Sheltered preservation of cyrtocrinid crinoids from the Lower Cretaceous of Madagascar and their palaeogeographic significance

Sheltered preservation, in which organisms are trapped within shells of cephalopods, is a well-known phenomenon. This preservational style constitutes an important source of paleontological data. Here, we report the first crinoid preserved inside the early Albian ammonite Cleoniceras besairiei Collignon from Madagascar. This crinoid is assigned to the aspidocrinid phyllocrinid (Apsidocrinus, Phyllocrinidae), and constitutes the first phyllocrinid from the African continent, the second from the southern margin of the Tethys (after New Zealand), and also from the southern hemisphere. This specimen represents the youngest occurrence of a phyllocrinid in the world as well, and constitutes one of the youngest occurrences of cyrtocrinids from shallow sea environments, before predation-induced migration of the stalked crinoids to the deep sea refugia due to the so-called Mesozoic Marine Revolution. This finding highlights that ammonite shells may also be a convenient material for studying echinoderms.