EARLIEST DIRECT EVIDENCE OF FISH PREDATION ON ECHINOIDS: BITTEN RHABDOCIDAROID SPINES IN THE MIDDLE JURASSIC (CALLOVIAN) OF SOUTHERN ISRAEL

Echinoids are abundant and well preserved in the Matmor Formation (Middle Jurassic, Callovian) of southern Israel, providing opportunities to test taphonomic and paleoecological models, including those for predator-prey interactions (specifically escalation of predation). A number of rhabdocidaroid spines in this formation have distinct bite marks that show the earliest direct evidence of fish predation on regular echinoids. The Matmor, primarily marls and patch reefs of sponges and corals, was deposited in shallow tropical waters on the western coast of the Neotethys in the Ethiopian Faunal Province. It has a diverse benthic fauna, and cidaroids are especially common as disarticulated spines and test fragments. A set of 1266 spines from subunit 51 of the Matmor Formation exposed in Hamakhtesh Hagadol contains 57 (4.5%) with distinct tooth marks. This figure varied in the field with some localities showing no bite marks and others with up to a third of the spines bitten. Large, flabellate primary spines are most commonly bitten; a few smaller round-shafted secondary spines also show bites. The bites were produced by sharp, pointed, blade-like teeth that either cut notches on the sides of the spine shafts, created doubly-terminated narrow incisions, or made punch-like impressions, leaving rounded pits with circular to oblong outlines. Several spines show multiple bite marks, but it is uncertain whether this was done with a single bite deploying multiple teeth or multiple bites. The sharp-sided bite marks show no serration or that the teeth were in series. The stereom surrounding the bite marks shows no evidence of regeneration or healing. Our bite marks are very similar to those attributed to sharks. A few shark denticles have been recovered from the formation, but no teeth. This may be a preservational effect since there is little phosphatic material in the formation. The diversity of bite marks and their variable orientation suggests that this predation was not simply biting and swallowing of prey but also involved some time for handling, as with many modern fishes. We expected rather high predation pressure in our settings if a latitudinal gradient is considered, but predation intensity on tropical echinoids appears to have been rather low in the Jurassic, a factor significant for hypotheses of echinoid infaunalization.