Araripemys and the pleurodire problem

Figure 1. Araripemys skull with squamosal fused to quadratojugal and squamosal reinterpreted as the supratemporal here, distinct from Meylan 1996.

Figure 1. Araripemys skull with squamosal fused to quadratojugal and squamosal reinterpreted as the supratemporal here, distinct from Meylan 1996. The purple line on the mandible is a better fit for the upper jawline.

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.

Figure 2. Araripemys overall in dorsal and ventral views, plus manus and pes from Meylan 1996.

Figure 2. Araripemys overall in dorsal and ventral views, plus manus and pes from Meylan 1996.

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.

Figure 2. Chelus frmbiata, the mata-mata has a temporal fenestra. Not sure if it's a lateral or upper type. Note also the mistake made by Dr. Gaffney in overlooking the squamosal and quadratojugal, and mislabeling the supratemporal.

Figure 3. Chelus frmbiata, the mata-mata has a temporal fenestra. Not sure if it’s a lateral or upper type. Note also the mistake made by Dr. Gaffney in overlooking the squamosal and quadratojugal, and mislabeling the supratemporal.

Araripemys nests with
Chelusthe very derived (some might say ‘weird’ and extant mata mata (Figs. 3, 4). 

Figure 4. Chelus, the mata mata extant side-neck turtle.

Figure 4. Chelus, the mata mata extant side-neck turtle.

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.

Figure 5. Subset of the large reptile tree focusing on turtles. Here pleurodires are derived from an earlier sister to Terrapene and turtles are diphyletic with origins among separate small pareiasaurs.

Figure 5. Subset of the large reptile tree focusing on turtles. Here pleurodires are derived from an earlier sister to Terrapene and turtles are diphyletic with origins among separate small pareiasaurs. Elginia is known from cranial material only.

Sterli 2010
studied the origins of Pleurodira using both molecules and morphology (Fig. 6). She reported:

  1. “In the present analysis, separate analyses of the molecular data always retrieve Pleurodira allied to Trionychia” (soft shells).
  2. “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.
Figure 5. Sterli 2010 cladograms attempting to nest the Pleurodira. One tests morphology. The other tests morphology and molecules.

Figure 6. GIF animation (2 frames) of Sterli 2010 cladograms attempting to nest the Pleurodira. One tests morphology. The other tests morphology and molecules. Sorry some of the taxa are illegible at this scale, hence the colors.

Issues with Sterli’s study:

  1. 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.
  2. Steling did not include Elginia, Sclerosaurus and other pertinent out-group taxa. So that’s an issue affecting her results.
  3. Terrapene and Foxemys are not included in the Sterli study.
  4. 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.

And finally,
even Gaffney’s well-respected team mistook the supratemporal for the squamosal because they didn’t use the correct horned outgroups (Fig. 7).

Figure 3. Dorsal views of bolosaur, diadectid, pareiasaur, turtle and lanthanosuchian skulls. The disappearance of the turtle orbit in lateral view occurs only in hard shell turtles.

Figure 7. Click to enlarge. Dorsal views of bolosaur, diadectid, pareiasaur, turtle and lanthanosuchian skulls. The disappearance of the turtle orbit in lateral view occurs only in hard shell turtles.

Coincidentally,
Dr. Darren Naish looked at Araripemys recently. Check out his blog here for more info.

References
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.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s