Mosaic morphology in Podocnemididae revealed by a new turtle from the Middle Miocene La Venta Biome, Colombia

A new genus and species of podocnemidid turtle, Shakiremys colombiana, is described here from the Middle Miocene La Venta Biome, located in south-central Colombia. The new taxon is represented by two specimens: one consisting of a complete skull and articulated shell, and the other of an articulated shell only. Shakiremys colombiana is distinguished from other podocnemidids by the following combination of features: intermediate roofing of the temporal emargination; a jugal retracted from the orbital margin; a flatter, more rectangular carapace outline; peripherals 2 with a short, protruding anteromedial margin; vertebral scute 1 narrower than the others and not reaching peripherals 1; the gular scute reaching the pectorals and completely separating the humerals; and anterior plastral lobe margin almost straight. It also has an additional mosaic of characteristics found in Podocnemidinae, Erymnochelyinae and Peltocephalinae. A phylogenetic analysis recovered Sh. colombiana as the basalmost member of a large clade that includes both Erymnochelyinae and Peltocephalinae. Additionally, computed tomography was used to reconstruct and compare the neuroanatomical features of Sh. colombiana with other podocnemidids. The mosaic traits observed in Sh. colombiana are interpreted as advantageous for a broader dietary and ecological spectrum, potentially including an omnivorous diet, and the ability to thrive in various aquatic environments, ranging from blackwater to whitewater habitats. This ecological versatility may have offered a competitive advantage for Sh. colombiana within the diverse palaeoecosystem of La Venta, where multiple podocnemidid and chelid turtle species coexisted.