other supporting traits), but argue that eye structure and chemistry alone cannot disprove invertebrate affinities.
Paleoecology
Tullimonstrum was probably a free-swimming carnivore that dwelt in open marine water, and was occasionally washed to the near-shore setting in which it was preserved.
The combination of rapid burial and rapid formation of siderite resulted in excellent preservation of the many animals and plants that were entombed in the mud. As a result, the Mazon Creek fossils are one of the world's major Lagerstätten, or concentrated fossil assemblages.
The dancing worms of Turkana
A 1966–1968 prank promulgated by paleontologist Bryan Patterson suggested that modern representatives could possibly be found in remote lakes of Kenya, known under the local name "Ekurut Loedonkakini". These "dancing worms of Turkana" could supposedly kill a man with a bite, produced some sort of milk, and were known even to school-age children.
Patterson had several letters sent from Kenya under various aliases to Eugene Richardson, the Field Museum's curator of fossil invertebrates. Patterson had previously been the museum's curator of vertebrate paleontology and retained an accomplice there who was aware of the prank (and prevented it from going too far). A planned expedition was cancelled after the hoax was disclosed in a good-natured Christmas letter.
Richardson later recounted the story and published the original letters, poems, and doctored photos in a book under the pseudonym E. Scumas Rory.
In culture
In 1989, Tullimonstrum gregarium was officially designated the state fossil of Illinois. Artwork of it is featured on U-Haul rental vehicles from the state.
See also
- Paleontology in Illinois
References
External links
- "Tully: Monster vs Method", a video by the Field Museum of Natural History
- "The Tully Monster", a video by the Field Museum of Natural History
- Mazon Creek Paleobotany References by the Field Museum of Natural History