Sexual dimorphism, allometry, and vertebral scute morphology were studied in the Malayan flat-shelled turtle, Notochelys platynota (Gray, 1834). Adult males (mean CL = 238.29 ± 50.68 mm, range 130.5-282.0, n = 16) were, on average, larger than adult females (mean CL = 203.48 ± 52.50 mm, range 125.3-330.0, n = 44). The five largest individuals in the study, however, were females (283-330 mm CL). The SDI value for this species was calculated as -1.17. Sexual dimorphism of the shell was not evident when examined by ANCOVA. The regression slopes of males and females differed significantly (P < 0.05) in only one of 26 characters examined. Allometric growth of the shell, however, was evident in N. platynota. Shell shape changed as CL increased proportionally more than shell width, shell height and plastral length (18/26 characters). This allometric growth pattern yields adults with relatively narrower and flatter shells than juveniles. Of 127 specimens examined, 3.9% (n = 5) had five vertebral scutes, 85.0% (n = 108) had six, 10.2 % (n = 13) had seven and 0.8% (n = 1) had eight vertebrals. In specimens with five vertebrals (presumably the ancestral condition), all scutes were large, broader than long, and of similar length. In specimens with six or seven vertebrals, the first four and last vertebrals (Vert6 or 7) were large and broader than long. The smaller supernumerary scutes characteristic of this species were usually found between the fourth and last vertebrals and were occasionally longer than broad (5% of specimens, n = 5). The presence of supernumerary scutes does not affect the relative length of the entire vertebral series, as evidenced by a lack of variation in this character among specimens with five, six and seven vertebrals. Instead, as suggested by an increased width to length ratio of several normal scutes in specimens with six or seven vertebrals, there is a shortening of several normal scutes to accommodate the additional ones. In specimens with six or seven vertebral scutes, the relative lengths of most normal vertebrals (all except Vert1) were noticeably shorter than in specimens with five vertebral scutes. The fourth and last (Vert6 or 7) vertebrals were the shortest of these normal scutes.
Brophy, Timothy R. and Ernst, Carl H., "Sexual Dimorphism, Allometry and Vertebral Scute Morphology in Notochelys platynota (Gray, 1834)" (2004). Faculty Publications and Presentations. Paper 59.