Data from: Using the axial skeleton as armor: mechanical behavior of sea turtle carapaces throughout ontogeny

The shells of turtles serve as protection, yet shell shape and natural
history widely vary among turtles. Here we identify the mechanical
behavior that provides marine turtles, species characterized with fusiform
shells, with biomechanical strength and resilience. The multi-layered
carapacial bone structure seemingly serves a protective role for the
muscles, nerves, and viscera it houses. What are the shell’s material
properties that provide protection?  Most previous work focused
on non-marine turtles that differ in natural history and shell morphology
from marine species. We measured carapacial mechanical behavior of green
turtle (Chelonia mydas), loggerhead (Caretta caretta), and Kemp’s ridleys
(Lepidochelys kempii) across a range of body sizes in juvenile, subadult,
and adults.  Carapace samples were tested using quasi-static
compression to quantify stiffness (Young’s modulus), yield strength, and
toughness. The mechanical characteristics of marine turtle shells are
grossly akin to that of other turtles and driven by the bone’s sandwich
structure. Yet, the material properties indicate that marine turtle shells
are less stiff and strong than those of their freshwater and terrestrial
counterparts. We hypothesize that increased flexibility of the shell may
reflect tradeoffs for life that includes experiencing pressures from
diving somewhat deeply, in marine environments. Shell material properties
also differed among species and ontogenetically. Green turtles had the
stiffest, strongest, and toughest shells while loggerhead carapaces were
the most compliant. Stiffness and yield strength showed positive
relationships with body size which were most pronounced in green turtles
and Kemp’s ridleys. Phylogenetic histories and ecological differences
likely drive this interspecific variation.