Dr. Simões incorporated data from Megachirella's anatomy into a larger data set he had assembled by studying squamate species from 50 museum collections in 17 countries.
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" The researchers also noted that for the first time, "orphological and molecular data are in agreement regarding early squamate evolution, with geckoes — and not iguanians — as the earliest crown clade squamates.
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DISCOVERY OF &aposREPTILIAN-MAMMAL&apos FOSSIL COULD REWRITE HISTORY "Megachirella provides unique insights into the early acquisition of squamatan features, as it is the first unequivocal squamate from the Triassic," the study reads.
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The earliest known squamate fossils hailed from the later Jurassic period, leaving a frustrating 75 million-year gap between the shared ancestor and the appearance of what are now some of the planet's most familiar animals.
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This is the smallest and least known squamate suborder. It contains the wormlike amphisbaenids. Florida has one species.
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The squamate antbird (Myrmoderus squamosus) is a species of bird in the family Thamnophilidae. It is endemic to Brazil. Its natural habitats are subtropical or tropical moist lowland forest and subtropical or tropical moist montane forest. The squamate antbird was described by the Austrian ornithologist August von Pelzeln in 1868 and given the binomial name Myrmeciza squamosa.
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The Plasmodium of birds and squamate reptiles all fall within a single clade with evidence for repeated switching between birds and squamate hosts. One study using Bayesian factors to identify the root of the phylogenetic tree has suggested that Plasmodium may be basal to Haemoproteus, Leucocytozoon, Paraheamoproteus and Polychromophilus. This tree also grouped Hepatocystis with Plasmodium. Rayella is thought to have originated from Hepatocystis.
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Biological Reviews 26:193–237. But so far, with cladistic analyses of squamate interrelationship, scientists still cannot come to an agreement about the origin of snakes.
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Squamata: Within squamate reptiles, acrodont tooth implantation is best known in Acrodonta and some species of amphisbaenians, though some snakes are also referred to as being acrodont. Acrodonta is unique in that the name of the clade is based upon this trait. Most other squamate reptiles have pleurodont dentition, though some snakes are occasionally described as having acrodont dentition. Rhynchocephalia: Acrodont tooth implantation is common within Rhynchocephalia, including Sphenodon.
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"The phylogeny of squamate reptiles (lizards, snakes and amphisbaenians) inferred from nine nuclear protein-coding genes". Comptes Rendus Biologies 328 (10-11): 1000-1008. Gorman GC, Gress F (1970).
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Gekkota is an infraorder of squamate reptiles in the suborder Scleroglossa, comprising all geckos and the limbless "snake-lizards" of family Pygopodidae. The legless lizards of the family Dibamidae, also referred to as blind lizards, have occasionally been counted as gekkotans, but recent molecular phylogenies suggest otherwise.Townsend, T., A. Larson, E. Louis, & J. R. Macey. 2004. Molecular phylogenetics of Squamata: The position of snakes, amphisbaenians, and dibamids, and the root of the squamate tree.
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Sineoamphisbaena is an extinct genus of squamate of uncertain phylogenetic placement. Its fossils are known from the Late Cretaceous deposits in Inner Mongolia, China. Wu et al. (1993), Wu et al.
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A molecular phylogenetic study published in 2013 found that Myrmeciza was polyphyletic. In the resulting rearrangement to create monotypic genera four species including the squamate antbird were moved to the resurrected genus Myrmoderus.
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Hoyalacerta is an extinct genus of lizard known from the type species Hoyalacerta sanzi, which is from the Early Cretaceous Las Hoyas fossil site in Spain. Hoyalacerta was named in 1999 and is considered either a member of the group Iguania or a stem squamate, meaning that it lies outside the squamate crown group that includes all living lizards and snakes. Hoyalacerta is a small lizard with an elongated body and short limbs. It is thought to have spent most of its time on the ground.
