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Susan E. Evans - One of the best experts on this subject based on the ideXlab platform.
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Lepidosaurian diversity in the Mesozoic-Palaeogene: the potential roles of sampling biases and environmental drivers.
Royal Society open science, 2018Co-Authors: Terri J. Cleary, Susan E. Evans, Roger B. J. Benson, Paul M. BarrettAbstract:Lepidosauria is a speciose clade with a long evolutionary history, but there have been few attempts to explore its taxon richness through time. Here we estimate patterns of terrestrial lepidosaur g...
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The Lepidosaurian Ear: Variations on a Theme
Evolution of the Vertebrate Ear, 2016Co-Authors: Susan E. EvansAbstract:Today, Lepidosauria encompasses more than 9,000 species of lizards, snakes, and amphisbaenians (Squamata), as well as the New Zealand Tuatara, Sphenodon (Rhynchocephalia). In many lizards, an efficient tympanic middle ear and an effective inner-ear compensatory mechanism permit acute hearing across a range of frequencies. Sphenodon lacks a tympanic membrane, but this is the result of secondary loss. Fossils of stem lepidosaurs and early rhynchocephalians indicate that the ancestral Lepidosaurian middle ear was tympanic, although the compensatory mechanism was probably rudimentary. Derived rhynchocephalians like Sphenodon lost the tympanic ear, possibly in association with feeding specializations, whereas squamates improved it by developing a more efficient compensatory window. However, the timing of this change is uncertain as the earliest lizard fossils are uninformative in this respect. Lizards from the Early Cretaceous onward show the derived condition. Squamates are morphologically and ecologically diverse, and some specialized lifestyles have affected ear anatomy. Among extant squamates, the only obligate marine swimmers are sea snakes, but in the Cretaceous, mosasaurs dominated the marine niche. These aquatic lizards show a middle ear morphology analogous to that of extant marine turtles (bulla-like quadrate, expanded extrastapes, loss of the tympanum?). Loss of the tympanum also occurs in squamate burrowers but in conjunction with the possession of a robust stapes with an enlarged footplate and, frequently, reduction or modification of the compensatory mechanism. Ears of this type are found in the enigmatic Cretaceous Sineoamphisbaena and in amphisbaenians from the Eocene to the present day. Where known, the ears of early snakes more closely resemble those of burrowers than swimmers.
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integration of molecules and new fossils supports a triassic origin for Lepidosauria lizards snakes and tuatara
BMC Evolutionary Biology, 2013Co-Authors: Marc E H Jones, Susan E. Evans, Cajsa Lisa Anderson, Christy A Hipsley, Johannes Muller, Rainer R SchochAbstract:Lepidosauria (lizards, snakes, tuatara) is a globally distributed and ecologically important group of over 9,000 reptile species. The earliest fossil records are currently restricted to the Late Triassic and often dated to 227 million years ago (Mya). As these early records include taxa that are relatively derived in their morphology (e.g. Brachyrhinodon), an earlier unknown history of Lepidosauria is implied. However, molecular age estimates for Lepidosauria have been problematic; dates for the most recent common ancestor of all lepidosaurs range between approximately 226 and 289 Mya whereas estimates for crown-group Squamata (lizards and snakes) vary more dramatically: 179 to 294 Mya. This uncertainty restricts inferences regarding the patterns of diversification and evolution of Lepidosauria as a whole. Here we report on a rhynchocephalian fossil from the Middle Triassic of Germany (Vellberg) that represents the oldest known record of a lepidosaur from anywhere in the world. Reliably dated to 238–240 Mya, this material is about 12 million years older than previously known lepidosaur records and is older than some but not all molecular clock estimates for the origin of lepidosaurs. Using RAG1 sequence data from 76 extant taxa and the new fossil specimens two of several calibrations, we estimate that the most recent common ancestor of Lepidosauria lived at least 242 Mya (238–249.5), and crown-group Squamata originated around 193 Mya (176–213). A Early/Middle Triassic date for the origin of Lepidosauria disagrees with previous estimates deep within the Permian and suggests the group evolved as part of the faunal recovery after the end-Permain mass extinction as the climate became more humid. Our origin time for crown-group Squamata coincides with shifts towards warmer climates and dramatic changes in fauna and flora. Most major subclades within Squamata originated in the Cretaceous postdating major continental fragmentation. The Vellberg fossil locality is expected to become an important resource for providing a more balanced picture of the Triassic and for bridging gaps in the fossil record of several other major vertebrate groups.
