On the fossil record of the Gekkota

Establishing species boundaries in Bornean geckos

Species delimitation using mitochondrial DNA (mtDNA) remains an important and accessible approach for discovering and delimiting species. However, delimiting species with a single locus (e.g. DNA barcoding) is biased towards overestimating species diversity. The highly diverse gecko genus Cyrtodactylus is one such group where delimitation using mtDNA remains the paradigm. In this study, we use genomic data to test putative species boundaries established using mtDNA within three recognized species of Cyrtodactylus on the island of Borneo. We predict that multi-locus genomic data will estimate fewer species than mtDNA, which could have important ramifications for the species diversity within the genus. We aim to (i) investigate the correspondence between species delimitations using mtDNA and genomic data, (ii) infer species trees for each target species, and (iii) quantify gene flow and identify migration patterns to assess population connectivity. We find that species diversity is overestimated and that species boundaries differ between mtDNA and nuclear data. This underscores the value of using genomic data to reassess mtDNA-based species delimitations for taxa lacking clear species boundaries. We expect the number of recognized species within Cyrtodactylus to continue increasing, but, when possible, genomic data should be included to inform more accurate species boundaries.

Insights into the adaptive evolution of chromosome and essential traits through chromosome-level genome assembly of Gekko japonicus

Gekko japonicus possesses flexible climbing and detoxification abilities under insectivorous habits. Still, the evolutionary mechanisms behind these traits remain unclarified. This study presents a chromosome-level G. japonicus genome, revealing that its evolutionary breakpoint regions were enriched with specific repetitive elements and defense response genes. Gene families unique to G. japonicus and positively selected genes are mainly enriched in immune, sensory, and nervous pathways. Expansion of bitter taste receptor type 2 primarily in insectivorous species could be associated with toxin clearance. Detox cytochrome P450 in G. japonicus has undergone more birth and death processes than biosynthesis-type P450 genes. Proline, cysteine, glycine, and serine in corneous beta proteins of G. japonicus might influence flexibility and setae adhesiveness. Certain thermosensitive transient receptor potential channels under relaxed purifying selection or positive selection in G. japonicus might enhance adaptation to climate change. This genome assembly offers insights into the adaptive evolution of gekkotans.

A Morrison stem gekkotan reveals gecko evolution and Jurassic biogeography

Geckos are a speciose and globally distributed clade of Squamata (lizards, including snakes and amphisbaenians) that are characterized by a host of modifications for nocturnal, scansorial and insectivorous ecologies. They are among the oldest divergences in the lizard crown, so understanding the origin of geckoes (Gekkota) is essential to understanding the origin of Squamata, the most species-rich extant tetrapod clade. However, the poor fossil record of gekkotans has obscured the sequence and timing of the assembly of their distinctive morphology. Here, we describe the first North American stem gekkotan based on a three-dimensionally preserved skull from the Morrison Formation of western North America. Despite its Late Jurassic age, the new species already possesses several key characteristics of the gekkotan skull along with retained ancestral features. We show that this new stem gekkotan, and several previously named species of uncertain phylogenetic relationships, comprise a widespread clade of early crown lizards, substantiating faunal homogeneity in Laurasia during the Late Jurassic that extended across disparate ecological, body-size and physiological classes.

On the sand and among the crowds: a new species of Woodworthia gecko (Reptilia: Diplodactylidae) from Auckland, Aotearoa/ New Zealand

Woodworthia is a diverse genus of diplodactylid geckos found in Aotearoa/ New Zealand, with 17 likely species. Despite this diversity, only two species have been formally described: Woodworthia maculata (Gray, 1845) and W. chrysosiretica (Robb, 1980). In this paper, we use an integrated taxonomic approach to describe a new species of Woodworthia gecko, Woodworthia korowai sp. nov., found along the western coastline of the Auckland Region, New Zealand. Although this species occurs in duneland habitat behind a popular beach near New Zealands most populated city, it was only recognised as a distinct taxon in 2016. We describe W. korowai sp. nov. based on a suite of morphological character states and substantial genetic divergence, based on the mitochondrial NADH dehydrogenase subunit 2 (ND2) gene, that distinguish it from W. maculata sensu stricto and all other known species of Woodworthia. Phylogenetic reconstruction and molecular dating place it sister to the W. maculata group, with an estimated time of divergence in the mid to late Pliocene. This gecko is one of the most geographically restricted of all Woodworthia geckos, occupying an area of less than 500 km2 within the Auckland Region. Its narrow range and coastal association make it susceptible to environmental and genetic stochasticity. Furthermore, the popularity and recreational usage of the dune system threaten its habitat. Therefore, we hope that this description will bring attention to the value of coastal environments and the unique and sensitive duneland of Te Korowai-o-Te-Tonga/ South Kaipara Peninsula and Te Oneone Rangatira/ Muriwai Beach in particular and encourage conservation efforts to protect this newly described species and its habitat.

