Search

The humerus is central for locomotion in turtles as quadrupedal animals. Osteological variation across testudine clades remains poorly documented. Here, we systematically describe the humerus anatomy for all major extant turtle clades based on 38 species representing the phylogenetic and ecological diversity of crown turtles. Three Late Triassic species of shelled stem turtles (Testudindata) are included to establish the plesiomorphic humerus morphology. Our work is based on 3D models, establishing a publicly available digital database. Previously defined terms for anatomical sides of the humerus (e.g., dorsal, ventral) are often not aligned with the respective body sides in turtles and other quadrupedal animals with sprawling gait. We propose alternative anatomical directional terms to simplify communication: radial and ulnar (the sides articulating with the radius/ulna), capitular (the side bearing the humeral head), and intertubercular (opposite to capitular surface). Turtle humeri show low morphological variation with exceptions concentrated in locomotory specialists. We propose 15 discrete characters to summarize osteological variation for future phylogenetic studies. Disparity analyses comparing non-shelled and shelled turtles indicate that the presence of the shell constrains humerus variation. Flippered aquatic turtles are released from this constraint and significantly increase overall disparity. Ontogenetic changes of turtle humeri are related to increased ossification and pronunciation of the proximal processes, the distal articulation areas, and the closure of the ectepicondylar groove to a foramen. Some turtle species retain juvenile features into adulthood and provide evidence for paedomorphic evolution. We review major changes of turtle humerus morphology throughout the evolution of its stem group., (© 2024 The Authors. The Anatomical Record published by Wiley Periodicals LLC on behalf of American Association for Anatomy.)

In Thailand, two snail-eating turtle species in the genus Malayemes (M. subtrijuga and M. macrocephala) are protected animals in which smuggling and trading are illegal. Recently, a new species M. khoratensis has been reported and it has not yet been considered as protected animal species. To enforce the law, species identification of Malayemes is crucial. However, it is quite challenging and requires expertise. Therefore, a simple tool, such as image analysis, to differentiate these three snail-eating species would be highly useful. This study proposes a novel ensemble multiview image processing approach for the automated classification of three turtle species in the genus Malayemys. The original YOLOv8 architecture was improved by utilizing a convolutional neural network (CNN) to overcome the limitations of traditional identification methods. This model captures unique morphological features by analyzing Malayemys species images from various angles, addressing challenges such as occlusion and appearance variations. The ensemble multiview strategy significantly increases the YOLOv8 classification accuracy using a comprehensive dataset, achieving an average mean average precision (mAP) of 98% for the genus Malayemys compared with the nonensemble multiview and single-view strategies. The species identification accuracy of the proposed models was validated by comparing genetic methods using mitochondrial DNA with morphological characteristics. Even though the morphological characteristics of these three species are ambiguous, the mitochondrial DNA sequences are quite distinct. Therefore, this alternative tool should be used to increase confidence in field identification. In summary, the contribution of this study not only marks a significant advancement in computational biology but also supports wildlife and turtle conservation efforts by enabling rapid, accurate species identification., (© 2024. The Author(s).)

The current investigation focuses on gross anatomy, light, and scanning electron microscopy (SEM) of the Testudo graeca oropharyngeal floor, with particular reference to the immunofluorescence technique to examine its tongue. The T. graeca oropharyngeal floor showed many anatomical structures: the lower rhamphotheca, paralingual ridge, lower alveolar ridge, tongue, laryngeal mound, and glottis. The lower rhamphotheca appeared as a V-shaped jaw line with a highly serrated edge and a median tomium (beak). SEM observations of the lingual apex and the lingual body showed rectangular and conical filiform papillae with porous surfaces and taste pores. Meanwhile, the lingual root had two wings that carried papillae with different shapes: dagger-shaped, conical, bifurcated, and leaf-like papillae, and these papillae lacked taste pores. The laryngeal mound had openings for the laryngeal mucus gland and its secretions. Light microscopy findings showed mucous glands in the propria submucosa and near the mucosal surface of the lingual apex. The lingual root had lingual papillae and two hyaline cartilaginous skeletons between skeletal muscles, and the lingual papillae were elongated filiform, rectangular filiform papillae, and fungiform papillae. The lamina propria constituted the core of the lingual papillae and the mucous gland, they had a positive reaction with the periodic acid schiff (PAS) reagent. The apical surface of the fungiform papillae had taste pores. Under immunofluorescence, the vimentin was detected in taste bud cells, and synaptophysin reacted to the taste buds and nerve bundles. The current study of the Greek tortoise oropharyngeal floor investigated its herbivorous eating habits using its serrated lower rhamphotheca, a large tongue with differently shaped papillae, and numerous mucous glands. RESEARCH HIGHLIGHTS: The Greek tortoise (T. graeca graeca) oropharyngeal floor showed many anatomical structures: lower rhamphotheca, paralingual ridge, lower alveolar ridge, tongue, laryngeal mound, and glottis. SEM and light microscopy observations of the tongue revealed varied types and shapes of lingual papillae with a porous surface on the tongue apex (rectangular or conical filiform papillae), on the tongue body (filiform and fungiform papillae), and on the tongue root (dagger-shaped, conical, bifurcated, and leaf-like papillae). Light microscopy findings: the lamina propria constituted the core of the lingual papillae and had numerous mucous glands that had a slightly magenta-red color with PAS reagent. The apical surface of the fungiform papillae had taste pores. Vimentin and synaptophysin gave a reaction to the taste buds., (© 2024 Wiley Periodicals LLC.)

The turtle shell is a remarkable structure that has intrigued not only evolutionary biologists but also engineering and material scientists because of its multi-scale complexity and various functions. Although protection is its most apparent role, the carapace and plastron are also related to many physiological functions and their shape influences hydrodynamics and self-righting ability. As such, analysing the functional morphology of the shell could help understanding the ecology of Triassic stem-turtles, which will contribute to the century-long debate on the evolutionary origins of turtles. Here, we used 3D imaging techniques to digitize the shells of two of the earliest stem-turtle taxa, Proganochelys and Proterochersis, and submitted their models to biomechanical and shape analyses. We analysed the strength performance under five predation scenarios and tested the function of two morphological traits found in stem-turtles, the epiplastral processes and an attached pelvic girdle. The latter, also present in the crown-lineage of side-necked turtles, has been suggested to increase load-bearing capacity of the shell or to improve swimming in pleurodires. Our results do not confirm the shell-strengthening hypothesis and, together with the results of our shape analyses, suggest that at least one of the first stem-turtles (Proterochersis) was an aquatic animal., (© 2024. The Author(s).)

The problem of the origin of the bony shell in turtles has a two-century history and still has not lost its relevance. First, this concerns the issues of the homology, the sources of formation and the ratio of bones of different nature, that is, thecal and epithecal, in particular. This article analyzes various views on the nature of the shell elements, and proposes their typification, based on modern data on developmental biology. It is proposed that the defining characteristic of the types of shell ossifications is not the level of their anlage in the dermis (thecality or epithecality), but, first of all, the primary sources of their formation: (1) neural crest (nuchal and plastral plates); (2) vertebral and rib periosteum (neural and costal plates); and (3) dermal mesenchyme (peripheral, suprapygal and pygal plates, as well as epithecal elements). In addition, there is complete correspondence between these types of ossifications and the sequence of their appearance in the turtle ontogenesis. The data show fundamental coincidence of the modifications of the ontogenetic development and evolutionary formation of the shell ossifications and are in agreement with a stepwise model for the origin of the turtle body plan. Particular attention is paid to the origin of the epithecal elements of the turtle shell, which correspond to the additional or supernumerary ossifications and seem to have wider distribution among turtles, than previously thought., (© 2024 Wiley Periodicals LLC.)

