Some recent non-dino papers about reptile evolution, most with free pdfs.
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Free pdf:
J. Robert Macey, Stephan Pabinger, Charles G. Barbieri, Ella S. Buring, Vanessa L. Gonzalez, Daniel G. Mulcahy, Dustin P. DeMeo, Lara Urban, Paul M. Hime, Stefan Prost, Aaron N. Elliott & Neil J. Gemmell (2020)
Evidence of two deeply divergent co-existing mitochondrial genomes in the Tuatara reveals an extremely complex genomic organization.
Communications Biology 4, Article number: 116
doi: https://doi.org/10.1038/s42003-020-01639-0
https://www.nature.com/articles/s42003-020-01639-0
Free pdf:
https://www.nature.com/articles/s42003-020-01639-0.pdf
Animal mitochondrial genomic polymorphism occurs as low-level mitochondrial heteroplasmy and deeply divergent co-existing molecules. The latter is rare, known only in bivalvian mollusks. Here we show two deeply divergent co-existing mt-genomes in a vertebrate through genomic sequencing of the Tuatara (Sphenodon punctatus), the sole-representative of an ancient reptilian Order. The two molecules, revealed using a combination of short-read and long-read sequencing technologies, differ by 10.4% nucleotide divergence. A single long-read covers an entire mt-molecule for both strands. Phylogenetic analyses suggest a 7-8 million-year divergence between genomes. Contrary to earlier reports, all 37 genes typical of animal mitochondria, with drastic gene rearrangements, are confirmed for both mt-genomes. Also unique to vertebrates, concerted evolution drives three near-identical putative Control Region non-coding blocks. Evidence of positive selection at sites linked to metabolically important transmembrane regions of encoded proteins suggests these two mt-genomes may confer an adaptive advantage for an unusually cold-tolerant reptile.
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Oleksandr Yaryhin, ÂJozef Klembara, ÂYuriy Pichugin, ÂMarketa Kaucka & Ingmar Werneburg (2021)
Limb reduction in squamate reptiles correlates with the reduction of the chondrocranium: a case study on serpentiform anguids.
Developmental Dynamics (advance online publication)
doi: https://doi.org/10.1002/dvdy.307
https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/dvdy.307
Background
Limb reduction in squamate reptiles correlates with the reduction of the chondrocranium: a case study on serpentiform anguids.
Developmental Dynamics (advance online publication)
doi: https://doi.org/10.1002/dvdy.307
https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/dvdy.307
Background
In vertebrates, the skull evolves from a complex network of dermal bones and cartilage â the latter forming the pharyngeal apparatus and the chondrocranium. Squamates are particularly important in this regard as they maintain at least part of the chondrocranium throughout their whole ontogeny until adulthood. Anguid lizards represent a unique group of squamates, which contains limbed and limbless forms and show conspicuous variation of the adult skull.
Results
Based on several embryonic stages of the limbless lizards Pseudopus apodus and Anguis fragilis, and by comparing with other squamates, we identified and interpreted major differences in chondrocranial anatomy. Among others, the most important differences are in the orbitotemporal region. P. apodus shows a strikingly similar development of this region to other squamates. Unexpectedly, however, A. fragilis differs considerably in the composition of the orbitotemporal region. In addition, A. fragilis retains a paedomorphic state of the nasal region.
Conclusions
Taxonomic comparisons indicate that even closely related species with reduced limbs show significant differences in chondrocranial anatomy. The Pearson correlation coefficient suggests strong correlation between chondrocranial reduction and limb reduction. We pose the hypothesis that limb reduction could be associated with the reduction in chondrocrania by means of genetic mechanisms.
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Free pdf:
Hugo Dutel, Flora GrÃning, Alana C. Sharp, Peter J. Watson, Anthony Herrel, Callum F. Ross, Marc E. H. Jones, Susan E. Evans & Michael J. Fagan (2021)
Comparative cranial biomechanics in two lizard species: impact of variation in cranial design.
