Ninjemys is now the most primitive hard-shell turtle.
It was derived from the small horned pareiasaur, Elginia mirabilis (Fig 1) in the LRT (Fig 2). Elginia was derived from the large horned pareiasaur, Bunostegos. Soft-shell turtles have a different ancestry (Fig 2) derived from different small horned pareiasaurs.
Described over a century ago by Woodward 1888,
Ninjemys (Fig 1) is known from the Pleistocene of Australia (1mya). Elginia is known from the Late Permian of Scotland and China (260mya). That’s 259 million years of stasis for the first known hard-shell turtle to have a carapace and plastron. Other meiolaniids, Niolamia (Fig 1) from South America and hornless Proganochelys from Europe, confirm a worldwide distribution of basalmost hard-shell turtles with armored tails plodding across Pangaea during the Triassic.
Today
in the large reptile tree (LRT, 2081 taxa, subset Fig 2) Ninjemys (Fig 1) is just one more addition to the well-established hard-shell turtle clade. This potentially exciting news at the base of this clade turns out to be nothing but old news eight years after this phylogenetic recovery was announced here and here. Back then turtle experts did not want the small horned pareiasaur hypothesis of turtle interrelationships published, but you can read the illustrated manuscript here on ResearchGate.net (Peters unpublished).
Taxon exclusion remains the number one problem in paleontology.
Traditionally the turtle origin problem has been the omission of pareiasaurs in general and small horned pareiasaurs in particular. Does anyone else find this surprising and disheartening that turtle experts continue to omit these taxa from their own studies eight years later? In March 2022 Dr. Hans-Dieter Sues explained his own hypothesis of turtle origins in a PaleoTalks video here, but again omitted small horned pareiasaurs. For those new to paleontology, that’s how it works. Turtle experts give the impression that they are scientists without curiosity or competitive spirit. Alternatively, the outdated Benton textbook might be the problem.
In your own paleo career
don’t be afraid to add taxa. Don’t avoid competitive studies. Embrace them. Test them. Be brave. Explore. Experiment. Make mistakes. Make discoveries.
Owen1881
mistakenly described and figured this specimen as Varanus (Megalania) priscus.
Woodward 1888
named the partial skull specimen Meiolania oweni.
A century later, Gaffney 1992
renamed the specimen Ninjemys to honor the Teenage Mutant Ninja turtles franchise. He wrote, “Ninja, in allusion to that totally rad, fearsome foursome epitomizing shelled success; emys, turtle.” Gaffney wrote, “Because of this unique morphology, there is no outgroup to provide comparisons.” In the LRT taxa Elginia and Bunostegos (Fig 1) and their ancestors are those outgroup taxa. They are mentioned by no other workers relative to turtles.
The identities of the skull bones in Ninjemys and Elginia
are homologized with colors here (Fig 1). Posterior skull identities (e.g. squamosal, supratemporal) differ from Gaffney’s identifications because he did not realize both clades of turtles arose from horned pareiasaurs like Elginia (Fig 1) and Sclerosaurus.
References
Geffney ES 1992. Ninjemys, a new name for “Meiolania” oweni (Woodward), a Horned Turtle from the Pleistocene of Queensland. American Museum Novitates. 3049: 1–10.
Woodward AS 1888. Notes on the Extinct Reptilian Genera Megalania, Owen, and Meiolania, Owen. Annals and Magazine of Natural History. Series 6. 1(1): 85–89.
Peters D unpublished. The dual origin of turtles from pareiasaurs. researchgate.net/The_dual_origin_of_turtles_from_pareiasaurs
The Pterosaur Heresies 