The osteology, neuroanatomy, and musculature are known for most primary clades of turtles (i.e., "families"), but knowledge is still lacking for one particular clade, the Carettochelyidae. Carettochelyids are represented by only one living taxon, the pig-nosed turtle Carettochelys insculpta. Here, we use micro-computed tomography of osteological and contrast-enhanced stained specimens to describe the cranial osteology, neuroanatomy, circulatory system, and jaw musculature of Carettochelys insculpta. The jaw-related myology is described in detail for the first time for this taxon, including m. zygomaticomandibularis, a muscular unit only found in trionychians. We also document a unique arterial pattern for the internal carotid artery and its subordinate branches and provide an extensive list of osteological ontogenetic differences. The present work provides new insights into the craniomandibular anatomy of turtles and will allow a better understanding of the evolutionary history of the circulatory system of trionychians and intraspecific variation among turtles., (© 2024 The Authors. The Anatomical Record published by Wiley Periodicals LLC on behalf of American Association for Anatomy.)

The cranium of turtles (Testudines) is characterized by the secondary reduction of temporal fenestrae and loss of cranial joints (i.e., characteristics of anapsid, akinetic skulls). Evolution and ontogeny of the turtle cranium are associated with shape changes. Cranial shape variation among Testudines can partially be explained by dietary and functional adaptations (neck retraction), but it is unclear if cranial topology shows similar ecomorphological signal, or if it is decoupled from shape evolution. We assess the topological arrangement of cranial bones (i.e., number, relative positioning, connections), using anatomical network analysis. Non-shelled stem turtles have similar cranial arrangements to archosauromorph outgroups. Shelled turtles (Testudinata) evolve a unique cranial organization that is associated with bone losses (e.g., supratemporal, lacrimal, ectopterygoid) and an increase in complexity (i.e., densely and highly interconnected skulls with low path lengths between bones), resulting from the closure of skull openings and establishment of unusual connections such as a parietal-pterygoid contact in the secondary braincase. Topological changes evolutionarily predate many shape changes. Topological variation and taxonomic morphospace discrimination among crown turtles are low, indicating that cranial topology may be constrained. Observed variation results from repeated losses of nonintegral bones (i.e., premaxilla, nasal, epipterygoid, quadratojugal), and changes in temporal emarginations and palate construction. We observe only minor ontogenetic changes. Topology is not influenced by diet and habitat, contrasting cranial shape. Our results indicate that turtles have a unique cranial topology among reptiles that is conserved after its initial establishment, and shows that cranial topology and shape have different evolutionary histories., (© 2023 The Authors. The Anatomical Record published by Wiley Periodicals LLC on behalf of American Association for Anatomy.)

Reciprocal connections between the thalamus and the cortex are one of the most characteristic features of forebrain organization in mammals. To date, this circuit has been documented only in turtles. However, reptiles, including turtles, have an additional path from the dorsal thalamus to the telencephalon. This terminates in a pallial structure known as the dorsal ventricular ridge. Yet, no reciprocal connection from the dorsal ventricular ridge to thalamic nuclei has been uncovered. Since axons from the thalamus pass through the basal nuclei on route to the dorsal ventricular ridge, the basal nuclei might be a source of reciprocal connections. Accordingly, the location and distribution of neurons after retrograde tracer placement into the dorsal thalamus were examined. Retrogradely labeled neurons in the basal nuclei were indeed found. One possibility to explain this observation is that connections with the dorsal ventricular ridge are present during development but later pruned during embryogenesis., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

The present investigation examined the oropharyngeal roof of two turtles having different feeding behaviors: the landform Greek tortoise (Testudo graeca graeca) primarily herbivores and the semi-aquatic red-eared slider turtle (Trachemys scripta elegans) lives in freshwater that opportunistic omnivorous grossly and by scanning and light microscopes. Grossly, the Greek tortoise had a V-shaped roof consisting of the upper rhamphotheca, peri-palatine region, upper alveolar ridge, peripheral palatine ridge, median palatine ridge, vomer, choanae, caudal palatine part, and pharynx. At the same time, the red-eared slider had a semilunar roof consisting of upper rhamphotheca, two peripheral palatine ridges, core of palatine ridges, upper alveolar band, vomer, choanae, caudal palatine part, and pharynx. SEM revealed that the red-eared slider roof appeared more straightforward. The upper rhamphotheca is sharp, with a median premaxillary notch in the red-eared slider that gives a powerful bite for cutting to compensate absence of the teeth. Additionally, the red-eared slider's upper alveolar band is interrupted by a single upper alveolar ridge that appears spiky, pointed, and longer as it needs powerful chewing of prey and there are two types of teeth-like projections at its peri-palatine area for food-crushing and chewing. The Greek tortoise palatine region had numerous ridges and folds to provide roughness for food processing. Greek tortoises had small-sized choanae with two choanal folds to minimize choanal openings when eating dusty grasses. Histologically, Greek tortoise palate was rostrally thicker and more keratinized than caudally, and the caudal palatine region was characterized by a single pair of circumvallate-like papilla with multiple mucous openings and secretions, while red-eared slider palate was slightly keratinized at the peri-choanal region, and the rest of the palate was non-keratinized with few mucous openings. The current investigation found various structural oropharyngeal roof adaptations to feeding behavior in the omnivore red-eared slide compared to the herbivorous Greek turtle., (© 2024. The Author(s).)

The larynx is in the lower respiratory tract and has the function of protecting the airways, controlling, and modulating breathing, assisting the circulatory system, and vocalizing. This study aims to describe the anatomy and histology of the skeleton of the larynx and trachea of the species Chelonia mydas, Caiman yacare and Caiman latirostris. The study was conducted at the Federal University of Espírito Santo (UFES), using nine specimens of Ch. mydas, 20 of Ca. yacare and four of Ca. latirostris. Samples of the larynx and trachea were collected, fixed, and sent for dissection of the structures and subsequent macroscopic analysis. For histology, samples were processed by the routine paraffin embedding method and stained with hematoxylin-eosin and Verhoeff. For the three species, two arytenoid cartilages, a cricoid cartilage, a hyoid apparatus composed of a base and two horns were found. In Ch. mydas, two structures called thyroid wings were observed, not found in crocodilians. The trachea of crocodilians presented incomplete tracheal rings and musculature, while the trachea of Ch. mydas presented complete tracheal rings. Histologically, the entire cartilaginous skeleton of the larynx of the three species, as well as the tracheal rings, are constituted by hyaline cartilage.

The study of the brain by magnetic resonance imaging (MRI) allows to obtain detailed anatomical images, useful to describe specific encephalic structures and to analyze possible variabilities. It is widely used in clinical practice and is becoming increasingly used in veterinary medicine, even in exotic animals; however, despite its potential, its use in comparative neuroanatomy studies is still incipient. It is a technology that in recent years has significantly improved anatomical resolution, together with the fact that it is non-invasive and allows for systematic comparative analysis. All this makes it particularly interesting and useful in evolutionary neuroscience studies, since it allows for the analysis and comparison of brains of rare or otherwise inaccessible species. In the present study, we have analyzed the prosencephalon of three representative sauropsid species, the turtle Trachemys scripta (order Testudine), the lizard Pogona vitticeps (order Squamata) and the snake Python regius (order Squamata) by MRI. In addition, we used MRI sections to analyze the total brain volume and ventricular system of these species, employing volumetric and chemometric analyses together. The raw MRI data of the sauropsida models analyzed in the present study are available for viewing and downloading and have allowed us to produce an atlas of the forebrain of each of the species analyzed, with the main brain regions. In addition, our volumetric data showed that the three groups presented clear differences in terms of total and ventricular brain volumes, particularly the turtles, which in all cases presented distinctive characteristics compared to the lizards and snakes., (© 2024. The Author(s).)

