Turtle Lineages Research Articles

Reassessing leatherback turtle lineages and unveiling the first evidence of nuclear mitochondrial DNA in sea turtles

A recent study proposed a new genetic lineage of leatherback turtles (Dermochelys coriacea) based on genetic analysis, environmental history, and local ecological knowledge (LEK), suggesting the existence of two possible species or subspecies on the beaches of Oaxaca, diverging ~ 13.5 Mya. However, this hypothesis may be influenced by nuclear mitochondrial DNA segments (NUMTs), which could have been misamplified as true mtDNA. NUMTs are sequences that have migrated from the mitochondrial genome to the nuclear genome and can co-amplify with mtDNA, potentially leading to erroneous phylogenetic interpretations. We re-examined the evidence for this proposed lineage by reviewing taxonomic literature and additional genetic data. Our analysis indicates that the divergent sequences, previously associated with a new lineage of D. coriacea, are NUMTs rather than true mitochondrial sequences. This is the first evidence of NUMTs in sea turtles. We also proposed a more specific primer for the mitochondrial control region (D-loop) for leatherback turtles to avoid amplifying nuclear copies. Our findings highlight the importance of rigorous genetic validation in conservation genetics, where misinterpretations can significantly impact species management. Finally, we developed a general protocol for detecting NUMTs applicable to any species.

Shell Constraints on Evolutionary Body Size-Limb Size Allometry Can Explain Morphological Conservatism in the Turtle Body Plan.

Turtles are a small clade of vertebrates despite having existed since the Late Triassic. Turtles have a conservative body plan relative to other amniotes, characterized by the presence of a shell and quadrupedality. This morphology is even retained in strong ecological specialists, such as sea turtles, which are secondarily adapted to marine locomotion by strong allometric scaling in their hands. It is possible that the body plan of turtles is strongly influenced by the presence of the shell, acting as a constraint to achieving greater diversity of body forms. Here, we explore the evolutionary allometric relationships of fore- and hindlimb stylopodia (i.e., humerus and femur) with one another as well as their relationship with shell size (carapace length) to assess evidence of constraint. All turtles, including Triassic shelled stem turtles, have near-isometric relationships that do not vary strongly between clades, and evolve at slow evolutionary rates. This indeed indicates that body proportions of turtles are constrained to a narrow range of possibilities. Minor allometric deviations are seen in highly aquatic sea turtles and softshell turtles, which modified their shells by bone losses. Our allometric regressions allow accurate body size estimations for fossils. Several independent sea turtle lineages converged on maximum sizes of 2.2 m of shell length, which may be a biological maximum for the group.

New data on the shell anatomy of Selenemys lusitanica, the oldest known pleurosternid turtle in Europe

One of the most diverse turtle lineages in the Upper Jurassic and Lower Cretaceous record of Europe is that of the stem turtles Pleurosternidae (Paracryptodira), also distributed in North America. The oldest European representative of this lineage is the Portuguese Selenemys lusitanica, known from upper Kimmeridgian to lower Tithonian levels (Late Jurassic). The information on the shell of this taxon is so far very limited, being exclusively restricted to that provided in the publication in which the taxon was defined. New specimens from several upper Kimmeridgian to Tithonian localities in the Consolação Sub-basin of the Portuguese Lusitanian Basin, both from the Leiria District and the Lisbon District, are studied here. They include the most complete shell of the species found so far, as well as several isolated plates that allow us to improve knowledge about it. Thus, new information about the shell anatomy of Selenemys lusitanica is provided, but also about its intraspecific variability.

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.

Mitochondrial DNA and local ecological knowledge reveal two lineages of leatherback turtle on the beaches of Oaxaca, Mexico

Despite multiple conservation efforts of the Mexican government, the leatherback turtle is at serious risk of extinction. In this study, we investigated the possible presence of a genetic bottleneck that could prevent the recovery of this species and compared these findings with those of the olive ridley turtle, which is in true recovery. Our results confirmed that a demographic change occurred in the past and the presence of two different leatherback turtle lineages that diverged approximately 13.5 million years ago. Local ecological knowledge (LEK) also described the presence of these two lineages and warned that one is at higher risk of extinction than the other. Genetic analysis confirmed 124 mutations between the two lineages, and much lower genetic diversity in one lineage than the other. Our study highlights and substantiates the power of mixing LEK, environmental history, and genetics to better understand conservation challenges of highly threatened species such as the leatherback turtle. Moreover, we report a new lineage of the leatherback turtle which may represent a distinct species. Future studies should focus on morphological, ecological, biogeographical, evolutionary and conservation perspectives for the analysis of the new lineage.

