Obinautilus is an extinct genus of shelled cephalopod that has been variously identified as an argonautid octopodOzawa, T. & S. Tomida (1996). Occurrence of Aturia coxi (Cephalopoda; Nautilida) from the uppermost Miocene of Japan and its implication for late Miocene marine climate in the northwestern Pacific. Journal of Paleontology 70(5): 795–798. Martill, D.M. & M.J. Barker (2006). A paper nautilus (Octopoda, Argonauta) from the Miocene Pakhna Formation of Cyprus. Palaeontology 49(5): 1035–1041. Strugnell, J.M., A.D. Rogers, P.A. Prodöhl, M.A. Collins & A.L. Allcock (2008). The thermohaline expressway: the Southern Ocean as a centre of origin for deep-sea octopuses. Cladistics 24(6): 853–860. Strugnell, J. & A.L. Allcock (2010). Co-estimation of phylogeny and divergence times of Argonautoidea using relaxed phylogenetics. Molecular Phylogenetics and Evolution 54(3): 701–708. or a nautilid.Ward, P. (1980). Comparative shell shape distributions in Jurassic–Cretaceous ammonites and Jurassic–Tertiary nautilids. Paleobiology 6(1): 32–43. Teichert, C. & T. Matsumoto (2010). The Ancestry of the Genus Nautilus. In: W.B. Saunders & N.H. Landman (eds.) Nautilus: The Biology and Paleobiology of a Living Fossil. Springer. pp. 25–32. UMUT CM 08493: Obinautilus pulchra Kobayashi, 1954. The University Museum, The University of Tokyo.Eyden, P. (2010). Fossil Octopuses. TONMO. It is known from the Late Oligocene to Pliocene of Japan.Saul, L.R. & C.J. Stadum (2005). Fossil argonauts (Mollusca: Cephalopoda: Octopodida) from Late Miocene siltstones of the Los Angeles Basin, California. Journal of Paleontology 79(3): 520–531. The shell is discoidal and very involute, with rapidly expanding and compressed whorls, fine radial ribs, a rounded venter with a shallow furrow, and almost closed umbilicus.
Based on the examination of O. pulcher fossils from the Oligocene, the Tremoctopus–Argonauta divergence has been estimated to have occurred at least 29 million years ago.Strugnell, J., J. Jackson, A.J. Drummond & A. Cooper (2006). Divergence time estimates for major cephalopod groups: evidence from multiple genes. Cladistics 22(1): 89–96.
Species
Two species are recognised in the genus.
†Obinautilus awaensis (originally described as Argonauta awaensisTomida, S. (1983). Two new fossil Argonauta and firstly discovered Aturia coxi Miller from the late Tertiary of Boso Peninsula, Japan. Muzunami-shi Fossil Museum Bulletin 10: 107–116.) — Pliocene (possibly also latest Miocene) Upper Senhata Formation of Bōsō Peninsula, Japan †Obinautilus pulcher (sometimes spelled O. pulchra) — Late Oligocene Nichinan Formation of Japan
References
Further reading Noda, H., K. Ogasawara & R. Nomura (1986). Systematic and paleobiogeographic studies on the Japanese Miocene argonautid “Nautilus” izumoensis. University of Tsukuba, Institute of Geoscience, Science Reports, Section B, Geological Sciences 7: 15–42. Yanagisawa, Y. (1990). Bulletin of the Geological Survey of Japan 41(3): 115–127.