Variation in the cranial osteology of the amphisbaenian genus Zygaspis based on high-resolution x-ray computed tomography

Amphisbaenians are a specialized fossorial group of reptiles, having developed head-first burrowing, a specialized skull architecture, and an elongated body. This group is generally small-bodied, with some species possessing skulls only a few millimeters long. In this study, we used high-resolution x-ray computed tomography to compare the skulls of 15 specimens from seven of the eight species in the amphisbaenian genus Zygaspis (Zygaspis dolichomenta, Zygaspis ferox, Zygaspis quadrifrons, Zygaspis kafuensis, Zygaspis nigra, Zygaspis vandami, and Zygaspis violacea). Both interspecific and intraspecific variation, including asymmetry, is observed among the cranial bones of the specimens. There are unique morphological features on some cranial bones, including the premaxilla and ectopterygoid of Z. quadrifrons, the pterygoid and vomer of Z. kafuensis, and the extracolumella of Z. nigra. Sexual dimorphism has been previously reported for the species Z. quadrifrons and is observed here as well.

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 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.

Chromosome-Level Genome Assembly Reveals Dynamic Sex Chromosomes in Neotropical Leaf-Litter Geckos (Sphaerodactylidae: Sphaerodactylus)

Sex determination is a critical element of successful vertebrate development, suggesting that sex chromosome systems might be evolutionarily stable across lineages. For example, mammals and birds have maintained conserved sex chromosome systems over long evolutionary time periods. Other vertebrates, in contrast, have undergone frequent sex chromosome transitions, which is even more amazing considering we still know comparatively little across large swaths of their respective phylogenies. One reptile group in particular, the gecko lizards (infraorder Gekkota), shows an exceptional lability with regard to sex chromosome transitions and may possess the majority of transitions within squamates (lizards and snakes). However, detailed genomic and cytogenetic information about sex chromosomes is lacking for most gecko species, leaving large gaps in our understanding of the evolutionary processes at play. To address this, we assembled a chromosome-level genome for a gecko (Sphaerodactylidae: Sphaerodactylus) and used this assembly to search for sex chromosomes among six closely related species using a variety of genomic data, including whole-genome re-sequencing, RADseq, and RNAseq. Previous work has identified XY systems in two species of Sphaerodactylus geckos. We expand upon that work to identify between two and four sex chromosome cis-transitions (XY to a new XY) within the genus. Interestingly, we confirmed two different linkage groups as XY sex chromosome systems that were previously unknown to act as sex chromosomes in tetrapods (syntenic with Gallus chromosome 3 and Gallus chromosomes 18/30/33), further highlighting a unique and fascinating trend that most linkage groups have the potential to act as sex chromosomes in squamates.

A new Early Cretaceous lizard in Myanmar amber with exceptionally preserved integument

We here report on a well-preserved juvenile lizard specimen in Albian amber (ca. 110 mya) from the Hkamti site (Myanmar). This new taxon is represented by an articulated skull and the anterior portion of the trunk, including the pectoral girdle and forelimbs. The scleral ossicles and eyelid are also visible, and the specimen exhibits pristine detail of the integument (of both head and body). In a combined molecular and morphological analysis, it was consistently recovered as a scincoid lizard (Scinciformata), as sister to Tepexisaurus + Xantusiidae. However, the phylogenetic position of the new taxon should be interpreted with caution as the holotype is an immature individual. We explored the possibility of miscoding ontogenetically variable characters by running alternative analyses in which these characters were scored as missing data for our taxon. With the exception of one tree, in which it was sister to Amphisbaenia, the specimen was recovered as a Pan-xantusiid. Moreover, we cannot rule out the possibility that it represents a separate lineage of uncertain phylogenetic position, as it is the case for many Jurassic and Cretaceous taxa. Nonetheless, this fossil offers a rare opportunity to glimpse the external appearance of one group of lizards during the Early Cretaceous.

OUP accepted manuscript

Zoos and natural history museums are both collections-based institutions with important missions in biodiversity research and education. Animals in zoos are a repository and living record of the world's biodiversity, whereas natural history museums are a permanent historical record of snapshots of biodiversity in time. Surprisingly, despite significant overlap in institutional missions, formal partnerships between these institution types are infrequent. Life history information, pedigrees, and medical records maintained at zoos should be seen as complementary to historical records of morphology, genetics, and distribution kept at museums. Through examining both institution types, we synthesize the benefits and challenges of cross-institutional exchanges and propose actions to increase the dialog between zoos and museums. With a growing recognition of the importance of collections to the advancement of scientific research and discovery, a transformational impact could be made with long-term investments in connecting the institutions that are caretakers of living and preserved animals.

