Taylor, T., 2004. Decay on the Delta: Estimating time-since-death for marine mammal carcasses in the northern Gulf of California, Mexico. Gulf of California Conference, Tucson, AZ, June, 2004.
Marine mammal carcasses decay after death. Their rate and pattern of decay is important to the use of carcasses in surveys of the living fauna and also to interpretations of fossil skeletons. I observed nine carcasses of marine mammals in the northern Gulf of California during survey trips in December 2001, December 2002, and March 2003. I found carcasses of four species known from the northern Gulf of California: Bottlenose Dolphin (Tursiops truncatus, 4 carcasses), California Sea Lion (Zalophus californianus, 2 carcasses), Balaenoptera spp. (Balaenoptera physalus or edeni, 2 carcasses), and Long-beaked Common Dolphin (Delphinus capensis, 1 carcass). Two of the Bottlenose Dolphin carcasses were observed during both the December 2001 and 2002 trips, providing 11 observations of nine carcasses.
My preliminary results suggest six taphonomic stages: Fresh/Bloat, Intact Mummy, Skull/Tail Exposure, Body Breach, Disarticulated Bones, and Scattered Bones. Stage 1: Fresh/Bloat is when the carcass has not yet degassed, the tongue, eyes, and most teeth are still present, and body fluids are present in or around the carcass. Stage 2: Intact Mummy is after the carcass has degassed and becomes dehydrated, tongue, eyes, and most teeth are missing, and the skin becomes leathery. Stage 3: Skull/Tail Exposure is when the skin around the rostrum is gone, the caudal vertebrae are exposed, and the carcass is very dehydrated. Stage 4: Body Breach (i.e. Bag o’ Bones) is when thoracic and lumbar vertebrae along with ribs are exposed, the skin is flaking, and the carcass is completely dehydrated. Stage 5: Disarticulated Bones (i.e. Pile o’ Bones) is when tendons and ligaments holding the bones together dry and become brittle and bones start to disarticulate, some skin and tendon may still be present, and bones may be greasy. Stage 6: Scattered Disarticulated Bones is when very little skin and tendon is present, bones are scattered over an area larger than the initial carcass, and bones are in some stage of bleaching.
I found one carcass in Stage 1, four carcasses in Stage 2, three carcasses in Stage 3, one carcass in Stage 4, one carcass in Stage 5, and one carcass in Stage 6. The two Bottlenose Dolphin carcasses that were observed in subsequent years were initially in Stage 2; the following year one carcass remained in Stage 2 while the other carcass was found in Stage 3 of decay. Based on published description of whale decay in the North Sea, and human decay in humid and arid environments, I estimate that Stage 1 is a few weeks in duration, Stage 2 is typically up to three to five years long, Stages 3, 4, and 5 are one to four years each, and Stage 6 can be as long as five years.