Turtles all the way down: loggerheads at the root of the chelonian tree

  title={Turtles all the way down: loggerheads at the root of the chelonian tree},
  author={Tyler R. Lyson and Scott F. Gilbert},
  journal={Evolution \& Development},
The recent discovery of the oldest and most primitive stem turtle, Odontochelys semitestacea (Li et al. 2009), from the lower Upper Triassic of China reopens the debate regarding the origin of the turtle shell, the paleoecology of basal turtles (terrestrial or aquatic), and the placement of turtles among amniotes. The debate surrounding the origin of the shell dates back to Cuvier (1800–1805) with two competing hypotheses. The de novo hypothesis, argues that the carapace (dorsal shell) formed… 
Evolutionary Origin of the Turtle Shell
A model of shell assembly that makes predictions for the as-yet unestablished history of the turtle stem group is built on by integrating novel data for Eunotosaurus africanus, which is congruent with molecular-based divergence estimates for the lineage, and remains viable whether turtles originated inside or outside crown Diapsida.
Report Evolutionary Origin of the Turtle Shell
This model is built on by integrating novel data for Eunotosaurus africanus—a Late Guadalupian (w260 mya) Permian reptile inferred to be an early stem turtle and integrates outgrowths of intra-membranous bone from the perichondrium of the developingribs and thoracolumbar vertebrae.
Evolutionary origin of the turtle skull
High-resolution computed tomography and a novel character/taxon matrix are used to study the skull of Eunotosaurus africanus, a 260-million-year-old fossil reptile from the Karoo Basin of South Africa, whose distinctive postcranial skeleton shares many unique features with the shelled body plan of turtles.
Turtles …… again
  • A. Burke
  • Medicine
    Evolution & development
  • 2009
Turtles have always presented a puzzle for evolutionary biologist because of their abrupt appearance in the fossil record and the difficulty in imagining a functional intermediate between a typical tetrapod and the unique chelonian anatomy.
Evolution and palaeoecology of early turtles: a review based on recent discoveries in the Middle Jurassic
It is demonstrated here that, by documenting yet unknown stages in the evolution of several morphological structures, these three species give stronger support to the model of an extended phylogenetic stem for turtles.
Triassic turtles from Pangea: The legacy from South America
Abstract The Triassic is a key period in turtle evolution for three main reasons: First, the oldest fully shelled body-fossil records of the clade Testudinata come from Late Triassic (Norian) rocks.
Evolutionary developmental perspective for the origin of turtles: the folding theory for the shell based on the developmental nature of the carapacial ridge
The turtle body plan can be explained with knowledge of vertebrate anatomy and developmental biology, consistent with the evolutionary origin of the turtle suggested by the recently discovered fossil species, Odontochelys.
Three Ways to Tackle the Turtle: Integrating Fossils, Comparative Embryology, and Microanatomy
Herein we review a series of case studies covering the evolution and phylogenesis of turtles, and the ontogenetic development of one of the most peculiar body plans within the Craniota. Comparative
Homology of the enigmatic nuchal bone reveals novel reorganization of the shoulder girdle in the evolution of the turtle shell
The turtle shell represents a unique modification of the ancestral tetrapod body plan. The homologies of its approximately 50 bones have been the subject of debate for more than 200 years. Although
Reptilian heart development and the molecular basis of cardiac chamber evolution
These findings provide a molecular mechanism for the evolution of the amniote ventricle, and support the concept that altered expression of developmental regulators is a key mechanism of vertebrate evolution.


A thin-shelled reptile from the Late Triassic of North America and the origin of the turtle shell
The novel observations of Chinlechelys tenertesta lend support to the hypothesis that the turtle shell was originally a complex composite in which dermal armour fused with the endoskeletal ribs and vertebrae of an ancestral lineage instead of forming de novo.
An ancestral turtle from the Late Triassic of southwestern China
A new 220-million-year-old turtle from China is described that documents an intermediate step in the evolution of the shell and associated structures and shows that the turtle shell is not derived from a fusion of osteoderms.
The Origin of the Turtle Body Plan: Bridging a Famous Morphological Gap
In pareiasaurs, the osteoderms represent the precursors of the chelonian shell and the morphology of the anterior region is consistent with the idea that the shoulder girdle in turtles has migrated posteriorly into the rib cage.
A critical reexamination of turtle relationships continues to support a sister-group relationship of turtles with a clade of marine reptiles, Sauropterygia, within crown-group Diapsida (Sauria), and an aquatic origin of turtles is suggested.
Morphogenesis of the turtle shell: the development of a novel structure in tetrapod evolution
An anatomical investigations into plastron and carapace formation in the red‐eared slider, Trachemys scripta, and the snapping turtle, Chelydra serpentina suggest that the rib is organizing dermal ossification by secreting paracrine factors.
The ontogeny of the shell in side‐necked turtles, with emphasis on the homologies of costal and neural bones
An alternative structural hypothesis for the neural reduction and, ultimately, the complete loss of the neural series is proposed and the complete reduction of neurals in Emydura spp.
Palaeoecology of Triassic stem turtles sheds new light on turtle origins
  • W. Joyce, J. Gauthier
  • Biology, Medicine
    Proceedings of the Royal Society of London. Series B: Biological Sciences
  • 2004
The palaeoecology of extinct turtles is investigated by first demonstrating that the forelimbs of extant turtles faithfully reflect habitat preferences, and it is found that although the common ancestor of all living turtles was aquatic, the earliest turtles clearly lived in a terrestrial environment.
How the turtle forms its shell: a paracrine hypothesis of carapace formation.
It is shown here that the carapacial ridge (CR) is critical for the entry of the ribs into the dorsal dermis, and that the maintenance of the CR and its ability to attract the migrating rib precursor cells depend upon fibroblast growth factor (FGF) signaling.
Reptile phylogeny and the interrelationships of turtles
The results refute earlier hypotheses that turtles are related to parareptiles, i.e. to procolophonids or pareiasaurs, and strongly supports a monophyletic Parareptilia, sister-group of a monphyletic Eureptilia.
A plywood structure in the shell of fossil and living soft-shelled turtles (Trionychidae) and its evolutionary implications
It is hypothesised that the evolutionary success of soft-shelled turtles is tied to this plywood-like structure of the skin and bone, resulting in decreased mineral needs for hard tissues, improved camouflage and hunting performance, biomechanical stability of the shell, as well as overall increased agility and short-term swimming boosts.