Unveiling the elusive: X-rays bring scolecophidian snakes out of the dark

Scolecophidian snakes have long posed challenges for scholars interested in elucidating their anatomy. The importance, and relative paucity, of high-quality anatomical data pertaining to scolecophidians was brought into sharp focus in the late 20^th century as part of a controversy over the phylogeny and ecological origin of snakes. The basal position of scolecophidians in the phylogeny of snakes makes their anatomy, behavior, ecology, and evolution especially important for such considerations. The depauperate fossil record for the group meant that advances in understanding their evolutionary history were necessarily tied to biogeographic distributions and anatomical interpretations of extant taxa. Osteological data, especially data pertaining to the skull and mandible, assumed a dominant role in shaping historical and modern perspectives of the evolution of scolecophidians. Traditional approaches to the exploration of the anatomy of these snakes relied heavily upon serial-sectioned specimens and cleared-and-stained specimens. The application of X-ray computed tomography (CT) to the study of scolecophidians revolutionized our understanding of the osteology of the group, and now, via diffusible iodine-based contrast-enhanced computed tomography (diceCT), is yielding data sets on internal soft anatomical features as well. CT data sets replicate many aspects of traditional anatomical preparations, are readily shared with a global community of scholars, and now are available for unique holotype and other rare specimens. The increasing prevalence and relevance of CT data sets is a strong incentive for the establishment and maintenance of permanent repositories for digital data.

The status of the anomalepidid snake Liotyphlops albirostris and the revalidation of three taxa based on morphology and ecological niche models

Liotyphlops is a genus of blindsnakes distributed in Central and South America. We reviewed specimens of Liotyphlops albirostris along its current distribution range and, based on morphological data and ecological niche modeling analyses, we restrict the geographical range of L. albirostris and validate three previously described species. In this revision, we describe the morphological variation in the populations from Panamá, Colombia, Ecuador, and Venezuela, and propose a new taxonomic arrangement. We revalidate three previous synonyms of L. albirostris to full species status, while dividing the populations from Colombia in two subspecies-one attributed to a previously recognized species from the Caribbean region, and a new one from the Andean region. The new species differs from L. albirostris from Panamá in cephalic scale arrangements that effectively reduces the previously reported variability of these scales in L. albirostris. We also explore some osteological differences that are congruent with the variation observed. We hope that the recognition of these new species better represents the diversity within Liotyphlops, helping to bring these new species out of their cryptic status so that they will be considered in future conservation efforts.

Blind snakes beneath the surface: Continuing the legacy of Richard Thomas

Blind snakes (Scolecophidia) are small-bodied, enigmatic burrowing reptiles with members found on all continents except Antarctica. This Special Issue on blind snakes honors and advances the foundational studies by a remarkable anatomist, Richard Thomas. Richard is currently one of the living herpetologists to have described the greatest number of herpetofauna species, including many blind snake taxa. Recent interest in scolecophidian research at several conferences led to the development of this Special Issue on blind snake anatomy. This issue spans a diversity of papers, from biographical accounts of Richard's life and works, to a brief history of scolecophidian anatomical studies and the benefits of computed tomography (CT) technology, to a variety of studies on the skull and post-cranial osteology, cranial and jaw biomechanics related to subterranean lifestyles, evolution, and systematics of blind snake taxa from around the globe. This Special Issue will hopefully serve as a valuable resource and contribution to the field of blind snake anatomy research, and a joyful reflection on the life and career of a herpetologist who mentored and inspired a new generation of researchers in this area.

Comparative anatomy of the middle ear in some lizard species with comments on the evolutionary changes within Squamata

The skeleton of the middle ear of lizards is composed of three anatomical elements: columella, extracolumella, and tympanic membrane, with some exceptions that show modifications of this anatomy. The main function of the middle ear is transforming sound waves into vibrations and transmitting these to the inner ear. Most middle ear studies mainly focus on its functional aspects, while few describe the anatomy in detail. In lizards, the morphology of the columella is highly conservative, while the extracolumella shows variation in its presence/absence, size, and the number of processes present on the structure. In this work, we used diaphanized and double-stained specimens of 38 species of lizards belonging to 24 genera to study the middle ear’s morphology in a comparative framework. Results presented here indicate more variation in the morphology of the extracolumella than previously known. This variation in the extracolumella is found mainly in the pars superior and anterior processes, while the pars inferior and the posterior process are more constant in morphology. We also provide new information about the shape of gekkotan extracolumella, including traits that are diagnostic for the iguanid and gekkonid middle ear types. The data collected in this study were combined with information from published descriptive works. The new data included here refers to the length of the columella relative to the extracolumella central axis length, the general structure of the extracolumella, and the presence of the internal process. These characters were included in ancestral reconstruction analysis using Bayesian and parsimony approaches. The results indicate high levels of homoplasy in the variation of the columella-extracolumella ratio, providing a better understanding of the ratio variation among lizards. Additionally, the presence of four processes in the extracolumella is the ancestral state for Gekkota, Pleurodonta, and Xantusiidae, and the absence of the internal processes is the ancestral state for Gekkota, Gymnophthalmidae, and Scincidae; despite the fact that these groups convergently develop these character states, they could be used in combination with other characters to diagnose these clades. The posterior extension in the pars superior and an anterior process with some small and sharp projections is also a diagnostic trait for Gekkota. A more accurate description of each process of the extracolumella and its variation needs to be evaluated in a comprehensive analysis, including a greater number of species. Although the number of taxa sampled in this study is small considering the vast diversity of lizards, the results provide an overall idea of the amount of variation of the middle ear while helping to infer the evolutionary history of the lizard middle ear.