Using histological cross-sections, the chondrocranium anatomy was reconstructed for two developmental stages of Hermann's tortoise (Testudo hermanni). The morphology differs from the chondrocrania of most other turtles by a process above the ectochoanal cartilage with Pelodiscus sinensis being the only other known species with such a structure. The anterior and posterior processes of the tectum synoticum are better developed than in most other turtles and an ascending process of the palatoquadrate is missing, which is otherwise only the case in pleurodiran turtles. The nasal region gets proportionally larger during development. We interpret the enlargement of the nasal capsules as an adaption to increase the surface area of the olfactory epithelium for better perception of volant odors. Elongation of the nasal capsules in trionychids, in contrast, is unlikely to be related to olfaction, while it is ambiguous in the case of Sternotherus odoratus. However, we have to conclude that research on chondrocranium anatomy is still at its beginning and more comprehensive detailed descriptions in relation to other parts of the anatomy are needed before providing broad-scale ecological and phylogenetic interpretations., (© 2024 The Author(s). Journal of Morphology published by Wiley Periodicals LLC.)

The mandible of turtles is rich in osteological characters that are relevant for systematic purposes. Shape variation additionally reflects upon various feeding strategies and are thus informative for the palaeoecological interpretation of extinct species based on fossils. The mandibular anatomy of non-baenid paracryptodires has so far been undescribed. Based on digital segmentation of a computed tomography scan, I herein describe the mandible of the pleurosternid paracryptodire Glyptops ornatus. This taxon has a slender and gracile jaw, with weakly developed muscle attachment sites for adductor muscles (i.e., adductor fossa, coronoid process, and retroarticular process) and strongly reduced triturating ridges. These features are typical for suction-feeding aquatic hunters, thereby contrasting with the robust, durophagous-adapted mandibles of many baenid or compsemydid paracryptodires. In addition, the mandible of G. ornatus is characterized by the presence of a large splenial with a dorsal splenial-dentary contact, the presence of a splenial foramen, and the strong reduction of the foramen dentofaciale majus and the absence of a posterior intermandibular foramen., (© 2023 The Authors. The Anatomical Record published by Wiley Periodicals LLC on behalf of American Association for Anatomy.)

Semi-articulated remains of a large chelonioid turtle from the Turonian strata (Upper Cretaceous; ca. 93.9-89.8 Myr) near Sant'Anna d'Alfaedo (Verona province, northeastern Italy) are described for the first time. Together with the skeletal elements, the specimen also preserves pebbles inside the thoracic area which are lithologically distinct from the surrounding matrix. These allochthonous clasts are here interpreted as geo-gastroliths, in-life ingested stones that resided in the digestive tract of the animal. This interpretation marks the first reported evidence of geophagy in a fossil marine turtle. SEM-EDS analysis, together with macroscopic petrological characterization, confirm the presence of both siliceous and carbonatic pebbles. These putative geo-gastroliths have morphometries and size ranges more similar to those of gastroliths in different taxa (fossils and extant) than allochthonous "dropstone" clasts from the same deposit that were carried by floating vegetation A dense pitted pattern of superficial erosion is microscopically recognizable on the carbonatic gastroliths, consistent with surface etching due to gastric acids. The occurrence of a similar pattern was demonstrated by the experimental etching of carbonatic pebbles with synthetic gastric juice. Gut contents of modern green sea turtles (Chelonia mydas) were surveyed for substrate ingestion, providing direct evidence of geophagic behavior in extant chelonioids. Comparison with modern turtle dietary habits may suggests that the pebbles were ingested as a way to supplement calcium after or in preparation for egg deposition, implying that the studied specimen was possibly a gravid female., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Serafini et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

One crucial component of the optical system is the ciliary body (CB). This body secretes the aqueous humour, which is essential to maintain the internal eye pressure as well as the clearness of the lens and cornea. The histological study was designed to provide the morphological differences of CB and iris in the anterior eye chambers of the following vertebrate classes: fish (grass carp), amphibians (Arabian toad), reptiles (semiaquatic turtle, fan-footed gecko, ocellated skink, Egyptian spiny-tailed lizard, Arabian horned viper), birds (common pigeon, common quail, common kestrel), and mammals (BALB/c mouse, rabbit, golden hamster, desert hedgehog, lesser Egyptian jerboa, Egyptian fruit bat). The results showed distinct morphological appearances of the CB and iris in each species, ranging from fish to mammals. The present comparative study concluded that the morphological structure of the CB and iris is the adaptation of species to either their lifestyle or survival in specific habitats., (© 2024 Wiley‐VCH GmbH. Published by John Wiley & Sons Ltd.)

Impressions of vertebrate bodies or their parts, such as trace fossils and natural molds of bones, are a valuable source of information about ancient faunas which may supplement the standard fossil record based on skeletal elements. Whereas trace fossils of animal activity are relatively common and actively studied within the field of ichnology, and natural impressions of internal or external surfaces are a frequent preservation mode in fossil invertebrates, natural molds of bones are comparatively rare and less extensively documented and discussed. Among them, internal molds (steinkerns) of turtle shells are a relatively well-known form of preservation, but the mechanisms and taphonomic prerequisites leading to their formation are poorly studied. External shell molds are even less represented in the literature. Herein, we describe a historic specimen of a natural external turtle plastron mold from the Triassic (Norian) Löwenstein Formation of Germany-a formation which also yielded a number of turtle steinkerns. The specimen is significant not only because it represents an unusual form of preservation, but also due to its remarkably large size and the presence of a potential shell pathology. Although it was initially interpreted as Proterochersis sp., the recent progress in the knowledge of proterochersid turtles leading to an increase in the number of known taxa within that group allows us to verify that assessment. We confirm that the specimen is morphologically consistent with the genus and tentatively identify it as Proterochersis robusta, the only representative of that genus from the Löwenstein Formation. We note, however, that its size exceeds the size observed thus far in Proterochersis robusta and fits within the range of Proterochersis porebensis from the Grabowa Formation of Poland. The marks interpreted as shell pathology are morphologically consistent with Karethraichnus lakkos-an ichnotaxon interpreted as a trace of ectoparasites, such as leeches. This may support the previously proposed interpretation of Proterochersis spp. as a semiaquatic turtle. Moreover, if the identification is correct, the specimen may represent a very rare case of a negative preservation of a named ichnotaxon. Finally, we discuss the taphonomy of the Löwenstein Formation turtles in comparison with other Triassic turtle-yielding formations which show no potential for the preservation of internal or external shell molds and propose a taphonomic model for the formation of such fossils., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Szczygielski et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Freshwater fauna is facing an uphill task for survival in the Ganga Basin, India, due to a range of factors causing habitat degradation and fragmentation, necessitating conservation interventions. As part of the ongoing efforts to conserve the freshwater fauna of the Basin, we are working on rehabilitating rescued freshwater chelonians. We carry out various interventions to restore rescued individuals to an apparent state of fitness for their release in suitable natural habitats. Morphometric measurements are crucial to managing captive wild animals for assessing their growth and well-being. Measurements are made using manual methods like vernier caliper that are prone to observer error experience and require handling the specimens for extended periods. Digital imaging technology is rapidly progressing at a fast pace and with the advancement of technology. We acquired images of turtles using smartphones along with manual morphometric measurements using vernier calipers of the straight carapace length and straight carapace width. The images were subsequently processed using ImageJ, a freeware and compared with manual morphometric measurements. A significant decrease in the time spent in carrying out morphometric measurements was observed in our study. The difference in error in measurements was, however, not significant. A probable cause for this may have been the extensive experience of the personnel carrying out the measurements using vernier caliper. Digital image processing technology can cause a significant reduction in the stress of the animals exposed to handling during measurements, thereby improving their welfare. Additionally, this can be used in the field to carry out morphometric measurements of free-ranging individuals, where it is often difficult to capture individuals, and challenges are faced in obtaining permission to capture specimens., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Panda et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Flat hydrodynamic shells likely represent an evolutionary trade-off between adaptation to an aquatic lifestyle and the instability of more rounded shells, thought beneficial for self-righting. Trade-offs often result in compromises, this is particularly true when freshwater turtles, with flatter shells, must self-right to avoid the negative effects of inverting. These turtles, theoretically, invest more biomechanical effort to achieve successful and timely self-righting when compared to turtles with rounded carapaces. This increase in effort places these hatchlings in a precarious position; prone to inversion and predation and with shells seemingly maladapted to the act of self-righting. Here, we examine hatchling self-righting performance in three morphologically distinct freshwater turtle species (Apalone spinifera, Chelydra serpentina and Trachemys scripta scripta) that inhabit similar environmental niches. We demonstrate that these hatchlings were capable of rapid self-righting and used considerably less biomechanical effort relative to adult turtles. Despite differences in shell morphology the energetic efficiency of self-righting remained remarkably low and uniform between the three species. Our results confound theoretical predictions of self-righting ability based on shell shape metrics and indicate that other morphological characteristics like neck or tail morphology and shell material properties must be considered to better understand the biomechanical nuances of Testudine self-righting., (© 2024. The Author(s).)