Crocodyliformes and Testudines from the Eocene of the Duero Basin (northwestern Spain): an update of their diversity and stratigraphic context

ABSTRACT The Palaeogene sedimentary successions of the Duero Basin host an important record of fossil vertebrates, especially mammals and reptiles. The main fossil sites are placed at the west margin (Salamanca and Zamora areas) spanning from the Lutetian to the late Priabonian; and at the southeast tip (Almazán Basin) mainly Bartonian in age. The continued study of the sites is supplying new data that will improve the chronostratigraphy and the correlation between the western and eastern regions of the basin. The diversity and phylogenetic relationships of the represented fauna have been revised in recent years with the reassignment of some remains and the diagnosis of some new taxa. Four lineages of turtles are represented: Podocnemididae (Neochelys), Carettochelyidae (Allaeochelys), Trionychidae and Testudinidae (Pelorochelon). Crocodyliform paleobiodiversity is composed of notosuchians (close to Iberosuchus) and, at least, three crocodylian lineages: Planocraniidae (Duerosuchus), Alligatoroidea (Diplocynodon) and Crocodyloidea (‘Asiatosuchus’). The distribution of these taxa is not homogeneous throughout the basin, and a deep transformation is recognised throughout the middle Eocene. The fitting of the distribution and relationships of the reptilian fauna from the Duero Basin provides valuable information to understand some faunistic dynamics such as the endemism process of northwestern Iberia from the middle of the Eocene.

The evolution of reproductive strategies in turtles.

Optimal egg size theory assumes that changes in the egg and clutch are driven by selection, resulting in adjustments for the largest possible production of offspring with the highest fitness. Evidence supports the idea that large-bodied turtles tend to produce larger clutches with small and round eggs, while smaller species produce small clutches with large and elongated eggs. Our goals were to investigate whether egg and clutch size follow the predictions of egg size theory, if there are convergent reproductive strategies, and identify ecological factors that influence clutch and egg traits across all clades of living turtles. Using phylogenetic methods, we tested the covariance among reproductive traits, if they are convergent among different turtle lineages, and which ecological factors influence these traits. We found that both egg shape and size inversely correlate with clutch size, although with different evolutionary rates, following the predictions of the egg size theory. We also present compelling evidence for convergence among different turtle clades, over at least two reproductive strategies. Furthermore, climatic zone is the only ecological predictor to influence both egg size and fecundity, while diet only influences egg size. We conclude that egg and clutch traits in Testudines evolved independently several times across non-directly related clades that converged to similar reproductive strategies. Egg and clutch characteristics follow the trade-offs predicted by egg size theory and are influenced by ecological factors. Climatic zone and diet play an important role in the distribution of reproductive characteristics among turtles.

Turtles all the way down: Neogene pig‐nosed turtle fossil from southern Australia reveals cryptic freshwater turtle invasions and extinctions

AbstractThe extant pig‐nosed turtle (Carettochelys insculpta), persisting in far northern Australia and southern New Guinea, is the last surviving member of Carettochelyidae and the only non‐Gondwanan freshwater turtle lineage in Australia. Despite having a global fossil record dating to the Cretaceous, the absence of carettochelyid fossils from Australia has implied a relatively recent colonization of this landmass. Here we report an upper Miocene to lower Pliocene carettochelyid fossil from Beaumaris, Victoria, in south‐eastern Australia. This record is the most southerly occurrence of the clade Carettochelyidae. The presence of carettochelyids in southern Australia, and a discontinuous record of trionychids (soft‐shell turtles) in the Cenozoic of Queensland, suggests at least two colonizations of Australia by Trionychia, pre‐dating the extant pig‐nosed turtle. This cryptic southern history of tropical soft‐shell and pig‐nosed turtles ended before the recent aridification of Australia, leaving the Gondwanan side‐necked turtles as the dominant turtle group in Australian freshwater ecosystems. Therefore, this singular fossil reveals a previously unknown shift in the diversity and evolutionary history of freshwater turtles in Australia.

Concurrent Evolution of Antiaging Gene Duplications and Cellular Phenotypes in Long-Lived Turtles.