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Kaganaias (meaning 'Kaga water nymph') is an extinct genus of mosasauroid lizard that lived in what is now Japan during the Early Cretaceous. Kaganaias was semi-aquatic and is the only known aquatic squamate to be found in Asia and is also the only known aquatic squamate known from before the Cenomanian stage of the Cretaceous. It is also the first to be found in an inland area, instead of on the coast where aquatic squamates are commonly found.Evans, S.E., Manabe, M., Noro, M., Isaji, S. & Yamaguchi, M. (2006).
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Though they survived the Cretaceous–Paleogene extinction event, many squamate species are now endangered due to habitat loss, hunting and poaching, illegal wildlife trading, alien species being introduced to their habitats (which puts native creatures at risk through competition, disease, and predation), and other anthropogenic causes. Because of this, some squamate species have recently become extinct, with Africa having the most extinct species. However, breeding programs and wildlife parks are trying to save many endangered reptiles from extinction. Zoos, private hobbyists and breeders help educate people about the importance of snakes and lizards.
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The height of the shell attains 45 mm, its diameter 40 mm. The shell is somewhat globose, swollen, and imperforated. The sutures of the spire are excavately channelled and spirally ridged. These ridges are very finely laminiferous and squamate.
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The ampulla of ductus deferens is an enlargement of the ductus deferens at the fundus of the bladder which acts as a reservoir for sperm. This structure is seen in some mammalian and squamate species and is sometimes tortuous in shape.
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The shell grows to a length of 20 mm. The imperforated shell is somewhat pyramidally ovate. The sutures of the spire are excavated. The whorls are spirally squamately ridged, slanting around the upper part, sharply angled, erectly squamate at the angle.
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Chlamydosauromyces punctatus was first found in the putatively healthy Squamate reptiles free of cutaneous lesions. The fungus was first isolated in 2001 from the shed skin of a 7-year-old healthy male frilled lizard, Chlamydosaurus kingii, from the San Diego Zoo (the lizard typically lives in trees found in the northern part of the Australia). Among samples of three different Squamate reptiles donated by the Zoo, the skin samples of two of the reptile species did not show any evidence of invasion by the fungus. The ex-type strain of C. punctatus is in depository at UAMH 9990.
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Iguanians are now united with snakes and anguimorphs in a clade called Toxicofera. Genetic data also suggests that the various limbless groups; snakes, amphisbaenians and dibamids, are unrelated, and instead arose independently from lizards. A study in 2018 found that Megachirella, an extinct genus of lepidosaur that lived about 240 million years ago during the Middle Triassic, was a stem-squamate, making it the oldest known squamate. The phylogenetic analysis was conducted by performing high-resolution microfocus X-ray computed tomography (micro-CT) scans on the fossil specimen of Megachirella to gather detailed data about its anatomy.
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A. alleni is found only in alpine moorlands of Mount Kenya, Mount Elgon, and the Aberdares Mountains in Kenya.Greer AE (1968). "Mode of reproduction in the squamate faunas of three altitudinally correlated life zones in East Africa". Herpetologica 24 (3): 229-232.
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Kevin de Queiroz is a vertebrate, evolutionary, and systematic biologist. He has worked in the phylogenetics and evolutionary biology of squamate reptiles, the development of a unified species concept and of a phylogenetic approach to biological nomenclature, and the philosophy of systematic biology.
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Parker, M. R., B. A. Young, and K. V. Kardong. 2008. The forked tongue and edge detection in snakes (Crotalus oreganus): an experimental test. Journal of Comparative Psychology 122:35-40. Forked tongues have evolved in these squamate reptiles (lizards and snakes) for various purposes.
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A new clade Bifurcata (bifurcated tongue) has been proposed to include Iguania as a sister taxon to Anguimorpha.Vidal, N. and Hedges, S.B. 2005. The phylogeny of squamate reptiles (lizards, snakes, and amphisbaenians) inferred from nine nuclear protein-coding genes. C.R. Biologies 328: 1000-1008.
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Turtle fossils are very common, but only two different groups have been identified, the bothremydids Polysternon and Rosasia, along with an undetermined Pancryptodiran. Squamate lizards are known only from a few undetermined specimens, and eusuchian crocodiles are known from a specimen with similarities to Allodaposuchus and Musturzabalsuchus.