Amniote skulls display diverse architectural patterns including remarkable variations in the number of temporal arches surrounding the upper and lower temporal fenestrae. However, the cellular and molecular basis underlying this diversification remains elusive. Turtles are a useful model to understand skull diversity due to the presence of secondarily closed temporal fenestrae and different extents of temporal emarginations (marginal reduction of dermal bones). Here, we analyzed embryos of three turtle species with varying degrees of temporal emargination and identified shared widespread coexpression of upstream osteogenic genes Msx2 and Runx2 and species-specific expression of more downstream osteogenic genes Sp7 and Sparc in the head. Further analysis of representative amniote embryos revealed differential expression patterns of osteogenic genes in the temporal region, suggesting that the spatiotemporal regulation of Msx2 , Runx2 , and Sp7 distinguishes the temporal skull morphology among amniotes. Moreover, the presence of Msx2- and/or Runx2 -positive temporal mesenchyme with osteogenic potential may have contributed to their extremely diverse cranial morphology in reptiles.

Sea turtles use olfaction to detect volatile and water-soluble substances. The nasal cavity of green turtles (Chelonia mydas) comprises morphologically defined the anterodorsal, anteroventral, and posterodorsal diverticula, as well as a single posteroventral fossa. Here, we detailed the histological features of the nasal cavity of a mature female green turtle. The posterodorsal diverticulum contained spongy-like venous sinuses and a wave-shaped sensory epithelium that favored ventilation. Secretory structures that were significant in sensory and non-sensory epithelia were probably involved in protection against seawater. These findings suggested that green turtles efficiently intake airborne substances and dissolve water-soluble substances in mucous, while suppressing the effects of salts. In addition, positive staining of Gα s/olf that couples with olfactory, but not vomeronasal, receptors was predominant in all three types of sensory epithelium in the nasal cavity. Both of airborne and water-soluble odorants seemed to be detected in cells expressing Gα olf and olfactory receptors., (© 2023 Anatomical Society.)

The limestones of the Solnhofen area in southern Germany are one of the most important fossil Lagerstätten from the entire Mesozoic era, especially famous for the exquisitely preserved vertebrates. The turtles from the Solnhofen Limestone have been always of special interest because they include some of the best-preserved specimens from the Mesozoic. Here, we describe a new turtle specimen from the Torleite Formation (Kimmeridgian) of Painten and refer it to the thalassochelydian turtle Solnhofia parsonsi based on the presence of a unique combination of characters. The far majority of morphological differences from previously published specimens can be explained by ontogeny as the new specimen represents a larger, more ossified, and presumably older individual. Additionally, the specimen from Painten is the first described specimen of S. parsonsi preserving the largely complete and articulated limbs, the preservation of which indicates that the taxon did not possess stiffened paddles present in more pelagic marine turtles and is consistent with a previously inferred nearshore marine lifestyle. Contrary to previous inferences, we argue that taphonomic preservation of digits in articulated fossil turtles from laminated deposits cannot be used alone to infer marine or freshwater habitat. Finally, the new specimen from Painten is only the second, for which detailed information on its stratigraphic position and locality of origin are known., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2023 Augustin et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Green sea turtles (Chelonia mydas) can swim up to 50 km per day while only consuming seagrass or microalgae. How the animal accomplishes this vast journey on such low energy intake points to the effectiveness of their swimming technique and is a testament to the power of evolution. Understanding the green sea turtle's ability to accomplish these journeys requires insight into their propulsive strategies. Conducting animal testing to uncover their propulsive strategies brings significant challenges: firstly, the ethical issues of conducting experiments on an endangered animal, and secondly, the animal may not even swim with its regular routine during the experiments. In this work, we develop a new soft-robotic sea turtle that reproduces the real animal's form and function to provide biomechanical insights without the need for invasive experimentation. We found that the green sea turtle may only produce propulsion for approximately 30% of the limb beat cycle, with the remaining 70% exploiting a power-preserving low-drag glide. Due to the animal's large mass and relatively low drag coefficient, losses in swim speed are minimal during the gliding stage. These findings may lead to the creation of a new generation of robotic systems for ocean exploration that use an optimised derivative of the sea turtle propulsive strategy., (© 2023. The Author(s).)

Turtles are a charismatic reptile group with a peculiar body plan, which most notably includes the shell. Anatomists have often focused descriptive efforts on the shell and other strongly derived body parts, such as the akinetic skull, or the cervical vertebrae. Other parts of turtle osteology, like the girdles, limbs, and mandibles, are documented with less rigor and detail. The mandible is the primary skeletal element involved in food acquisition and initial food processing of turtles, and its features are thus likely linked to feeding ecology. In addition, the mandible of turtles is composed of up to seven bones (sometimes fused to as little as three) and has thus anatomical complexity that may be insightful for systematic purposes and phylogenetic research. Despite apparent complexity and diversity to the mandible of turtles, this anatomical system has not been systematically studied, not even in search of characters that might improve phylogenetic resolution. Here, we describe the mandibular osteology for all major subclades of extant turtles with the help of digitally dissected 3D models derived from high-resolution computed tomography (μCT) scans of 70 extant species. We provide 31 fully segmented mandibles, as well as 3D models of the mandibular musculature, innervation, and arterial circulation of the cryptodire Dermatemys mawii. We synthesize observed variation into 51 morphological characters, which we optimize onto a molecular phylogeny. This analysis shows some mandibular characters to have high systematic value, whereas others are highly homoplastic and may underlie ecological influences or other factors invoking variation., (© 2022 The Authors. The Anatomical Record published by Wiley Periodicals LLC on behalf of American Association for Anatomy.)

Changes in the structural association of skeletal traits are crucial to the evolution of novel forms and functions. In vertebrates, such rearrangements often occur gradually and may precede or coincide with the functional activation of skeletal traits. To illustrate this process, we examined the ontogeny of African hinge-back tortoises (Kinixys spp.). Kinixys species feature a moveable "hinge" on the dorsal shell (carapace) that enables shell closure (kinesis) when the hind limbs are withdrawn. This hinge, however, is absent in juveniles. Herein, we describe how this unusual phenotype arises via alterations in the tissue configuration and shape of the carapace. The ontogenetic repatterning of osseous and keratinous tissue coincided with shifts in morphological integration and the establishment of anterior (static) and posterior (kinetic) carapacial modules. Based on ex vivo skeletal movement and raw anatomy, we propose that Kinixys employs a "sliding hinge" shell-closing system that overcomes thoracic rigidity and enhances the protective capacity of the carapace. Universal properties of the vertebrate skeleton, such as plasticity, modularity, and secondary maturation processes, contributed to adaptive evolutionary change in Kinixys. We discuss a hypothetical model to explain the delayed emergence of skeletal traits and its relevance to the origins of novel form-to-function relationships., (© 2022 The Authors. The Anatomical Record published by Wiley Periodicals LLC on behalf of American Association for Anatomy.)

