Data from: Shell geometry and habitat determination in extinct and extant turtles (Reptilia: Testudinata)

A number of means, including forelimb proportions and shell bone histology
have been used to infer the paleoecology of extinct turtles. However, the
height to width ratio of the shell (as a one-parameter shell model) has
been dismissed because of its unreliability, and more complex aspects of
shell geometry have generally been overlooked. Here we employ a more
reliable, three-parameter geometric model of the shell outline in anterior
view as a means to assess turtle paleoecology. The accuracy of predictions
of extant turtle ecology based on our three-parameter shell model is
comparable to that derived from forelimb proportions when distinguishing
between three ecological classes (terrestrial, semi-aquatic and aquatic).
Higher accuracy is obtained when distinguishing between two classes
(terrestrial and non-terrestrial) since the contours of aquatic and
semi-aquatic turtles are often very similar. Our model classifies
Proterochersis robusta, a stem turtle from the Late Triassic of Germany,
as non-terrestrial, and likely semi-aquatic. Our method, combined with
inferences based on limb proportions, indicates a diverse range of
ecotypes represented by Late Triassic stem turtles. This implies that the
ecological diversification of stem-group turtles may have been rapid, or a
substantial period of currently cryptic diversification preceded the first
fossil appearance of the turtle stem lineage during the Late Triassic.