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John J Wiens - One of the best experts on this subject based on the ideXlab platform.
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integrated analyses resolve conflicts over Squamate reptile phylogeny and reveal unexpected placements for fossil taxa
PLOS ONE, 2015Co-Authors: Tod W Reeder, Daniel G Mulcahy, Brice P Noonan, Ted M Townsend, Jack W Sites, Perry L Wood, John J WiensAbstract:Squamate reptiles (lizards and snakes) are a pivotal group whose relationships have become increasingly controversial. Squamates include >9000 species, making them the second largest group of terrestrial vertebrates. They are important medicinally and as model systems for ecological and evolutionary research. However, studies of Squamate biology are hindered by uncertainty over their relationships, and some consider Squamate phylogeny unresolved, given recent conflicts between molecular and morphological results. To resolve these conflicts, we expand existing morphological and molecular datasets for Squamates (691 morphological characters and 46 genes, for 161 living and 49 fossil taxa, including a new set of 81 morphological characters and adding two genes from published studies) and perform integrated analyses. Our results resolve higher-level relationships as indicated by molecular analyses, and reveal hidden morphological support for the molecular hypothesis (but not vice-versa). Furthermore, we find that integrating molecular, morphological, and paleontological data leads to surprising placements for two major fossil clades (Mosasauria and Polyglyphanodontia). These results further demonstrate the importance of combining fossil and molecular information, and the potential problems of estimating the placement of fossil taxa from morphological data alone. Thus, our results caution against estimating fossil relationships without considering relevant molecular data, and against placing fossils into molecular trees (e.g. for dating analyses) without considering the possible impact of molecular data on their placement.
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A phylogeny and revised classification of Squamata, including 4161 species of lizards and snakes
BMC Evolutionary Biology, 2013Co-Authors: R Alexander Pyron, Frank T Burbrink, John J WiensAbstract:Background The extant Squamates (>9400 known species of lizards and snakes) are one of the most diverse and conspicuous radiations of terrestrial vertebrates, but no studies have attempted to reconstruct a phylogeny for the group with large-scale taxon sampling. Such an estimate is invaluable for comparative evolutionary studies, and to address their classification. Here, we present the first large-scale phylogenetic estimate for Squamata. Results The estimated phylogeny contains 4161 species, representing all currently recognized families and subfamilies. The analysis is based on up to 12896 base pairs of sequence data per species (average = 2497 bp) from 12 genes, including seven nuclear loci (BDNF, c-mos, NT3, PDC, R35, RAG-1, and RAG-2), and five mitochondrial genes (12S, 16S, cytochrome b , ND2, and ND4). The tree provides important confirmation for recent estimates of higher-level Squamate phylogeny based on molecular data (but with more limited taxon sampling), estimates that are very different from previous morphology-based hypotheses. The tree also includes many relationships that differ from previous molecular estimates and many that differ from traditional taxonomy. Conclusions We present a new large-scale phylogeny of Squamate reptiles that should be a valuable resource for future comparative studies. We also present a revised classification of Squamates at the family and subfamily level to bring the taxonomy more in line with the new phylogenetic hypothesis. This classification includes new, resurrected, and modified subfamilies within gymnophthalmid and scincid lizards, and boid, colubrid, and lamprophiid snakes.
