Vörös A. szerk.: Fragmenta Mineralogica Et Palaentologica 16. 1993. (Budapest, 1993)

appropriate cause. It is important to note that in our case, the three groups of giant forms occur in different faunal provinces: "R." decorata and Sardorhynchia in the NW European, Septirhynchia and Heteromychus in the Ethiopian (or Abyssinian), Lessiniella in the Mediterranean province (Text-fig. 2). The success of "R." decorata may be interpreted as an excellent adaptation to extremely shallow water carbonate environment (see Dardeau & Laurin 1982) and this holds true for Sardorhynchia too (Taddei Ruggiero & Ungaro 1983, p. 242). Septirhynchia was also found in micrites, almost invariably with umbones downward; therefore a special, semi-infaunal, unattached mode of life was suggested to explain the rapid invasion of the the African epicontinental seas (Mancenido & Walley 1979). A similar, semi-infaunal habit may be supposed in the case of Lessiniella. Though in the early adult stage it definitely had an active pedicle, the strong, gryphaeoid beak of the biggest specimen might have served as an anchor in the lime mud and the pedicle might have been atrophied. However, in contrast to the very shallow, epicontinental settings favourized by the group of decorata and Septirhynchia, Lessiniella was found in pelagic micrites (Rosso Ammonitico) where the deep water environment is evidenced by the very poor benthos (only brachiopods) and the dense and very diverse ammonoid population. Text-fig. 2 - Middle Jurassic paleogeographic map showing the distribution of three groups of giant rhynchonellids. Base map compiled from Vörös (1984,1992). Distribution of "R." decorata after Drot & Fischer (1966), including Sardorhynchia after Taddei Ruggiero & Ungaro (1983), Septirhynchia after Manceflido & Walley (1979). Stippled: land, horizontally ruled: shallow sea, cross-ruled: deep sea, blank: ocean