The herpetological contributions of Richard Thomas

John Paul Richard Thomas is among the living herpetologists to have described the greatest number of new species of amphibians and reptiles, and his contributions to the herpetology of the West Indies, particularly the Greater Antilles, have been exceptional. His academic career followed an unusual path, having established a strong reputation and described 50 new taxa prior to beginning his doctoral studies. His career was strongly influenced by Albert Schwartz and later was characterized by extensive and fruitful collaboration with S. Blair Hedges. Thomas' contributions to the study of blind snakes have been noteworthy. In addition to describing 28 species of scolecophidians he has been a keen observer of blind snake morphology and his 1976 dissertation remains a valuable source of osteological data. We outline some of the highlights of the career of Richard Thomas and provide a bibliography of his scientific works and a listing of the 108 taxa of amphibians and reptiles described by him.

Underground Down Under: Skull anatomy of the southern blind snake Anilios australis Gray, 1845 (Typhlopidae: Serpentes: Squamata)

The cranial anatomy of blindsnakes has been markedly understudied, with the small size and relative rarity of encountering these subterranean reptiles being significant limiting factors. In this article, we re-visit the skull anatomy of the Australian southern blind snake Anilios australis Gray, 1845 using microCT data, and produce the first complete atlas for the cranial anatomy of a representative of this speciose typhlopid genus. The skull is formed by 18 paired and four unpaired elements. We here produce a bone-by-bone description of each element as well as an inner ear endocast for each of two specimens differing in skull size. This approach has revealed the presence of a highly perforated dorsal plate on the septomaxilla-a structure convergent with the cribriform plate of the mammalian ethmoid bone-and a feature previously unknown for typhlopid snakes. This detailed anatomical study will facilitate ongoing taxonomic and systematic studies in the genus Anilios as well as provide comparative data for future studies on blindsnake anatomy more broadly.

Unusual morphology in the mid-Cretaceous lizard Oculudentavis

Oculudentavis khaungraae was described based on a tiny skull trapped in amber. The slender tapering rostrum with retracted narial openings, large eyes, and short vaulted braincase led to its identification as the smallest avian dinosaur on record, comparable to the smallest living hummingbirds. Despite its bird-like appearance, Oculudentavis showed several features inconsistent with its original phylogenetic placement. Here, we describe a more complete specimen that demonstrates Oculudentavis is actually a bizarre lizard of uncertain position. The new specimen is described as a new species within the genus Oculudentavis. The new interpretation and phylogenetic placement highlight a rare case of convergent evolution in skull proportions but apparently not in morphological characters. Our results re-affirm the importance of Myanmar amber in yielding unusual taxa from a forest ecosystem rarely represented in the fossil record.

Ecomorphometric Analysis of Diversity in Cranial Shape of Pygopodid Geckos

Pygopodids are elongate, functionally limbless geckos found throughout Australia. The clade presents low taxonomic diversity (∼45 spp.), but a variety of cranial morphologies, habitat use, and locomotor abilities that vary between and within genera. In order to assess potential relationships between cranial morphology and ecology, computed tomography scans of 29 species were used for 3D geometric morphometric analysis. A combination of 24 static landmarks and 20 sliding semi-landmarks were subjected to Generalized Procrustes Alignment. Disparity in cranial shape was visualized through Principal Component Analysis, and a multivariate analysis of variance (MANOVA) was used to test for an association between shape, habitat, and diet. A subset of 27 species with well-resolved phylogenetic relationships was used to generate a phylomorphospace and conduct phylogeny-corrected MANOVA. Similar analyses were done solely on Aprasia taxa to explore species-level variation. Most of the variation across pygopodids was described by principal component (PC) 1(54%: cranial roof width, parabasisphenoid, and occipital length), PC2 (12%: snout elongation and braincase width), and PC3 (6%: elongation and shape of the palate and rostrum). Without phylogenetic correction, both habitat and diet were significant influencers of variation in cranial morphology. However, in the phylogeny-corrected MANOVA, habitat remained weakly significant, but not diet, which can be explained by generic-level differences in ecology rather than among species. Our results demonstrate that at higher levels, phylogeny has a strong effect on morphology, but that influence may be due to small sample size when comparing genera. However, because some closely related taxa occupy distant regions of morphospace, diverging diets, and use of fossorial habitats may contribute to variation seen in these geckos.