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A tiny lizard (Lepidosauria, Squamata) from the Lower Cretaceous of Spain
Palaeontology, 2012Co-Authors: Arnau Bolet, Susan E. EvansAbstract:: The smallest living amniotes are all lizards, but the fossil history of this size trait in Squamata is difficult to follow because small skeletons have low preservation potential and are often hard to detect in the field. A new squamate taxon, Jucaraseps grandipes gen. et sp. nov., is here described on the basis of an articulated skeleton from the Early Cretaceous Spanish lagerstatten of Las Hoyas. It differs from other known Mesozoic lizards in combining very small body size with a short rostrum, low maxillary tooth count, a relatively slender and elongated body, and short limbs with large hind feet. Phylogenetic analysis using TNT places it on the stem of a clade encompassing scincomorphs, gekkotans, snakes, amphisbaenians and anguimorphs. Comparison with modern lizards suggests it was probably a cryptic surface or subsurface ground dweller but not a burrower.
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The Origin, Early History and Diversification of Lepidosauromorph Reptiles
New Aspects of Mesozoic Biodiversity, 2010Co-Authors: Susan E. Evans, Marc E H JonesAbstract:The reptilian group Lepidosauria diversified through the Mesozoic, survived the end-Cretaceous extinction relatively unscathed, and has more than 7,000 living species. Although originally constituted as a “waste-bin” for non-archosaurian diapsids, modern definitions limit Lepidosauria to its two constituent groups, Rhynchocephalia and Squamata, and their most recent common ancestor. To date, the earliest known lepidosaurs are from the Late Triassic (Carnian) of Europe and India, but their derived morphology provides indirect evidence of a longer, unrecorded, history. Rhynchocephalians and squamates probably diverged in the Early-Middle Triassic, and new material from the Early Triassic of Poland sheds some light on their common ancestor. The roots of Lepidosauria may extend into the Palaeozoic, but there are critical gaps in the fossil record.
Marc E H Jones - One of the best experts on this subject based on the ideXlab platform.
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a review of tooth implantation among rhynchocephalians Lepidosauria
Journal of Herpetology, 2017Co-Authors: Kelsey M Jenkins, Marc E H Jones, Tomáš Zikmund, Alan Boyde, Juan D. DazaAbstract:Abstract Acrodont dental implantation is widely considered an important character for referring fossil material to Rhynchocephalia. Under its purest definition, acrodonty involves teeth being attached to the crest of the marginal bones without roots. A similar mode of tooth attachment is known in a variety of other reptile groups including some squamates and procolophonids. There is a lack of consensus on the definition of acrodont, how best to characterize tooth implantation, and the relationship between implantation and tooth replacement. Rhynchocephalians already are known to demonstrate variation in their mode of tooth attachment. Unambiguous acrodonty associated with little or no tooth replacement has been associated with Sphenodon, but it appears to have been the most widespread condition for much of the Mesozoic. A form of pleurodonty, where teeth are attached to the inside of the jaw bone with shallow roots, appears to be the plesiomorphic condition for both Lepidosauria and Rhynchocephalia. Jaws ...
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Sesamoid bones in tuatara (Sphenodon punctatus) investigated with X-ray microtomography, and implications for sesamoid evolution in Lepidosauria.
