TAPHONOMIC ANALYSIS OF SHORTFIN MAKO SHARK (ISURUS OXYRINCHUS) TEETH TUMBLED IN SILICICLASTIC AND CARBONATE SEDIMENTS

Elasmobranchs originated in the Late Ordovician, and since then, they have been represented in the fossil record based primarily on their teeth, which are used to determine species. However, little is known about how shark teeth are preserved in different environments. Here, we tumbled anterior teeth from the Shortfin Mako Shark (Isurus oxyrinchus) in siliciclastic and carbonate sediment to determine if different environments (as represented by the sediments) yield unique preservational signatures and/or loss of species-specific information. For the first experiment, we tested three types of sediment (siliciclastic granules, coarse sand with granules, and coarse sand) on anterior teeth of similar size; the next experiment tested three types of carbonate sediments (carbonate sand, carbonate sand with invertebrate fragments, and carbonate pebbles). After tumbling for 5- to 10-hr intervals, the teeth were dried, weighed and examined for abrasion, microfractures, luster/color change, and edge rounding. Results revealed that all teeth were better preserved in carbonate than siliciclastic sediments. In siliciclastic sediments, basals were more abraded than crowns, and also had slight microfractures and color change; crowns had more luster loss and edge rounding. Teeth tumbled in carbonates had limited abrasion and fragmentation on basals. Unexpectedly, teeth tumbled in carbonate sediments experienced more weight loss after 100 hrs of tumbling than siliciclastic sediments. Overall, the shark teeth remained intact and distinguishable as to species regardless of sediment type. In summary, shark teeth have unique taphonomic signatures related to the sediments that they occur in and are remarkably robust against preservational loss in the fossil record.