A biographical account of John Paul Richard Thomas, the man who leaves no stone unturned

This biographical account summarizes the professional career and scientific contributions of John Paul Richard Thomas, a contemporary leading figure in the systematics of West Indian amphibians and non-avian reptiles, especially of blind snakes of the families Typhlopidae and Leptotyphlopidae. Since his first expedition to the West Indies in 1957, Richard's vast field experience (including three trips to Peru between 1968 and 1974), impressive collecting skills, and remarkable ability to detect phenotypic variation among natural populations have resulted in the description of more than 70 species of snakes (24 typhlopids, 4 leptotyphlopids), lizards, and frogs in 16 genera and 11 taxonomic families. Richard joined the faculty of the Department of Biology, University of Puerto Rico, Río Piedras, in 1976 and ever since his efforts significantly advanced organismal biology research at the institution. Although primarily a systematist, his desire to understand multiple aspects of an organism's biology and contagious passion for becoming intimately familiar with animals in their natural environments provided his students the opportunity to conduct research in fields such as behavioral and evolutionary ecology. Richard's mentoring fostered the scientific interests of his graduate students, who were exposed first-hand to every aspect of research, an invaluable experience that served as a springboard for the development of their professional careers inside and outside academia. This Commentary is a fitting tribute to an influential, unassuming scientist whose passion for turning over rocks has led to the discovery of many interesting species.

Extended diagnosis of the type species of Pseudogonatodes Ruthven 1915 (Gekkota: Sphaerodactylidae)

Pseudogonatodes furvus is an endemic gecko from the region of the Sierra Nevada de Santa Marta, an isolated massif located in the continental Caribbean region of Colombia. Pseudogonatodes furvus is the type species of the genus, and its morphology and natural history remain poorly known. This lizard was described based on two specimens. After its description, the species has only been mentioned in a handful of taxonomic studies of Pseudogonatodes, in which a few morphological characters of P. furvus have been mentioned. One other paper reported two new localities, without providing new information on the external morphology, especially the lepidosis of the newly obtained specimens. Here we review the external morphology of P. furvus, based on examination of the holotype and six additional specimens. We provide an extended diagnosis and definition, description of holotype, variation, comparisons with other Pseudogonatodes, geographic distribution (adding a fourth locality to the known distribution for the species), and conservation status. Additionally, we describe osteological features for the diagnosis of the genus.

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.

Phylogeny and evolution of unique skull morphologies in dietary specialist African shovel-snouted snakes (Lamprophiidae: Prosymna)

Prosymna is a specialized African snake genus lacking close relatives. The evolutionary relationships and history within Prosymna are poorly understood. Here we assembled a multi-gene data set including representatives for 11 of 16 species to investigate the phylogenetic relationships of this group. Our analyses support the monophyly of Prosymna and are congruent with species groups previously recognized on the basis of external morphology. Divergences among extant Prosymna began in the mid-Cenozoic, with the earliest divergence splitting northern from southern lineages. High-resolution computed tomography scans confirm that a specialized skull morphology is found across the genus and was probably present in the common ancestor of Prosymna. This specialization is exemplified by dentition featuring reduced anterior but greatly enlarged, blade-like posterior maxillary teeth and an unusually high degree of fusion of cranial bones. One species, P. visseri, has a hammer-like maxilla unlike that of any other known snake. Evidence for oophagy in Prosymna and the possible roles of morphological specializations in egg-slitting or egg-crushing feeding mechanisms are discussed.

