Atolchelys lepida, a new side-necked turtle from the Early Cretaceous of Brazil and the age of crown Pleurodira

Neuroanatomical Study and Three-Dimensional Cranial Reconstruction of the Brazilian Albian Pleurodiran Turtle Euraxemys essweini

The Pleurodira represent one of the two clades that compose the crown Testudines, and their temporal range is Late Jurassic–present. However, knowledge about the neuroanatomy of extinct pleurodires is still very limited. In this context, scarce neuroanatomical information about the Cretaceous clade Euraxemydidae is currently available, limited to some characters of the Moroccan Cenomanian Dirqadim schaefferi. In the present work, we perform the detailed neuroanatomical study of its sister taxon, the Brazilian Albian Euraxemys essweini, based on the analysis of the skull of its holotype and only known individual of the species. The detailed virtual three-dimensional reconstruction of all its cranial bones is performed, also improving the information about its osseous anatomy. The different neuroanatomical cavities (i.e., cranial, nasal, and labyrinthic ones) and canals (i.e., nervous and circulatory ones) are compared with those identified thus far for other extinct and extant members of the Pleurodira in order to characterize the neuroanatomy of the extinct clade Euraxemydidae in detail.

The Ornamented Shell of a New Bothremydid Turtle from the Uppermost Cretaceous of Niger

A new pleurodiran turtle is described here. It is identified as attributable to Bothremydidae. The new taxon comes from an upper Maastrichtian (Upper Cretaceous) outcrop located in Southwestern Niger (in the Indamane Mount area, belonging to the Abalak Department of the Tahoua Region). Abalakemys chapmanae gen. et sp. nov. is identified by an almost complete large shell of about 65 cm in length. The new bothremydid turtle is recognized as a member of Bothremydodda, showing several autapomorphies (an exclusive ornamental pattern on the plate’s outer surface, covered by small depressions; small fourth pleural scutes, only anteromedially reaching the sixth pair of costal plates; and noticeably wedged posterior plastral lobe toward the posterior region), as well as a unique combination of characters for this clade. This turtle could belong to Nigeremydini, a poorly understood Maastrichtian to Paleocene lineage of Bothremydodda, which integrates large coastal taxa that inhabited the African Trans-Saharan seaway, and for which shell information is currently extremely limited.

Phylogenomics reconciles molecular data with the rich fossil record on the origin of living turtles

Although a consensus exists that all living turtles fall within either Pleurodira or Cryptodira clades, estimating when these lineages split is still under debate. Most molecular studies date the split in the Triassic Period, whereas a Jurassic age is unanimous among morphological studies. Each hypothesis implies different paleobiogeographical scenarios to explain early turtle evolution. Here we explored the rich turtle fossil record with the Fossilized Birth-Death (FBD) and the traditional node dating (ND) methods using complete mitochondrial genomes (147 taxa) and a set of nuclear orthologs with over 10 million bp (25 taxa) to date the major splits in Testudines. Our results support an Early Jurassic split (191-182 Ma) for the crown Testudines with great consistency across different dating methods and datasets, with a narrow confidence interval. This result is independently supported by the oldest fossils of Testudines that postdate the Middle Jurassic (174 Ma), which were not used for calibration in this study. This age coincides with the Pangaea fragmentation and the formation of saltwater barriers such as the Atlantic Ocean and the Turgai Strait, supporting that diversification in Testudines was triggered by vicariance. Our ages of the splits in Pleurodira coincide with the geologic events of the Late Jurassic and Early Cretaceous. Conversely, the early Cryptodira radiation remained in Laurasia, and its diversification ensued as all its major lineages expanded their distribution into every continent during the Cenozoic. We provide the first detailed hypothesis of the evolution of Cryptodira in the Southern Hemisphere, in which our time estimates are correlated with each contact between landmasses derived from Gondwana and Laurasia. Although most South American Cryptodira arrived through the Great American Biotic Interchange, our results indicate that the Chelonoidis ancestor probably arrived from Africa through the chain islands of the South Atlantic during the Paleogene. Together, the presence of ancient turtle diversity and the vital role that turtles occupy in marine and terrestrial ecosystems underline South America as a chief area for conservation.