Proper taxonomic identification is critical to our understanding of biodiversity and the underlying evolutionary history. Here we re-examine the cast of the holotype of Chinemys pani, a geoemydid turtle from the Pleistocene of Taiwan; the actual specimen was not curated appropriately after the original publication and was most likely lost. Our results provide substantial evidence to show that Chinemys pani should be identified as Mauremys reevesii. The replica, though not ideal, preserves various morphological features that allow reliable taxonomic identification of Mauremys reevesii, including the presence of three longitudinal keels on the carapace, the second to sixth neural bones anteriorly short-sided, and the lack of a movable plastral hinge. In addition, we also confirm that the original diagnostic features that established the new taxon: Chinemys pani - are polymorphic characters of Mauremys reevesii. Our taxonomic revision of a Pleistocene geoemydid turtle from Taiwan confirms the existence of the Pleistocene Mauremys reevesii. More importantly, this study offers new insights into the origin of modern biodiversity in Taiwan and gives a straightforward example of how fossils can be applied to conservation policies., (© 2022 The Authors. The Anatomical Record published by Wiley Periodicals LLC on behalf of American Association for Anatomy.)

Detailed anatomical knowledge is a prerequisite for studying a variety of biological questions. This holds true particularly for the evolutionary realm, in which fossils play an important role. Putting paleontological data in perspective consequently requires a profound knowledge of the corresponding structures of the extant representatives of a given lineage as well. Numerous morphological studies have contributed to our understanding of chelonian anatomy over the past centuries, but one of the earliest ones-whose completion celebrated its bicentenary with this symposium-still stands out among all of them: Anatome Testudinis Europaeae, published by Ludwig Heinrich Bojanus (1776-1827) in two installments in 1819 and 1821. Numerous myths around this publication have evolved ever since. The intent of this article is to set the record straight for some of them, and, based on personal inspection of multiple copies, to discuss currently unrecognized aspects about the existence of exceptional colored variant editions. This ends in a proposal for how this work could be used even more effectively in its upcoming third century of existence. Last but not least and despite the controversies related to its bibliographical aspects, one fact remains an unchallenged reality: Anatome Testudinis Europaeae, even 200 years after its first publication, still ranks very high among the most detailed and accurate anatomical works on a single chelonian-and for that matter reptilian-species ever produced and has lost absolutely none of its value for modern-day science., (© 2022 The Author. The Anatomical Record published by Wiley Periodicals LLC on behalf of American Association for Anatomy.)

Softshell turtles (Trionychidae) display characteristic pits and ridges, or "sculpturing," on the bony carapace. Variation in sculpturing pattern may be useful in classifying fossilized shell fragments. Although past attempts could discern qualitative differences in certain best-case scenarios, many early taxonomic uses of sculpturing traits have been reevaluated as unreliable in the face of intraspecific variation. The potential of sculpturing to contain consistently reliable, quantitative, taxonomically informative traits remains underexplored. Here, we revisit this idea by quantifying trionychid shell patterning with topographic measurement techniques more commonly applied to nonhomologous quantification of mammalian teeth and geographic surface topography. We assess potential sources of variation and accuracy of these metrics for species identification. Carapaces of extant specimens used in this study included members of the species Apalone ferox, Apalone spinifera, and Amyda cartilaginea and were obtained from the herpetology collections of the Florida Museum of Natural History. 3D scans of shells were systematically sampled to create digital "fragments." These fragments were quantified using three topographic measurements: Dirichlet Normal Energy (DNE), Relief Index (RFI), and Orientation Patch Count Rotated (OPCR). A nested MANOVA suggests there is significant variation at the species, individual, and carapace location levels of analysis. Linear discriminant analysis correctly predicts a sample's species identity from DNE, RFI, and OPCR 75.2% of the time. These promising results indicate that topographic measures may provide a method for identifying shell fragments that are currently identifiable only as Trionychidae indet. Future work should explore this approach in additional species and account for ontogenetic changes., (© 2022 American Association for Anatomy.)

Previously, only one small-sized species of Testudinidae (Chelonoidis gringorum) was named from Lower-Middle Miocene of Central Patagonia. In this short article, we describe a new large Testudinidae, here named Chelonoidis meridiana sp. nov. This large new species (carapace up to 80 cm) differs from other large species of the southern South American fossil record by the absence of gibbosities on neural and costal carapacial bones, a short and wide entoplastron with a humeropectoral sulcus that was placed well behind its posterior end, and pectoral scutes that are medially longer, approximately one-third of the medial length of the hyoplastra. The discovery of this new species in the Middle Miocene increases the raw turtle diversity in Chubut, permitting to reduce the gap between the raw and phylogenetic diversity previously proposed. This occurrence is also important from both a temporal and geographic point of view. It permits fixing the presence of large-sized tortoises in the continent since ~15 million years ago (Middle Miocene). This occurrence predates all other large and giant tortoises from Argentina and South America and it is older than the giant Chelonoidis from the Langhian-Tortonian of Colombia. This is also the southernmost occurrence of a large-sized testudinid in the world., (© 2022 American Association for Anatomy.)

With their particular body plan within amniotes and their amazing fossil record, turtles represent a great interest for both neontologists and paleontologists with a strong anatomical background. The Turtle Evolution Symposia are regular international meetings that gather scientists working with different aspects related to the evolutionary history of turtles, from their origin and early evolution until recent times. The latest edition of the Turtle Evolution Symposium was organized in 2021 amidst the COVID-19 outbreak and held virtually from the facilities of the Museo Paleontológico Egidio Feruglio in Trelew (Patagonia, Chubut, Argentina). More than 75 scientists from 25 countries presented their latest advances on topics related to turtle evolution, some of which are published in this Special Volume of The Anatomical Record. Both the Turtle Evolution Symposium 2021 and this Special Volume are dedicated to Marcelo S. de la Fuente who was the first researcher who specialized in the study of extinct turtles in South America, and his studies have an important regional and international impact., (© 2023 American Association for Anatomy.)

The study of pathological bone modifications of extinct organisms of lineages, which are still living today, in combination with extant representatives, allows to infer data about population dynamics, lifestyle, and diseases they were subject to. Pathological studies in turtles are extensive; however, these contributions are mainly focused on extant representative records of survival rates or on non-skeletonized material, and do not generally include morphological descriptions, illustrations, or data concerning their etiology and pathogenesis. As a consequence, paleopathology in turtles remains relatively poorly understood, especially considering extinct forms. In this context, we herein analyze marks of possible pathological origin recognized in two disarticulated plastral plates of the Spanish freshwater basal pan-pleurodiran turtle Dortoka vasconica (Dortokidae), from its type locality, the Upper Cretaceous (late Campanian-early Maastrichtian) fossil site of Laño 1 (Treviño County, Burgos, Spain). As a result, information regarding the possible etiology, pathogenesis, and stages of healing of the marks studied here are provided. A probable infectious origin is recognized as the etiology in both plates, these marks being considered as pathologies. This study contributes to our understanding of pathologies in extinct turtle taxa, specifically a stem-pleurodiran turtle., (© 2022 The Authors. The Anatomical Record published by Wiley Periodicals LLC on behalf of American Association for Anatomy.)

