Bones on the Beach: Marine Mammal Taphonomy of the

How well does a death assemblage of marine mammal bones reflect the diversity, species composition, and propor-tion of bone types in the living fauna? Marine mammal re-mains were surveyed along the beaches of the Colorado Riv-er delta, Baja California, Mexico. Three carcasses and 470 bones were found among 112 localities along 4.0 km of shoreline. The location of each site was recorded and each bone was identified, photographed, and measured and its taphonomic condition was noted. The proportion of bone types found was compared to the proportions known in liv-ing marine mammals. The list of species found as bones was compared to the list of species known to live in the northern Gulf of California. The maximum skeletal ratio of skull:vertebrae:ribs:pha-langes:girdles/limbs in a typical Gulf of California marine mammal is 1:74:30:56:16. The 28 skulls and 442 post-cra-nial bones found provided a skeletal ratio of 1:12:3:1:1. Al-though vertebrae are the most common bones in the bone as-semblage, only 316 were found, not the;2,000 predicted by the 28 skulls, indicating that vertebrae are under-represent-ed. Therefore, skulls provide the best estimate of the mini-mum number of individuals. Smaller bones appear to be more easily destroyed, buried, or transported away. Most vertebrae were in good condition, suggesting that most bones arrived on the beach recently