The neuroanatomy of the bothremydid pleurodiran turtle Galianemys, from the Late Cretaceous (Cenomanian) of Morocco

Galianemys is one of the three genera of Cearachelyini (Pleurodira, Bothremydidae) so far defined, being the only one identified in Africa (in the Cenomanian of Morocco). It is represented by two species, Galianemys whitei and Galianemys emringeri, both being identified by several skulls. The other two representatives of Cearachelyini are both South-American forms, and only the species Cearachelys placidoi (from the Albian of Brazil) preserves cranial remains, including a partial skull corresponding to its holotype. However, despite the relatively great number of skulls identified for both Galianemys spp. and Cearachelys placidoi, information about the neuroanatomy of this lineage is very limited. The three-dimensional (3D) reconstruction of the skulls of two specimens belonging to the genus Galianemys, each of them representing a different species, is performed here for the first time. All of the cranial bones of one of them are also virtually reconstructed to accurately characterize them. In addition, the 3D models of the main neuroanatomical structures (i.e., cranial, nasal, and labyrinthic cavities, and nervous and carotid canals) of both specimens were generated, most of them being described in detail for first time in Cearachelyini. Neuroanatomical differences are recognized when the skulls of both species of Galianemys analyzed here are compared. In addition, the comparison between the neuroanatomy of Galianemys spp. and that of other non-Cearachelyini bothremydids allow us to identify some differences between those lineages, but also recognize other shared characters for the entire lineage of Bothremydidae, to providing a more precise characterization within Pleurodira.

Matamatas Chelus spp. (Testudines, Chelidae) have a remarkable evolutionary history of sex chromosomes with a long-term stable XY microchromosome system

The genus Chelus, commonly known as Matamata is one of the most emblematic and remarkable species among the Neotropical chelids. It is an Amazonian species with an extensive distribution throughout Negro/Orinoco and Amazonas River basins. Currently, two species are formally recognized: Chelus orinocensis and Chelus fimbriata and although it is still classified as "Least Concern" in the IUCN, the Matamatas are very appreciated and illegally sold in the international pet trade. Regardless, little is known regarding many aspects of its natural history. Chromosomal features for Chelus, for instance, are meagre and practically restricted to the description of the diploid number (2n = 50) for Chelus fimbriata, and its sex determining strategies are yet to be fully investigated. Here, we examined the karyotype of Chelus fimbriata and the newly described Chelus orinocensis, applying an extensive conventional and molecular cytogenetic approach. This allowed us to identify a genetic sex determining mechanism with a micro XY sex chromosome system in both species, a system that was likely present in their most common recent ancestor Chelus colombiana. Furthermore, the XY system found in Chelus orinocensis and Chelus fimbriata, as seen in other chelid species, recruited several repeat motifs, possibly prior to the split of South America and Australasian lineages, indicating that such system indeed dates back to the earliest lineages of Chelid species.

An early bothremydid from the Arlington Archosaur Site of Texas

Four turtle taxa are previously documented from the Cenomanian Arlington Archosaur Site (AAS) of the Lewisville Formation (Woodbine Group) in Texas. Herein, we describe a new side-necked turtle (Pleurodira), Pleurochayah appalachius gen. et sp. nov., which is a basal member of the Bothremydidae. Pleurochayah appalachius gen. et sp. nov. shares synapomorphic characters with other bothremydids, including shared traits with Kurmademydini and Cearachelyini, but has a unique combination of skull and shell traits. The new taxon is significant because it is the oldest crown pleurodiran turtle from North America and Laurasia, predating bothremynines Algorachelus peregrinus and Paiutemys tibert from Europe and North America respectively. This discovery also documents the oldest evidence of dispersal of crown Pleurodira from Gondwana to Laurasia. Pleurochayah appalachius gen. et sp. nov. is compared to previously described fossil pleurodires, placed in a modified phylogenetic analysis of pelomedusoid turtles, and discussed in the context of pleurodiran distribution in the mid-Cretaceous. Its unique combination of characters demonstrates marine adaptation and dispersal capability among basal bothremydids.