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., (© 2022 The Authors. The Anatomical Record published by Wiley Periodicals LLC on behalf of American Association for Anatomy.)

A cranium belonging to a baenid turtle was recently recovered from the lower half of the Judith River Formation, Montana. Badlands Dinosaur Museum (BDM) 004 is a well-preserved partial cranium that includes the posterior cranial vault, cranial base, and otic capsules. Based on diagnostic characters, the skull can be attributed to Plesiobaena antiqua, which has been previously reported from the Judith River Formation. It also shares with palatobaenines projecting posterior processes of the tubercula basioccipitale and a prominent condylus occipitalis with a deep central pit, demonstrating variation within the Pl. antiqua hypodigm. In a phylogenetic analysis, an operational taxonomic unit of BDM 004 was positioned within Baenodda in an unresolved polytomy with Pl. antiqua, Edowa zuniensis, Palatobaeninae, and Eubaeninae. Microcomputed tomographic (μCT) scans revealed morphology of the middle and inner ear and endocast that are largely unknown in baenids. Semicircular canals of BDM 004 are virtually identical to those of Eubaena cephalica and consistent in dimensions to those of other turtle taxa, including anterior and posterior semicircular canals that are robust and taller than the common crus and diverge from each other at an angle of approximately 90°. The digital endocast reveals a moderately flexed brain with rounded cerebral hemispheres and minimal separation between the metencephalon and myelencephalon. Its well-preserved columella auris (stapes) is gracile with a posterodorsally flared basis columella. It arcs across the middle ear and flattens near its terminus. This study adds to the understanding of baenid middle and inner ear and neuroanatomical morphology and expands the morphological understanding of Pl. antiqua., (© 2023 American Association for Anatomy.)

Although the existence of fossil turtles in Makrygialos and the surrounding areas, on the west side of the Thermaikos Gulf in Northern Greece, has been known for almost two decades, it has not been studied so far in detail. Over the last 5 years, we have conducted systematic fieldwork and exploration, focusing on the discovery and recovery of fossils in the coastal broader area of Makrygialos. Eleven turtle specimens have been found so far, eight of which have been collected, on the outcrops of the beaches of Makrygialos and Agiannis. Their age is estimated between the latest Miocene and Pliocene. Four of these specimens are terrestrial giant tortoises, two of them are small tortoises which we identify as the species Chersine hermanni sensu lato, and the last two are freshwater turtles which we attribute to the genus Mauremys sensu lato. Here, we present our studies on the small-sized turtle species from this region. The fossil turtle fauna of Makrygialos is among the richest and most diverse in Greece, as in only a few other Greek localities at least three species of fossil turtles have been found. The C. hermanni specimens found in Makrygialos are probably the oldest fossils of the species found in Europe. The small-turtle faunal composition during the Neogene along the east and west sides of the Thermaikos Gulf was completely different., (© 2022 American Association for Anatomy.)

The abundant record of marine turtles from the Late Cretaceous of Appalachia contrasts with the relatively poor record of contemporaneous terrestrial and freshwater species. A new taxon from the Santonian-Campanian of Alabama, Appalachemys ebersolei gen. et sp. nov., is described here and assigned to a grade of freshwater turtles known as "macrobaenids." Appalachemys can be differentiated from other "macrobaenids" by the presence of a nearly round carapace, deep nuchal emargination, and nine pairs of costals. With a carapace more than 80 cm in length, Appalachemys is among the largest freshwater turtles to ever inhabit North America. The absence of pre-Campanian "macrobaenids" from Laramidia indicates that the North American distribution of this grade may have been restricted to Appalachia prior to the recession of the Western Interior Seaway. Phylogenetic analysis places Appalachemys as the sister taxon to all post-Santonian "macrobaenids." Although the phylogeny lacks statistical support, it demonstrates morphological similarities between the K/Pg boundary species Osteopygis emarginatus and Maastrichtian-Danian species referred to Judithemys. We, therefore, refer all but the Campanian type species of Judithemys to the genus Osteopygis. A review of all North American "macrobaenid" occurrences reveals that despite originating in Asia, the record of the grade (as defined here) is predominantly North American. Future studies can test whether late Paleocene records in Asia and Europe resulted from dispersal from North America., (© 2022 American Association for Anatomy.)

Nanhsiungchelyidae are a group of large turtles that lived in Asia and North America during the Cretaceous. Here we report a new species of nanhsiungchelyid, Nanhsiungchelys yangi sp. nov., from the Upper Cretaceous of Nanxiong Basin, China. The specimen consists of a well-preserved skull and lower jaw, as well as the anterior parts of the carapace and plastron. The diagnostic features of Nanhsiungchelys include a large entire carapace length (∼55.5 cm), a network of sculptures consisting of pits and ridges on the surface of the skull and shell, shallow cheek emargination and temporal emargination, deep nuchal emargination, and a pair of anterolateral processes on the carapace. However, Nanhsiungchelys yangi differs from the other species of Nanhsiungchelys mainly in having a triangular-shaped snout (in dorsal view) and wide anterolateral processes on the carapace. Additionally, some other characteristics ( e.g. , the premaxilla is higher than wide, the maxilla is unseen in dorsal views, a small portion of the maxilla extends posterior and ventral of the orbit, and the parietal is bigger than the frontal) are strong evidence to distinguish Nanhsiungchelys yangi from Nanhsiungchelys wuchingensis . A phylogenetic analysis of nanhsiungchelyids places Nanhsiungchelys yangi and Nanhsiungchelys wuchingensis as sister taxa. Nanhsiungchelys yangi and some other nanhsiungchelyids bear distinct anterolateral processes on the carapace, which have not been reported in any extant turtles and may have played a role in protecting the head. The Nanxiong Basin was extremely hot during the Late Cretaceous, and so we suggest that nanhsiungchelyids might have immersed themselves in mud or water to avoid the heat, similar to some extant tortoises. If they were capable of swimming, our computer simulations of fluid flow suggest the anterolateral processes could have reduced drag during locomotion., Competing Interests: The authors declare there are no competing interests., (©2023 Ke et al.)

Morphological studies on the oropharyngeal cavity of turtles are an interesting tool in understanding evolutionary processes associated with feeding habits. There is paucity of morphological information on the oropharyngeal cavity of the Trachemys adiutrix turtle. Thus, the aim of this study was to describe the tongue and palate morphology of T. adiutrix to establish a standard model for the species, providing information that may improve knowledge on the species feeding habits. Gross dissection, light microscopy and scanning electron microscopy assessments of 11 specimens were carried out. The tongue of T. adiutrix is triangular with a slightly rounded apex and broad base and lingual papillae widely distributed throughout the entire dorsal surface. The palate is composed of bony structures, displaying a triangular apex with one pair of choanae and palatine raphe that begin in the middle region, dividing the two openings. The body was elongated and smooth. The root was wrinkled and opened into the oesophagus. The tongue was lined by non-keratinized stratified squamous epithelium, rich in mucous cells and a large number of different-shaped papillae and taste buds. The palate was mainly lined by a pseudostratified cylindrical ciliated epithelium rich in mucous cells. In conclusion, the tongue and palate characteristics of T. adiutrix include evidence that these animals are semiaquatic, displaying morphological characteristics associated with aquatic and terrestrial trophic ecology, similar to that observed in other semiaquatic and terrestrial chelonian species., (© 2023 Wiley-VCH GmbH. Published by John Wiley & Sons Ltd.)