Journal of Experimental Biology 2021 : jeb.234831
doi: 10.1242/jeb.234831
https://jeb.biologists.org/content/early/2021/01/27/jeb.234831
Free pdf:
https://jeb.biologists.org/content/jexbio/early/2021/01/27/jeb.234831.full.pdf
Cranial morphology in lepidosaurs is highly disparate and characterized by the frequent loss or reduction of bony elements. In varanids and geckos, the loss of the postorbital bar is associated with changes in skull shape, but the mechanical principles underlying this variation remain poorly understood. Here, we seek to determine how the overall cranial architecture and the presence of the postorbital bar relate to the loading and deformation of the cranial bones during biting in lepidosaurs. Using computer-based simulation techniques, we compare cranial biomechanics in the varanid Varanus niloticus and the teiid Salvator merianae, two large, active foragers. The overall strain magnitudes and distribution across the cranium is similar in both species, despite lower strain gradients in Varanus niloticus. In Salvator merianae, the postorbital bar is important for the resistance of the cranium to feeding loads. The postorbital ligament, which partially replaces the postorbital bar in varanids, does not affect bone strain. Our results suggest that the reduction of the postorbital bar impaired neither biting performance nor the structural resistance of the cranium to feeding loads in Varanus niloticus. Differences in bone strain between the two species might reflect demands imposed by feeding and non-feeding functions on cranial shape. Beyond variation in cranial bone strain related to species-specific morphological differences, our results reveal that similar mechanical behaviour is shared by lizards with distinct cranial shapes. Contrary to mammals, the morphology of the circumorbital region, calvaria and palate appears to be important for withstanding high feeding loads in these lizards.
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Carlos J PavÃn-VÃzquez, Ian G Brennan & J Scott Keogh (2021)
A Comprehensive Approach to Detect Hybridization Sheds Light on the Evolution of Earthâs Largest Lizards.
Systematic Biology, syaa102Â(advance online publication)
doi: https://doi.org/10.1093/sysbio/syaa102
https://academic.oup.com/sysbio/advance-article-abstract/doi/10.1093/sysbio/syaa102/6123761
A Comprehensive Approach to Detect Hybridization Sheds Light on the Evolution of Earthâs Largest Lizards.
Systematic Biology, syaa102Â(advance online publication)
doi: https://doi.org/10.1093/sysbio/syaa102
https://academic.oup.com/sysbio/advance-article-abstract/doi/10.1093/sysbio/syaa102/6123761
Hybridization between species occurs more frequently in vertebrates than traditionally thought but distinguishing ancient hybridization from other phenomena that generate similar evolutionary patterns remains challenging. Here, we used a comprehensive workflow to discover evidence of ancient hybridization between the Komodo dragon (Varanus komodoensis) from Indonesia and a common ancestor of an Australian group of monitor lizards known colloquially as sand monitors. Our data comprises >300 nuclear loci, mitochondrial genomes, phenotypic data, fossil and contemporary records, and past/present climatic data. We show that the four sand monitor species share more nuclear alleles with V. komodoensis than expected given a bifurcating phylogeny, likely as a result of hybridization between the latter species and a common ancestor of sand monitors. Sand monitors display phenotypes that are intermediate between their closest relatives and V. komodoensis. Biogeographic analyses suggest that V. komodoensis and ancestral sand monitors co-occurred in northern Australia. In agreement with the fossil record, this provides further evidence that the Komodo dragon once inhabited the Australian continent. Our study shows how different sources of evidence can be used to thoroughly characterize evolutionary histories that deviate from a treelike pattern, that hybridization can have long-lasting effects on phenotypes and that detecting hybridization can improve our understanding of evolutionary and biogeographic patterns.
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Free pdf:
Brookesia nana sp. nov. Â(extant species) [smallest living reptile]
Frank Glaw, JÃrn KÃhler, Oliver Hawlitschek, Fanomezana M. Ratsoavina, Andolalao Rakotoarison, Mark D. Scherz & Miguel Vences (2021)
Extreme miniaturization of a new amniote vertebrate and insights into the evolution of genital size in chameleons.
