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[dinosaur] Waluchelys, new Triassic turtle from Argentina + Origin and Evolution of Turtle Body Plan





Ben Creisler
bcreisler@gmail.com


A new paper:

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Waluchelys cavitesta gen. et sp. nov.Â

Juliana Sterli, ÂRicardo N. MartÃnez, ÂIgnacio A. Cerda Â& ÂCecilia Apaldetti (2020)
Appearances can be deceptive: bizarre shell microanatomy and histology in a new Triassic turtle (Testudinata) from Argentina at the dawn of turtles.
Papers in Palaeontology (advance online publication)
doi: https://doi.org/10.1002/spp2.1334
https://onlinelibrary.wiley.com/doi/abs/10.1002/spp2.1334


Data archiving statement:
This published work and the nomenclatural acts it contains have been registered with ZooBank: http://zoobank.org/References/9afeecf3-4d4e-4bf5-88ee-4f9b8a6cb9b5

Data for this study are available in the Dryad Digital Repository: https://doi.org/10.5061/dryad.7pvmcvdq7



The origin and homology of the turtle shell is one of the most captivating topics in amniote evolution. In this contribution, we present a new species of turtle from the Late Triassic of Argentina whose peripheral plates raise questions about the homology of these bones in turtles. The external morphology of the peripheral plates of Waluchelys cavitesta gen. et sp. nov. (Testudinata, Australochelyidae) is as in any other turtle, however, appearances can be deceptive. Internally, these plates have an unexpected internal cavity. The absence of structural similarities and of ontogenetic or phylogenetic transitional forms between the peripheral plates of W . cavitesta and other testudinatans might suggest that the periphery of turtles represents a case of deep homology. Furthermore, the present and recent findings suggest that the structure and ossification patterns of the periphery of the turtle shell were more plastic and subject to variation than other elements of the shell, at least in the earliest stages of turtle evolution. These findings also suggest that the typical mesochelydian turtle shell could have been acquired in a twoâstage process.

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Not yet mentioned:

Tyler R. Lyson and Gabriel S. Bever (2020)
Origin and Evolution of the Turtle Body Plan
Annual Review of Ecology, Evolution, and Systematics Vol. 51: (Volume publication date November 2020)
doi: https://doi.org/10.1146/annurev-ecolsys-110218-024746
https://www.annualreviews.org/doi/abs/10.1146/annurev-ecolsys-110218-024746



The origin of turtles and their uniquely shelled body plan is one of the longest standing problems in vertebrate biology. The unfulfilled need for a hypothesis that both explains the derived nature of turtle anatomy and resolves their unclear phylogenetic position among reptiles largely reflects the absence of a transitional fossil record. Recent discoveries have dramatically improved this situation, providing an integrated, time-calibrated model of the morphological, developmental, and ecological transformations responsible for the modern turtle body plan. This evolutionary trajectory was initiated in the Permian (>260 million years ago) when a turtle ancestor with a diapsid skull evolved a novel mechanism for lung ventilation. This key innovation permitted the torso to become apomorphically stiff, most likely as an adaptation for digging and a fossorial ecology. The construction of the modern turtle body plan then proceeded over the next 100 million years following a largely stepwise model of osteological innovation.

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