Hyperphalangy in a new sinemydid turtle from the Early Cretaceous Jehol Biota

Morphological Diversity of Turtle Hyoid Apparatus is Linked to Feeding Behavior

The hyoid apparatus of tetrapods is highly diverse in its morphology. It plays an important role in feeding, breathing, sound production, and various other behaviors. Among turtles, the diversity of the hyoid apparatus has been recurrently linked to their habitat. The ossification of the hyoid corpus is often the main trait used in correlations with "niche" occupancy, an ossified corpus being associated with aquatic environments and a cartilaginous corpus with terrestrial life. Most studies conducted so far have focused on species belonging to Testudinoidea, the clade that occupies the biggest diversity of habitats (i.e., terrestrial, semi-terrestrial, and aquatic animals), while other turtle lineages have been largely understudied. We assessed the adult anatomy of the hyoid apparatus of 92 turtle species from all "families", together with ossification sequences from embryological series of 11 species, some described for the first time here. Using nearly 40 different discrete anatomical characters, we discuss the evolutionary patterns and the biological significance of morphological transformations in the turtle hyoid elements. Morphological changes are strongly associated to feeding modes, with several instances of convergent evolution within and outside the Testudines clade, and are not as strongly connected to habitat as previously thought. Some of the hyoid character states we describe are diagnostic of specific turtle clades, thus providing phylogenetically relevant information.

Turtle body size evolution is determined by lineage-specific specializations rather than global trends

Organisms display a considerable variety of body sizes and shapes, and macroevolutionary investigations help to understand the evolutionary dynamics behind such variations. Turtles (Testudinata) show great body size disparity, especially when their rich fossil record is accounted for. We explored body size evolution in turtles, testing which factors might influence the observed patterns and evaluating the existence of long-term directional trends. We constructed the most comprehensive body size dataset for the group to date, tested for correlation with paleotemperature, estimated ancestral body sizes, and performed macroevolutionary model-fitting analyses. We found no evidence for directional body size evolution, even when using very flexible models, thereby rejecting the occurrence of Cope's rule. We also found no significant effect of paleotemperature on overall through-time body size patterns. In contrast, we found a significant influence of habitat preference on turtle body size. Freshwater turtles display a rather homogeneous body size distribution through time. In contrast, terrestrial and marine turtles show more pronounced variation, with terrestrial forms being restricted to larger body sizes, up to the origin of testudinids in the Cenozoic, and marine turtles undergoing a reduction in body size disparity after the extinctions of many groups in the mid-Cenozoic. Our results, therefore, suggest that long-term, generalized patterns are probably explained by factors specific to certain groups and related at least partly to habitat use.

Yakemys multiporcata n. g. n. sp., a Large Macrobaenid Turtle from the Basal Cretaceous of Thailand, with a Review of the Turtle Fauna from the Phu Kradung Formation and Its Stratigraphical Implications

Yakemys multiporcata n. g. n. sp. is described on the basis of shell elements from the upper part of the Phu Kradung Formation (basal Cretaceous), Khorat Plateau, NE Thailand and assigned to Macrobaenidae. The new taxon is unusually large for an early macrobaenid (with an estimated carapace length about 70 cm) and is characterized by a large, rounded, low shell, the presence of a midline keel and numerous additional strong ridges on the carapace, the anterolateral margin upturned to form a gutter, posterolateral peripherals mesiolaterally expanded, narrow vertebrals, the vertebral 4 triangular and narrowed posteriorly, a greatly reduced plastron with a short bridge, an oval and elongate entoplastron with reduced ventral exposure, and strip-shaped epiplastra. The discovery of a macrobaenid turtle provides further support for an Early Cretaceous age for the upper part of the Phu Kradung Formation.

Two turtles with soft tissue preservation from the platy limestones of Germany provide evidence for marine flipper adaptations in Late Jurassic thalassochelydians

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.

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.

The sinemydid turtle Ordosemys from the Lower Cretaceous Mengyin Formation of Shandong, China and its implication for the age of the Luohandong Formation of the Ordos Basin

Chronostratigraphic correlation of terrestrial Early Cretaceous biotas in China is highly problematic due to the lack of marine deposits, few absolute dates, and limited number of index fossils. This often leaves vertebrate faunas as one of the few potential tools for a preliminary biostratigraphy. Taxonomic identity of fragmentary fossils is, however, often uncertain and many faunas are insufficiently sampled. Turtles are one of the most common elements of Early Cretaceous biotas of Asia and their skeleton is frequently preserved more completely than that of other vertebrates- they yet receive little attention from vertebrate paleontologists. We here record the presence of the sinemydid turtle Ordosemys leios from the Lower Cretaceous Mengyin Formation of Shandong Province, China, best known for the first dinosaurs and Mesozoic turtles described from the country. Ordosemys is the third turtle reported from the Mengyin Formation along with Sinemys lens and Sinochelys applanata and the only other formation where Ordosemys is known to co-occur with Sinemys is the Luohandong Formation of the Ordos Basin (Inner Mongolia), the type and so far only horizon of Ordosemys leios. The presence of the crocodyliform Shantungosuchus may further define a fauna that is so far only known from these two formations. The stratigraphic position of the Luohandong Formation is poorly controlled and it has been placed anywhere between the Valanginian and Aptian. Published absolute dates from the Mengyin Formation and the numerous shared vertebrate and invertebrate taxa (now also including turtles) implies a Valanginian—early Hauterivian age for the Luohandong Formation—in contrast to late Hauterivian-Albian as previously proposed using the temporal distribution of Psittacosaurus. The new specimen of Ordosemys leios preserves the only known manus of this species and ecomorphological analysis of limb proportions implies that it was a less capable swimmer compared to Ordosemys liaoxiensis coming from the younger Jehol Biota.