A Review of the Fossil Record of Turtle Reproduction: Eggs, Embryos, Nests and Copulating Pairs (original) (raw)
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Three Ways to Tackle the Turtle: Integrating Fossils, Comparative Embryology, and Microanatomy
Vertebrate Paleobiology and Paleoanthropology, 2012
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 analyses of skeletal development, ontogenetic timing, and bone microstructure in both extant and extinct taxa are used to document patterns and make inferences about the origin of turtles, turtle ingroup relationships, and the evolution of turtle ontogenetic development. The need for a balanced sampling of both cryptodiran and pleurodiran turtle species for future comparative studies is highlighted.
Abstract Adding new taxa to morphological phylogenetic analyses without substan- tially revising the set of included characters is a common practice, with drawbacks (undersampling of relevant characters) and potential benefits (character selection is not biased by preconceptions over the affinities of the ‘retrofitted’ taxon). Retrofitting turtles (Testudines) and other taxa to recent reptile phylogenies consistently places turtles with anapsid-grade parareptiles (especially Eunotosaurus and/or pareiasauromorphs), under both Bayesian and parsimony analyses. This morphological evidence for turtle–parareptile affinities appears to contradict the robust genomic evidence that extant (liv- ing) turtles are nested within diapsids as sister to extant archosaurs (birds and crocodilians). However, the morphological data are almost equally con- sistent with a turtle–archosaur clade: enforcing this molecular scaffold onto the morphological data does not greatly increase tree length (parsimony) or reduce likelihood (Bayesian inference). Moreover, under certain analytic conditions, Eunotosaurus groups with turtles and thus also falls within the turtle–archosaur clade. This result raises the possibility that turtles could simultaneously be most closely related to a taxon traditionally considered a parareptile (Eunotosaurus) and still have archosaurs as their closest extant sister group.
ABSTRACT: Dinosaur reproductive biology is often inferred from the biology of extant taxa; however, taphonomic studies of modern nest sites have focused exclusively on avian, rather than reptilian species. We documented eight Agassiz’s desert tortoise (Gopherus agassizii) nests and ten loggerhead sea turtle (Caretta caretta) nests. Gopherus agassizii excavated burrows up to 70 cm long and laid rigid-shelled eggs 10–12 cm below the burrow floor. The 19 cm 3 12 cm depressions consisted of hard consolidated sand surrounded by a 3–4-cm-high rim and contained 2–5 hatched eggs in a single layer. These hatched egg bottoms represent , 25% of the original egg, and five of 27 contained fully developed dead neonates. Desiccated membrane separated from the egg interior forming pockets that filled with eggshell and sand. Of 106 and 79 eggshell fragments in the hatched egg and surrounding sand, 48% and 23% occurred concave up, respectively. However, the combined numbers of eggshell fragments inside the eggs and in the immediately surrounding sand approximates the 60:40 ratios at in situ avian nests. Therefore, this ratio may provide reliable evidence for hatching sites regardless of the incubation strategy employed by the adult. Caretta caretta nests differed from those of tortoises in their greater depth (, 50 cm) and occurrence in moist, cohesive sand. Clutches contained over 100 pliable-shelled eggs that tore and collapsed upon hatching, without brittle fracture. Failed eggs in two clutches showed five development stages, indicating that the deaths occurred over an extended time period. With the exception of predation, the G. agassizii and C. caretta nests showed no significant eggshell or hatched eggs above the egg chamber.
Zoology, 2008
Sex identification in young sea turtles is challenging. Sea turtle neonates lack external dimorphic characteristics and heteromorphic sex chromosomes. We compared the morphology of the gonads and reproductive ducts of dead formalin-preserved hatchling and post-hatchling Caretta caretta, Dermochelys coriacea, and Chelonia mydas and identified sex-specific differences in these structures that are useful in assigning sex. We tested 11 gross gonadal and reproductive duct characteristics in 57 neonate sea turtles and verified the sex by histological examination. A suite of four characters was found to reliably indicate sex in the three species considered: paramesonephric duct size, mobility of the duct, presence of a complete lumen and gonad mobility. Additionally, gonad shape and edge form were dependable sex-specific characters in cheloniids but not in D. coriacea. Together, these morphological characteristics provide new and reliable methods to quickly distinguish sex in preserved neonate sea turtles without using more extensive histological methods. (J. Wyneken).
THE ORIGIN AND EARLY EVOLUTION OF TURTLES
Annual Review of Ecology and Systematics, 1999
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). The high Homoplasy Index raises concerns about the phylogenetic information content of various morphological characters in broadscale phylogenetic analyses. Such analyses may also suffer from inadequate statements of primary homology. Several such statements that have played an important role in the analysis of turtle relationships (dermal armor, acromion, astragalo-calcaneal complex, hooked fifth metatarsal) are reviewed in detail. An evolutionary scenario for the origin of the turtle bauplan suggests an aquatic origin of turtles, which is supported not only by their sauropterygian relationships, but also by paleobiogeographic and stratigraphic considerations. However, turtle relationships remain labile, and further investigations of their relationships are required, involving molecular and physiological data.
Palaeoecology of Triassic stem turtles sheds new light on turtle origins
2004
We present a rank-free phylogenetic nomenclature for 25 well-established ancient clades of living turtles. This is the first attempt to document fully the nomenclatural history of a clade with the intent of proposing a coherent nomenclatural system to replace the traditional rank-based nomenclature. Because of the imperative to retain connectivity to the literature for information retrieval, due consideration is given to balancing the desire to develop a consistent system against the desire to conserve traditional associations between names, taxa (i.e., clades), and characters. Novel issues and problems that emerged during this review include: the unclear name/clade association of traditional names; the creation of synonymy lists from which to choose a name; difficulties associated with selecting a single criterion for choosing among multiple 'subjectively synonymous' names; identifying authorship for a converted traditional name; and the potential loss of nomenclatural information due to 'functional homonyms.' This work may provide a useful road map to those intent on converting their traditional rank-based nomenclatures to explicitly phylogenetic nomenclatures under the precepts of the PhyloCode.
A nomenclature for fossil and living turtles using phylogenetically defined clade names
Swiss Journal of Palaeontology
Over the last 25 years, researchers, mostly paleontologists, have developed a system of rank-free, phylogenetically defined names for the primary clades of turtles. As these names are not considered established by the PhyloCode, the newly created nomenclatural system that governs the naming of clades, we take the opportunity to convert the vast majority of previously defined clade names for extinct and extant turtles into this new nomenclatural framework. Some previously defined names are converted with minor adjustments. We also define a number of new clade names to close apparent nomenclatural gaps. In total, we establish 113 clade names, of which 79 had already received phylogenetic definitions and 34 are new.