Miocene sepiids (Cephalopoda, Coleoidea) from Australia

Two sepiid genera, Notosepia Chapman, 1915, andSepia Linnaeus, 1758, are described from the Neogene deposits ofAustralia. A new and unique record of the middle Miocene Sepia sp.is reported from southern Australia. Based on similarities to contemporaneoussepiids, the new sepiid cuttlebonedescribed herein belongs to the genus Sepia. Notosepiacliftonensis is suggested herein to be a descendant of the archaeosepiidstem lineage. Microstructures (lamella-fibrillar nacre is the nacre Type II ofsepta and pillar prismatic layers) of the excellently preserved cuttlebone ofSepia sp. display a modern character of the phragmocone, fullycomparable to the recent taxa. The stratigraphically well-calibrated (basedon foraminifera) cuttlebone represents the first unambiguous fossil record ofthe genus Sepia from the Southern Hemisphere. It significantlyextends the biogeographical distribution of modern sepiids in the Miocene andsuggests the existence of a sepiid eastward migratory route. Moreover, thepresence of both conservative- and modern-type cuttlebones suggests a dualcolonisation of Australian waters: the first (archaeosepiid) during the lateEocene–late Oligocene and the second (sepiid) during the early Miocene.