Data from: Gradual adaptation of bone structure to aquatic lifestyle in extinct sloths from Peru

Non-pathological densification (osteosclerosis) and swelling
(pachyostosis) of bones are the main modifications affecting the skeleton
of land vertebrates (tetrapods) that returned to water. However, a precise
temporal calibration of the acquisition of such adaptations is still
wanting. Here, we assess the timing of such acquisition using the aquatic
sloth Thalassocnus, from the Neogene of the Pisco Formation, Peru. This
genus is represented by five species occurring in successive
vertebrate-bearing horizons of distinct ages. It yields the most detailed
data about the gradual acquisition of aquatic adaptations among tetrapods,
in displaying increasing osteosclerosis and pachyostosis through time.
Such modifications, reflecting a shift in the habitat from terrestrial to
aquatic, occurred over a short geological time span (ca 4 Myr). Otherwise,
the bones of terrestrial pilosans (sloths and anteaters) are much more
compact than the mean mammalian condition, which suggests that the
osteosclerosis of Thalassocnus may represent an exaptation.