Eduardo Ascarrunz’s research while affiliated with University of Fribourg and other places

Depending on taxonomic opinion, between four and five turtle species are well attested for the Middle Eocene Messel Pit formation of Germany. Here, we describe specimen SMF ME-3495 from the Messel collection of the Senckenberg Museum in Frankfurt, which unambiguously corresponds to an additional turtle species. The specimen consists of a partial anterior plastral lobe that can be distinguished from other Messel turtle taxa on the basis of the presence of gular tubercles, an extensive epiplastral lip, narrow gulars that lap onto the entoplastron, and a sinuous gulo-humeral sulcus. The fragment is not sufficient to diagnose another contemporary European turtle taxon, but its epiplastral lip morphology is reminiscent of “ptychogasterid” geoemydids (Cryptodira). We also remark on bone corrosion consistent with “shell disease” and distinctive coloration.

The scutes of the carapace of extant turtles exhibit common elements in a narrow range of topographical arrangements. The typical arrangement has remained constant since its origin in the clade Mesochelydia (Early Jurassic), after a period of apparent greater diversity in the Triassic. This contribution is a review of the development and evolutionary history of the scute patterns of the carapace, seen through the lens of recent developmental models. This yields insights on pattern variations in the fossil record. We reinterpret the “supracaudal” scute and propose that Proganochelys had five vertebral scutes. We discuss the relationship between supramarginal scutes and Turing processes, and we show how a simple change during embryogenesis could account for origin of the configuration of the caudal region of the carapace in mesochelydians. We also discuss the nature of the decrease in number of scutes over the course of evolution, and whether macroevolutionary trends can be discerned. We argue that turtles with complete loss of scutes (e.g., softshells) follow clade-specific macroevolutionary regimes, which are distinct from the majority of other turtles. Finally, we draw a parallel between the variation of scute patterns on the carapace of turtles and the scale patterns in the pileus region (roof of the head) of squamates. The size and numbers of scales in the pileus region can evolve over a wide range, but we recognized tentative evidence of convergence towards a typical configuration when the scales become larger and fewer. Thus, typical patterns could be a more general property of similar systems of integumentary appendages.

The geoemydid turtles of the Eocoene Messel Pit Quarry of Hesse, Germany, are part of a rich Western European fossil record of testudinoids. Originally referred to as “ Ocadia” kehreri and “ Ocadia” messeliana , their systematic relationships remain unclear. A previous study proposed that a majority of the Western European geoemydids, including the Messel geoemydids, are closely related to the Recent European representatives of the clade Mauremys . Another study hypothesised that the Western European geoemydid fauna is more phylogenetically diverse, and that the Messel geoemydids are closely related to the East Asian turtles Orlitia and Malayemys . Here we present the first quantitative analyses to date that investigate this question. We use continuous characters in the form of ratios to estimate the placement of the Messel geoemydids in a reference tree that was estimated from molecular data. We explore the placement error obtained from that data with maximum likelihood and Bayesian methods, as well as linear parsimony in combination with discrete characters. We find good overall performance with Bayesian and parsimony analyses. Parsimony performs even better when we also incorporated discrete characters. Yet, we cannot pin down the position of the Messel geoemydids with high confidence. Depending on how intraspecific variation of the ratio characters is treated, parsimony favours a placement of the Messel fossils sister to Orlitia borneensis or sister to Geoemyda spengleri , with weak bootstrap support. The latter placement is suspect because G. spengleri is a phylogenetically problematic species with molecular and morphological data. There is even less support for placements within the Mauremys clade.

Background In the last 20 years, a general picture of the evolutionary relationships between geoemydid turtles (ca. 70 species distributed over the Northern hemisphere) has emerged from the analysis of molecular data. However, there is a paucity of good traditional morphological characters that correlate with the phylogeny, which are essential for the robust integration of fossil and molecular data. Part of this problem might be due to intrinsic limitations of traditional discrete characters. Here, we explore the use of continuous data in the form of 3D coordinates of homologous landmarks on the turtle shell for phylogenetic inference and the phylogenetic placement of single species on a scaffold molecular tree. We focus on the performance yielded by sampling the carapace and/or plastral lobes and using various phylogenetic methods. Methods We digitised the landmark coordinates of the carapace and plastron of 42 and 46 extant geoemydid species, respectively. The configurations were superimposed and we estimated the phylogenetic tree of geoemydids with landmark analysis under parsimony, traditional Farris parsimony, unweighted squared-change parsimony, maximum likelihood with a Brownian motion model, and neighbour-joining on a matrix of pairwise Procrustes distances. We assessed the performance of those analyses by comparing the trees against a reference phylogeny obtained from seven molecular markers. For comparisons between trees we used difference measures based on quartets and splits. We used the same reference tree to evaluate phylogenetic placement performance by a leave-one-out validation procedure. Results Whatever method we used, similarity to the reference phylogeny was low. The carapace alone gave slightly better results than the plastron or the complete shell. Assessment of the potential for placement of single species on the reference tree with landmark data gave much better results, with similar accuracy and higher precision compared to the performance of discrete characters with parsimony.

