SEXUAL DIMORPHISM AND LIFE HISTORY OF KEICHOUSAURUS HUI (REPTILIA: SAUROPTERYGIA)

A large collection of recently prepared, complete specimens of Keichousaurus hui provides a wealth of new anatomical data for this taxon. Sexual dimorphism call be unambiguously quantified by proportions of the humerus as well as ratios of humerus length to standard length and femoral length. Multivariate (principal components and discriminant) analysis identified ratios most useful in distinguishing the sexes. Sexual maturity was reached in males at approximately 126 SVL, snout-vent length (SVL), and in females by 122 mm SVL. Mean SVL for mature males is approximately 161 SVL, and for mature females, at most 149 mm SVL. Although the last dimension predicts a mean hatchling SVL of approximately 50 mm based oil data from extant squamates, the relationship between mean SVL of mature females and mean SVL of hatchling/neonate in squamates is quite variable. As a result, a mean Value of 40.4 mm SVL for several tiny isolated individuals of Keichousaurus is well within the 95 percent confidence ellipse calculated from data from extant squamates. Therefore, there is not reason to postulate that the common occurrence of tiny individuals of between 33.5 mm and 48.2 mm SVL is the result of spontaneous abortions.