EPI-BIONTIC AND ENDOBIONTIC ORGANISMS ON LATE JURASSIC CRINOID COLUMNS FROM THE NEGEV DESERT, ISRAEL - IMPLICATIONS FOR COEVOLUTION

Columns of the articulate crinoids Millericrinus and Apiocrinites from the Upper Jurassic (Upper Callovian) Zohar and Matmor formations of t he Negev Desert of Israel display abundant encrusting organisms of abo ut ten species, as well as diverse trace fossils produced by endobiont s. Pluricolumnals were colonized by epi-and endobiontic organisms both during life and post-mortem. Skeletonized encrusting organisms includ e abundant ostreid bivalves (which evidently colonized both live and d ead crinoid columnals), two types of serpulid worms, encrusting forami nifera, three species of bryozoans, and small encrusting sclerosponges . Several types of borings are present: Trypanites (possibly produced by sipunculids), Gastrochaenolites, (crypts of boring lithophagid biva lves), elliptical barnacle? borings, and channel-like annelid? borings . In addition, approximately 16% of the pluricolumnals display circula r parabolic embedment pits assignable to the ichnogenus Tremichnus. Th ey are associated with substantial deformation of the containing colum nals and were probably the work of host-specific ectoparasitic organis ms. Discovery of Tremichnus on Jurassic crinoids extends the range of this trace by almost 100 million years, providing evidence for one of the longest-ranging host-parasite interactions documented thus far lov er 200 million years). The relationship of epibionts to the Jurassic c rinoids thus ranged from simple utilization of dead hard substrate to probable opportunistic commensalism in forms that colonized the live u pright stems, as in some oysters,through host-specific parasitism in t he case of Tremichnus.