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a phylogeny and revised classification of squamata including 4161 species of lizards and snakes
BMC Evolutionary Biology, 2013Co-Authors: R Alexander Pyron, Frank T Burbrink, John J WiensAbstract:The extant Squamates (>9400 known species of lizards and snakes) are one of the most diverse and conspicuous radiations of terrestrial vertebrates, but no studies have attempted to reconstruct a phylogeny for the group with large-scale taxon sampling. Such an estimate is invaluable for comparative evolutionary studies, and to address their classification. Here, we present the first large-scale phylogenetic estimate for Squamata. The estimated phylogeny contains 4161 species, representing all currently recognized families and subfamilies. The analysis is based on up to 12896 base pairs of sequence data per species (average = 2497 bp) from 12 genes, including seven nuclear loci (BDNF, c-mos, NT3, PDC, R35, RAG-1, and RAG-2), and five mitochondrial genes (12S, 16S, cytochrome b, ND2, and ND4). The tree provides important confirmation for recent estimates of higher-level Squamate phylogeny based on molecular data (but with more limited taxon sampling), estimates that are very different from previous morphology-based hypotheses. The tree also includes many relationships that differ from previous molecular estimates and many that differ from traditional taxonomy. We present a new large-scale phylogeny of Squamate reptiles that should be a valuable resource for future comparative studies. We also present a revised classification of Squamates at the family and subfamily level to bring the taxonomy more in line with the new phylogenetic hypothesis. This classification includes new, resurrected, and modified subfamilies within gymnophthalmid and scincid lizards, and boid, colubrid, and lamprophiid snakes.
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resolving the phylogeny of lizards and snakes squamata with extensive sampling of genes and species
Biology Letters, 2012Co-Authors: John J Wiens, Carl R Hutter, Daniel G Mulcahy, Brice P Noonan, Ted M Townsend, Jack W Sites, Tod W ReederAbstract:Squamate reptiles (lizards and snakes) are one of the most diverse groups of terrestrial vertebrates. Recent molecular analyses have suggested a very different Squamate phylogeny relative to morphological hypotheses, but many aspects remain uncertain from molecular data. Here, we analyse higher-level Squamate phylogeny with a molecular dataset of unprecedented size, including 161 Squamate species for up to 44 nuclear genes each (33 717 base pairs), using both concatenated and species-tree methods for the first time. Our results strongly resolve most Squamate relationships and reveal some surprising results. In contrast to most other recent studies, we find that dibamids and gekkotans are together the sister group to all other Squamates. Remarkably, we find that the distinctive scolecophidians (blind snakes) are paraphyletic with respect to other snakes, suggesting that snakes were primitively burrowers and subsequently re-invaded surface habitats. Finally, we find that some clades remain poorly supported, despite our extensive data. Our analyses show that weakly supported clades are associated with relatively short branches for which individual genes often show conflicting relationships. These latter results have important implications for all studies that attempt to resolve phylogenies with large-scale phylogenomic datasets.
R Alexander Pyron - One of the best experts on this subject based on the ideXlab platform.
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A phylogeny and revised classification of Squamata, including 4161 species of lizards and snakes
BMC Evolutionary Biology, 2013Co-Authors: R Alexander Pyron, Frank T Burbrink, John J WiensAbstract:Background The extant Squamates (>9400 known species of lizards and snakes) are one of the most diverse and conspicuous radiations of terrestrial vertebrates, but no studies have attempted to reconstruct a phylogeny for the group with large-scale taxon sampling. Such an estimate is invaluable for comparative evolutionary studies, and to address their classification. Here, we present the first large-scale phylogenetic estimate for Squamata. Results The estimated phylogeny contains 4161 species, representing all currently recognized families and subfamilies. The analysis is based on up to 12896 base pairs of sequence data per species (average = 2497 bp) from 12 genes, including seven nuclear loci (BDNF, c-mos, NT3, PDC, R35, RAG-1, and RAG-2), and five mitochondrial genes (12S, 16S, cytochrome b , ND2, and ND4). The tree provides important confirmation for recent estimates of higher-level Squamate phylogeny based on molecular data (but with more limited taxon sampling), estimates that are very different from previous morphology-based hypotheses. The tree also includes many relationships that differ from previous molecular estimates and many that differ from traditional taxonomy. Conclusions We present a new large-scale phylogeny of Squamate reptiles that should be a valuable resource for future comparative studies. We also present a revised classification of Squamates at the family and subfamily level to bring the taxonomy more in line with the new phylogenetic hypothesis. This classification includes new, resurrected, and modified subfamilies within gymnophthalmid and scincid lizards, and boid, colubrid, and lamprophiid snakes.
