Among various drill holes located in ancient shells, the ichnospecies Oichnus ovalis is particularly important for understanding the presence and behaviour of cephalopods. In modern seas, incirrate octopuses of the superfamily Octopodoidea produce small, oval drill holes ascribed to O. ovalis in the shells of various molluscs and crustaceans. Until now, fossil O. ovalis has been primarily known mostly from the Pliocene and Pleistocene, whereas the oldest examples have been reported from the Late Cretaceous (Campanian). Here, we describe the first Jurassic record of O. ovalis, found in the ammonite Quenstedtoceras lamberti from the Middle Jurassic (latest Callovian) of Russia. The oval drill hole measuring 1.0 to 0.5 mm is located on the ammonite body chamber in the area of attachment of retractor muscles, which suggests this hole most likely was made by a predator that attacked a living ammonite in the water column. If this drill hole had been found in the Late Cretaceous or Cenozoic, it would have been attributed to an octopodoid predator. However, body fossils of octopodoids are still unknown from the Jurassic. Nevertheless, judging by some molecular clock data, incirrate octopuses might have already existed in the Late Jurassic and probably even earlier. Therefore, the Jurassic O. ovalis may have been drilled by one of the oldest octopodoids, their ancestors, or an unknown predator. Regardless of the identity of the predator, this finding expands our knowledge on the Middle Jurassic predators of ammonoids and suggests drilling on active pelagic prey arose during the Jurassic phase of the Mesozoic Marine Revolution.
Oichnus, Oichnus ovalis, Jurassic, Callovian, ammonites, ichnotaxa