There are many costs associated with increased body size and longevity in animals, including the accumulation of genotoxic and cytotoxic damage that comes with having more cells and living longer. Yet, some species have overcome these barriers and have evolved remarkably large body sizes and long lifespans, sometimes within a narrow window of evolutionary time. Here, we demonstrate through phylogenetic comparative analysis that multiple turtle lineages, including Galapagos giant tortoises, concurrently evolved large bodies, long lifespans, and reduced cancer risk. We also show through comparative genomic analysis that Galapagos giant tortoises have gene duplications related to longevity and tumor suppression. To examine the molecular basis underlying increased body size and lifespan in turtles, we treated cell lines from multiple species, including Galapagos giant tortoises, with drugs that induce different types of cytotoxic stress. Our results indicate that turtle cells, in general, are resistant to oxidative stress related to aging, whereas Galapagos giant tortoise cells, specifically, are sensitive to endoplasmic reticulum stress, which may give this species an ability to mitigate the effects of cellular stress associated with increased body size and longevity.

The genetic and morphological diversity of Haemogregarina infecting turtles in Colombia: Are mitochondrial markers useful as barcodes for these parasites?

Adeleorinid parasites commonly infect turtles and tortoises in nature. Currently, our knowledge about such parasites is extremely poor. Their characterization is based on morphological and molecular approaches using the 18S rDNA molecular marker. However, there is a limitation with the 18S rDNA due to its slow rate of evolution. For that reason, the goals of this study were to 1) design primers for new molecular mitochondrial markers to improve the phylogenetic reconstructions of adeleorinid parasites and 2) to determine the morphological and genetic diversity of Haemogregarina infecting turtles and tortoises in Colombia. Turtles from 16 species representing six families were examined for the presence of haemoparasites. We analyzed 457 samples using PCR, and 203 of them were also analyzed by microscopy. Using a mitochondrial genome of Haemogregarina sequenced in this study, we designed primers to amplify fragments of the cytochrome oxidase I (coxI), cytochrome oxidase III (coxIII), and cytochrome b (cytb) mitochondrial markers in adeleorinid parasites. Lineages obtained from nuclear and mitochondrial molecular markers clustered according to the turtle lineages from which they were isolated. It is noteworthy that we found different evolutionary lineages within the same morphotype, which may indicate heteroplasmy and/or cryptic diversity in Haemogregarina. Due to this situation, we could not make a species delimitation, even when integrating the different lines of evidence we had in this study. However, the primers presented here are useful for diagnosis and, moreover, according to the available information, all three genes retain phylogenetic signals; thereby fragments amplified can be used in reconstructing evolutionary relationships. This effort contributes to the knowledge of the diversity of these parasites infecting continental turtles from Colombia.

Population Viability Analysis of Kinosternon hirtipes murrayi in Central México, with Notes on the Conservation Status of the Other Three Subspecies of the Lineage

With 6 subspecies described, the rough-footed mud turtle (Kinosternon hirtipes) has been considered a species with high morphological diversity. One subspecies, K. h. megacephalum, is already extinct. The remaining subspecies are poorly studied, with very limited information available only for K. h. murrayi (a widespread subspecies). The remaining taxa (K. h. tarascense, K. h. chapalense, K. h. magdalense, and K. h. hirtipes) are microendemic and restricted to endorheic valleys in the Mexican Transvolcanic Belt. Using baited fyke nets, hoop traps, and a seine, we surveyed for these microendemic subspecies for 3 yrs across their known distributions. With the data gathered in the field and published information, we conducted a population viability analysis (PVA) to model the minimum characteristics needed to improve population growth under 3 scenarios (optimistic, intermediate, and pessimistic). Very few K. hirtipes turtles were collected. No K. h. chapalense were located in Lake Chapala, but we did capture 4 individuals in Lake Zapotlan. Similarly, only 6 individuals of K. h. magdalense were captured. No K. h. hirtipes individuals were collected in the Valley of México. Two populations of K. h. tarascense were located in the Pátzcuaro basin: the first populations reported for that subspecies. The PVA showed that harvest on adults in populations with fewer than 200 turtles significantly compromises population persistence. However, a population size of 200 and limited or no harvest are enough to increase population size and persistence for at least 100 yrs. Assurance colonies and head-starting may be the only chance for long-term survival of some of these microendemic turtle lineages.