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a phylogeny and revised classification of squamata including 4161 species of lizards and snakes
BMC Evolutionary Biology, 2013Co-Authors: R Alexander Pyron, Frank T Burbrink, John J WiensAbstract:The extant Squamates (>9400 known species of lizards and snakes) are one of the most diverse and conspicuous radiations of terrestrial vertebrates, but no studies have attempted to reconstruct a phylogeny for the group with large-scale taxon sampling. Such an estimate is invaluable for comparative evolutionary studies, and to address their classification. Here, we present the first large-scale phylogenetic estimate for Squamata. The estimated phylogeny contains 4161 species, representing all currently recognized families and subfamilies. The analysis is based on up to 12896 base pairs of sequence data per species (average = 2497 bp) from 12 genes, including seven nuclear loci (BDNF, c-mos, NT3, PDC, R35, RAG-1, and RAG-2), and five mitochondrial genes (12S, 16S, cytochrome b, ND2, and ND4). The tree provides important confirmation for recent estimates of higher-level Squamate phylogeny based on molecular data (but with more limited taxon sampling), estimates that are very different from previous morphology-based hypotheses. The tree also includes many relationships that differ from previous molecular estimates and many that differ from traditional taxonomy. We present a new large-scale phylogeny of Squamate reptiles that should be a valuable resource for future comparative studies. We also present a revised classification of Squamates at the family and subfamily level to bring the taxonomy more in line with the new phylogenetic hypothesis. This classification includes new, resurrected, and modified subfamilies within gymnophthalmid and scincid lizards, and boid, colubrid, and lamprophiid snakes.
Michael W Caldwell - One of the best experts on this subject based on the ideXlab platform.
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discovery of the oldest south american fossil lizard illustrates the cosmopolitanism of early south american Squamates
Communications biology, 2020Co-Authors: Jonathas S Bittencourt, Tiago R. Simões, Michael W Caldwell, Max C LangerAbstract:Squamates have an extremely long evolutionary history with a fossil record that extends into the Middle Triassic. However, most of our knowledge of their early evolutionary history is derived from Laurasian records. Therefore, fundamental questions regarding the early evolution of Squamates in the Southern Hemisphere, such as the origins of the extremely diverse and endemic South American fauna, remain unanswered. Here, we describe a new lizard species that represents the oldest fossil Squamate from South America, demonstrating that Squamates were present on that continent at least 20 million years earlier than previously recorded. The new species represents the first occurrence of the extinct Squamate family Paramacellodidae in South America and displays an unusual limb morphology. Finally, our findings suggest early South American Squamates were part of a much broader distribution of their respective clades, in sharp contrast to the high levels of endemicity characteristic of modern faunas. Jonathas Bittencourt et al. report the discovery of a fossil lizard in South America dated to at least 130 mya, about 20 million years earlier than previously thought. This finding suggests early lizards in South America were much more broadly distributed than extant species in this region.
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X-ray computed microtomography of Megachirella wachtleri.
Scientific Data, 2018Co-Authors: Tiago R. Simões, Mateusz Tałanda, Federico Bernardini, Oksana Vernygora, Lucia Mancini, Massimo Bernardi, Alessandro Palci, Michael W Caldwell, Randall L. NydamAbstract:Understanding the origin and early evolution of Squamates has been a considerable challenge given the extremely scarce fossil record of early Squamates and their poor degree of preservation. In order to overcome those limitations, we conducted high-resolution X-ray computed tomography (CT) studies on the fossil reptile Megachirella wachtleri (Middle Triassic, northern Italy), which revealed an important set of features indicating this is the oldest known fossil Squamate in the world, predating the previous oldest record by ca. 75 million years. We also compiled a new phylogenetic data set comprising a large sample of diapsid reptiles (including morphological and molecular data) to investigate the phylogenetic relationships of early Squamates and other reptile groups along with the divergence time of those lineages. The re-description of Megachirella and a new phylogenetic hypothesis of diapsid relationships are presented in a separate study. Here we present the data descriptors for the tomographic scans of Megachirella, which holds fundamental information to our understanding on the early evolution of one of the largest vertebrate groups on Earth today. Machine-accessible metadata file describing the reported data (ISA-Tab format)
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X-ray computed microtomography of Megachirella wachtleri.
