Academic literature on the topic 'Chelonioidea'

AbstractTurtle remains ascribed to the family Cheloniidae (Testudines, Cryptodira, Chelonioidea), collected from the lamarcki zone (Middle Turonian) at Wüllen (NW Germany) are described. The material consists of a right humerus, a scapula, a complete costalia, and costalia fragments of a single individual with the humerus indicating a primitive cheloniid of the ‘toxochelyid grade’. The present material, as well as previously recorded chelonioid humeri from the Cenomanian and Turonian of Germany illustrate a progressive diversification of chelonioids during the early Late Cretaceous.

Knowledge of the early evolution of sea turtles (Chelonioidea) has been limited by conflicting phylogenetic hypotheses resulting from sparse taxon sampling and a superficial understanding of the morphology of key taxa. This limits our understanding of evolutionary adaptation to marine life in turtles, and in amniotes more broadly. One problematic group are the protostegids, Early–Late Cretaceous marine turtles that have been hypothesised to be either stem-cryptodires, stem-chelonioids, or crown-chelonioids. Different phylogenetic hypotheses for protostegids suggest different answers to key questions, including (1) the number of transitions to marine life in turtles, (2) the age of the chelonioid crown-group, and (3) patterns of skeletal evolution during marine adaptation. We present a detailed anatomical study of one of the earliest protostegids,Rhinochelys pulchricepsfrom the early Late Cretaceous of Europe, using high-resolution μCT. We synonymise all previously named European species and document the variation seen among them. A phylogeny of turtles with increased chelonioid taxon sampling and revised postcranial characters is provided, recovering protostegids as stem-chelonioids. Our results imply a mid Early Cretaceous origin of total-group chelonioids and an early Late Cretaceous age for crown-chelonioids, which may inform molecular clock analyses in future. Specialisations of the chelonioid flipper evolved in a stepwise-fashion, with innovations clustered into pulses at the origin of total-group chelonioids, and subsequently among dermochelyids, crown-cheloniids, and gigantic protostegids from the Late Cretaceous.

Sea turtles (Chelonioidea) are a prominent group of modern marine reptiles whose early history is poorly understood. Analysis of exceptionally well preserved fossils of Bouliachelys suteri gen. et sp. nov., a large-bodied basal protostegid (primitive chelonioid) from the Early Cretaceous (Albian) of Australia, indicates that early sea turtles were both larger and more diverse than previously thought. The analysis implies at least five distinct sea turtle lineages existed around 100 million years ago. Currently, the postcranially primitive Ctenochelys and Toxochelys are interpreted as crown-group sea turtles closely related to living cheloniids (e.g. Chelonia ); in contrast, the new phylogeny suggests that they are transitional (intermediate stem-taxa) between continental testudines and derived, pelagic chelonioids.

Resolving the phylogeny of sea turtles is uniquely challenging given the high potential for the unification of convergent lineages due to systematic homoplasy. Equivocal reconstructions of marine turtle evolution subsequently inhibit efforts to establish fossil calibrations for molecular divergence estimates and prevent the accurate reconciliation of biogeographic or palaeoclimatic data with phylogenetic hypotheses. Here we describe a new genus and species of marine turtle, Asmodochelys parhami , from the Upper Campanian Demopolis Chalk of Alabama and Mississippi, USA represented by three partial shells. Phylogenetic analysis shows that A. parhami belongs to the ctenochelyids, an extinct group that shares characteristics with both pan-chelonioids and pan-cheloniids. In addition to supporting Ctenochelyidae as a sister taxon of Chelonioidea, our analysis places Protostegidae outside of the Chelonioidea crown group and recovers Allopleuron hofmanni as a stem dermochelyid. Gap excess ratio (GER) results indicate a strong stratigraphic congruence of our phylogenetic hypothesis; however, the highest GER value is associated with the phylogenetic hypothesis of marine turtles which excludes Protostegidae from the Cryptodira crown group. Ancestral range estimations derived from our phylogeny imply a European or North American origin of Chelonioidea in the middle-to-late Campanian, approximately 20 Myr earlier than current molecular divergence studies suggest.