Journal of Morphology, 2016Co-Authors: Sophie Regnault, John R. Hutchinson, Marc E H JonesAbstract:: Sesamoids bones are small intra-tendinous (or ligamentous) ossifications found near joints and are often variable between individuals. Related bones, lunulae, are found within the menisci of certain joints. Several studies have described sesamoids and lunulae in lizards and their close relatives (Squamata) as potentially useful characters in phylogenetic analysis, but their status in the extant outgroup to Squamata, tuatara (Sphenodon), remains unclear. Sphenodon is the only living rhynchocephalian, but museum specimens are valuable and difficult to replace. Here, we use non-destructive X-ray microtomography to investigate the distribution of sesamoids and lunulae in 19 Sphenodon specimens and trace the evolution of these bones in Lepidosauria (Rhynchocephalia + Squamata). We find adult Sphenodon to possess a sesamoid and lunula complement different from any known squamate, but also some variation within Sphenodon specimens. The penultimate phalangeal sesamoids and tibial lunula appear to mineralize prior to skeletal maturity, followed by mineralization of a sesamoid between metatarsal I and the astragalocalcaneum (MTI-AC), the palmar sesamoids, and tibiofemoral lunulae around attainment of skeletal maturity. The tibial patella, ulnar, and plantar sesamoids mineralize late in maturity or variably. Ancestral state reconstruction indicates that the ulnar patella and tibiofemoral lunulae are synapomophies of Squamata, and the palmar sesamoid, tibial patella, tibial lunula, and MTI-AC may be synapomorphies of Lepidosauria. J. Morphol. 278:62-72, 2017. ©© 2016 Wiley Periodicals,Inc.
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Anatomy, morphology and evolution of the patella in squamate lizards and tuatara (Sphenodon punctatus)
Journal of Anatomy, 2016Co-Authors: Sophie Regnault, Marc E H Jones, Andrew A. Pitsillides, John R. HutchinsonAbstract:The patella (kneecap) is the largest and best-known of the sesamoid bones, postulated to confer biomechanical advantages including increasing joint leverage and reinforcing the tendon against compression. It has evolved several times independently in amniotes, but despite apparently widespread occurrence in lizards, the patella remains poorly characterised in this group and is, as yet, completely undescribed in their nearest extant relative Sphenodon (Rhynchocephalia). Through radiography, osteological and fossil studies we examined patellar presence in diverse lizard and lepidosauromorph taxa, and using computed tomography, dissection and histology we investigated in greater depth the anatomy and morphology of the patella in 16 lizard species and 19 Sphenodon specimens. We have found the first unambiguous evidence of a mineralised patella in Sphenodon, which appears similar to the patella of lizards and shares several gross and microscopic anatomical features. Although there may be a common mature morphology, the squamate patella exhibits a great deal of variability in development (whether from a cartilage anlage or not, and in the number of mineralised centres) and composition (bone, mineralised cartilage or fibrotendinous tissue). Unlike in mammals and birds, the patella in certain lizards and Sphenodon appears to be a polymorphic trait. We have also explored the evolution of the patella through ancestral state reconstruction, finding that the patella is ancestral for lizards and possibly Lepidosauria as a whole. Clear evidence of the patella in rhynchocephalian or stem Lepidosaurian fossil taxa would clarify the evolutionary origin(s) of the patella, but due to the small size of this bone and the opportunity for degradation or loss we could not definitively conclude presence or absence in the fossils examined. The pattern of evolution in lepidosaurs is unclear but our data suggest that the emergence of this sesamoid may be related to the evolution of secondary ossification centres and/or changes in knee joint conformation, where enhancement of extensor muscle leverage would be more beneficial.
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integration of molecules and new fossils supports a triassic origin for Lepidosauria lizards snakes and tuatara
BMC Evolutionary Biology, 2013Co-Authors: Marc E H Jones, Susan E. Evans, Cajsa Lisa Anderson, Christy A Hipsley, Johannes Muller, Rainer R SchochAbstract:Lepidosauria (lizards, snakes, tuatara) is a globally distributed and ecologically important group of over 9,000 reptile species. The earliest fossil records are currently restricted to the Late Triassic and often dated to 227 million years ago (Mya). As these early records include taxa that are relatively derived in their morphology (e.g. Brachyrhinodon), an earlier unknown history of Lepidosauria is implied. However, molecular age estimates for Lepidosauria have been problematic; dates for the most recent common ancestor of all lepidosaurs range between approximately 226 and 289 Mya whereas estimates for crown-group Squamata (lizards and snakes) vary more dramatically: 179 to 294 Mya. This uncertainty restricts inferences regarding the patterns of diversification and evolution of Lepidosauria as a whole. Here we report on a rhynchocephalian fossil from the Middle Triassic of Germany (Vellberg) that represents the oldest known record of a lepidosaur from anywhere in the world. Reliably dated to 238–240 Mya, this material is about 12 million years older than previously known lepidosaur records and is older than some but not all molecular clock estimates for the origin of lepidosaurs. Using RAG1 sequence data from 76 extant taxa and the new fossil specimens two of several calibrations, we estimate that the most recent common ancestor of Lepidosauria lived at least 242 Mya (238–249.5), and crown-group Squamata originated around 193 Mya (176–213). A Early/Middle Triassic date for the origin of Lepidosauria disagrees with previous estimates deep within the Permian and suggests the group evolved as part of the faunal recovery after the end-Permain mass extinction as the climate became more humid. Our origin time for crown-group Squamata coincides with shifts towards warmer climates and dramatic changes in fauna and flora. Most major subclades within Squamata originated in the Cretaceous postdating major continental fragmentation. The Vellberg fossil locality is expected to become an important resource for providing a more balanced picture of the Triassic and for bridging gaps in the fossil record of several other major vertebrate groups.
