A SHALLOW-WATER MICROSOLENID COMMUNITY FROM THE JURASSIC (CALLOVIAN) OF SOUTHERN ISRAEL

Platy microsolenid corals have been used as paleoenvironmental indicators of deep water for at least three decades because of structural similarities between them and the extant coral Leptoseris fragilis, which is found only in deep water (90-130 meters) in the Gulf of Aqaba near Eilat, Israel. L. fragilis has evolved two major adaptations to this deep water environment: a modified feeding apparatus and specialized bioluminous cell clusters associated with its symbiotic algae that allows for deep-water photosysnthesis. The modified feeding apparatus consists of secondary openings to the gut, meaning it can filter-feed continuously by expelling waste through an opening separate from the mouth. These openings were present in the microsolenids as shown by a particular skeletal modification essential to them, but there can be no evidence of bioluminous cell clusters in these fossils. A newly discovered microsolenid community from the Matmor Formation (Callovian, Middle Jurassic) of Hamakhtesh Hagadol in the Negev Desert of southern Israel is not consistent with the current paleoenvironmental model derived from L. fragilis. Sedimentological, stratigraphical, and paleontological indicators within the fossil community show it to have been living in extremely shallow-water. Paleoenvironmental evidence for a shallow depth includes the following: (1) ooid-bearing units are found above and below the microsolenid-bearing sediments; (2) the Matmor Formation terminates in a rocky shoreline only a few kilometers to the east, and extends for dozens of kilometers to the west before thickening into deeper sediments; and (3) fossils found with the microsolenids include corals with microatoll form, regular echinoids, terebratulid and rhynchonellid brachiopods, calcareous sponges, and abundant mollusks (especially oysters). These observations require a reevaluation of the use of microsolenid corals as indicators of deep-water environments during the Jurassic.