The role of selection in the evolution of marine turtles mitogenomes

Sea turtles are the only extant chelonian representatives that inhabit the marine environment. One key to successful colonization of this habitat is the adaptation to different energetic demands. Such energetic requirement is intrinsically related to the mitochondrial ability to generate energy through oxidative phosphorylation (OXPHOS) process. Here, we estimated Testudines phylogenetic relationships from 90 complete chelonian mitochondrial genomes and tested the adaptive evolution of 13 mitochondrial protein-coding genes of sea turtles to determine how natural selection shaped mitochondrial genes of the Chelonioidea clade. Complete mitogenomes showed strong support and resolution, differing at the position of the Chelonioidea clade in comparison to the turtle phylogeny based on nuclear genomic data. Codon models retrieved a relatively increased dN/dS (ω) on three OXPHOS genes for sea turtle lineages. Also, we found evidence of positive selection on at least three codon positions, encoded by NADH dehydrogenase genes (ND4 and ND5). The accelerated evolutionary rates found for sea turtles on COX2, ND1 and CYTB and the molecular footprints of positive selection found on ND4 and ND5 genes may be related to mitochondrial molecular adaptation to stress likely resulted from a more active lifestyle in sea turtles. Our study provides insight into the adaptive evolution of the mtDNA genome in sea turtles and its implications for the molecular mechanism of oxidative phosphorylation.

Phylogenetic and spatial distribution of evolutionary diversification, isolation, and threat in turtles and crocodilians (non-avian archosauromorphs)

BackgroundThe origin of turtles and crocodiles and their easily recognized body forms dates to the Triassic and Jurassic. Despite their long-term success, extant species diversity is low, and endangerment is extremely high compared to other terrestrial vertebrate groups, with ~ 65% of ~ 25 crocodilian and ~ 360 turtle species now threatened by exploitation and habitat loss. Here, we combine available molecular and morphological evidence with statistical and machine learning algorithms to present a phylogenetically informed, comprehensive assessment of diversification, threat status, and evolutionary distinctiveness of all extant species.ResultsIn contrast to other terrestrial vertebrates and their own diversity in the fossil record, the recent extant lineages of turtles and crocodilians have not experienced any global mass extinctions or lineage-wide shifts in diversification rate or body-size evolution over time. We predict threat statuses for 114 as-yet unassessed or data-deficient species and identify a concentration of threatened turtles and crocodilians in South and Southeast Asia, western Africa, and the eastern Amazon. We find that unlike other terrestrial vertebrate groups, extinction risk increases with evolutionary distinctiveness: a disproportionate amount of phylogenetic diversity is concentrated in evolutionarily isolated, at-risk taxa, particularly those with small geographic ranges. Our findings highlight the important role of geographic determinants of extinction risk, particularly those resulting from anthropogenic habitat-disturbance, which affect species across body sizes and ecologies.ConclusionsExtant turtles and crocodilians maintain unique, conserved morphologies which make them globally recognizable. Many species are threatened due to exploitation and global change. We use taxonomically complete, dated molecular phylogenies and various approaches to produce a comprehensive assessment of threat status and evolutionary distinctiveness of both groups. Neither group exhibits significant overall shifts in diversification rate or body-size evolution, or any signature of global mass extinctions in recent, extant lineages. However, the most evolutionarily distinct species tend to be the most threatened, and species richness and extinction risk are centered in areas of high anthropogenic disturbance, particularly South and Southeast Asia. Range size is the strongest predictor of threat, and a disproportionate amount of evolutionary diversity is at risk of imminent extinction.

A European Cenozoic ‘Macrobaenid:’ New Data about the Paleocene Arrival of Several Turtle Lineages to Europe

ABSTRACT The European Paleocene terrestrial and freshwater turtle fauna is radically different from that in the Upper Cretaceous. This Paleocene fauna is largely formed by groups of turtles not found in the Mesozoic record of the continent. However, European Paleocene sites have produced several lineages that dispersed from other continents, including basal turtles (i.e., stem Testudines) and compsemydids (i.e., Paracryptodira). Both groups are well represented at the French upper Paleocene site of Mont de Berru, Marne Department. A new taxon from this locality, Gallica lapparentiana, gen. et sp. nov., is described here and attributed to the eucryptodiran lineage ‘Macrobaenidae.’ Heretofore, no ‘macrobaenid’ has yet been identified in the Cenozoic record of Europe. ‘Macrobaenids’ have their origin in the Upper Jurassic of Asia. In fact, they represent the most diverse group of turtles currently known for the Lower Cretaceous record in that continent. They reach North America in the Upper Cretaceous, where they continue to diversify during the Upper Cretaceous and lower Paleocene. The first justified identification of ‘Macrobaenidae’ from the upper Paleocene of Europe, both in France and in Belgium, provides new data on the replacement process of European Late Cretaceous turtle fauna by new groups from other continents. http://zoobank.org/urn:lsid:zoobank.org:pub:B417CC80-F47C-4AE5-B8B2-0BAA249A177F

Geography best explains global patterns of genetic diversity and postglacial co-expansion in marine turtles.