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A Late Cretaceous "tuatara" (Lepidosauria: Sphenodontinae) from South America
Cretaceous Research, 2012Co-Authors: Sebastián Apesteguía, Marc E H JonesAbstract:Abstract Rhynchocephalia achieved a global distribution during the Mesozoic but the history of sphenodontines, the clade containing the extant genus Sphenodon (the New Zealand tuatara), remains poorly understood. Here, we describe a partial maxilla from the Late Cretaceous of Argentina bearing teeth that closely resemble those of modern Sphenodon. This material helps to fill in a notable gap in the fossil history of lepidosaurs because it represents the first evidence of a sphenodontine from South America and increases the number of known Late Cretaceous rhynchocephalian taxa from that region. The morphological disparity encompassed by these records is consistent with suggestions that rhynchocephalians remained diverse in the Late Cretaceous of South America despite a concurrent disappearance from Laurasia. Moreover, the new record supports the hypothesis that sphenodontines were once found widely throughout Gondwana, before its constituent landmasses began to separate about 80 million years ago. The extant Sphenodon probably represents a biogeographic remnant of this distribution, but whether its relatively large size and its ability to remain active at cold temperatures reflects a high latitude ancestry requires further examination.
Victor Hugo Reynoso - One of the best experts on this subject based on the ideXlab platform.
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a beaded sphenodontian diapsida Lepidosauria from the early cretaceous of central mexico
Journal of Vertebrate Paleontology, 1997Co-Authors: Victor Hugo ReynosoAbstract:ABSTRACT The Albian sphenodontian Pamizinsaurus tlayuaensis, gen. et sp. nov., from the Tlayua Quarry, Central Mexico, is described. The holotype is a posthatchling characterized by the presence of rows of small rounded osteoderms transversally oriented, relatively few hatchling teeth each with well-developed ridges, and a posteriorly displaced ventral process of the mandibular symphysis at an early ontogenetic stage. A small retroarticular process, long central region of the pterygoid, and the narrowness of the posterior end of the interpterygoid vacuity suggest sister-group relationships with sphenodontines + eilenodontines. The conspicuous dermal skeleton is similar to that of helodermatids, suggesting that it could have served to protect against predation in open environments. This unique structure argues against the idea of low morphological diversity within sphenodontians. Pamizinsaurus is the latest occurring fossil sphenodontian.
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A “beaded” sphenodontian (Diapsida: Lepidosauria) from the Early Cretaceous of central Mexico
Journal of Vertebrate Paleontology, 1997Co-Authors: Victor Hugo ReynosoAbstract:ABSTRACT The Albian sphenodontian Pamizinsaurus tlayuaensis, gen. et sp. nov., from the Tlayua Quarry, Central Mexico, is described. The holotype is a posthatchling characterized by the presence of rows of small rounded osteoderms transversally oriented, relatively few hatchling teeth each with well-developed ridges, and a posteriorly displaced ventral process of the mandibular symphysis at an early ontogenetic stage. A small retroarticular process, long central region of the pterygoid, and the narrowness of the posterior end of the interpterygoid vacuity suggest sister-group relationships with sphenodontines + eilenodontines. The conspicuous dermal skeleton is similar to that of helodermatids, suggesting that it could have served to protect against predation in open environments. This unique structure argues against the idea of low morphological diversity within sphenodontians. Pamizinsaurus is the latest occurring fossil sphenodontian.
