Miocene sepiids (Cephalopoda, Coleoidea) from Australia
Abstract. Two sepiid genera, Notosepia Chapman, 1915, and Sepia Linnaeus, 1758, are described from the Neogene deposits of Australia. A new and unique record of the middle Miocene Sepia sp. is reported from southern Australia. Based on similarities to contemporaneous sepiids, the new sepiid cuttlebone described herein belongs to the genus Sepia. Notosepia cliftonensis is suggested herein to be a descendant of the archaeosepiid stem lineage. Microstructures (lamella-fibrillar nacre is the nacre Type II of septa and pillar prismatic layers) of the excellently preserved cuttlebone of Sepia sp. display a modern character of the phragmocone, fully comparable to the recent taxa. The stratigraphically well-calibrated (based on foraminifera) cuttlebone represents the first unambiguous fossil record of the genus Sepia from the Southern Hemisphere. It significantly extends the biogeographical distribution of modern sepiids in the Miocene and suggests the existence of a sepiid eastward migratory route. Moreover, the presence of both conservative- and modern-type cuttlebones suggests a dual colonisation of Australian waters: the first (archaeosepiid) during the late Eocene–late Oligocene and the second (sepiid) during the early Miocene.