POSSIBLE EVIDENCE OF EURYHALINITY IN CRETALAMNA APPENDICULATA (LAMNIFORMES, CRETOXYRHINIDAE)

Recent work in the Pari Aike Formation (Maastrichtian?) of Santa Cruz Province, Argentina, has yielded numerous shark teeth, including two nearly complete specimens which we refer to Cretalamna appendiculata, an extinct species of lamniform shark with a broad temporal range (Early Cretaceous—Paleocene) and a nearly world-wide distribution (described from every continent except Antarctica). C. appendiculata has been presumed to be an ecological generalist, and can be found in marine rocks ranging from nearshore to offshore environments. However, these specimens, discovered in fluvial channel deposits, may represent the first evidence that C. appendiculata inhabited freshwater environments, suggesting that this taxon was euryhaline and not strictly a marine species as previously believed. It is possible that these teeth were subject to reworking from the nearshore sediments of the La Anita Formation approximately 100 meters below the discovery site. However, no evidence of reworking is present, and the C. appendiculata material was found in the same lithosome as terrestrial fossils (an ornithopod dinosaur tooth and titanosaur dinosaur limb bones) and other freshwater species (lungfish and gar). Additional geological work to address the possibility of reworking at this site is necessary to further support our hypothesis. If confirmed, these results significantly expand the environmental and behavioral range of C. appendiculata.