A SKELETOCHRONOLOGICAL ASSESSMENT OF FOSSIL AND RECENT BUFO-COGNATUS FROM SOUTH-CENTRAL COLORADO

Age from skeletochronological analysis of phalanges, sex, weight, and snout-vent length were analyzed for a population of Bufo cognatus livi ng in the high altitude San Luis Valley of southcentral Colorado. Only one and two year old toads were found. In general, toad size increase d with age although there was considerable overlap between age groups. Males were consistently smaller than females at all ages. A high prop ortion of false lines occurred in the 1987 season of growth and can be correlated with a drought that occurred during Tune and July of that year. Age and size distribution of fossil B. cognatus from Alamosa For mation sediments in the San Luis Valley were determined from skeletoch ronological analysis of ilial shafts prepared as thin sections. Age st ructure of the fossil assemblages were similar to the modern; false li nes in the fossil ilia may indicate summer drought during ancient time s.