The Making of Calibration Sausage Exemplified by Recalibrating the Transcriptomic Timetree of Jawed Vertebrates

Molecular divergence dating has the potential to overcome the incompleteness of the fossil record in inferring when cladogenetic events (splits, divergences) happened, but needs to be calibrated by the fossil record. Ideally but unrealistically, this would require practitioners to be specialists in molecular evolution, in the phylogeny and the fossil record of all sampled taxa, and in the chronostratigraphy of the sites the fossils were found in. Paleontologists have therefore tried to help by publishing compendia of recommended calibrations, and molecular biologists unfamiliar with the fossil record have made heavy use of such works (in addition to using scattered primary sources and copying from each other). Using a recent example of a large node-dated timetree inferred from molecular data, I reevaluate all 30 calibrations in detail, present the current state of knowledge on them with its various uncertainties, rerun the dating analysis, and conclude that calibration dates cannot be taken from published compendia or other secondary or tertiary sources without risking strong distortions to the results, because all such sources become outdated faster than they are published: 50 of the (primary) sources I cite to constrain calibrations were published in 2019, half of the total of 280 after mid-2016, and 90% after mid-2005. It follows that the present work cannot serve as such a compendium either; in the slightly longer term, it can only highlight known and overlooked problems. Future authors will need to solve each of these problems anew through a thorough search of the primary paleobiological and chronostratigraphic literature on each calibration date every time they infer a new timetree, and that literature is not optimized for that task, but largely has other objectives.

A new pelomedusoid turtle, Sahonachelys mailakavava, from the Late Cretaceous of Madagascar provides evidence for convergent evolution of specialized suction feeding among pleurodires

The Maevarano Formation in northwestern Madagascar has yielded a series of exceptional fossils over the course of the last three decades that provide important insights into the evolution of insular ecosystems during the latest Cretaceous (Maastrichtian). We here describe a new genus and species of pelomedusoid turtle from this formation, Sahonachelys mailakavava, based on a nearly complete skeleton. A phylogenetic analysis suggests close affinities of Sahonachelys mailakavava with the coeval Madagascan Sokatra antitra. These two taxa are the only known representatives of the newly recognized clade Sahonachelyidae, which is sister to the speciose clade formed by Bothremydidae and Podocnemidoidae. A close relationship with coeval Indian turtles of the clade Kurmademydini is notably absent. A functional assessment suggests that Sahonachelys mailakavava was a specialized suction feeder that preyed upon small-bodied invertebrates and vertebrates. This is a unique feeding strategy among crown pelomedusoids that is convergent upon that documented in numerous other clades of turtles and that highlights the distinct evolutionary pathways taken by Madagascan vertebrates.

Osteohistology and microanatomy of a new specimen of Cearachelys placidoi (Testudines: Pleurodira) a side-necked turtle from the lower Cretaceous of Brazil

Pelomedusoides had a recognised diverse Early Cretaceous fauna of turtles in Northeast Brazil. Within them, the bothremydid Cearachelys placidoi has a relatively abundant record. This diversity contrasts with the scarcity of osteohistological studies in this group. The relatively well-preserved shell of C. placidoi (UFRPE 5600), from the Aptian age of Araripe Basin, is studied here for the purpose of filling this gap. We performed the osteohistological description of the plastron of a new specimen of C. placidoi. Also, to conduct a comparative study, we carried out histological sections in bones of the recent chelid Phrynops sp. Our histological findings indicate similarities between the histological pattern of freshwater turtles and the coastal marine C. placidoi. Moreover, osteohistological features imply metaplastic incorporation of dermal interwoven structural fiber bundles. Lastly, the xiphiplastron of C. placidoi shows an increase of bone compactness over its craniocaudal axis. This microanatomical feature is exclusive to Cearachelys so far.

The Amazonian Red Side-Necked Turtle Rhinemys rufipes (Spix, 1824) (Testudines, Chelidae) Has a GSD Sex-Determining Mechanism with an Ancient XY Sex Microchromosome System

The Amazonian red side-necked turtle Rhynemis rufipes is an endemic Amazonian Chelidae species that occurs in small streams throughout Colombia and Brazil river basins. Little is known about various biological aspects of this species, including its sex determination strategies. Among chelids, the greatest karyotype diversity is found in the Neotropical species, with several 2n configurations, including cases of triploidy. Here, we investigate the karyotype of Rhinemys rufipes by applying combined conventional and molecular cytogenetic procedures. This allowed us to discover a genetic sex-determining mechanism that shares an ancestral micro XY sex chromosome system. This ancient micro XY system recruited distinct repeat motifs before it diverged from several South America and Australasian species. We propose that such a system dates back to the earliest lineages of the chelid species before the split of South America and Australasian lineages.

