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Fossil Friday: Moniopterus — Snake, Beetle, or Mollusk?

Günter Bechly
Photo: Moniopterus japonicus, modified after Haga et al. 2010, https://doi.org/10.1666/09-126.1, fair use.

Egg-shaped fossils of about two inch size have been described as Moniopterus japonicus from the Miocene of Japan. It is a perfect showcase for how paleontologists play fast and loose with the over-interpretation of poorly preserved fossils. Moniopterus was initially described as the only known example of fossil sea-snake eggs by Hatai et al. (1974). Wow, that sounds interesting, if we gloss over the little lapse that the authors accidentally placed the fossils in the bony fish family Ophichthyidae instead of the sea-snake subfamily Hydrophiinae, because both animals have the same common name in Japanese. Ooops, that’s an embarrassing mistake for professional scientists writing a technical paper, but anyway, at least they found the first sea-snake eggs, or did they?

About twenty years later, another study recognized the same material as fossilized pupal chambers of a coleopteran insect (Johnston et al. 1996). Hmmm, that’s quite a different take on the same fossils, but it gets even better. A re-examination of the holotype specimen by Haga et al. (2010) provided no evidence in support of these previous interpretations. Instead the fossils turned out to be borings of a rock-boring mytilid bivalve of the genus Lithophaga. So, a trace fossil of a mollusk had been misidentified in different phyla as snake egg and as beetle pupa.

That this case of blatant misidentifications is not an isolated example is shown by the case of alleged vertebrate eggs from the Cretaceous of the Gobi Desert, which turned out to be fossilized pupal chambers of beetles (Johnston et al. 1996). But on the other hand, should we trust the latter study at all, given the blunder they made with Moniopterus? Scientists are only humans and many of them see what they want to see. Fossils often leave a lot of room for wild imagination and wishful thinking. Of course, they still prove Darwinian evolution beyond a reasonable doubt! Just follow the science and don’t ask silly questions.


  • Hatai K, Masuda K & Noda H 1974. Marine fossils from the Moniwa Formation along the Natori river, Sendai, northeast Honshu, Japan, part 2. Problematica from the Moniwa Formation. Transactions and Proceedings of the Paleontological Society of Japan NS 95, 364–371. DOI: https://doi.org/10.14825/prpsj1951.1974.95_364.
  • Johnston PA, Eberth DA & Anderson PK 1996. Alleged vertebrate eggs from Upper Cretaceous redbeds, Gobi Desert, are fossil insect (Coleoptera) pupal chambers: Fictovichnus new ichnogenus. Canadian Journal of Earth Sciences 33(4), 511–525. DOI: https://doi.org/10.1139/e96-040.
  • Haga T, Kurihara Y, Kase T 2010. Reinterpretation of the Miocene Sea-Snake Egg Moniopterus japonicus as a Boring of Rock-Boring Bivalve Lithophaga (Mytilidae: Mollusca). Journal of Paleontology 84(5), 848–857. DOI: https://doi.org/10.1666/09-126.1.