The sprightly little sphaerodactyl: Systematics and biogeography of <br />the Puerto Rican dwarf geckos Sphaerodactylus (Gekkota, Sphaerodactylidae)

Studies of the Caribbean herpetofauna (amphibians and reptiles) have made significant contributions to our knowledge of evolutionary patterns and processes. A prerequisite for these studies are accurate taxonomies and robust phylogenetic hypotheses. One notable Caribbean radiation lacking such data are dwarf geckos of the genus Sphaerodactylus. Systematics of the Puerto Rican Sphaerodactylus have been turbulent since the initial species descriptions and no molecular phylogenies exist that include complete or near-complete taxon sampling. Here, we combine a multi-locus molecular phylogeny with extensive morphological information to investigate the current diversity of Sphaerodactylus geckos from the Puerto Rican Bank, with a large number of species from Hispaniola as an outgroup. In particular, we focus our efforts on resolving the taxonomy of the Sphaerodactylus macrolepis Günther species complex. We find S. macrolepis sensu lato (currently two nominal species with nine subspecies) is made up of at least four diagnosable species within two clades: (1) the sister species Sphaerodactylus macrolepis sensu stricto from the Virgin Islands (including St. Croix) and Culebra, and S. parvus King from islands in the northern Lesser Antilles; and (2) all other Sphaerodactylus macrolepis subspecies from Puerto Rico, Vieques, and Culebra. We resurrect Sphaerodactylus grandisquamis Stejneger from synonymy to refer to all subspecies from Puerto Rico and elevate the subspecies Sphaerodactylus inigoi Thomas Schwartz for geckos from Vieques and western Culebra. The resulting phylogeny and revised taxonomy will be a useful tool for subsequent research into Sphaerodactylus conservation and evolution.

You Can't Run, but You Can Hide: The Skeleton of the Sand-Swimmer Lizard Calyptommatus leiolepis (Squamata: Gymnophthalmidae)

Squamates exhibit a vast diversity of body plans, which directly determines habitat use and preference. Here the skeleton of the sand-swimmer burrower gymnophthalmid, Calyptommatus leiolepis, is analyzed to investigate how its peculiar fossorial locomotion affects its osteology. Calyptommatus leiolepis is a limb-reduced, short-intermediate tailed lizard. Although there are other studies on its general anatomy, we performed a detailed description of its skeleton. Using high-resolution computer tomography, each bone element within the skeleton was digitally segmented and a detailed description rendered. Anatomical features related to burrowing include the head having a shovel-like snout with a well-developed horizontal soft tissue ridge, nasal cartilages that exclude sand from the nostrils, reduced eyes covered by a brille, lack of forelimbs, extreme reduction of hind limbs, and imbricated scales among others. The genus Calyptommatus has unique features such as a triradiate jugal (with digit-like posterior projections), a reduced pectoral girdle and forelimbs, parasternal processes that interconnect the ribs, and a single digit in the hind limbs. When comparing this species with other gymnophthalmid lizards including, fossorial species, it is clear that Calyptommatus exhibits the highest number of structural modifications within the family. Despite its specialized morphology, it still retains characters that link this genus to other members of Gymnophthalmidae when included in a phylogeny based solely on phenotypic data. Anat Rec, 303:1305-1326, 2020. © 2019 American Association for Anatomy.

Persistence of a Geographically-Stable Hybrid Zone in Puerto Rican Dwarf Geckos

Determining the mechanisms that create and maintain biodiversity is a central question in ecology and evolution. Speciation is the process that creates biodiversity. Speciation is mediated by incompatibilities that lead to reproductive isolation between divergent populations and these incompatibilities can be observed in hybrid zones. Gecko lizards are a speciose clade possessing an impressive diversity of behavioral and morphological traits. In geckos, however, our understanding of the speciation process is negligible. To address this gap, we used genetic sequence data (both mitochondrial and nuclear markers) to revisit a putative hybrid zone between Sphaerodactylus nicholsi and Sphaerodactylus townsendi in Puerto Rico, initially described in 1984. First, we addressed discrepancies in the literature on the validity of both species. Second, we sampled a 10-km-wide transect across the putative hybrid zone and tested explicit predictions about its dynamics using cline models. Third, we investigated potential causes for the hybrid zone using species distribution modeling and simulations; namely, whether unique climatic variables within the hybrid zone might elicit selection for intermediate phenotypes. We find strong support for the species-level status of each species and no evidence of movement, or unique climatic variables near the hybrid zone. We suggest that this narrow hybrid zone is geographically stable and is maintained by a combination of dispersal and selection. Thus, this work has identified an extant model system within geckos that that can be used for future investigations detailing genetic mechanisms of reproductive isolation in an understudied vertebrate group.