Reappraising the evolutionary history of the largest known gecko, the presumably extinct Hoplodactylus delcourti, via high-throughput sequencing of archival DNA

Hoplodactylus delcourti is a presumably extinct species of diplodactylid gecko known only from a single specimen of unknown provenance. It is by far the largest known gekkotan, approximately 50% longer than the next largest-known species. It has been considered a member of the New Zealand endemic genus Hoplodactylus based on external morphological features including shared toe pad structure. We obtained DNA from a bone sample of the only known specimen to generate high-throughput sequence data suitable for phylogenetic analysis of its evolutionary history. Complementary sequence data were obtained from a broad sample of diplodactylid geckos. Our results indicate that the species is not most closely related to extant Hoplodactylus or any other New Zealand gecko. Instead, it is a member of a clade whose living species are endemic to New Caledonia. Phylogenetic comparative analyses indicate that the New Caledonian diplodactylid clade has evolved significantly more disparate body sizes than either the Australian or New Zealand clades. Toe pad structure has changed repeatedly across diplodactylids, including multiple times in the New Caledonia clade, partially explaining the convergence in form between H. delcourti and New Zealand Hoplodactylus. Based on the phylogenetic results, we place H. delcourti in a new genus.

A redescription of Palaeogekko risgoviensis (Squamata, Gekkota) from the Middle Miocene of Germany, with new data on its morphology

After its original description, the Middle Miocene gekkotan Palaeogekko risgoviensis remained an enigma for palaeontologists due to a rather poor knowledge of its osteology and relationships. Coming from a single locality in southern Germany, this gecko lived in central Europe during a period when a single gekkotan lineage (i.e., euleptine sphaerodactylids) is confidently reported to have inhabited the continent. However, it is unclear whether P. risgoviensis may represent a member of this same lineage or a second clade of Gekkota. In order to shed light on this issue, the type material of P. risgoviensis is here redescribed, refigured and extensively compared with extinct and extant geckos from Europe. A phylogenetic analysis is also conducted in order to investigate its relationships. The new observations confirm the validity of the German species as a distinct taxon, and exclude the previously-suggested chimeric status of the type material of this gecko (with the exception of a single dentary included in the type series, which clearly belong to a different lizard). Phylogenetic relationships of Palaeogekko are still unclear, though, with different positions within the gekkotan tree recovered for the taxon. Nevertheless, it is confidently supported as a non-eublepharid gekkonoid, in agreement with hypothesys presented by other scholars.

A new gecko from the earliest Eocene of Dormaal, Belgium: a thermophilic element of the 'greenhouse world'

We here describe a new gekkotan lizard from the earliest Eocene (MP 7) of the Dormaal locality in Belgium, from the time of the warmest global climates of the past 66 million years (Myr). This new taxon, with an age of 56 Myr, together with indeterminate gekkotan material reported from Silveirinha (Portugal, MP 7) represent the oldest Cenozoic gekkotans known from Europe. Today gekkotan lizards are distributed worldwide in mainly warm temperate to tropical areas and the new gecko from Dormaal represents a thermophilic faunal element. Given the Palaeocene-Eocene thermal maximum at that time, the distribution of this group in such northern latitudes (above 50° North - the latitude of southern England) is not surprising. Although this new gekkotan is represented only by a frontal (further, dentaries and a mandibular fragment are described here as Gekkota indet. 1 and 2-at least two gekkotan species occurred in Dormaal), it provides a new record for squamate diversity from the earliest Eocene 'greenhouse world'. Together with the Baltic amber gekkotan Yantarogekko balticus, they document the northern distribution of gekkotans in Europe during the Eocene. The increase in temperature during the early Eocene led to a rise in sea level, and many areas of Eurasia were submerged. Thus, the importance of this period is magnified by understanding future global climate change.

