Araripemys barretoi (Price 1973, Meylan 1996; Early Cretaceous, 120 mya; Figs. 1, 2) is one of the oldest known pleurodires (side-neck turtles). It had a very long neck and a rather low skull. The palate is solid. A lateral temporal fenestra rises from the jawline. The rostrrum was very short. The posttemporal fenestra extended anterior to the jugal. The unguals were arrow-shaped. Metatarsal 5 was a deep crescent. Three fenestrae pierced the plastron. No central bone/interclavicle appears to be present in the plastron.
Distinct from Meylan 1996,
and based on basal turtles, like Elgiinia, the squamosal is actually fused with the quadratojugal and the supratemporal was misidentified as the squamosal.
Distinct from prior phylogenetic studies
the large reptile tree (LRT, 1042 taxa; Fig. 5) nests pleurodires with the box turtle, Terrapenne, rather than as a basal clade derived from Proganochelys, a Triassic turtle unable to withdraw its neck beneath its carapace.
studied the origins of Pleurodira using both molecules and morphology (Fig. 6). She reported:
- “In the present analysis, separate analyses of the molecular data always retrieve Pleurodira allied to Trionychia” (soft shells).
- “Separate analysis of the morphological dataset, by contrast, depicts a more traditional arrangement of taxa, with Pleurodira as the sister group of Cryptodira, being Chelonioidea the most basal cryptodiran clade.” So, molecules do not support morphology in Sterli’s study.
Issues with Sterli’s study:
- Sterli (Fig. 6) used the rhynchocehalian, Sphenoodon, the pareiasaur, Anthodon, and the plesiosaur, Simosaurus, as outgroup taxa to a monophyletic Testudines, excluding or overlooking outgroups recovered by the LRT. Worse yet, who would EVER nest plesiosaurs with pareiasaurs? That’s a big RED FLAG. Clearly Sterli has no idea what turtles are. Flinging random outgroups at a cladogram is not good science. When you don’t have the correct outgroup, you don’t realize that turtles retain a supratemporal, and its not the squamosal.
- Steling did not include Elginia, Sclerosaurus and other pertinent out-group taxa. So that’s an issue affecting her results.
- Terrapene and Foxemys are not included in the Sterli study.
- As Sterli learned (Fig. 6), molecules do not recover the same tree topology as morphology.
Gaffney et al. 2006 looked at pleurodires
in a huge tome about a decade ago. They report: “In order to root the turtle taxa, the main groups of amniotes outside turtles are included as a single taxon. We consider turtles to be the sister group of diapsids, not within diapsids or within pareiasaurs/procolophonids. ” The evidence within the LRT does not support this assertion.
Gaffney et al. 2006 reported:
“We are not dealing with the relationships of extinct groups like pareiasaurs and procolophonids to turtles, because to do so would not alter relationships within turtles.” Gaffney et al. say this because they believed that turtles were monophyletic with Proganochelys at its base. The evidence within the LRT, benefitting from more recent discoveries like Odontochelys, Bunostegos and Sclerosaurus, finds turtles are diphyletic, with soft shells arising distinct from hard shells. THAT greatly affects relationships within turtles. When Elginia starts showing up in turtle trees, then things will settle down into consensus.
even Gaffney’s well-respected team mistook the supratemporal for the squamosal because they didn’t use the correct horned outgroups (Fig. 7).
Gaffney ES, Tong H and Meylan PA 2006. Evolution of the side-necked turtles: the families Bothremydidae, Euraxemydidae, and Araripemydidae. Bulletin of the American Museum of Natural History 300, 1-698.
Meylan PA 1996. Skeletal morphology and relationships of the early Cretaceous side-necked turtle, Araripemys barretoi (Testudines: Pelomedusoides: Araripemydidae), from the Santana Formation of Brazil. Journal of Vertebrate Paleontology 16(1):20-33.
Price L 1973. Quelonio amphichelydia no Cretaceo inferior do nordeste do Brazil. Revista Brasileira de Geociencias 3:84-96.
Sterli J 2010. Phylogenetic relationships among extinct and extant turtles: the position of Pleurodira and the effects of the fossils on rooting crown-group turtles. Contributions to Zoology 79(3):93–106.