Late Jurassic tethyan ancestry of recent southern high-latitude marine isopods (Crustacea, Malacostraca)

Isopods are one of the key marine groups that radiated extensively in the s outhern high-latitude regions, and it is widely assumed that they did so es sentially through the Cenozoic era. Nevertheless, palaeontological evidence is now beginning to accumulate which suggests that some at least of the ke y isopod taxa may be of considerably greater antiquity. In particular, Schw eglerella strobli Polz from the Early Tithonian Plattenkalk of Solnhofen, s outhern Germany indicates that the suborder Sphaeromatidea is of at least L ate Jurassic ancestry, and possibly much older. Schweglerella strobli is ph ylogenetically close to both the Bathynataliidae and Serolidae, but is here placed in a new family, Schweglerellidae. Like the decapods, the early phy logenetic history of the isopuds may be characterized by a considerable mac roevolutionary lag. Perhaps a number of major marine invertebrate groups un derwent a Mesozoic phase of widespread dispersal when the Pangaean margins were still largely intact and climates globally more equable? The subsequen t radiation of groups such as the sphaeromatidean isopods may have been lar gely contingent upon the: Cenozoic thermal isolation of the Southern Ocean.