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Similar mammal-like adaptations also occur in the skink genera Chalcides, Eumecia, Mabuya, Niveoscincus, and Trachylepis.Van Dyke JU, Brandley MC, Thompson MB (2014). "The evolution of viviparity: molecular and genomic data from squamate reptiles advance understanding of live birth in amniotes". Reproduction 147 (1): R15-R26.
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Adriosaurus is an extinct genus of squamate which lived in what is now Slovenia and other parts of Europe during the Late Cretaceous. It was snake- like and grew 10 to 12 inches. This is the first fossil record of vestigial limbs in lizards.Ancient lizard missing front limbs - LiveScience - nbcnews.
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According to the scientists "... reptilian oral secretions contribute to many biological roles other than to quickly dispatch prey". They concluded, "Calling all in this clade venomous implies an overall potential danger that does not exist, misleads in the assessment of medical risks, and confuses the biological assessment of squamate biochemical systems".
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Monstersauria is a clade of varanoid lizards, defined as all taxa more closely related to Heloderma than Varanus. It includes Heloderma, as well as several extinct genera, such as Estesia, Primaderma and Gobiderma, but it was found to be polyphyletic in the most recent and complete squamate phylogenetic analysis by Reeder et al. (2015).
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Townsend, T. M., A. Larson, E. Louis, and J. R. Macey. 2004. Molecular phylogenetics of Squamata: the position of snakes, Amphisbaenians, and Dibamids, and the root of the squamate tree. Systematic Biology 53:735-757. A common behavioral characteristic that has evolved in those with forked tongues is that they tend to be wide foragers.
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Herbivory is rare in species outside the Iguania clade, but is present in isolated squamate groups. Within the Scincomorpha (a clade that includes skinks), herbivory independently evolves at least seven times. Specifically, herbivory independently develops at least once in the Lacertidae, Gerrhosauridae, Teiidae clades, and four times in the Scincidae (in the Corucia, Egernia, Macroscincus, and Tiliqua genera).
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The Lacertoidea is a group of lizards that includes the Lacertidae, Teiidae, Gymnophthalmidae, and the burrowing Amphisbaenia. Studies of anatomy have traditionally grouped the lacertoids with skinks;Gauthier, Jacques A., et al. "Assembling the squamate tree of life: Perspectives from the phenotype and the fossil record." Bulletin of the Peabody Museum of Natural History 53.1 (2012): 3-308.
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A. skrbinensis was a small marine squamate with 30 dorsal vertebrae. Unlike A. suessi, A. skrbinesis had forelimbs which were much more reduced than the hindlimbs. It had a humerus/femur ratio of 0.40, compared to 0.61 in A. suessi and 0.62 in A. microbrachis. In its gastric contents, there was phosphatic matter which was probably the remains of small fishes.
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There are more than 7,800 species of squamate reptiles living today and approximately 2% of them are herbivorous, though the number is continually increasingStruck, U., Altenbach, A. V., Gaulke, M., Glaw, F. 2002. Tracing the diet of the monitor lizard Varanus mabitang by stable isotope analyses (δ15N, δ13C). Naturwissenschaften 89:470–473.). Herbivorous squamates are known from all major groups, including varanids.
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Tetrapodophis (meaning "four-footed snake" in Greek) is an extinct genus of squamate from the Early Cretaceous. It was previously thought to be one of the oldest members of Ophidia. However it is currently thought to be a dolichosaurid based morphological analysis of the hind limbs. This species existed in the Cretaceous Period about 120 million years ago, located in modern day Brazil.
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This process leads to genome wide homozygosity, expression of deleterious recessive alleles and often to developmental abnormalities. Both captive-born and wild-born A. contortrix and A. piscivorus appear to be capable of this form of parthenogenesis. Reproduction in squamate reptiles is almost exclusively sexual. Males ordinarily have a ZZ pair of sex determining chromosomes, and females a ZW pair.