Valanginian occurrence of Pelomedusoides turtles in northern South America: revision of this hypothesis based on a new fossil remain

Pelomedusoides constitutes the most diverse group of Mesozoic and Cenozoic side-necked turtles. However, when it originated is still being poorly known and controversial. Fossil remains from the Early Cretaceous (Valanginian) Rosa Blanca Formation of Colombia were described almost a decade ago as potentially belonging to Podocnemidoidea (a large subclade inside Pelomedusoides) and representing one of the earliest records of this group of turtles. Here, I revise this hypothesis based on a new fragmentary specimen from the Rosa Blanca Formation, represented by a right portion of the shell bridge, including the mesoplastron and most of peripherals 5 to 7. The equidimensional shape of the mesoplatron allows me to support its attribution as belonging to Pelomedusoides, a group to which the previously podocnemidoid material is also attributed here. Although the Valanginian pelomesudoid material from Colombia is still too fragmentary as to be considered the earliest indisputable record of the Pelomedusoides clade, their occurrence is at least in agreement with current molecular phylogenetic hypotheses that suggest they split from Chelidae during the Jurassic and should occur in the Late Jurassic and Early Cretaceous fossil record.

Phylogeny, biogeography and diversification patterns of side-necked turtles (Testudines: Pleurodira)

Pleurodires or side-necked turtles are today restricted to freshwater environments of South America, Africa-Madagascar and Australia, but in the past they were distributed much more broadly, being found also on Eurasia, India and North America, and marine environments. Two hypotheses were proposed to explain this distribution; in the first, vicariance would have shaped the current geographical distribution and, in the second, extinctions constrained a previously widespread distribution. Here, we aim to reconstruct pleurodiran biogeographic history and diversification patterns based on a new phylogenetic hypothesis recovered from the analysis of the largest morphological dataset yet compiled for the lineage, testing which biogeographical process prevailed during its evolutionary history. The resulting topology generally agrees with previous hypotheses of the group and shows that most diversification shifts were related to the exploration of new niches, e.g. littoral or marine radiations. In addition, as other turtles, pleurodires do not seem to have been much affected by either the Cretaceous-Palaeogene or the Eocene-Oligocene mass extinctions. The biogeographic analyses highlight the predominance of both anagenetic and cladogenetic dispersal events and support the importance of transoceanic dispersals as a more common driver of area changes than previously thought, agreeing with previous studies with other non-turtle lineages.

Intra-specific variation and allometry of the skull of Late Cretaceous side-necked turtle Bauruemys elegans (Pleurodira, Podocnemididae) and how to deal with morphometric data in fossil vertebrates

Background

Previous quantitative studies on Bauruemys elegans (Suárez, 1969) shell variation, as well as the taphonomic interpretation of its type locality, have suggested that all specimens collected in this locality may have belonged to the same population. We rely on this hypothesis in a morphometric study of the skull. Also, we tentatively assessed the eating preference habits differentiation that might be explained as due to ontogenetic changes.

Methods

We carried out an ANOVA testing 29 linear measurements from 21 skulls of B. elegans taken by using a caliper and through images, using the ImageJ software. First, a Principal Components Analysis (PCA) was performed with 27 measurements (excluding total length and width characters; =raw data) in order to visualize the scatter plots based on the form variance only. Then, a second PCA was carried out using ratios of length and width of each original measurement to assess shape variation among individuals. Finally, original measurements were log-transformed to describe allometries over ontogeny.

Results

No statistical differences were found between caliper and ImageJ measurements. The first three PCs of the PCA with raw data comprised 70.2% of the variance. PC1 was related to size variation and all others related to shape variation. Two specimens plotted outside the 95% ellipse in PC1∼PC2 axes. The first three PCs of the PCA with ratios comprised 64% of the variance. When considering PC1∼PC2, all specimens plotted inside the 95% ellipse. In allometric analysis, five measurements were positively allometric, 19 were negatively allometric and three represented enantiometric allometry. Many bones of the posterior and the lateral emarginations lengthen due to increasing size, while jugal and the quadratojugal decrease in width.

