Description
The olive ridley is a small extant sea turtle, with an adult carapace length averaging 60 to 70 cm 1. The heart-shaped carapace is characterized by four pairs of pore-bearing inframarginal scutes on the bridge, two pairs of prefrontals, and up to nine lateral scutes per side.1,2 Olive ridleys are unique in that they can have a variable and asymmetrical lateral scute count ranging from five to nine plates on each side, with six to eight being most commonly observed.1 Each side of the carapace has 12–14 marginal scutes. The carapace is flattened dorsally and highest anterior to the bridge. It has a medium–sized, broad head that appears triangular from above.1,2 The head's concave sides are most obvious on the upper part of the short snout. It has paddle-like forelimbs, each having two anterior claws 1. The upperparts are grayish green to olive in color, but sometimes appear reddish due to algae growing on the carapace 2. The bridge and hingeless plastron of an adult varies from greenish white in younger individuals to a creamy yellow in older specimens 1.
Hatchlings are dark gray with a pale yolk scar, but appear all black when wet 1. Carapace length ranges from 37–50mm 2. A thin white line borders the carapace, as well as the trailing edge of the fore and hind flippers.2 Both hatchlings and juveniles have serrated posterior marginal scutes, which become smooth with age. Juveniles also have three dorsal keels; the central longitudinal keel gives younger turtles a serrated profile, which remains until sexual maturity is reached.1
Olive ridleys rarely weigh over 50 kilograms. A study in Oaxaca, Mexico, reported a sample of adults that ranged from 25 to 46 kilograms; adult females weighed an average of 35.45 kg (n=58), while adult males weighed significantly less averaging 33.00 kg (n=17). Hatchlings usually weigh between 12.0 to 23.3 grams. Adults are somewhat sexually dimorphic. Mature males have a longer and thicker tail, which is used for copulation,1 and the presence of an enlarged and hooked claw on the males' front flipper allows them to grasp the female carapace during copulation. Males also have a longer, more tapered carapace than females, which have a round, dome-like carapace.1 Males also have a more concave plastron, believed to be another adaptation for mating. The plastra of males may also be softer than females.2
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