The digestive tract development of the Pelodiscus sinensis embryo is described through the observation of the embryonic morphology on hematoxylin and eosin stained tissue sections. During the first 9 days of embryonic development, the anterior intestine of the embryo divides into the oral cavity, pharyngeal cavity, esophagus, stomach, and small intestine, while the caudal intestine differentiates into the cloaca, the anterior and caudal tubes of the large intestine. Between days 10-24, the wall of the digestive tract forms a two-layer structure consisting of mucosa and submucosa. The endoderm evolves into epithelial tissue in each part of the digestive tract, the mesoderm goes from a dense cluster of cells to looser mesenchymal tissue then divides into loose connective tissue, mesothelium, and muscle tissue. There is no clear temporal boundary between development of mesenchymal tissue and the early loose connective tissue, which is a gradual process.

Morphological studies of the oropharyngeal cavity of chelonians have become an interesting tool in the understanding of evolutionary processes associated with feeding habits in aquatic animals and the transition from aquatic to terrestrial forms. In this context, the aim of the present study was to describe the oropharyngeal cavity floor morphology of hawksbill sea turtle (Eretmochelys imbricata) hatchlings. Ten dead hatchlings of undefined sex were obtained from nests hatched on the coast of the state of Rio Grande do Norte, Brazil. The heads of each specimen were fixed, dissected, and analyzed at the macroscopic and microscopic levels. The oropharyngeal cavity floor of the hawksbill sea turtle hatchlings is formed by the tongue, pharynx, floor muscles, and hyolingual skeleton, delimited in the rostral and lateral directions by a keratinized beak, called the rhamphotheca, and in the caudal region at the limit between the pharynx and the esophagus. The tongue muscles and the muscles that support the floor of the oral cavity comprise the following: m. hypoglossohyoideus, m. hypoglossoglossus, m. hyoglossus, m. genioglossus, m. constrictor laryngis, m. geniohyoideus pars lateralis, and m. intermandibularis. The oropharyngeal cavity floor mucosa is formed by keratinized stratified squamous epithelium and the lamina propria is formed by loose connective tissue. The floor mucosa is devoid of taste buds. We believe that the basic oropharyngeal cavity floor characteristics in hawksbill sea turtle hatchlings may comprise indications that these animals are plesiomorphic and that semiaquatic and terrestrial turtles may have undergone adaptations to feed out of water., (© 2022 American Association for Anatomy.)

The late Quaternary is characterized by the extinction of many terrestrial megafauna, which included tortoises (Family: Testudinidae). However, limited information is available on how extinction shaped the phenotype of surviving taxa. Here, based on a global dataset of straight carapace length, we investigate the temporal variation, spatial distribution and evolution of tortoise body size over the past 23 million years, thereby capturing the effects of Quaternary extinctions in this clade. We found a significant change in body size distribution characterized by a reduction of both mean body size and maximum body size of extant tortoises relative to fossil taxa. This reduction of body size occurred earlier in mainland (Early Pleistocene 2.588-0.781 Ma) than in island tortoises (Late Pleistocene/Holocene 0.126-0 Ma). Despite contrasting body size patterns between fossil and extant taxa on a spatial scale, tortoise body size showed limited variation over time until this decline. Body size is a fundamental functional trait determining many aspects of species ecologies, with large tortoises playing key roles as ecosystem engineers. As such, the transition from larger sized to smaller sized classes indicated by our findings likely resulted in the homogenization of tortoises' ecological functions and diminished the role of tortoises in structuring the vegetation community.

Marine turtles were common in the subtropical Upper Cretaceous epi-continental seas that once washed the coasts of the ancient European archipelago. But unlike its contemporaneous faunas from North America, in Europe no taxon surpassed the 1.5 m shell-length. Here, the remains of a new large marine turtle, Leviathanochelys aenigmatica gen. et sp. nov., from the Middle Campanian of the Southern Pyrenees are described. Anatomical and histological evidence concur in identifying the specimen as a basal chelonioid. The new taxon autapomorphically differs from other marine turtles by possessing an additional process on the anteromedial side of the pelvis, and an acetabulum directed strongly ventrally. Based on the pelvis size, it is likely that Leviathanochelys was as large as Archelon, thus becoming one of the largest marine turtles found to ever exist. The large body size of the new taxon could have evolved as a response to the unique habitat conditions of the European Cretaceous archipelago seas. The presence of the accessory pubic process further suggests the occurrence of an additional insertion point of the Musculus rectus abdominis, which together with the paleohistologic evidences support the hypothesis that the new taxon had an open marine pelagic lifestyle., (© 2022. The Author(s).)

We describe the skull of the Early Cretaceous (Aptian-Albian) baenid turtle Trinitichelys hiatti using micro-computed tomography to provide new insights into the cranial anatomy of basal baenids and into the evolution of paracryptodires. We show that the validity of Trinitichelys hiatti vs Arundelemys dardeni still holds true, that the most basal known baenids for which skull material is known share an intriguing combination of features that are typical of either Pleurosternidae or Baenidae , and that the carotid system of Trinitichelys hiatti is intermediate to that of pleurosternids and more advanced baenids. Our expanded phylogenetic analysis confirms the traditional placement of Arundelemys dardeni , Lakotemys australodakotensis , and Trinitichelys hiatti as basal baenids, retrieves Helochelydridae along the stem of Baenoidea, but recovers Dinochelys whitei , Glyptops ornatus , Dorsetochelys typocardium , and Uluops uluops as basal branching Paracryptodira ., Competing Interests: Stephanie E. Pierce is a PeerJ Academic Editor. The authors declare that they have no competing interests., (© 2022 Rollot et al.)

Turtles have a highly modified body plan, including a rigid shell that constrains postcranial anatomy. Skull morphology and neck mobility may therefore be key to ecological specialization in turtles. However, the ecological signal of turtle skull morphologies has not been rigorously evaluated, leaving uncertainties about the roles of ecological adaptation and convergence. We evaluate turtle cranial ecomorphology using three-dimensional geometric morphometrics and phylogenetic comparative methods. Skull shape correlates with allometry, neck retraction capability, and different aquatic feeding ecologies. We find that ecological variables influence skull shape only, whereas a key functional variable (the capacity for neck retraction) influences both shape and size. Ecology and functional predictions from three-dimensional shape are validated by high success rates for extant species, outperforming previous two-dimensional approaches. We use this to infer ecological and functional traits of extinct species. Neck retraction evolved among crownward stem-turtles by the Late Jurassic, signaling functional decoupling of the skull and neck from the shell, possibly linked to a major episode of ecomorphological diversification. We also find strong evidence for convergent ecological adaptations among marine groups. This includes parallel loss of neck retraction, evidence for active hunting, possible grazing, and suction feeding in extinct marine groups. Our large-scale assessment of dietary and functional adaptation throughout turtle evolution reveals the timing and origin of their distinct ecomorphologies, and highlights the potential for ecology and function to have distinct effects on skull form., (© 2022 The Authors. Evolution published by Wiley Periodicals LLC on behalf of The Society for the Study of Evolution.)

The labyrinth of the vertebrate inner ear is a sensory system that governs the perception of head rotations. Central hypotheses predict that labyrinth shape and size are related to ecological adaptations, but this is under debate and has rarely been tested outside of mammals. We analyze the evolution of labyrinth morphology and its ecological drivers in living and fossil turtles, an understudied group that underwent multiple locomotory transitions during 230 million years of evolution. We show that turtles have unexpectedly large labyrinths that evolved during the origin of aquatic habits. Turtle labyrinths are relatively larger than those of mammals, and comparable to many birds, undermining the hypothesis that labyrinth size correlates directly with agility across vertebrates. We also find that labyrinth shape variation does not correlate with ecology in turtles, undermining the widespread expectation that reptilian labyrinth shapes convey behavioral signal, and demonstrating the importance of understudied groups, like turtles., (© 2022. The Author(s).)