Scientific Data, 2018Co-Authors: Tiago R. Simões, Mateusz Tałanda, Federico Bernardini, Oksana Vernygora, Lucia Mancini, Massimo Bernardi, Alessandro Palci, Michael W Caldwell, Randall L. NydamAbstract:Understanding the origin and early evolution of Squamates has been a considerable challenge given the extremely scarce fossil record of early Squamates and their poor degree of preservation. In order to overcome those limitations, we conducted high-resolution X-ray computed tomography (CT) studies on the fossil reptile Megachirella wachtleri (Middle Triassic, northern Italy), which revealed an important set of features indicating this is the oldest known fossil Squamate in the world, predating the previous oldest record by ca. 75 million years. We also compiled a new phylogenetic data set comprising a large sample of diapsid reptiles (including morphological and molecular data) to investigate the phylogenetic relationships of early Squamates and other reptile groups along with the divergence time of those lineages. The re-description of Megachirella and a new phylogenetic hypothesis of diapsid relationships are presented in a separate study. Here we present the data descriptors for the tomographic scans of Megachirella, which holds fundamental information to our understanding on the early evolution of one of the largest vertebrate groups on Earth today. Machine-accessible metadata file describing the reported data (ISA-Tab format)
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The origin of Squamates revealed by a Middle Triassic lizard from the Italian Alps
Nature, 2018Co-Authors: Tiago R. Simões, Mateusz Tałanda, Federico Bernardini, Oksana Vernygora, Lucia Mancini, Massimo Bernardi, Alessandro Palci, Michael W Caldwell, Randall L. NydamAbstract:Modern Squamates (lizards, snakes and amphisbaenians) are the world’s most diverse group of tetrapods along with birds 1 and have a long evolutionary history, with the oldest known fossils dating from the Middle Jurassic period—168 million years ago2–4. The evolutionary origin of Squamates is contentious because of several issues: (1) a fossil gap of approximately 70 million years exists between the oldest known fossils and their estimated origin5–7; (2) limited sampling of Squamates in reptile phylogenies; and (3) conflicts between morphological and molecular hypotheses regarding the origin of crown Squamates6,8,9. Here we shed light on these problems by using high-resolution microfocus X-ray computed tomography data from the articulated fossil reptile Megachirella wachtleri (Middle Triassic period, Italian Alps 10 ). We also present a phylogenetic dataset, combining fossils and extant taxa, and morphological and molecular data. We analysed this dataset under different optimality criteria to assess diapsid reptile relationships and the origins of Squamates. Our results re-shape the diapsid phylogeny and present evidence that M. wachtleri is the oldest known stem Squamate. Megachirella is 75 million years older than the previously known oldest Squamate fossils, partially filling the fossil gap in the origin of lizards, and indicates a more gradual acquisition of squamatan features in diapsid evolution than previously thought. For the first time, to our knowledge, morphological and molecular data are in agreement regarding early Squamate evolution, with geckoes—and not iguanians—as the earliest crown clade Squamates. Divergence time estimates using relaxed combined morphological and molecular clocks show that lepidosaurs and most other diapsids originated before the Permian/Triassic extinction event, indicating that the Triassic was a period of radiation, not origin, for several diapsid lineages.