Background: The branchiostegal series consists of an alignment of bony elements in the posterior portion of the skull of osteichthyan vertebrates. We trace the evolution of the number of elements in a comprehensive survey that includes 440 extant and 66 extinct species. Using a newly updated actinopterygian tree in combination with phylogenetic comparative analyses, we test whether osteichthyan branchiostegals follow an evolutionary trend under 'Williston's law', which postulates that osteichthyan lineages experienced a reduction of bony elements over time. Results: We detected no overall macroevolutionary trend in branchiostegal numbers, providing no support for 'Williston's law'. This result is robust to the subsampling of palaeontological data, but the estimation of the model parameters is much more ambiguous. Conclusions: We find substantial evidence for a macroevolutionary dynamic favouring an 'early burst' of trait evolution over alternative models. Our study highlights the challenges of accurately reconstructing macroevolutionary dynamics even with large amounts of data about extant and extinct taxa.

Several attempts to resolve the phylogeny of turtles in the clade Geoemydidae using morphology have been unsuccessful, in part because of unusually high levels of polymorphism. This has hindered the integration of the geoemydid fossil record into a phylogenetic framework. Many methods, shown to improve phylogenetic inference, allow the incorporation of different amounts of state frequency information from polymorphic characters into a phylogenetic analysis. Here, we present a new character matrix for the shell of geoemydids and assess the performance of polymorphism coding methods (‘majority’, ‘generalized frequency coding’, ‘polymorphic’ and ‘missing’) in a phylogenetic analysis by comparing the result topology of each method with a reference molecular phylogeny. The four coding methods failed to recover trees that were both well resolved and highly congruent with the reference phylogeny. Moreover, contrary to previous studies, the coding methods that made more use of character states frequencies did not perform better. However, a leave-one-out subsampling analysis suggested that despite these problems, the new matrix can still be used to place fossils in the geoemydid phylogeny with some reliability. Finally, we provide a list of characters that diagnose the major clades in our molecular reference tree.

Several attempts to resolve the phylogeny of turtles in the clade Geoemydidae using morphology have been unsuccessful , in part because of unusually high levels of polymorphism. This has hindered the integration of the geoemydid fossil record into a phylogenetic framework. Many methods, shown to improve phylogenetic inference, allow the incorporation of different amounts of state frequency information from polymorphic characters into a phylogenetic analysis. Here, we present a new character matrix for the shell of geoemydids and assess the performance of poly-morphism coding methods ('majority', 'generalized frequency coding', 'polymorphic' and 'missing') in a phylogenetic analysis by comparing the result topology of each method with a reference molecular phylogeny. The four coding methods failed to recover trees that were both well resolved and highly congruent with the reference phylogeny. Moreover, contrary to previous studies, the coding methods that made more use of character states frequencies did not perform better. However, a leave-one-out subsampling analysis suggested that despite these problems, the new matrix can still be used to place fossils in the geoemydid phylogeny with some reliability. Finally, we provide a list of characters that diagnose the major clades in our molecular reference tree.

In a previous study, we estimated the cranial disparity of turtles (Testudinata) through time using geometric morphometric data from both terminal taxa and hypothetical ancestors to compensate for temporal gaps in the fossil record. While this method yielded reasonable results for the Mesozoic and the early Cenozoic, we found a large drop in cranial disparity for the Miocene, for which we found no correlation with known environmental changes or extinction events. Instead,we speculated that the Miocene dip was a result of poor sampling of fossils or ancestors in this time bin. To countervail this problem, we here updated our original dataset and interpolated changes of shape along the branch lengths and compared them with the previous data. We furthermore explored the impact of topological and temporal uncertainty, demonstrating that the Miocene dip, indeed, is a sampling artefact. All remaining conclusions of the previous study could be more or less supported, nevertheless, including an apparent correlation with global biogeographic events, a minor correlation between cranial disparity and global temperature, and resilience across the K/T extinction event.

Triadobatrachus massinoti is a batrachian known from a single fossil from the Early Triassic of Madagascar that presents a combination of apomorphic salientian and plesiomorphic batrachian characters. Herein we offer a revised description of the specimen based on X-ray micro-tomography data. We report previously unknown caudal vertebrae, possible mentomeckelians, and hidden parts of other structures. We also confirm the presence of a ventrolateral ledge on the opisthotic, and we rectify some previous interpretations. There are no cervical ribs and the jaw may have had an angular. The presacral region is composed of 15 vertebrae with a unique atlas-axis complex instead of 14 vertebrae with a bipartite atlas. The configuration of the pelvic girdle is not very clear, although it is likely more plesiomorphic than the anu-ran-like condition previously assumed. Our re-assessment of the saltatorial performance of Triadobatrachus supports the traditional interpretation that this animal was not a specialised jumper. In order to assess the sequence of events in the early evolution of the salientian morphotype, we estimated the ancestral length of the trunk region of batrachians under different hypotheses of lissamphibian relationships and divergence times. Most of our results suggest that some trunk reduction took place before the divergence of caudates and salientians (presumably in the Per-mian), and that the trunk of Triadobatrachus mostly reflects this ancestral condition. Thus, trunk reduction possibly preceded the anteroposterior elongation of the ilia and the shortening of the tail seen in Triadobatrachus. We also provide an updated review of the data relevant for the use of Triadobatrachus as a calibration constraint in molecular divergence age analyses that meets recently-suggested standards.