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Treasure Trove of Museum Specimens Leads to Identity of 300 Million-Year-Old 

Tomoyuki Mikami (Research Fellow, National Museum of Nature and Science) *
Wataru Iwasaki (Professor, Graduate School of Frontier Sciences / Department of Biological Sciences)


Many fossils, which are proof of the life of ancient organisms, are found on the present-day Earth.
Some of these fossils have forms so different from those of organisms we see in our daily lives that we have no idea how they are related to modern organisms.
We have focused our attention on the "Tally Monster," which is famous for being particularly enigmatic among such fossils, and as a result of making full use of the latest 3D measurement technology, we have disproved most of the evidence of recent studies that concluded that the Tally Monster is a vertebrate, and suggested that the Tally Monster is some kind of invertebrate. The tally monster is an invertebrate of some kind.

The Maison Creek biota from the Coal Period strata of Illinois, USA, is famous for its fossil remains of organisms that do not have hard tissues and are not usually fossilized. Tally Monsters, found only in the Maison Creek biome, are marine creatures that lived approximately 300 million years ago and have a very strange shape, unlike any animal on Earth today, characterized by a long ocular pattern and a jaw-like organ at the end of an elongated structure growing from the head. Previous studies have suggested that it may be closely related to various groups of animals, including mollusks, annelids, and cordates, but all theories lack conclusive evidence, and its true identity is still shrouded in mystery. In particular, a surprising theory that the tally monster is a vertebrate closely related to lamprey eels has recently been proposed in Nature magazine and has been attracting much attention. If this theory is correct, our understanding of vertebrate morphological diversity will have to be fundamentally revised.

While conducting a museum survey for another research theme, we happened to notice that a large number of fossil specimens of this world-renowned tally monster were housed in a Japanese museum. Upon closer examination of these specimens, we noticed that the surfaces of Tally monster fossils have a fine three-dimensional structure that has not been paid much attention so far. We thought that the observation of these fine three-dimensional structures might bring about a new development in the debate on the study of tally monsters, and we analyzed the surface profiles of 153 tally monster specimens using a 3D scanner. The results suggest that the tally monster is not a vertebrate because each of the structures identified as supporting the musculature, brain, gill slits, and fins in previous studies as evidence that the tally monster is a vertebrate has distinctly different features from those in vertebrates. For example, the head of the tally monster has a continuous segmental structure from the trunk, which is morphologically very different from that of vertebrates that do not have a distinct segmental structure in the head. In this study, we also used X-ray micro-CT to precisely observe the "teeth" found in the jaw-like organs of tally monsters. As a result, it became clear that, contrary to previous studies that claimed that the morphology of the teeth resembled those of lamprey eels and sea eels, some of the teeth of tally monsters are different from those of lamprey eels and sea eels.

While museums are close to us, they also house valuable research samples that we may not expect to find. If you have the opportunity to visit a museum, do not remain passively looking at the exhibits, but think about how you can extract important scientific information from them.

Tally Monster fossils and reconstructions based on the results of this study. Scale bar is 1 cm.

This study was published in T. Mikami et al. Palaeontology, 66,e12646 (2023).


* At the time of the study: graduate student, Department of Biological Sciences


(Press release, April 17, 2023)

Published in The Rigaku-bu News, September 2023


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