ZZ/ZW Sex Chromosomes in the Endemic Puerto Rican Leaf-Toed Gecko (Phyllodactylus wirshingi)

Investigating the evolutionary processes influencing the origin, evolution, and turnover of vertebrate sex chromosomes requires the classification of sex chromosome systems in a great diversity of species. Among amniotes, squamates (lizards and snakes) - and gecko lizards in particular - are worthy of additional study. Geckos possess all major vertebrate sex-determining systems, as well as multiple transitions among them, yet we still lack data on the sex-determining systems for the vast majority of species. We here utilize restriction-site associated DNA sequencing (RADseq) to identify the sex chromosome system of the Puerto Rican endemic leaf-toed gecko (Phyllodactylidae: Phyllodactylus wirshingi), in order to confirm a ZZ/ZW sex chromosome system within the genus, as well as to better categorize the diversity within this poorly characterized family. RADseq has proven an effective alternative to cytogenetic methods for determining whether a species has an XX/XY or ZZ/ZW sex chromosome system - particularly in taxa with non-differentiated sex chromosomes - but can also be used to identify which chromosomes in the genome are the sex chromosomes. We here identify a ZZ/ZW sex chromosome system in P. wirshingi. Furthermore, we show that 4 of the female-specific markers contain fragments of genes found on the avian Z and discuss homology with P. wirshingi sex chromosomes.

Skull Morphology of the Lizard Ptychoglossus vallensis (Squamata: Alopoglossidae) With Comments on the Variation Within Gymnophthalmoidea

In recent years, major changes have been proposed for the phylogenetic relationships within the Gymnophthalmoidea, including the description of Alopoglossidae. Recent studies relied primarily on molecular data and have not accounted for evidence from alternative sources, such as morphology. In this study, we provide a detailed bone-by-bone description of the skull of Ptychoglossus vallensis and compare this species with other gymnophthalmoideans. The description was based on 10 cleared-and-stained specimens, four disarticulated skulls, and computed microtomography data of P. vallensis. Most recent phylogenetic hypothesis for the Gymnophthalmoidea was used as a framework to compare the skull of P. vallensis with other species of the Alopoglossidae, Gymnophthalmidae, and Teiidae. Marked similarities between alopoglossids and gymnophthalmids were observed in contrast to teiids, probably due to convergence generated by miniaturization. We also qualitatively analyzed the kinesis of the skull of P. vallensis concluding that is highly akinetic, a trait commonly evolved in fossorial, primarily burrowing squamates. We also describe one unique osteological feature for Alopoglossidae that is not known in any other squamate group. Anat Rec, 302:1074-1092, 2019. © 2018 Wiley Periodicals, Inc.

How common are cranial sesamoids among squamates?

Sesamoids are elements that originate as intratendinous structures due to genetic and epigenetic factors. These elements have been reported frequently in vertebrates, although cranial sesamoids have been recorded almost exclusively in non-tetrapod Osteichthyes. The only tetrapod cranial sesamoids reported until now have been the transiliens cartilage (of crocodiles and turtles), and another one located in the quadrate-mandibular joint of birds. Here, we examined seven squamate species using histological sections, dissections of preserved specimens, dry skeletons, cleared and stained specimens, computed tomographies (CT), and report the presence of other cranial sesamoids. One is attached to the cephalic condyle of the quadrate, embedded in the bodenaponeurosis and jaw adductor muscles of Ophiodes intermedius (Anguidae). The other sesamoid is found at the base of the basicranium of several squamates, capping the sphenoccipital tubercle, on the lateral side of the basioccipital-basisphenoid suture. This bone has previously been reported as "element X." We reinterpret it as a basicranial sesamoid, as it is associated with tendons of the cranio-cervical muscles. This bone seems to have the function of resisting tension-compression forces generated by the muscle during flexion the head. This element was previously known in several squamates, and we confirmed its presence in three additional squamate families: Gymnophthalmidae, Gekkonidae, and Pygopodidae. The evidence suggests that cranial sesamoids are a widespread character in squamates, and it is possible that this feature has been present since the origin of the group.

Off the scale: a new species of fish-scale gecko (Squamata: Gekkonidae: Geckolepis) with exceptionally large scales

The gecko genus Geckolepis, endemic to Madagascar and the Comoro archipelago, is taxonomically challenging. One reason is its members ability to autotomize a large portion of their scales when grasped or touched, most likely to escape predation. Based on an integrative taxonomic approach including external morphology, morphometrics, genetics, pholidosis, and osteology, we here describe the first new species from this genus in 75 years: Geckolepis megalepissp. nov. from the limestone karst of Ankarana in northern Madagascar. The new species has the largest known body scales of any gecko (both relatively and absolutely), which come off with exceptional ease. We provide a detailed description of the skeleton of the genus Geckolepis based on micro-Computed Tomography (micro-CT) analysis of the new species, the holotype of G. maculata, the recently resurrected G. humbloti, and a specimen belonging to an operational taxonomic unit (OTU) recently suggested to represent G. maculata. Geckolepis is characterized by highly mineralized, imbricated scales, paired frontals, and unfused subolfactory processes of the frontals, among other features. We identify diagnostic characters in the osteology of these geckos that help define our new species and show that the OTU assigned to G. maculata is probably not conspecific with it, leaving the taxonomic identity of this species unclear. We discuss possible reasons for the extremely enlarged scales of G. megalepis in the context of an anti-predator defence mechanism, and the future of Geckolepis taxonomy.