For many species, climate oscillations drove cycles of population contraction during cool glacial periods followed by expansion during interglacials. Some groups, however, show evidence of uniform and synchronous expansion, while others display differences in the timing and extent of demographic change. We compared demographic histories inferred from genetic data across marine turtle species to identify responses to postglacial warming shared across taxa and to examine drivers of past demographic change at the global scale. Using coalescent simulations and approximate Bayesian computation (ABC), we estimated demographic parameters, including the likelihood of past population expansion, from a mitochondrial data set encompassing 23 previously identified lineages from all seven marine turtle species. For lineages with a high posterior probability of expansion, we conducted a hierarchical ABC analysis to estimate the proportion of lineages expanding synchronously and the timing of synchronous expansion. We used Bayesian model averaging to identify variables associated with expansion and genetic diversity. Approximately 60% of extant marine turtle lineages showed evidence of expansion, with the rest mainly exhibiting patterns of genetic diversity most consistent with population stability. For lineages showing expansion, there was a strong signal of synchronous expansion after the Last Glacial Maximum. Expansion and genetic diversity were best explained by ocean basin and the degree of endemism for a given lineage. Geographic differences in sensitivity to climate change have implications for prioritizing conservation actions in marine turtles as well as for identifying areas of past demographic stability and potential resilience to future climate change for broadly distributed taxa.

Performance Surface Analysis Identifies Consistent Functional Patterns across 10 Morphologically Divergent Terrestrial Turtle Lineages.

Newly-developed methods for utilizing performance surfaces-multivariate representations of the relationship between phenotype and functional performance-allow researchers to test hypotheses about adaptive landscapes and evolutionary diversification with explicit attention to functional factors. Here, information from performance surfaces of three turtle shell functions-shell strength, hydrodynamics, and self-righting-is used to test the hypothesis that turtle lineages transitioning from aquatic to terrestrial habitats show patterns of shell shape evolution consistent with decreased importance of hydrodynamic performance. Turtle shells are excellent model systems for evolutionary functional analysis. The evolution of terrestriality is an interesting test case for the efficacy of these methods because terrestrial turtles do not show a straightforward pattern of morphological convergence in shell shape: many terrestrial lineages show increased shell height, typically assumed to decrease hydrodynamic performance, but there are also several lineages where the evolution of terrestriality was accompanied by shell flattening. Performance surface analyses allow exploration of these complex patterns and explicit quantitative analysis of the functional implications of changes in shell shape. Ten lineages were examined. Nearly all terrestrial lineages, including those which experienced decreased shell height, are associated with morphological changes consistent with a decrease in the importance of shell hydrodynamics. This implies a common selective pattern across lineages showing divergent morphological patterns. Performance studies such as these hold great potential for integrating adaptive and performance data in macroevolutionary studies.

The rise and fall of differentiated sex chromosomes in geckos.

Amniotes possess variability in sex determination, ranging from environmental sex determination to genotypic sex determination with differentiated sex chromosomes. Differentiated sex chromosomes have emerged independently several times. Their noteworthy convergent characteristic is the evolutionary stability, documented among amniotes in mammals, birds, and some lineages of lizards, snakes and turtles. Combining the analysis of multiple partial transcriptomes with the comparison of copy gene numbers between male and female genomes, we uncovered partial gene content of the highly differentiated ZZ/ZW sex chromosomes in the gecko genusParoedura. The differentiated ZZ/ZW sex chromosomes of these geckosshare genes with the part of the chicken chromosome 4 homologous with the XX/XY sex chromosomes of viviparous mammals and the ZZ/ZW sex chromosomes of lacertid lizards, as well as with the chicken chromosome 15, homologous with the XX/XY sex chromosomes of iguanas and ZZ/ZW sex chromosomes of softshell turtles. Along with other analogous cases, this finding reinforces the observation that particular chromosomes are repeatedly coopted for the function of sex chromosomes in amniotes. Notably, according to the phylogenetic distribution, the subclade of the genus Paroedura represents a rare case of the reversal of the for a considerable evolutionary time highly differentiated ZZ/ZW sex chromosomes back to poorly differentiated state.