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A Middle Jurassic Sphenodon-like sphenodontian (Diapsida: Lepidosauria) from Huizachal Canyon, Tamaulipas, Mexico
Journal of Vertebrate Paleontology, 1996Co-Authors: Victor Hugo ReynosoAbstract:ABSTRACT A new Middle Jurassic North American sphenodontian, Cynosphenodon huizachalensis, gen. et sp. nov. is described on the basis of several dentaries and maxillae. It is characterized by its small size and its striking similarity to Sphenodon. The presence of a deep posteromedial wear facet on the caniniform tooth, a small denticle in the additional tooth series, and an anterior small groove dorsal and convergent to the Meckelian Canal, are unique characteristics of this species. In adult individuals the caniniform tooth placed posteriorly to an edentulous ridge, and the presence of wear facets on teeth and jaws caused by propalinal jaw action, suggest that C. huizachalensis is closely related to Sphenodon; the wear facet on the posteromedial face of the caniniform tooth, however, may suggest a different arrangement of the anterior palatal region.
Paula Santi Malnis - One of the best experts on this subject based on the ideXlab platform.
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a new sphenodontian Lepidosauria rhynchocephalia from the late triassic of argentina and the early origin of the herbivore opisthodontians
Proceedings of The Royal Society B: Biological Sciences, 2013Co-Authors: Ricardo Martínez, Cecilia Apaldetti, Carina E Colombi, Angel Praderio, Eliana Fernandez, Paula Santi MalnisAbstract:Sphenodontians were a successful group of rhynchocephalian reptiles that dominated the fossil record of Lepidosauria during the Triassic and Jurassic. Although evidence of extinction is seen at the end of the Laurasian Early Cretaceous, they appeared to remain numerically abundant in South America until the end of the period. Most of the known Late Cretaceous record in South America is composed of opisthodontians, the herbivorous branch of Sphenodontia, whose oldest members were until recently reported to be from the Kimmeridgian–Tithonian (Late Jurassic). Here, we report a new sphenodontian, Sphenotitan leyesi gen. et sp. nov., collected from the Upper Triassic Quebrada del Barro Formation of northwestern Argentina. Phylogenetic analysis identifies Sphenotitan as a basal member of Opisthodontia, extending the known record of opisthodontians and the origin of herbivory in this group by 50 Myr.
Hervé Seligmann - One of the best experts on this subject based on the ideXlab platform.
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Bijective codon transformations show genetic code symmetries centered on cytosine’s coding properties
Theory in Biosciences, 2018Co-Authors: Hervé SeligmannAbstract:Homology of some RNAs with template DNA requires systematic exchanges between nucleotides. Such exchanges produce ‘swinger’ RNA along 23 bijective transformations (nine symmetric, X ↔ Y; and 14 asymmetric, X → Y → Z → X, for example A ↔ C and A → C → G → A, respectively). Here, analyses compare amino acids coded by swinger-transformed codons to those coded by untransformed codons, defining coding invariance after transformations. Swinger transformations cluster according to coding invariance in four groups characterized by transformations into cytosine (C = C, T → C, A → C, and G → C). C’s central mutational coding role shows that swinger transformations constrained genetic code genesis. Coding invariance post-transformations correlate positively/negatively with mitochondrial swinger transcription/Lepidosaurian body temperature. Presumably, low/high temperatures stabilize/revert rare swinger polymerization modes, producing long swinger sequences/point mutations, respectively. Coding invariance after swinger transformations might compensate effects of swinger polymerizations in species with low body temperatures. Hypothetically, swinger transcription increased coding potential of RNA self-replicating protolife systems under heating/cooling cycles.
