KIIMETRA MIOCENICA, A NEW GENUS AND SPECIES OF THE FAMILY CALOMETRIDAE (ECHINODERMATA: CRINOIDEA) FROM THE MIDDLE MIOCENE OF SOUTHWESTERN JAPAN

Abstract

Extant comatulid (stalkless) crinoids consist of approximately 530 species, classified in 143 genera and 18 families (Clark, 1931, 1941, 1947, 1950; Clark and Clark, 1967; Messing and White, 2001). Recent comatulids account for almost 85% of all the extant crinoid species (comatulids plus stalked crinoids), and their taxonomy is currently being extensively revised (e.g., Hoggett and Rowe, 1986; Rowe et al., 1986; Messing and White, 2001). In stark contrast to such a high extant diversity, records of fossil comatulids are far less common. This is partly due to their low fossilization potential. From the Cretaceous, only 18 genera and nine families of comatulids have been documented (Rasmussen, 1978). The oldest record of a comatulid dates back to the late Triassic ( Paracomatula Hess, 1951; Hagdorn and Campbell, 1993; Simms et al., 1993). Up to the late Cretaceous, the most diverse taxa were notocrinids and solanocrinids (Rasmussen, 1961; Jagt, 1999). The comatulids probably diversified during the Cenozoic (compare Jagt et al., 2002). Cenozoic records of comatulids are thus very important for understanding comatulid diversification. In contrast to stalked crinoids, which occur only at depths below 100 m in modern seas, comatulids are the only crinoid group which flourishes in shallow-water settings. In order to understand the timing and pattern of comatulid survival and diversification, data on Cenozoic comatulids are crucial. Until now, most reports of fossil comatulids chiefly described centrodorsals, because other skeletal parts are easily disarticulated and lost after death (Meyer and Meyer, 1986). In the current paper, we describe a very well-preserved new comatulid species from the Miocene of southwestern Japan, the first report of a fossil member of the Calometridae. It is named Kiimetra miocenica n. gen. and sp. The sample studied contains over 100 specimens …