Marine turtles are large reptiles that
compensate for high juvenile mortality by producing
hundreds of hatchlings during a long reproductive lifespan.
Most hatchlings are taken by predators during
their migration to, and while resident in, the open
ocean. Their survival depends upon crypticity, minimizing
movement to avoid detection, and foraging efficiently
to grow to a size too difficult for predators to
either handle or swallow. While these behavioral antipredator
tactics are known, changes in morphology
accompanying growth may also improve survival prospects.
These have been only superficially described in
the literature. Here, we compare the similarities and
differences in presumed morphological defenses of
growing loggerhead (Caretta caretta) and Kemp’s ridley
(Lepidochelys kempii) posthatchlings, related species
that differ in growth rate, timing of habitat shift (the
return from oceanic to neritic locations), and size at
maturity. In both species, vertebral spination and carapace
widening increase disproportionally as small turtles
grow, but later in ontogeny, the spines regress,
sooner in ridley than in loggerhead turtles.