The feces of the Shasta ground sloth (Nothrotheriops shastense), preserved by the arid climate of the lower Grand Canyon, were collected at various levels and examined by microhistological analyses to identify and quantify plant taxa in the diet. Over 500 pieces of different Shasta sloth coprolites were examined. Sloth dung from the nearby Muav Caves was examined and compared with that from Rampart Cave.
Seventy-two genera of plants were identified in the sloth dung deposited discontinuously from over 40,000 to about 11,000 yr BP. The major plant taxa in the Rampart Cave sloth diets were desert globemallow (Sphaeralcea ambigua = 52%), Nevada mormontea (Ephedra nevadensis = 18%), saltbushes (Atriplex spp. = 7%), catclaw acacia (Acacia greggii = 6%), Cactaceae spp. (= 3%), common reed (Phragmites communis = 5%), and yucca (Yucca spp. = 2%).
Six of the most abundant plants in sloth diets were collected in the environs of Rampart Cave and were analyzed for their energy, fiber and nutrient values. The simulated diets of Rampart Cave sloths averaged 1679 cal/g in digestible gross energy and 7.9% for digestible protein. Apart from a substantial increase in digestible energy and in mormontea there was no unusual change in the sloth diet immediately prior to the time of their extinction.
The ecological role of Nothrotheriops shastense is less dramatically different from that of extant desert herbivores than was previously believed.