Scientific Reports 11, Article number: 2522
DOI: https://doi.org/10.1038/s41598-020-80955
https://www.nature.com/articles/s41598-020-80955-1
Free pdf:
https://www.nature.com/articles/s41598-020-80955-1.pdf
Evolutionary reduction of adult body size (miniaturization) has profound consequences for organismal biology and is an important subject of evolutionary research. Based on two individuals we describe a new, extremely miniaturized chameleon, which may be the worldâs smallest reptile species. The male holotype of Brookesia nana sp. nov. has a snoutâvent length of 13.5 mm (total length 21.6 mm) and has large, apparently fully developed hemipenes, making it apparently the smallest mature male amniote ever recorded. The female paratype measures 19.2 mm snoutâvent length (total length 28.9 mm) and a micro-CT scan revealed developing eggs in the body cavity, likewise indicating sexual maturity. The new chameleon is only known from a degraded montane rainforest in northern Madagascar and might be threatened by extinction. Molecular phylogenetic analyses place it as sister to B. karchei, the largest species in the clade of miniaturized Brookesia species, for which we resurrect Evoluticauda Angel, 1942 as subgenus name. The genetic divergence of B. nana sp. nov. is rather strong (9.9-14.9% to all other Evoluticauda species in the 16S rRNA gene). A comparative study of genital length in Malagasy chameleons revealed a tendency for the smallest chameleons to have the relatively largest hemipenes, which might be a consequence of a reversed sexual size dimorphism with males substantially smaller than females in the smallest species. The miniaturized males may need larger hemipenes to enable a better mechanical fit with female genitals during copulation. Comprehensive studies of female genitalia are needed to test this hypothesis and to better understand the evolution of genitalia in reptiles.
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Free pdf:
Yann Rollot, Serjoscha W. Evers & Walter G. Joyce (2021)
A review of the carotid artery and facial nerve canal systems in extant turtles.
PeerJ 8:e10475
doi: https://doi.org/10.7717/peerj.10475
https://peerj.com/articles/10475/
The cranial circulation and innervation systems of turtles have been studied for more than two centuries and extensively used to understand turtle systematics. Although a significant number of studies related to these structures exists, a broader comprehension of variation across the tree has been hindered by poor sampling and a lack of synthetic studies that addressed both systems together. We here provide new insights regarding the carotid circulation and facial nerve innervation systems in a broad set of extant turtles using CT (computed tomography) scans, which allow us to trace the canals these structures form in bone and understand the interaction between both systems. We document that the palatine artery, including the lateral carotid canal, is absent in all pleurodires and carettochelyids and was likely reduced or lost several times independently within Testudinoidea. We also highlight osteological correlates for the location of the mandibular artery. We finally summarize variation regarding the placement of the mandibular artery, location of the geniculate ganglion, placement of the hyomandibular and vidian nerves, and situations where we recommend caution when assessing canals in fossils. A morphometric study confirms that the relative sizes of the carotid canals are correlated with one another. Our results have the potential for building new phylogenetic characters and investigating the circulation systems of fossil taxa, which are expected to shed light on the evolution of the circulation system of turtles and clarify some unresolved relationships between fossil turtle clades.
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Jie Yang, Wei Song, Caiyan Li, Chanlin Fang, Yuting Zhang, Qingqing Wang, Mingxing Zhang & Guoying Qian (2021)
Comparative study of collagen distribution in the dermis of the embryonic carapace of softâ and hardâshelled cryptodiran turtles.
Journal of Morphology (advance online publication)
doi: https://doi.org/10.1002/jmor.21327
https://onlinelibrary.wiley.com/doi/10.1002/jmor.21327
Comparative study of collagen distribution in the dermis of the embryonic carapace of softâ and hardâshelled cryptodiran turtles.
Journal of Morphology (advance online publication)
doi: https://doi.org/10.1002/jmor.21327
https://onlinelibrary.wiley.com/doi/10.1002/jmor.21327
Turtles are characterized by their typical carapace, which is primarily composed of corneous beta proteins in the horny part and collagen in the dermal part. The formation of the extracellular matrix in the dermis of the carapace in a hardâshelled and a softâshelled turtle has been compared. The study examines carapace development, with an emphasis on collagen accumulation, in the softâshelled turtle Pelodiscus sinensis and hardâshelled turtle Trachemys scripta elegans, using comparative morphological and embryological analyses. The histological results showed that collagen deposition in the turtle carapace increased as the embryos developed. However, significant differences were observed between the two turtle species at the developmental stages examined. The microstructure of the dermis of the carapace of P. sinensis showed light and dark banding of collagen bundles, with a higher overall collagen content, whereas the carapacial matrix of T. scripta was characterized by loosely packed and thinner collagenous fiber bundles with a lower percentage of type I collagen. Overall, the formation and distribution of collagen fibrils at specific developmental stages are different between the softâand hardâshelled turtles. These results indicate that the pliable epidermis of the softâshelled turtle is supported by a strong dermis that is regularly distributed with collagen and that it allows improved maneuvering, whereas a strong but inflexible epidermis as observed in case of hardâshelled turtles limits movement.
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