de la Fuente et al. 2020 focus on
Triassic hard-shell turtles from South America.
Highlights from de la Fuente et al.
“We report new information about the oldest turtles from South America.”
Unfortunately, the oldest turtles are not the most primitive. Joyce 2007 wrote: “Currently there is little reason to doubt that Proganochelys quenstedti Bauer from the Upper Triassic of Europe is the most primitive well-understood representative of Testudinata.”
That has been wrong since 2016. Adding taxa to the large reptile tree (LRT, 1740+ taxa) sheds new light on the dual origin of turtles, with soft-shell turtles distinct from and parallel to hard-shell turtles from different small, horned pareiasaurs. We didn’t know that in 2007, but we’ve known this for the last four years, so de al Fuente is working with old data and traditions.
“We discuss the putative ichnological Triassic record of turtles.”
Turtle digits making imprints are interesting, especially since turtle arms extend anteriorly, not laterally, as in more primitive hard-shell turtles like Meiolania (Fig. 1) and most tetrapods.
“Triassic testudinatans show different strategies in building up the shell periphery.”
But if they don’t include the most primitive hard-shell turtles, Niolamia (Fig. 3) and Meiolania (Fig. 1), then de al Fuente et al. 2020 are not starting from the beginning, nor do they employ valid outgroups.
“We discuss new perspectives on the origin and early evolution of the turtle shell.”
Those new perspectives include irrelevant turtle-mimic taxa, like Pappochelys and Eorhynchochelys and omit all pareiasaurs and pre-pareiasaurs, Stephanospondylus and Carbonodraco. Without a valid phylogenetic contact and foundation, the whole study is somewhere between shaky and doomed.
de la Fuente et al. consider
Odontochelys semitestacea (Fig. 2) from the Carnian of China, “the undisputed sister taxon” of turtles.
This is only half right. Adding taxa shows Odontochelys is basal to soft-shell turtles only. Sclerosaurus and Arganaceras are outgroup taxa not mentioned by de la Fuente et al. Hard-shell turtles have a different lineage arising from pareiasaurs (Fig. 3) which was omitted or overlooked by de al. Fuente et al. 2020.
de la Fuente et al. continue
“and some putative successive sister group taxa were found in Middle and Late Triassic rocks (e.g., Pappochelys rosinae from the Ladinian of Germany, Eorhynchochelys yuantouzhuensis from the Carnian of China).”
Adding taxa shows Pappochelys is a basal placodont. Eorhynchchelys is closer to Acleistorhinus. I’m still wondering when turtle workers are going to add taxa to confirm what the LRT recovered by minimizing taxon exclusion, rather than purposefully cherry-picking traditional taxa and omitting taxa tested against all other candidates and therefore shown to be valid.
de la Fuente et al. continue
“These three facts highlight the importance of the Triassic for the origin and early evolution of turtles.”
These are not facts. Simply adding taxa shows these were untested hypotheses falsified in 2016 by taxon inclusion. Let the software do what it does best. Keep your biases, traditions and cherry-picking out of it.
Latest additions to the LRT
Recently we looked at Palaeochersis, a third Triassic turtle derived from the late-surviving, most primitive turtles with horns (Fig. 3), not the traditional other way around. Horned turtles are also from South America, but were overlooked by de la Fuente, Sterli and Krapovickas 2020 because they believed traditional myths invalidated in 2016,
de la Fuente MS, Sterli J and Krapovickas V 2020. Triassic turtles from Pangea: The legacy from South America. Journal of South American Earth Sciences 102910
Joyce WG 2007. Phylogenetic relationships of Mesozoic turtles. Bulletin of the Peabody Museum of Natural History 48(1):3–102..
Abstract from The Dual Origin of Turtles from Pareiasaurs
“The origin of turtles (traditional clade: Testudines) has been a vexing problem in paleontology. New light was shed with the description of Odontochelys, a transitional specimen with a plastron and teeth, but no carapace. Recent studies nested Owenetta (Late Permian), Eunotosaurus (Middle Permian) and Pappochelys (Middle Triassic) as turtle ancestors with teeth, but without a carapace or plastron. A wider gamut phylogenetic analysis of tetrapods nests Owenetta, Eunotosaurus and Pappochelys far from turtles and far apart from each other. Here dual turtle clades arise from a clade of stem turtle pareiasaurs. Bunostegos (Late Permian) and Elginia (Late Permian) give rise to dome/hard-shell turtles with late-surviving Niolamia (Eocene) at that base, inheriting its Baroque horned skull from Elginia. In parallel, Sclerosaurus (Middle Triassic) and Arganaceras (Late Permian) give rise to flat/soft-shell turtles with Odontochelys (Late Triassic) at that base. In all prior phylogenetic analyses taxon exclusion obscured these relationships. The present study also exposes a long-standing error. The traditional squamosal in turtles is here identified as the supratemporal. The actual squamosal remains anterior to the quadrate in all turtles, whether fused to the quadratojugal or not.”