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Squamate phylogeny and the relationships of snakes and mosasauroids
Zoological Journal of the Linnean Society, 1999Co-Authors: Michael W CaldwellAbstract:Abstract Cladistic analysis of extant and fossil Squamates (95 characters, 26 taxa) finds the fossil Squamate,Coniasaurus Owen, 1850, to be the sister-group of the Mosasauroidea (mosasaurs and aigialosaurs). This clade is supported in all 18 shortest cladograms (464 steps; CI 0.677; HI 0.772) by nine characters of the dermatocranium, maxilla, and mandible. A Strict Consensus Tree of the 18 shortest trees collapses to a basal polytomy for most major Squamate clades including the clade (Coniasaurus, Mosasauroidea). A Majority Rule Consensus Tree shows that, in 12 of 18 shortest cladograms, the cladeConiasaurus –Mosasauroidea is the sister-group to snakes (Scolecophidia (Alethinophidia, Dinilysia); this entire clade, referred to as the Pythonomorpha ([[Scolecophidia [Alethinophidia, Dinilysia]], [Coniasaurus, Mosasauroidea]]) is the sister-group to all other scleroglossans. Pythonomorpha is supported in these 12 cladograms by nine characters related to the lower jaw and cranial kinesis. In 6 of 18 shortest cladograms, snakes are the sister-group to the clade (Amphisbaenia (Dibamidae (Gekkonoidea, Eublepharidae))). None of the cladograms support the hypothesis that coniasaurs and mosasauroids are derived varanoid anguimorphs. Two additional analyses were conducted: (1) manipulation and movement of problematic Squamate clades while constraining «accepted» relationships; (2) additional cladistic analyses beginning with extant taxa, and sequentially adding fossil taxa. From Test I, at 467 steps, Pythonomorpha can be the sister-group to the Anguimorpha, Scincomorpha, «scinco-gekkonomorpha» [scincomorphs, gekkotans, and amphibaenids-dibamids]. At 471 steps Pythonomorpha can be placed within Varanoidea. Treating only mosasauroids and coniasaurs as a monophyletic group: 469 steps, mosasauroids and coniasaurs as sister-group to Anguimorpha; 479 steps, mosasauroids and coniasaurs nested within Varanoidea. Test II finds snakes to nest within Anguimorpha in a data set of only Mosasauroidea+Extant Squamates; the sistergroup to snakes+anugimorphs is (Amphisbaenia (Dibamidae (Gekkonoidea, Eublepharidae))). No one particular taxon is identified as a keystone taxon in this analysis, though it appears true that fossil taxa significantly alter the structure of Squamate phylogenetic trees.
Randall L. Nydam - One of the best experts on this subject based on the ideXlab platform.
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X-ray computed microtomography of Megachirella wachtleri.
Scientific Data, 2018Co-Authors: Tiago R. Simões, Mateusz Tałanda, Federico Bernardini, Oksana Vernygora, Lucia Mancini, Massimo Bernardi, Alessandro Palci, Michael W Caldwell, Randall L. NydamAbstract:Understanding the origin and early evolution of Squamates has been a considerable challenge given the extremely scarce fossil record of early Squamates and their poor degree of preservation. In order to overcome those limitations, we conducted high-resolution X-ray computed tomography (CT) studies on the fossil reptile Megachirella wachtleri (Middle Triassic, northern Italy), which revealed an important set of features indicating this is the oldest known fossil Squamate in the world, predating the previous oldest record by ca. 75 million years. We also compiled a new phylogenetic data set comprising a large sample of diapsid reptiles (including morphological and molecular data) to investigate the phylogenetic relationships of early Squamates and other reptile groups along with the divergence time of those lineages. The re-description of Megachirella and a new phylogenetic hypothesis of diapsid relationships are presented in a separate study. Here we present the data descriptors for the tomographic scans of Megachirella, which holds fundamental information to our understanding on the early evolution of one of the largest vertebrate groups on Earth today. Machine-accessible metadata file describing the reported data (ISA-Tab format)
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X-ray computed microtomography of Megachirella wachtleri.