The first iguanian lizard from the Mesozoic of Africa

The fossil record shows that iguanian lizards were widely distributed during the Late Cretaceous. However, the biogeographic history and early evolution of one of its most diverse and peculiar clades (acrodontans) remain poorly known. Here, we present the first Mesozoic acrodontan from Africa, which also represents the oldest iguanian lizard from that continent. The new taxon comes from the Kem Kem Beds in Morocco (Cenomanian, Late Cretaceous) and is based on a partial lower jaw. The new taxon presents a number of features that are found only among acrodontan lizards and shares greatest similarities with uromastycines, specifically. In a combined evidence phylogenetic dataset comprehensive of all major acrodontan lineages using multiple tree inference methods (traditional and implied weighting maximum-parsimony, and Bayesian inference), we found support for the placement of the new species within uromastycines, along with Gueragama sulamericana (Late Cretaceous of Brazil). The new fossil supports the previously hypothesized widespread geographical distribution of acrodontans in Gondwana during the Mesozoic. Additionally, it provides the first fossil evidence of uromastycines in the Cretaceous, and the ancestry of acrodontan iguanians in Africa.

Histology of the Skin of Three Limbless Squamates Dwelling in Mesic and Arid Environments

The skin of limbless squamates has an increased contact with the substrate compared with limbed counterparts. Comparatively, the contact with the substrate is intensified in fossorial species, where the whole circumference of the body interacts with the soil during underground locomotion. Although fossoriality in Squamata, specifically lizards and snakes, has been studied ecologically and morphologically (e.g., osteological changes), not enough detail is yet available regarding changes in organs critical for underground lifestyle such as the skin. Here we used histological and microscopical techniques (scanning electron microscopy and transmission electron microscopy) to uncover the structural detail of the epidermis and dermis in three limbless reptiles, the amphisbaenian Diplometopon zarudnyi, and two snakes, Indotyphlops braminus (Typhlopidae) and Cerastes cerastes (Viperidae). The skin of these taxa shows pronounced morphological diversity, which is likely associated to different environmental and functional demands upon these reptiles. Anat Rec, 299:979-989, 2016. © 2016 Wiley Periodicals, Inc.

Diffusible iodine-based contrast-enhanced computed tomography (diceCT): an emerging tool for rapid, high-resolution, 3-D imaging of metazoan soft tissues

Morphologists have historically had to rely on destructive procedures to visualize the three‐dimensional (3‐D) anatomy of animals. More recently, however, non‐destructive techniques have come to the forefront. These include X‐ray computed tomography (CT), which has been used most commonly to examine the mineralized, hard‐tissue anatomy of living and fossil metazoans. One relatively new and potentially transformative aspect of current CT‐based research is the use of chemical agents to render visible, and differentiate between, soft‐tissue structures in X‐ray images. Specifically, iodine has emerged as one of the most widely used of these contrast agents among animal morphologists due to its ease of handling, cost effectiveness, and differential affinities for major types of soft tissues. The rapid adoption of iodine‐based contrast agents has resulted in a proliferation of distinct specimen preparations and scanning parameter choices, as well as an increasing variety of imaging hardware and software preferences. Here we provide a critical review of the recent contributions to iodine‐based, contrast‐enhanced CT research to enable researchers just beginning to employ contrast enhancement to make sense of this complex new landscape of methodologies. We provide a detailed summary of recent case studies, assess factors that govern success at each step of the specimen storage, preparation, and imaging processes, and make recommendations for standardizing both techniques and reporting practices. Finally, we discuss potential cutting‐edge applications of diffusible iodine‐based contrast‐enhanced computed tomography (diceCT) and the issues that must still be overcome to facilitate the broader adoption of diceCT going forward.

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.

Peramorphic traits in the tokay gecko skull

Traditionally, geckos have been conceived to exhibit paedomorphic features relative to other lizards (e.g., large eyes, less extensively ossified skulls, and amphicoelous and notochordal vertebrae). In contrast, peramorphosis has not been considered an important process in shaping their morphology. Here, we studied different sized specimens of Gekko gecko to document ontogenetic changes in cranial anatomy, especially near maturity. Comparison of this species with available descriptions of other geckos resulted in the identification of 14 cranial characteristics that are expressed more strongly with size increase. These characteristics become move evident in later stages of post-hatching development, especially near maturation, and are, therefore, attributed to peramorphosis (hyperossification). ACCTRAN and DELTRAN character optimizations were applied to these characters using a tree of 11 genera derived from a gekkotan molecular phylogeny. This analysis revealed that G. gecko expresses the majority of these putative peramorphic features near maturity, and that some of these features are also expressed in species closely related to G. gecko. The characters studied have the potential to be applied in future phylogenetic and taxonomic studies of this group of lizards.