Multiple evolutionary origins and losses of tooth complexity in squamates

Teeth act as tools for acquiring and processing food, thus holding a prominent role in vertebrate evolution. In mammals, dental-dietary adaptations rely on tooth complexity variations controlled by cusp number and pattern. Complexity increase through cusp addition has dominated the diversification of mammals. However, studies of Mammalia alone cannot reveal patterns of tooth complexity conserved throughout vertebrate evolution. Here, we use morphometric and phylogenetic comparative methods across fossil and extant squamates to show they also repeatedly evolved increasingly complex teeth, but with more flexibility than mammals. Since the Late Jurassic, multiple-cusped teeth evolved over 20 times independently from a single-cusped common ancestor. Squamates frequently lost cusps and evolved varied multiple-cusped morphologies at heterogeneous rates. Tooth complexity evolved in correlation with changes in plant consumption, resulting in several major increases in speciation. Complex teeth played a critical role in vertebrate evolution outside Mammalia, with squamates exemplifying a more labile system of dental-dietary evolution.

Lizards and snakes from the earliest Miocene of Saint-Gérand-le-Puy, France: an anatomical and histological approach of some of the oldest Neogene squamates from Europe

BACKGROUND

The earliest Miocene (Aquitanian) represents a crucial time interval in the evolution of European squamates (i.e., lizards and snakes), witnessing a high diversity of taxa, including an array of extinct forms but also representatives of extant genera. We here conduct a taxonomical survey along with a histological/microanatomical approach on new squamate remains from the earliest Miocene of Saint-Gérand-le-Puy, France, an area that has been well known for its fossil discoveries since the nineteenth century.

RESULTS

We document new occurrences of taxa, among which, the lacertid Janosikia and the anguid Ophisaurus holeci, were previously unknown from France. We provide a detailed description of the anatomical structures of the various cranial and postcranial remains of lizards and snakes from Saint-Gérand-le-Puy. By applying micro-CT scanning in the most complete cranial elements of our sample, we decipher previously unknown microanatomical features. We report in detail the subsurface distribution and 3D connectivity of vascular channels in the anguid parietal. The fine meshwork of channels and cavities or sinuses in the parietal of Ophisaurus could indicate some thermoregulatory function, as it has recently been demonstrated for other vertebrate groups, providing implications for the palaeophysiology of this earliest Miocene anguine lizard.

CONCLUSIONS

A combination of anatomical and micro-anatomical/histological approach, aided by micro-CT scanning, enabled the documentation of these new earliest Miocene squamate remains. A distinct geographic expansion is provided for the extinct anguine Ophisaurus holeci and the lacertid Janosikia (the closest relative of the extant insular Gallotia from the Canary Islands).

Skeletal variation in extant species enables systematic identification of New Zealand's large, subfossil diplodactylids

New Zealand’s diplodactylid geckos exhibit high species-level diversity, largely independent of discernible osteological changes. Consequently, systematic affinities of isolated skeletal elements (fossils) are primarily determined by comparisons of size, particularly in the identification of Hoplodactylus duvaucelii, New Zealand’s largest extant gecko species. Here, three-dimensional geometric morphometrics of maxillae (a common fossilized element) was used to determine whether consistent shape and size differences exist between genera, and if cryptic extinctions have occurred in subfossil ‘Hoplodactylus cf. duvaucelii’. Sampling included 13 diplodactylid species from five genera, and 11 Holocene subfossil ‘H. cf. duvaucelii’ individuals. We found phylogenetic history was the most important predictor of maxilla morphology among extant diplodactylid genera. Size comparisons could only differentiate Hoplodactylus from other genera, with the remaining genera exhibiting variable degrees of overlap. Six subfossils were positively identified as H. duvaucelii, confirming their proposed Holocene distribution throughout New Zealand. Conversely, five subfossils showed no clear affinities with any modern diplodactylid genera, implying either increased morphological diversity in mainland ‘H. cf. duvaucelii’ or the presence of at least one extinct, large, broad-toed diplodactylid species.

Surface sculpturing in the skull of gecko lizards (Squamata: Gekkota)

It has previously been stated that geckos are characterized by smooth cranial bones bearing no sculpturing; however, there are many exceptions. Here we systematically characterize variation in sculpturing in cranial bones across all seven gekkotan families and examine patterns of evolutionary transitions in these traits on a multigene molecular gekkotan phylogeny to elucidate trends in phenotypic diversification in bone sculpturing. Over 195 species were reviewed using specimens where smooth, grooved, pitted and rugose sculpturing patterns were found. Of the 26 cranial bones, only seven (premaxilla, maxilla, nasal, prefrontal, frontal, parietal and postorbitofrontal) were found to bear sculpturing across more than three species. Sculpturing was found to extend beyond these seven bones onto either the dentary, surangular and/or quadrate within five species. Phylogenetic analysis showed that sculpturing evolved recently and repeatedly in several distinct lineages. The remaining 19 skull bones were smooth, except in the five species above, supporting the suggestion that smooth skull bones were ancestral in gekkotans. There is no apparent relationship between body size and the presence of bone sculpturing. The functional significance, if any, of sculpturing requires further investigation.

