Paper No. 127-42
Presentation Time: 9:00 AM-6:30 PM
FIRST BRYOZOAN FAUNA DESCRIBED FROM THE JURASSIC TROPICS: SPECIMENS FROM THE MATMOR FORMATION (MIDDLE JURASSIC, UPPER CALLOVIAN) IN SOUTHERN ISRAEL
Several specimens of cyclostome bryozoans have been collected from the Matmor Formation (Upper Callovian) exposed in Makhtesh Gadol of the Negev Highlands in southern Israel. All were found encrusting columnals and calyx fragments of the crinoid Apiocrinites negevensis and spines of the cidaroid echinoid Rhabdocidaris in Subunit 51 of the formation, which is in the Quenstedtoceras (Lamberticeras) lamberti Zone. The Matmor sediments were deposited very close to the paleoequator in the Ethiopian Province of the Tethyan Faunal Realm. Thus far in our investigation we have identified two species of the genus Stomatopora, two species of Hyporosopora, and one species of an Oncousoecia-like bryozoan (which is an early example of a cyclostome with adventitious lateral branching). This subunit of the Matmor is also richly fossiliferous with brachiopods, corals, and mollusks, but none of these are bryozoan-encrusted. All of the bryozoans appear to have occupied upward-facing, non-cryptic surfaces (cf. several species of serpulid and sabellid tubeworms that dominate cryptic surfaces.) The paleoenvironment was a shallow water embayment with a marly substrate. Crinoids and small corals were likely the pioneers on this soft bottom, providing increasing amounts of skeletal debris to facilitate the settlement of bryozoans and other invertebrates. Fine sediment periodically buried these patches in thick marl during storms, limiting diversity and keeping this community in its early successional stages. The Matmor bryozoans are the first to be systematically described from tropical paleolatitudes of the Jurassic. This assemblage of five species is low in diversity compared to equivalent bryozoan faunas in Europe, which can have three to five times as many species. This lower diversity in the Jurassic tropics is not unexpected considering Cretaceous and Cenozoic examples of tropical bryozoan faunas. Whereas the bryozoans from the Matmor Formation likely include new species, the genera are similar to those found in the Middle Jurassic of Europe and North America. There do not appear to be endemic taxa here that later spread to higher latitudes. The Matmor bryozoans lack erect colonies, though, which is a significant difference from their European counterparts.