Modern marine turtles (chelonioids) are the remnants of an ancient radiation that roots in the Cretaceous. The oldest members of that radiation are first recorded from the Early Cretaceous and a series of species are known from the Albian-Cenomanian interval, many of which have been allocated to the widespread but poorly defined genus Rhinochelys, possibly concealing the diversity and the evolution of early marine turtles. In order to better understand the radiation of chelonioids, we redescribe the holotype and assess the taxonomy of Rhinochelys amaberti Moret (1935) (UJF-ID.11167) from the Late Albian (Stoliczkaia dispar Zone) of the Vallon de la Fauge (Isère, France). We also make preliminary assessments of the phylogenetic relationships of Chelonioidea using two updated datasets that widely sample Cretaceous taxa, especially Rhinochelys. Rhinochelys amaberti is a valid taxon that is supported by eight autapomorphies; an emended diagnosisis proposed. Our phylogenetic analyses suggest that Rhinochelys could be polyphyletic, but constraining it as a monophyletic entity does not produce trees that are significantly less parsimonious. Moreover, support values and stratigraphic congruence indexes are fairly low for the recovered typologies, suggesting that missing data still strongly affect our understanding of the Cretaceous diversification of sea turtles.

Ordosemys leios, n.gen., n.sp., from the Early Cretaceous Luohandong Formation, Zhidan Group, Ordos Basin, Inner Mongolia, is a primitive aquatic turtle with a reduced, fenestrated plastron. It shares with the members of the Centrocryptodira the presence of well-formed articular surfaces on the cervical and caudal vertebrae. Within the Centrocryptodira, characters of the cervical vertebrae suggest it is more closely related to the Polycryptodira than is the Meiolaniidae. Ordosemys shares with the Chelydridae the presence of two procoelous anterior caudals, but this character may be primitive for the Polycryptodira. Characters of the basicranial region of the braincase shared by Ordosemys and the Chelonioidea support a sister-group relationship between these two taxa, but a sister-group relationship between Ordosemys and the Polycryptodira is more strongly supported by characters shared by the Chelonioidea and other members of the Polycryptodira.

An incomplete specimen of Desmatochelys cf. D. lowi (Reptilia: Chelonioidea) from the Trent River Formation (Santonian–Campanian) of the Comox Basin of eastern Vancouver Island is the first documented account of Cretaceous marine vertebrates from the Pacific coast of Canada. It represents both stratigraphic and geographic range extensions for the genus Desmatochelys.

Previously reported and new specimens of marine turtles from the late Campanian of Alberta, Canada, provide additional information on the diversity and distribution of chelonioid turtles at this time. An articulated carapace from the Bearpaw Formation previously interpreted as Lophochelys niobrarae is considered to be a juvenile of a specifically indeterminate chelonioid and is referred to Lophochelys sp. Isolated neurals and a hyoplastron from nonmarine estuarine deposits in the uppermost beds of the Dinosaur Park Formation are tentatively referred to Lophochelys sp. These specimens suggest that this chelonioid could enter freshwater environments. A new chelonioid, Kimurachelys slobodae gen. et sp. nov., is recognized on the basis of two mandibles and a maxilla from the uppermost beds of the Dinosaur Park Formation of southeastern Alberta. A partial postcranial skeleton of an indeterminate chelonioid from the Bearpaw Formation provides additional evidence that chelonioids of this formation included taxa that were phylogenetically intermediate between chelonioids of the late Santonian and members of the crown group.