Scientific Data, 2018Co-Authors: Tiago R. Simões, Mateusz Tałanda, Federico Bernardini, Oksana Vernygora, Lucia Mancini, Massimo Bernardi, Alessandro Palci, Michael W Caldwell, Randall L. NydamAbstract:Understanding the origin and early evolution of Squamates has been a considerable challenge given the extremely scarce fossil record of early Squamates and their poor degree of preservation. In order to overcome those limitations, we conducted high-resolution X-ray computed tomography (CT) studies on the fossil reptile Megachirella wachtleri (Middle Triassic, northern Italy), which revealed an important set of features indicating this is the oldest known fossil Squamate in the world, predating the previous oldest record by ca. 75 million years. We also compiled a new phylogenetic data set comprising a large sample of diapsid reptiles (including morphological and molecular data) to investigate the phylogenetic relationships of early Squamates and other reptile groups along with the divergence time of those lineages. The re-description of Megachirella and a new phylogenetic hypothesis of diapsid relationships are presented in a separate study. Here we present the data descriptors for the tomographic scans of Megachirella, which holds fundamental information to our understanding on the early evolution of one of the largest vertebrate groups on Earth today. Machine-accessible metadata file describing the reported data (ISA-Tab format)
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The origin of Squamates revealed by a Middle Triassic lizard from the Italian Alps
Nature, 2018Co-Authors: Tiago R. Simões, Mateusz Tałanda, Federico Bernardini, Oksana Vernygora, Lucia Mancini, Massimo Bernardi, Alessandro Palci, Michael W Caldwell, Randall L. NydamAbstract:Modern Squamates (lizards, snakes and amphisbaenians) are the world’s most diverse group of tetrapods along with birds 1 and have a long evolutionary history, with the oldest known fossils dating from the Middle Jurassic period—168 million years ago2–4. The evolutionary origin of Squamates is contentious because of several issues: (1) a fossil gap of approximately 70 million years exists between the oldest known fossils and their estimated origin5–7; (2) limited sampling of Squamates in reptile phylogenies; and (3) conflicts between morphological and molecular hypotheses regarding the origin of crown Squamates6,8,9. Here we shed light on these problems by using high-resolution microfocus X-ray computed tomography data from the articulated fossil reptile Megachirella wachtleri (Middle Triassic period, Italian Alps 10 ). We also present a phylogenetic dataset, combining fossils and extant taxa, and morphological and molecular data. We analysed this dataset under different optimality criteria to assess diapsid reptile relationships and the origins of Squamates. Our results re-shape the diapsid phylogeny and present evidence that M. wachtleri is the oldest known stem Squamate. Megachirella is 75 million years older than the previously known oldest Squamate fossils, partially filling the fossil gap in the origin of lizards, and indicates a more gradual acquisition of squamatan features in diapsid evolution than previously thought. For the first time, to our knowledge, morphological and molecular data are in agreement regarding early Squamate evolution, with geckoes—and not iguanians—as the earliest crown clade Squamates. Divergence time estimates using relaxed combined morphological and molecular clocks show that lepidosaurs and most other diapsids originated before the Permian/Triassic extinction event, indicating that the Triassic was a period of radiation, not origin, for several diapsid lineages.
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“Mesozoic and Cenozoic lissamphibian and Squamate assemblages of Laurasia”—introduction to the special issue
Palaeobiodiversity and Palaeoenvironments, 2013Co-Authors: James D. Gardner, Randall L. NydamAbstract:Lissamphibia (frogs, salamanders, caecilians, and albanerpetontids) and Squamata (lizards, snakes, and amphisbaenians) have been persistent components of many non-marine ecosystems on Earth since the early part of the Mesozoic. Both clades have extant and fossil occurrences on every modern continent, except Antarctica. The three Northern Hemisphere continents of Europe, Asia, and North America, which owe their origins largely to the mid-Mesozoic break-up of the former supercontinent Laurasia, have yielded the lion’s share of fossils for both groups. Consequently, the Laurasian fossil record has been critical for shaping our ideas about the diversities and evolutionary histories of lissamphibians and Squamates. The earliest collections and descriptions of fossil lissamphibians and Squamates from the former