Sea turtles have well developed lacrimal glands for their electrolyte homeostasis. In turtles, stapedial artery and palatine artery send branches to supply orbital region, but supply artery for lacrimal glands was not identified. Micro-CT scans showed dorsoventrally large lacrimal glands of sea turtle are supplied by both stapedial artery and palatine artery. The circulatory pattern in cranial region was reconstructed based on the micro-CT scans, showing that sea turtle has basically similar pattern with the common snapping turtle: stapedial artery supplies orbital region and mandibular artery is ramified from stapedial artery. We also investigate the foramen stapedio-temporalis in turtles using osteological specimens. The foramen stapedio-temporalis, where the stapedial artery passes through, has different size among four families of turtles. We compared the sum of cross sections of left and right foramen stapedio-temporalis since homeostasis of one individual is maintained by a pair of lacrimal glands. The size difference may reflect primarily the share of stapedial artery against palatine artery in cranial circulation pattern and blood supply of orbital regions. Our observations confirmed a significantly larger cross-section in the foramen stapedio-temporalis of sea turtles than other freshwater/terrestrial turtles. Since the circulatory pattern is shared, the size difference of foramen stapedio-temporalis reflects the amount of arterial blood supply to lacrimal glands. Therefore, the size of the foramen stapedio-temporalis may indicate marine adaptation of turtles and are applicable to both fossil and osteological specimens.

The subcarapacial vessel is a popular site for venipuncture and intravenous medication administration in chelonians. Reports of adverse effects when using this site have increased, prompting evaluation of its safety. This study aimed to evaluate the anatomy of the subcarapacial vessel in 25 individual chelonians (2 box turtles, 3 red-eared sliders, and 20 red-footed tortoises) using computed tomography (CT). Individuals were sedated and administered contrast in the subcarapacial vessel. The vessel was visualized in 50% of the box turtles and red-footed tortoises, and 100% of the red-eared sliders. All species had contrast extravasation in the subarachnoid space, with red-footed tortoises having the largest percentage (70% compared to 50% and 33% of box turtles and red-eared sliders, respectively). Extravasation of contrast in the trachea or bronchi (70%) and lungs (80%) was seen in the red-footed tortoises only. Higher prevalence of contrast extravasation in the red-footed tortoises is likely because of anatomical differences, including a more cranially extending lung field and domed-shaped carapace compared to the other species. These findings highlight the risk associated with using the subcarapacial vessel for intravenous medication administration in certain species of chelonian.

We present new fossil records of the geoemydid turtle Bridgeremys pusilla from the Uinta Formation of Utah. Turtles are abundant throughout the unit, and known taxa are similar to those from the older strata in the Upper Green River Basin in Wyoming from the Bridger and Washakie Formations. B. pusilla is known from Bridgerian deposits but was not previously known from after the Turtle Bluff Member of the Bridger Formation. The taxon was coveal with two species of the geoemydid Echmatemys (E. callopyge and E. wyomingensis), a common genus of extinct pond turtles known primarily from lacustrine and fluvial deposits in western North America, including the Uinta Basin. In addition to previously documented morphological differences, our geometric morphometric analyses revealed significant differences in epiplastral morphology between B. pusilla and the two coeval Echmatemys species. Bridgeremys pusilla shared several morphological characters with Testudinidae. However, our anatomical network analysis suggests that the carapace of B. pusilla distributed stress forces in a manner more similar to emydids (basal and derived) than to derived testudinoids (Testudinidae and Emydidae), including Echmatemys species. This finding changes our understanding of the ecology of the species and sheds light onto how geoemydid turtles of the Uinta Formation may have partitioned the available ecospace. These new Uintan records extend the geographic range of B. pusilla into the Uinta Basin and stratigraphically through the top of the Uinta Formation, extending the temporal range of the taxon by more than 4 million years through the Uintan North American Land Mammal Age to the base of the Duchesne River Formation., (© 2021 American Association for Anatomy.)

Lakotemys australodakotensis is an Early Cretaceous paracryptodire known from two shells and a skull from the Lakota Formation of South Dakota, USA. Along with the Early Cretaceous Arundelemys dardeni and the poorly known Trinitichelys hiatti , Lakotemys australodakotensis is generally retrieved as an early branching baenid, but more insights into the cranial anatomy of these taxa is needed to obtain a better understanding of paracryptodiran diversity and evolution. Here, we describe the skull of Lakotemys australodakotensis using micro-computed tomography to provide the anatomical basis for future phylogenetic analyses that will be needed to investigate more precisely the intrarelationships of Paracryptodira . Preliminary comparisons reveal that the cranial anatomy of Lakotemys australodakotensis is very similar to that of the Aptian-Albian basal baenid Arundelemys dardeni , that both taxa exhibit a remarkable combination of derived characters found in baenodds and characters found in non-baenid paracryptodires, particularly Pleurosternidae , and that Lakotemys australodakotensis is the only known baenid to date to possess a canal for the palatine artery., Competing Interests: The authors declare there are no competing interests., (©2022 Rollot et al.)

Tortoises (land turtles) are familiar animals and are generally assumed to be strict herbivores. Their ecological roles are most obvious in giant tortoise species which, due to their size and local abundance, play major roles as keystone species and ecosystem engineers 1-3 . In the Galápagos and Seychelles islands these species are known to play major roles as the islands' largest herbivores, with exceptionally high biomass and consuming up to 11% of primary production 1 . In addition they act as ecosystem engineers, dispersing seeds, breaking vegetation and eroding rocks 2 . However, as slow-moving poikilotherms most people assume their behaviour to be simple. Here we present video evidence of a Seychelles giant tortoise (Aldabrachelys gigantea) attacking a tern chick and pursuing it along a log. Finally the tortoise killed the chick and was observed to eat it. Other tortoises in the same area have been seen making similar attacks, although those were not fully documented. We believe that the exceptional combination of a tree-nesting tern colony with a resident giant tortoise population has created conditions leading to systematic hunting of birds by several individual tortoises; an entirely novel behavioural strategy for any tortoise species. VIDEO ABSTRACT., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Late Jurassic deposits across Europe have yielded a rich fauna of extinct turtles. Although many of these turtles are recovered from marine deposits, it is unclear which of these taxa are habitually marine and which may be riverine species washed into nearby basins, as adaptations to open marine conditions are yet to be found. Two new fossils from the Late Jurassic of Germany provide unusually strong evidence for open marine adaptations. The first specimen is a partial shell and articulated hind limb from the Late Jurassic (early Tithonian) platy limestones of Schernfeld near Eichstätt, which preserves the integument of the hind limb as an imprint. The skin is fully covered by flat, polygonal scales, which stiffen the pes into a paddle. Although taxonomic attribution is not possible, similarities are apparent with Thalassemys. The second specimen is a large, articulated skeleton with hypertrophied limbs referable to Thalassemys bruntrutana from the Late Jurassic (early Late Kimmeridgian) platy limestone of Wattendorf, near Bamberg. Even though the skin is preserved as a phosphatic film, the scales are not preserved. This specimen can nevertheless be inferred to have had paddles stiffened by scales based on the pose in which they are preserved, the presence of epibionts between the digits, and by full morphological correspondence to the specimen from Schernfeld. An analysis of scalation in extant turtles demonstrated that elongate flippers stiffed by scales are a marine adaptation, in contrast to the elongate but flexible flippers of riverine turtles. Phylogenetic analysis suggests that Thalassemys bruntrutana is referable to the mostly Late Jurassic turtle clade Thalassochelydia. The marine adapted flippers of this taxon therefore evolved convergently with those of later clades of marine turtles. Although thalassochelydian fossils are restricted to Europe, with one notable exception from Argentina, their open marine adaptations combined with the interconnectivity of Jurassic oceans predict that the clade must have been even more wide-spread during that time., Competing Interests: The authors have declared that no competing interests exist.