The embryology of the retinal pigmented epithelium in dwarf geckos (Gekkota: Sphaerodactylinae): a unique developmental pattern

Background

The retinal pigmented epithelium (RPE) is a rounded shaped structure in almost all lizards. In the New World dwarf geckos, this structure shows an unusual morphology. In addition to this ocular character, we describe notable differences in the development of these geckos in comparison with available developmental staging tables for other geckos and squamate reptiles.

Results

We identified two main patterns of development of the RPE for squamates. These patterns were mapped onto a metatree of concordant hypotheses of squamates based on molecular data. During post-ovopositional stages the representative species of sphaerodactyls exhibit a RPE layer that transforms gradually from an ovoid form into the generalized spherical form. Sphaerodactyls are the only group of squamates in which this pattern is known.

Conclusions

This transition might be circumstantial evidence that the accessory RPE plays a role in providing additional protection for their apomorphic concaviclivate temporal fovea. We also report the presence of conjunctival papillae in a developmental stage prior to the formation of scleral ossicles. This developmental progression is similar to that of birds and turtles.

On the fossil record of the Gekkota

Gekkota is often interpreted as sister to all remaining squamates, exclusive of dibamids, or as sister to Autarchoglossa. It is the only diverse lineage of primarily nocturnal lizards and includes some of the smallest amniotes. The skeleton of geckos has often been interpreted as paedomorphic and/or "primitive" but these lizards also display a wide range of structural specializations of the postcranium, including modifications associated with both scansorial locomotion and limb reduction. Although the concept of "Gekkota" has been variously applied by different authors, we here apply a rigorous apomorphy based definition, recent advances in gekkotan morphology and phylogenetics, and diverse comparative material to provide a comprehensive assessment of 28 known pre-Quaternary geckos, updating the last such review, published three decades ago. Fossils evaluated include both sedimentary fossils and amber-embedded specimens. Known Cretaceous geckos are exclusively Asian and exhibit character combinations not seen in any living forms. Cenozoic gekkotans derive from sites around the world, although Europe is especially well represented. Paleogene geckos are largely known from disarticulated remains and show similarities to Sphaerodactylidae and Diplodactylidae, although resemblances may be plesiomorphic in some cases. Many Neogene gekkotans are referable to living families or even genera, but their geographic occurrences are often extralimital to those of modern groups, as is consistent with paleoclimatic conditions. The phylogenetic placement of fossil gekkotans has important repercusions for timetree calibration, but at present only a small number of fossils can be confidently assigned to even family level groupings, limiting their utility in this regard.

New records of the mourning gecko Lepidodactylus lugubris (Duméril and Bibron, 1836) (Squamata: Gekkonidae) from Colombia

The mourning gecko (Lepidodactylus lugubris) is a nocturnal, parthenogenetic species that has been introduced in Colombia. Despite more than 70 years of collecting activity in the country, there has yet to be a thorough evaluation of its distribution in Colombia. Here we review all records from eight museum collections, along with literature reports, to generate a locality map documenting this gecko’s distribution in space and time. Additionally, new sightings are reported and its range expansion in the Cauca rift valley is discussed.

A new genus of miniaturized and pug-nosed gecko from South America (Sphaerodactylidae: Gekkota)

Sphaerodactyl geckos comprise five genera distributed across Central and South America and the Caribbean. We estimated phylogenetic relationships among sphaerodactyl genera using both separate and combined analyses of seven nuclear genes. Relationships among genera were incongruent at different loci and phylogenies were characterized by short, in some cases zero length, internal branches and poor phylogenetic support at most nodes. We recovered a polyphyletic Coleodactylus, with Coleodactylus amazonicus being deeply divergent from the remaining Coleodactylus species sampled. The C. amazonicus lineage possessed unique codon deletions in the genes PTPN12 and RBMX while the remaining Coleodactylus species had unique codon deletions in RAG1. Topology tests could not reject a monophyletic Coleodactylus, but we show that short internal branch lengths decreased the accuracy of topology tests because there were not enough data along short branches to support one phylogenetic hypothesis over another. Morphological data corroborated results of the molecular phylogeny, with Coleodactylus exhibiting substantial morphological heterogeneity. We identified a suite of unique craniofacial features that differentiate C. amazonicus not only from other Coleodactylus species, but also from all other geckos. We describe this novel sphaerodactyl lineage as a new genus, Chatogekko gen. nov. We present a detailed osteology of Chatogekko, characterizing osteological correlates of miniaturization that provide a framework for future studies in sphaerodactyl systematics and biology.