Single-molecule long-read transcriptome profiling of Platysternon megacephalum mitochondrial genome with gene rearrangement and control region duplication

ABSTRACTPlatysternon megacephalum is the sole living representative of the poorly studied turtle lineage Platysternidae. Their mitochondrial genome has been subject to gene rearrangement and control region duplication, resulting in a unique mitochondrial gene order in vertebrates. In this study, we sequenced the first full-length turtle (P. megacephalum) liver transcriptome using single-molecule real-time sequencing to study the transcriptional mechanisms of its mitochondrial genome. ND5 and ND6 anti-sense (ND6AS) forms a single transcript with the same expression in the human mitochondrial genome, but here we demonstrated differential expression of the rearranged ND5 and ND6AS genes in P. megacephalum. And some polycistronic transcripts were also reported in this study. Notably, we detected some novel long non-coding RNAs with alternative polyadenylation from the duplicated control region, and a novel ND6AS transcript composed of a long non-coding sequence, ND6AS, and tRNA-GluAS. These results provide the first description of a mtDNA transcriptome with gene rearrangement and control region duplication. These findings further our understanding of the fundamental concepts of mitochondrial gene transcription and RNA processing, and provide a new insight into the mechanism of transcription regulation of the mitochondrial genome.

Adaptive Patterns of Mitogenome Evolution Are Associated with the Loss of Shell Scutes in Turtles.

The mitochondrial genome encodes several protein components of the oxidative phosphorylation (OXPHOS) pathway and is critical for aerobic respiration. These proteins have evolved adaptively in many taxa, but linking molecular-level patterns with higher-level attributes (e.g., morphology, physiology) remains a challenge. Turtles are a promising system for exploring mitochondrial genome evolution as different species face distinct respiratory challenges and employ multiple strategies for ensuring efficient respiration. One prominent adaptation to a highly aquatic lifestyle in turtles is the secondary loss of keratenized shell scutes (i.e., soft-shells), which is associated with enhanced swimming ability and, in some species, cutaneous respiration. We used codon models to examine patterns of selection on mitochondrial protein-coding genes along the three turtle lineages that independently evolved soft-shells. We found strong evidence for positive selection along the branches leading to the pig-nosed turtle (Carettochelys insculpta) and the softshells clade (Trionychidae), but only weak evidence for the leatherback (Dermochelys coriacea) branch. Positively selected sites were found to be particularly prevalent in OXPHOS Complex I proteins, especially subunit ND2, along both positively selected lineages, consistent with convergent adaptive evolution. Structural analysis showed that many of the identified sites are within key regions or near residues involved in proton transport, indicating that positive selection may have precipitated substantial changes in mitochondrial function. Overall, our study provides evidence that physiological challenges associated with adaptation to a highly aquatic lifestyle have shaped the evolution of the turtle mitochondrial genome in a lineage-specific manner.

The Iberian fossil record of turtles: an update

The record of fossil turtles of the Iberian Peninsula is abundant and diverse, considering both the Mesozoic and the Cenozoic forms. The knowledge about the Iberian representatives has been significantly improved through the studies carried out in recent years. More than a third of the species nominated in the Iberian record have been described in the 21st century, corresponding to more than half of the currently valid species defined there. These recent studies allowed to recognize unknown lineages for the Iberian record, to refute several attributions or the validity of several taxa, to raise new hypotheses about the palaeobiogeographical and biostratigraphic distributions of several linages, as well as to provide new data on their dispersal events to Europe and, more specifically, to the Iberian Peninsula. Several previous determinations were not reviewed so far, and the validity of several taxa was not evaluated. Thus, the hypotheses about their systematic positions were not updated. The information on the diversity of the Iberian turtles is collected and evaluated here. Some synonyms are supported or proposed here, the phylogenetic position of several forms is revised, and all the Iberian taxa, which are revised here, are figured. The evolutionary history of the turtles of the Iberian Peninsula, from the Upper Jurassic to the present, is compiled, evaluated and synthesized for the first time. The palaeobiogeography and the information on the origin of each of the lineages of turtles recognized here are considered, as well as the knowledge on their temporal distributions.