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Codon expansion and systematic transcriptional deletions produce tetra-, pentacoded mitochondrial peptides
Journal of theoretical biology, 2015Co-Authors: Hervé SeligmannAbstract:Genes include occasionally isolated codons with a fourth (and fifth) silent nucleotide(s). Assuming tetracodons, translated hypothetical peptides align with regular GenBank proteins; predicted tetracodons coevolve with predicted tRNAs with expanded anticodons in each mammal, Drosophila and Lepidosauria mitogenomes, GC contents and with Lepidosaurian body temperatures, suggesting that expanded codons are an adaptation of translation to high temperature. Hypothetically, continuous stretches of tetra- and pentacodons code for peptides. Both systematic nucleotide deletions during transcription, and translation by tRNAs with expanded anticodons could produce these peptides. Reanalyses of human nanoLc mass spectrometry peptidome data detect numerous tetra- and pentapeptides translated from the human mitogenome. These map preferentially on (BLAST-detected) human RNAs matching the human mitogenome, assuming systematic mono- and dinucleotide deletions after each third nucleotide (delRNAs). Translation by expanded anticodons is incompatible with silent nucleotides in the midst rather than at codon 3' extremity. More than 1/3 of detected tetra- and pentapeptides assume silent positions at codon extremity, suggesting that both mechanisms, regular translation of delRNAs and translation of regular RNAs by expanded anticodons, produce this peptide subgroup. Results show that systematically deleting polymerization occurs, and confirm serial translation of expanded codons. Non-canonical transcriptions and translations considerably expand the coding potential of DNA and RNA sequences.
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The relation between hairpin formation by mitochondrial WANCY tRNAs and the occurrence of the light strand replication origin in Lepidosauria.
Gene, 2014Co-Authors: Hervé Seligmann, Antonieta LabraAbstract:Mitochondrial light strand DNA replication is initiated at light strand replication origins (OLs), short stem-loop hairpins formed by the heavy strand DNA. OL-like secondary structures are also formed by heavy strand DNA templating for the five tRNAs adjacent to OLs, the WANCY tRNA cluster. We tested whether natural OL absence associates with greater capacities for formation of OL-like structures by WANCY tRNA genes. Using Lepidosaurian taxa (Sphenodon, lizards and amphisbaenids), we compared WANCY tRNA capacities to form OL-like structures between 248 taxa possessing an OL with 131 taxa without OL (from different families). On average, WANCY tRNA genes form more OL-like structures in the absence of a regular OL than in its presence. Formation of OL-like structures by WANCY tRNAs follows hierarchical patterns that may reduce competition between the tRNA's translational function and its secondary OL function: the rarer the tRNA's cognate amino acid, the greater the capacity to form OL-like structures. High OL-forming capacities for neighboring tRNAs are avoided. Because OL absence usually occurs in taxa with reduced genomes, increased formation of OL-like structures by WANCY tRNAs might result from selection for greater metabolic efficiency. Further analyses suggest that OL loss is one of the latest steps in genome reduction, and promotes the increase in formation of OL-like structures by WANCY tRNA genes in Lepidosauria.
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Tetracoding increases with body temperature in Lepidosauria.
Bio Systems, 2013Co-Authors: Hervé Seligmann, Antonieta LabraAbstract:Abstract Codons expanded by a silent position (quadruplet or tetracodons) may solve the conundrum that at life's origins, the weak tricodon–anticodon interactions could not promote translation in the absence of complex ribosomes. Modern genomes have isolated tetracodons resulting from insertion mutations. Some bioinformatic analyses suggest that tetracoding stretches overlap with regular mitochondrial protein coding genes. These tetragenes are probably decoded by (antisense) tRNAs with expanded anticodons. They are GC-rich, which produce stronger basepairs than A:T interactions, suggesting expression at high temperatures. The hypothesis that tetracoding is an adaptation to high temperatures is tested here by comparing predicted mitochondrial tetracoding in Lepidosauria (lizards, amphisbaenia, and Sphenodon ), in relation to body temperature, expecting more tetracoding in species with high body temperature. The association between tRNAs with expanded anticodons and tetracoding previously described for mammals and Drosophila is confirmed for Lepidosauria. Independent evidence indicates that tetracoding increases with body temperature, supporting the hypothesis that tetracoding is an adaptation for efficient translation when conditions (temperature) make triplet codon-anticodons too unstable to allow efficient protein elongation.