Thalassemys bruntrutana (Rütimeyer 1873; Joyce, Mäuser and Evans 2021; Late Jurassic; 1.2m) is a basal sea turtle from the Solnhofen Formation. The shell is disc-like and the skull is small. Manual digit 5 is the longest and metacarpal 4 is the longest.

Chelonia mydas (formerly Chelone, Linneaus 1758) is the living green sea turtle with limbs transformed into flippers. Note the different labels applied to the skull bones. Skull shown above C. mydas is C. longiceps with a longer premaxilla, lower skull and shorter supraoccipital.

Derived from a sister toTrionyx and Odontochelys, Chelonia struggles on land to lay eggs, but is adapted to long distance oceanic journeys.

Note the lateral extension of the fifth distal tarsal to widen the hind flipper. Sea turtles have the longest fingers and toes of any turtle.

Santanachelys gaffneyi (Hirayama 1998, Early Cretaceous, 110 mya, 20 cm long, carapace: 14.5 cm) was once considered the oldest sea turtle, but now Desmatochelys is ten million years older.. Note the small flippers. The skull is specialized in the manner of later chelonioids, with large interorbital foramina that are indicative of huge lachrymal salt glands surrounding the eyes. The small overall size indicates a hatchling or juvenile.

Caretta caretta (Linneaus 1758; aka Thalassochelys Rafinesque 1814) is the extant loggerhead turtle. The flippers (hands) are much larger in this much larger than in the related Santanachelys.

Desmatochelys padillai (Cadena and Parham 2015) is ten million years older than Santanachelys, and larger than many extant sea turtles. It nests with Chelonia in the LRT.

Cadena EA and Parham. JF 2015. Oldest Known Marine Turtle? A New protostegid from the Lower Cretaceous of Colombia. PaleoBios. 32(1).

Hirayama R 1998. Oldest known sea turtle. Nature 392 (6677): 705–708.

Joyce WG, Mäuser M and Evers SW 2021. Two turtles with soft tissue preservation from the platy limestones of Germany provide evidence for marine flipper adaptations in Late Jurassic thalassochelydians. PLoS ONE 16(6): e0252355. https://doi.org/10.1371/journal.pone.0252355

Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.

Rütimeyer L 1873. Die fossilen Schildkröten von Solothurn und der übrigen Juraformation. Neue Denkschriften der allgemeinen Schweizerischen Gesellschaft für die gesamten Naturwissenschaften 25:1–185.

wiki/Chelonia
wiki/Thalassemys
wiki/Desmatochelys
wiki/Loggerhead_sea_turtle