Discussion

ImageJ is useful in replacing caliper since there was no statistical differences. Yet iterative imputation is more appropriate to deal with missing data in PCA. Some specimens show small differences in form and shape. Form differences were interpreted as occuring due to ontogeny, whereas shape differences are related to feeding changes during growth. Moreover, all outlier specimens are crushed and/or distorted, thus the form/shape differences may be partially due to taphonomy. The allometric lengthening of the parietal, quadrate, squamosal, maxilla, associated with the narrowing of jugal and quadratojugal may be related to changes in feeding habit between different stages of development. This change in shape might represent a progressive skull stretching and enlargement of posterior and lateral emargination during ontogeny, and consequently, the increment of the feeding-apparatus musculature. Smaller individuals may have fed on softer diet, whereas larger ones probably have had a harder diet, as seen in some living species of Podocnemis. We conclude that the skull variation might be related to differences in feeding habits over ontogeny in B. elegans.

A toothed turtle from the Late Jurassic of China and the global biogeographic history of turtles

BACKGROUND

Turtles (Testudinata) are a successful lineage of vertebrates with about 350 extant species that inhabit all major oceans and landmasses with tropical to temperate climates. The rich fossil record of turtles documents the adaptation of various sub-lineages to a broad range of habitat preferences, but a synthetic biogeographic model is still lacking for the group.

RESULTS

We herein describe a new species of fossil turtle from the Late Jurassic of Xinjiang, China, Sichuanchelys palatodentata sp. nov., that is highly unusual by plesiomorphically exhibiting palatal teeth. Phylogenetic analysis places the Late Jurassic Sichuanchelys palatodentata in a clade with the Late Cretaceous Mongolochelys efremovi outside crown group Testudines thereby establishing the prolonged presence of a previously unrecognized clade of turtles in Asia, herein named Sichuanchelyidae. In contrast to previous hypotheses, M. efremovi and Kallokibotion bajazidi are not found within Meiolaniformes, a clade that is here reinterpreted as being restricted to Gondwana.

CONCLUSIONS

A revision of the global distribution of fossil and recent turtle reveals that the three primary lineages of derived, aquatic turtles, including the crown, Paracryptodira, Pan-Pleurodira, and Pan-Cryptodira can be traced back to the Middle Jurassic of Euramerica, Gondwana, and Asia, respectively, which resulted from the primary break up of Pangaea at that time. The two primary lineages of Pleurodira, Pan-Pelomedusoides and Pan-Chelidae, can similarly be traced back to the Cretaceous of northern and southern Gondwana, respectively, which were separated from one another by a large desert zone during that time. The primary divergence of crown turtles was therefore driven by vicariance to the primary freshwater aquatic habitat of these lineages. The temporally persistent lineages of basal turtles, Helochelydridae, Meiolaniformes, Sichuanchelyidae, can similarly be traced back to the Late Mesozoic of Euramerica, southern Gondwana, and Asia. Given the ambiguous phylogenetic relationships of these three lineages, it is unclear if their diversification was driven by vicariance as well, or if they display a vicariance-like pattern. The clean, primary signal apparent among early turtles is secondarily obliterated throughout the Late Cretaceous to Recent by extensive dispersal of continental turtles and by multiple invasions of marine habitats.

An early bothremydid (Testudines, Pleurodira) from the Late Cretaceous (Cenomanian) of Utah, North America

BACKGROUND

Bothremydidae is a clade of extinct pleurodiran turtles known from the Cretaceous to Paleogene of Africa, Europe, India, Madagascar, and North and South America. The group is most diverse during the Late Cretaceous to Paleogene of Africa. Little is known, however, about the early evolution of the group.

METHODS

We here figure and describe a fossil turtle from early Late Cretaceous deposits exposed at MacFarlane Mine in Cedar Canyon, southwestern Utah, USA. The sediments associated with the new turtle are utilized to infer its stratigraphic provenience and the depositional settings in which it was deposited. The fossil is compared to previously described fossil pleurodires, integrated into a modified phylogenetic analysis of pelomedusoid turtles, and the biogeography of bothremydid turtles is reassessed. In light of the novel phylogenetic hypotheses, six previously established taxon names are converted to phylogenetically defined clade names to aid communication.

