A palaeobiogeographical synthesis of Australasian Mesozoic marine tetrapods

Kear, B.P., Fordyce, R.E., Hiller, N. & Siversson, M., December 2017. A palaeobiogeographical synthesis of Australasian Mesozoic marine tetrapods. Alcheringa 42, 461-486. ISSN 0311-5518.THE LAST 15years has witnessed a blossoming of research on Australasian Mesozoic marine tetrapod fossils. Much of this work has focused on amniotes, particularly those from the prolific Lower Cretaceous (Aptian-Albian) Lagerstatten of the Eromanga Basin in central and eastern Australia, and Upper Cretaceous (Campanian-Maastrichtian) sequences of the North and South islands of New Zealand. However, rare and less popularized remains have also been found in Lower Triassic-mid-Cretaceous rocks from Australia, New Zealand and the Chatham Islands, and on the tectonically proximal landmasses of New Caledonia and Timor. Currently identified taxa include estuarine-paralic rhytidostean, brachyopid, capitosaurian and trematosaurian temnospondyls from the earliest Triassic (Induan-Olenekian), Middle-Late Triassic (Anisian-Norian) eosauropterygians, and mixosaurian, shastasaurian and euichthyosaurian ichthyosaurians, Early-Middle Jurassic (Sinemurian-Bajocian) ichthyosaurians, together with plesiosauroid and rhomaleosaurid-like plesiosaurians, and diverse Early (Aptian-Albian) through to Late Cretaceous (Campanian-Maastrichtian) elasmosaurid, leptocleidid, polycotylid, probable cryptoclidid and pliosaurid plesiosaurians, as well as ophthalmosaurid ichthyosaurians, sea turtles incorporating protostegids, and mosasaurid squamates. This faunal succession evidences almost continuous occupation of southern high-palaeolatitude seas, and repeated endemic diversifications (including nascent members of some key lineages) amongst emigrant cosmopolitan clades. The primary dispersal routes are likely to have been peri-Gondwanan, with coastal migrations along the western Tethys and polar margins of the Panthalassan Ocean. However, augmentation by increasing continental fragmentation and seaway corridor connectivity probably occurred from the Middle Jurassic to Late Cretaceous. Latest Cretaceous mosasaurid and elasmosaurid taxa also reveal regional affinities with the emergent western Pacific and Weddellian austral bioprovinces. The extreme rarity, or complete absence, of many major groups prevalent elsewhere in Gondwana (e.g., tanystropheids, Triassic sauropterygians, bothremydid marine turtles, thalattosuchians and dyrosaurid crocodylomorphs) is conspicuous, and might be related to stratigraphical/collecting biases, or the predominantly higher-palaeolatitude, cooler-water Mesozoic palaeogeography of the Australasian region. Although the burgeoning record is substantial, much still awaits discovery and adequate documentation; thus Australasia is still one of the most exciting prospects for future insights into the global history of Mesozoic marine tetrapods.