Sahonachelys: a new pelomedusid turtle from Madagascar

Finally
the large reptile tree (LRT, 1840+ taxa) nests a new taxon pretty close to where original authors said it should nest. The LRT cladogram includes a wider gamut of turtles in general with ancestors going back to Ediacaran worms. By contrast the Joyce et al. 2021 cladogram has more closely related pelomedusid turtles from the Late Cretaceous of Madagascar and India.

Figure 1. Sahonachelys skull from Joyce et al. 2021, colorized here based on pareiasaur homologs. The frontas are fused with the parietals, based in basal taxa, like Macrochelys, the alligator snapping turtles. The prefrontals are fused to the nasals.

Joyce et al. wrote:
“A functional assessment suggests that Sahonachelys was a specialized suction feeder that preyed upon small-bodied invertebrates and vertebrates. This is a unique feeding strategy among crown pelomedusoids that is convergent upon that documented in numerous other clades of turtles.”

In the LRT Sahonachelys is not unique, but nests between Pelomedusa (Fig. 3) and two other, long-necked suction feeding turtles, Early Cretaceous Araripemys (Fig. 2) and extant Chelus. Ancestors include the ancestors of box turtles (Terrapene), snapping turtles (Macrochelys).

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.

So, first these turtles snapped,
then they sucked and snapped. Flat-headed Sahonachelys is the transitional taxon in the LRT.

References
Joyce WG et al. 2021. A new pelomedusoid turtle, Sahonachelys mailakavava, from the Late Cretaceous of Madagascar provides evidence for convergent evolution of specialized suction feeding among pleurodires. Royal Society. Open Scence. 8: 210098.
https://doi.org/10.1098/rsos.210098

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