Embryonic skull development in the gecko, Tarentola annularis (Squamata: Gekkota: Phyllodactylidae)

Tarentola annularis is a climbing gecko with a wide distribution in Africa north of the equator. In the present paper, we describe the development of the osteocranium of this lizard, from the first appearance of the cranial elements up to the point of hatching. This is based on a combination of histology and cleared and stained specimens. This is the first comprehensive account of gekkotan pre-hatching skull development based on a comprehensive series of embryos, rather than a few selected stages. Given that Gekkota is now widely regarded as representing the sister group to other squamates, this account helps to fill a significant gap in the literature. Moreover, as many authors have considered features of the gekkotan skull and skeleton to be indicative of paedomorphosis, it is important to know whether this hypothesis is supported by delays in the onset of cranial ossification. In fact, we found the sequence of cranial bone ossification to be broadly comparable to that of other squamates studied to date, with no significant lags in development.

Gecko Adhesion in Space and Time: A Phylogenetic Perspective on the Scansorial Success Story

An evolutionary perspective on gecko adhesion was previously hampered by a lack of an explicit phylogeny for the group and of robust comparative methods to study trait evolution, an underappreciation for the taxonomic and structural diversity of geckos, and a dearth of fossil evidence bearing directly on the origin of the scansorial apparatus. With a multigene dataset as the basis for a comprehensive gekkotan phylogeny, model-based methods have recently been employed to estimate the number of unique derivations of the adhesive system and its role in lineage diversification. Evidence points to a single basal origin of the spinulate oberhautchen layer of the epidermis, which is a necessary precursor for the subsequent elaboration of a functional adhesive mechanism in geckos. However, multiple gains and losses are implicated for the elaborated setae that are necessary for adhesion via van der Waals forces. The well-supported phylogeny of gekkotans has demonstrated that convergence and parallelism in digital design are even more prevalent than previously believed. It also permits the reexamination of previously collected morphological data in an explicitly evolutionary context. Both time-calibrated trees and recently discovered amber fossils that preserve gecko toepads suggest that a fully-functional adhesive apparatus was not only present, but also represented by diverse architectures, by the mid-Cretaceous. Further characterization and phylogenetically-informed analyses of the other components of the adhesive system (muscles, tendons, blood sinuses, etc.) will permit a more comprehensive reconstruction of the evolutionary pathway(s) by which geckos have achieved their structural and taxonomic diversity. A phylogenetic perspective can meaningfully inform functional and performance studies of gecko adhesion and locomotion and can contribute to advances in bioinspired materials.

A comparative study of eggshells of Gekkota with morphological, chemical compositional and crystallographic approaches and its evolutionary implications

The Gekkota is an important clade in the evolution of calcified eggshells in that some of its families lay rigid eggshells like archosaurs. However, the fundamental differences and similarities between the mechanism of rigid eggshell formation of the Gekkota and Archosauria have not been investigated thoroughly due to the lack of knowledge of gekkotan eggshells. Here, we report for the first time a comprehensive analysis of morphological, chemical compositional, and crystallographic features of rigid and soft gekkotan eggshells. Exhaustive morphological description provided common characters for gekkotan eggshells, as well as unique features of each species. We found that elemental distribution of rigid gekkotan eggshells is different from that of avian eggshells, especially in the case of Mg and P. In addition, the crystallographic features (size, shape, and alignment of calcite grains) of gekkotan eggshells are completely different from those of archosaur eggshells. The result of this study suggests that soft gekkotan eggshells are morphologically more similar to tuatara eggshells rather than soft eggshells of derived squamates. The chemical compositional analysis suggests that the eggshell may act as a mineral reservoir for P and F as well as Ca. More importantly, all chemical compositions and crystallographic features imply that the gekkotan eggshell formation may begin at the outer surface and growing down to the inner surface, which is opposite to the direction of the archosaur eggshell formation. This character would be crucial for identifying fossil gekkotan eggs, which are poorly known in paleontology. All these lines of evidence support that soft gekkotan and tuatara eggshells share the primitive characters of all lepidosaurid eggshells. Finally, gekkotan and archosaur rigid eggshells represent a typical example of convergent evolution in the lineage of the Sauropsida.