Laurasian continents date back to the early 1800s in Europe, followed decades later by discoveries in North America (western USA) in the 1870s and in Asia (Mongolia) in the 1920s (e.g. see historical summaries by Caldwell 2007; Estes 1981, 1983; Sanchiz 1998). Until the middle part of the twentieth century, descriptive work on fossil lissamphibians and Squamates tended to focus on articulated skeletons, such as those of Oligo–Miocene anurans from Central Europe (e.g. von Meyer 1860; Wolterstorff 1885) and of Early Cretaceous lizards and of what is now regarded as an albanerpetontid from Italy (e.g. Costa 1864). Although generally of less interest, isolated and articulated bones recovered by quarrying, surface collecting, or dry screening also merited some attention; to cite two examples, a mandible from the late Oligocene of France became the holotype of the earliest named fossil lizard, Dracaenosaurus croizeti Gervais 1848–1852, and the dozen or so fossil lissamphibians and Squamates named by Cope and Marsh in the late 1800s from the Late Jurassic and latest Cretaceous of the western USA were described on isolated bones (e.g. Cope 1876; Marsh 1872, 1887, 1892). Even after more than a century of work, by the middle part of the twentieth century our understanding of fossil lissamphibians and Squamates was limited to a small number of taxa known mostly from Europe and western North America, and largely from the Cenozoic. Aside from scattered and intriguing Mesozoic occurrences, little was known about either group from that era and much of the entire Asian fossil record remained a blank. Two developments in the latter part of the twentieth century dramatically improved our access to the lissamphibian and Squamate fossil records. The first development was the widespread adoption in the 1950s of screen washing (McKenna 1962) as a method to bulk process fossiliferous matrix by washing it through fine screens in order to recover small bones, teeth, and scales preserved in the rock. Screen washing was pioneered by palaeomammalogists and is still widely used by them as a way to recover mammalian teeth and jaws, particularly from fossil localities that are not suitable for hand quarrying and as a way to salvage fossils from the rubble left behind after quarrying. The “by-catch” of non-mammalian fossils caught in the screens often includes jaws, vertebrae, and other bones of lissamphibians and Squamates. Estes’ (1964) monograph, “Fossil vertebrates from the Late Cretaceous Lance Formation, eastern Wyoming” demonstrated that screen washing could provide large enough samples to This article is a contribution to the special issue "Mesozoic and Cenozoic lissamphibian and Squamate assemblages of Laurasia"
Lukáš Kratochvíl - One of the best experts on this subject based on the ideXlab platform.
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Evolution of Karyotypes in Chameleons.
Genes, 2017Co-Authors: Michail Rovatsos, Marie Altmanová, Martina Johnson Pokorná, Petr Velenský, Antonio Sánchez Baca, Lukáš KratochvílAbstract:: The reconstruction of the evolutionary dynamics of karyotypes and sex determining systems in Squamate reptiles is precluded by the lack of data in many groups including most chameleons (Squamata: Acrodonta: Chamaeleonidae). We performed cytogenetic analysis in 16 species of chameleons from 8 genera covering the phylogenetic diversity of the family and also phylogenetic reconstruction of karyotype evolution in this group. In comparison to other Squamates, chameleons demonstrate rather variable karyotypes, differing in chromosome number, morphology and presence of interstitial telomeric signal (ITS). On the other hand, the location of rDNA is quite conserved among chameleon species. Phylogenetic analysis combining our new results and previously published data tentatively suggests that the ancestral chromosome number for chameleons is 2n = 36, which is the same as assumed for other lineages of the clade Iguania, i.e., agamids and iguanas. In general, we observed a tendency for the reduction of chromosome number during the evolution of chameleons, however, in Rieppeleon brevicaudatus, we uncovered a chromosome number of 2n = 62, very unusual among Squamates, originating from a number of chromosome splits. Despite the presence of the highly differentiated ZZ/ZW sex chromosomes in the genus Furcifer, we did not detect any unequivocal sexual differences in the karyotypes of any other studied species of chameleons tested using differential staining and comparative genomic hybridization, suggesting that sex chromosomes in most chameleons are only poorly differentiated.
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Interstitial Telomeric Motifs in Squamate Reptiles: When the Exceptions Outnumber the Rule.