RESULTS

The new fossil turtle can be inferred with confidence to have originated from a brackish water facies within the late Cenomanian Culver Coal Zone of the Naturita Formation. The fossil can be distinguished from all other previously described pleurodires and is therefore designated as a new taxon, Paiutemys tibert gen. et. sp. nov. Phylogenetic analysis places the new taxon as sister to the European Polysternon provinciale, Foxemys trabanti and Foxemys mechinorum at the base of Bothremydinae. Biogeographic analysis suggests that bothremydids originated as continental turtles in Gondwana, but that bothremydines adapted to near-shore marine conditions and therefore should be seen as having a circum-Atlantic distribution.

A new turtle confirms the presence of Bothremydidae (Pleurodira) in the Cenozoic of Europe and expands the biostratigraphic range of Foxemydina

Pleurodira is a clade of Gondwanan turtles that reached Europe at the beginning of the Late Cretaceous. It is recognized as the most abundant and diverse group of freshwater turtles in the uppermost Cretaceous record of this continent, being represented by several members of Bothremydidae. Two well-preserved and relatively complete skulls are studied in this paper. They come from lower Eocene levels of the French locality of Saint-Papoul (Aude). These specimens are recognized as attributable to a new taxon, Tartaruscola teodorii gen. et sp. nov., identified as a bothremydid. This new form constitutes the only known unambiguous and valid representative of Bothremydidae in the Cenozoic of Europe. The new taxon is diagnosed by several autapomorphies and also by an exclusive combination of characters. It is one of the few members of Bothremydini identified in the Cenozoic record and the only one described for the Eocene outside of the Ouled Abdoun Basin of Morocco. Tartaruscola teodorii is identified as a member of Foxemydina, a clade recognized here as exclusive of the European record, and whose presence in post-Mesozoic levels is demonstrated in this paper. The European Foxemydina T. teodorii and the African Bothremydina Bothremys kellyi, both from the Ypresian, are the youngest members of Bothremydini hitherto known.

A global phylogeny of Pelomedusoides turtles with new material of Neochelys franzeni Schleich, 1993 (Testudines, Podocnemididae) from the middle Eocene, Messel Pit, of Germany

Background. Neochelys franzeni Schleich, 1993 is the only pleurodire or side-necked turtle from the middle Eocene, Messel Pit (the first UNESCO, World Natural Heritage Site in Germany, since 1995). The original description of the species is based on two specimens SMF ME 1091 (Holotype) and 715 (Paratype) housed at the Senckenberg Museum Frankfurt. The excellent preservation of complete and articulated skeletons of this species makes it a key taxon for understanding the evolution and phylogeny of the European Neochelys genus and its relationships with South American and African-Madagascar podocnemidids. Results. Five new specimens of Neochelys franzeni from Messel Pit are described here, together with the redescription of SMF ME 1091 and 715. Specimens correspond to individuals of different ontogenetic stages showing conservative morphology from hatching to adults. A revised diagnosis for the species is presented here, together with its inclusion in a global phylogenetic analysis of Pelomedusoides that shows that this species and the whole Neochelys spp. is sister to the Erymnochelys madagascariensis-Peltocephalus dumerilianus clade within Podocnemididae.

The last marine pelomedusoids (Testudines: Pleurodira): a new species of Bairdemys and the paleoecology of Stereogenyina

The extinct Stereogenyina turtles form a relatively diverse Podocnemididae lineage, with twelve described and phylogenetically positioned species. They are characterized by a wide geographic and temporal range, from the Eocene of Africa to the Pleistocene of Southeast Asia, and a peculiar palate morphology, with a secondary palate that is unique among side-necked turtles. Here, we describe a new Stereogenyina species, based on an almost complete skull from the middle Miocene Capadare Formation, of Venezuela. A new phylogenetic analysis supports the assignment of the new species to the genus Bairdemys. Based on geometric morphometrics analyses, we related the development of the stereogenyin secondary palate with the acquisition of a durophagous diet. Based on a review of the sedimentary environments where their fossils are found, we also propose that stereogenyins were a marine radiation of podocnemidid turtles, as corroborated by previous studies of fossil eggs and limb morphology. These two inferences allowed us to hypothesize that stereogenyins occupied an ecological niche similar to that of the extant Carettini sea turtles, and that the rise of the latter group may be related to the Stereogenyina diversity fall in the end of the Miocene.