Lizards ran bipedally 110 million years ago

Four heteropod lizard trackways discovered in the Hasandong Formation (Aptian-early Albian), South Korea assigned to Sauripes hadongensis, n. ichnogen., n. ichnosp., which represents the oldest lizard tracks in the world. Most tracks are pes tracks (N = 25) that are very small, average 22.29 mm long and 12.46 mm wide. The pes tracks show "typical" lizard morphology as having curved digit imprints that progressively increase in length from digits I to IV, a smaller digit V that is separated from the other digits by a large interdigital angle. The manus track is 19.18 mm long and 19.23 mm wide, and shows a different morphology from the pes. The predominant pes tracks, the long stride length of pes, narrow trackway width, digitigrade manus and pes prints, and anteriorly oriented long axis of the fourth pedal digit indicate that these trackways were made by lizards running bipedally, suggesting that bipedality was possible early in lizard evolution.

Evolution of developmental sequences in lepidosaurs

BACKGROUND

Lepidosaurs, a group including rhynchocephalians and squamates, are one of the major clades of extant vertebrates. Although there has been extensive phylogenetic work on this clade, its interrelationships are a matter of debate. Morphological and molecular data suggest very different relationships within squamates. Despite this, relatively few studies have assessed the utility of other types of data for inferring squamate phylogeny.

METHODS

We used developmental sequences of 20 events in 29 species of lepidosaurs. These sequences were analysed using event-pairing and continuous analysis. They were transformed into cladistic characters and analysed in TNT. Ancestral state reconstructions were performed on two main phylogenetic hypotheses of squamates (morphological and molecular).

RESULTS

Cladistic analyses conducted using characters generated by these methods do not resemble any previously published phylogeny. Ancestral state reconstructions are equally consistent with both morphological and molecular hypotheses of squamate phylogeny. Only several inferred heterochronic events are common to all methods and phylogenies.

DISCUSSION

Results of the cladistic analyses, and the fact that reconstructions of heterochronic events show more similarities between certain methods rather than phylogenetic hypotheses, suggest that phylogenetic signal is at best weak in the studied developmental events. Possibly the developmental sequences analysed here evolve too quickly to recover deep divergences within Squamata.

Mid-Cretaceous amber fossils illuminate the past diversity of tropical lizards

Modern tropical forests harbor an enormous diversity of squamates, but fossilization in such environments is uncommon and little is known about tropical lizard assemblages of the Mesozoic. We report the oldest lizard assemblage preserved in amber, providing insight into the poorly preserved but potentially diverse mid-Cretaceous paleotropics. Twelve specimens from the Albian-Cenomanian boundary of Myanmar (99 Ma) preserve fine details of soft tissue and osteology, and high-resolution x-ray computed tomography permits detailed comparisons to extant and extinct lizards. The extraordinary preservation allows several specimens to be confidently assigned to groups including stem Gekkota and stem Chamaleonidae. Other taxa are assignable to crown clades on the basis of similar traits. The detailed preservation of osteological and soft tissue characters in these specimens may facilitate their precise phylogenetic placement, making them useful calibration points for molecular divergence time estimates and potential keys for resolving conflicts in higher-order squamate relationships.

Gekko japonicus genome reveals evolution of adhesive toe pads and tail regeneration

Reptiles are the most morphologically and physiologically diverse tetrapods, and have undergone 300 million years of adaptive evolution. Within the reptilian tetrapods, geckos possess several interesting features, including the ability to regenerate autotomized tails and to climb on smooth surfaces. Here we sequence the genome of Gekko japonicus (Schlegel's Japanese Gecko) and investigate genetic elements related to its physiology. We obtain a draft G. japonicus genome sequence of 2.55 Gb and annotated 22,487 genes. Comparative genomic analysis reveals specific gene family expansions or reductions that are associated with the formation of adhesive setae, nocturnal vision and tail regeneration, as well as the diversification of olfactory sensation. The obtained genomic data provide robust genetic evidence of adaptive evolution in reptiles.

Geckos are small, agile reptiles with nocturnal habits. Here, the authors sequence the genome of the Schlegel's Japanese Gecko and reveal gene family expansions and reductions associated with formation of adhesive setae, nocturnal vision, tail regeneration, and diversification of olfactory sensation.