La taxonomie de la super-famille des Chelonioidea (toutes les tortues marines actuelles, excepté la tortue luth) a beaucoup fluctué depuis sa création en 1811 par Oppel. Si de nombreuses études ont été réalisées, concernant d’une part la description de caractères qualitatifs et quantitatifs permettant de distinguer les espèces, et d’autre part le génome, aucune n’a été véritablement menée dans l’optique de quantifier les conformations géométriques du squelette et d’exposer leurs particularités. Les crânes, les mandibules et cinq os longs de 307 spécimens des collections du Chelonian Research Institute (USA) ont été numérisés à l’aide de trois méthodologies différentes de morphométrie géométrique : positionnement de points repères 2D, positionnement de points repères 3D et relevés de contours 3D. Pour tous les spécimens, nous connaissions l’espèce, le stade de développement, la provenance et le sexe. Ainsi, nous avons pu étudier la variabilité liée à ces quatre facteurs au sein de ces structures osseuses. La morphométrie géométrique permet de faire la synthèse, à l’échelle de précision souhaitée, de la géométrie d’un objet dans sa globalité. Elle bénéficie d’un fondement mathématique rigoureux qui garantit des statistiques robustes. Plusieurs champs d’analyses ont été développés et tout particulièrement au sein du genre Chelonia où nous avons estimé, comparé et visualisé la variabilité des individus de l’Atlantique ouest, de la région Indo-Pacifique et du Pacifique aux différents stades de développement. Ces populations présentent en effet des différences importantes au niveau de la géométrie de leur squelette pouvant expliquer en partie la fluctuation de la taxonomie du genre Chelonia et la discussion du paraphylétisme de Chelonia mydas. La géométrie de tous les os étudiés est différemment corrélée avec les facteurs retenus, excepté le sexe pour lequel la variabilité des conformations semble moins structurée. Ceci permet d’envisager de nombreuses applications pratiques : amélioration des connaissances générales de la biologie de ces reptiles (le suivi satellite étant très coûteux en raison des fortes mortalités naturelles et autres), mais aussi détermination de spécimens, voire de restes archéologiques de tortues marines qui aujourd’hui ne sont pas étudiés, bien qu’il soit fréquent d’en retrouver sur des sites littoraux de nombreuses régions du monde
The taxonomy of the super-family Chelonioidea (all the extant marine turtles except the leatherback) has changed many times since its creation in 1811 by Oppel. Today numerous studies have been carried out both on the descriptive characters (qualitative and quantitative) for distinguishing species and about their genomes. But none has really been devoted to quantifying the bone’s geometrical shape and conformations that should better their knowledge. The skulls, lower jaws and five long bones of 307 specimens belonging to the Chelonian Research Institute (USA) were digitized using three different geometric morphometrics methods: 2D landmarks, 3D landmarks, 3D outlines. For each specimen, we had information about the species, stage of development, origin and sex. We studied the shape variability related to these four factors in the bony structures. Geometric morphometrics allow to synthesis the global geometry of an object. It has a rigorous mathematical background and ensures robust statistics. We tested several hypotheses, especially among the genus Chelonia where we compared and visualized the shape variability of western Atlantic, Indo-Pacific and Pacific individuals, including the three stages of development. As these populations presented significant differences in the bony structure geometry, thus may partly explain the fluctuation of the taxonomy of the genus Chelonia and the discussion of the paraphyletism of the current species Chelonia mydas. The geometry of all the bones we studied was correlated with the different factors we tested, except for the sex for which the shape variability seems to be less structured. This allows to consider several practical applications: to improve the general knowledge of the biology of these reptiles (as satellite tracking is very expensive because of the high natural level of mortality), but also to make determinations of specimens or of archaeological sea turtles remains, which are fairly frequent

Chelonioidea (sea turtles) are a group where available morphological evidence for crown group relationships are incongruent with those established using molecular data. However, morphological surveys of crown group taxa tend to focus on a recurring subset of the extant species. The Australian flatback sea turtle, Natator depressus, is often excluded from comparisons and it is the most poorly known of the seven extant species of Chelonioidea. Previous descriptions of its skull morphology are limited and conflict. Here we describe two skulls of adult N. depressus and re-examine the phylogenetic relationships according to morphological character data. Using X-ray micro Computed Tomography we describe internal structures of the braincase and identify new phylogenetically informative characters not previously reported. Phylogenetic analysis using a Bayesian approach strongly supports a sister group relationship between Chelonia mydas and N. depressus, a topology which wasn’t supported by previous analyses of morphological data but one that matches the topology supported by analysis of molecular data. Our results highlight the general need to sample the morphological anatomy of crown group taxa more thoroughly before concluding that morphological and molecular evidence is incongruous.
Thesis (Ph.D.) -- University of Adelaide, School of Biological Sciences, 2021