PloS one, 2015Co-Authors: Michail Rovatsos, Lukáš Kratochvíl, Marie Altmanová, Martina Johnson PokornáAbstract:Telomeres are nucleoprotein complexes protecting the physical ends of linear eukaryotic chromosomes and therefore helping to ensure their stability and integrity. Additionally, telomeric sequences can be localized in non-terminal regions of chromosomes, forming so-called interstitial telomeric sequences (ITSs). ITSs are traditionally considered to be relics of chromosomal rearrangements and thus very informative in the reconstruction of the evolutionary history of karyotype formation. We examined the distribution of the telomeric motifs (TTAGGG)n using fluorescence in situ hybridization (FISH) in 30 species, representing 17 families of Squamate reptiles, and compared them with the collected data from another 38 species from literature. Out of the 68 Squamate species analyzed, 35 possess ITSs in pericentromeric regions, centromeric regions and/or within chromosome arms. We conclude that the occurrence of ITSs is rather common in Squamates, despite their generally conserved karyotypes, suggesting frequent and independent cryptic chromosomal rearrangements in this vertebrate group.
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Strong conservation of the bird Z chromosome in reptilian genomes is revealed by comparative painting despite 275 million years divergence
Chromosoma, 2011Co-Authors: Martina Pokorná, Lukáš Kratochvíl, Massimo Giovannotti, Vincenzo Caputo, Ettore Olmo, Malcolm A. Ferguson-smith, Fumio Kasai, Vladimir A. Trifonov, Patricia C. M. O’brien, Willem RensAbstract:The divergence of lineages leading to extant Squamate reptiles (lizards, snakes, and amphisbaenians) and birds occurred about 275 million years ago. Birds, unlike Squamates, have karyotypes that are typified by the presence of a number of very small chromosomes. Hence, a number of chromosome rearrangements might be expected between bird and Squamate genomes. We used chromosome-specific DNA from flow-sorted chicken ( Gallus gallus ) Z sex chromosomes as a probe in cross-species hybridization to metaphase spreads of 28 species from 17 families representing most main Squamate lineages and single species of crocodiles and turtles. In all but one case, the Z chromosome was conserved intact despite very ancient divergence of sauropsid lineages. Furthermore, the probe painted an autosomal region in seven species from our sample with characterized sex chromosomes, and this provides evidence against an ancestral avian-like system of sex determination in Squamata. The avian Z chromosome synteny is, therefore, conserved albeit it is not a sex chromosome in these Squamate species.
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phylogeny of sex determining mechanisms in Squamate reptiles are sex chromosomes an evolutionary trap
Zoological Journal of the Linnean Society, 2009Co-Authors: Martina Johnson Pokorná, Lukáš KratochvílAbstract:Squamate reptiles possess two general modes of sex determination: (1) genotypic sex determination (GSD), where the sex of an individual is determined by sex chromosomes, i.e. by sex-specific differences in genotype; and (2) temperature-dependent sex determination (TSD), where sex chromosomes are absent and sex is determined by nongenetic factors. After gathering information about sex-determining mechanisms for more than 400 species, we employed comparative phylogenetic analyses to reconstruct the evolution of sex determination in Squamata. Our results suggest relative uniformity in sex-determining mechanisms in the majority of the Squamate lineages. Well-documented variability is found only in dragon lizards (Agamidae) and geckos (Gekkota). Polarity of the sex-determining mechanisms in outgroups identified TSD as the ancestral mode for Squamata. After extensive review of the literature, we concluded that to date there is no known well-documented transition from GSD to TSD in reptiles, although transitions in the opposite direction are plentiful and well corroborated by cytogenetic evidence. We postulate that the evolution of sex-determining mechanisms in Squamata was probably restricted to the transitions from ancestral TSD to GSD. In other words, transitions were from the absence of sex chromosomes to the emergence of sex chromosomes, which have never disappeared and constitute an evolutionary trap. This evolutionary trap hypothesis could change the understanding of phylogenetic conservatism of sex-determining systems in many large clades such as butterflies, snakes, birds, and mammals. © 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2009, 156, 168–183.