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Tuatara have been referred to as living fossils, due to a perception that they retain many basal characteristics from around the time of the squamate–rhynchocephalian split (240 MYA). Morphometric analyses of variation in jaw morphology among tuatara and extinct rhynchocephalian relatives have been argued to demonstrate morphological conservatism and support for the classification of tuatara as a 'living fossil', but the reliability of these results has been criticised and debated. Paleontological research on rhynchocephalians indicates that the group has undergone a variety of changes throughout the Mesozoic, and the rate of molecular evolution for tuatara has been estimated to be among the fastest of any animal yet examined. However, a 2020 analysis of the tuatara genome reached the opposite conclusion, that its rate of DNA substitutions per site is actually lower than for any analysed squamate.
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From morphological data, Iguanid lizards have been thought to have diverged from other squamates very early, but recent molecular phylogenies, both from mitochondrial and nuclear DNA, do not support this early divergence. Because snakes have a faster molecular clock than other squamates, and there are few early snake and snake ancestor fossils, it is difficult to resolve the relationship between snakes and other squamate groups.
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A. suessi was a small marine squamate with an elongate neck and body. It had 10 cervical, 29 dorsal, and at least 65 caudal vertebrae. It had a unique feature called pachyostosis, an anatomical feature that thickened the periosteal bone by increasing the osteogenic activity of periosteum. Both its forelimbs and hindlimbs were reduced in size, which suggests that it lived in a marine environment.
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Danum Valley, Malaysia The genus is morphologically very peculiar within the poneromorph subfamily group and has the following combination of characteristics: the very wide head; spatulate or squamate hairs on the head; and long, narrow mandibles with a double row of teeth on the inner margins. Monophyly of the genus is strongly supported by a recent molecular phylogenetic study by Saux et al. (2004).
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Welton, L. J., Siler, C. D., Bennett, D., Diesmos, A., Duya, M. R., Dugay, R., Rico, E. L. B., Van Weerd, M., and R. M. Brown. 2010. A spectacular new Philippine monitor lizard reveals a hidden biogeographic boundary and a novel flagship species for conservation. Biology Letters 6:654–658. Though present in all major squamate clades, herbivory is most prevalent within the Iguania.
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The Chilean hawk's food is almost exclusively birds (97.8% of all prey remains in one study),Figueroa Rojas et al. (2004) in particular a diverse selection of forest passerines. More than 30 bird species are documented to be eaten by this hawk at least occasionally. Rodents of at least 4 species and every now and then an occasional insect or squamate round off its diet.
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Skin of a sand lizard, showing squamate reptiles iconic scales Reptilian skin is covered in a horny epidermis, making it watertight and enabling reptiles to live on dry land, in contrast to amphibians. Compared to mammalian skin, that of reptiles is rather thin and lacks the thick dermal layer that produces leather in mammals.Hildebran, M. & Goslow, G. (2001): Analysis of Vertebrate Structure. 5th edition.
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Limatula hodgsoni grows to a length of , a height of and a diameter of . The shell is white, oblong, thin, narrow above and somewhat convex; the posterior side is less curved than the anterior. The umbones are central and the ligament area is narrow and diamond-shaped. The valves are sculpted by 30 to 35 squamate ribs separated by grooves slightly narrower than the ribs.
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This list of mosasaur type specimens is a list of fossils that are official standard-bearers for inclusion in the species and genera of the squamate clade Mosasauroidea, which includes the line of predatory marine lizards that culminates in the mosasaurids. Type specimens are definitionally members of biological taxa, and additional specimens are "referred" to these taxa only if an expert deems them sufficiently similar to the type.
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Several species of whiptail lizards are entirely female and no males are known.AAAS – All-Female Species of the Lizard Genus Cnemidophorus, Teiidae These all-female species reproduce by obligate parthenogenesis (obligate, because the lizards do not involve males and cannot reproduce sexually). Like all squamate obligate parthenogenetic lineages, parthenogenetic Teiids are hybrids. Two or more species rarely hybridize and the offspring are thought to occasionally be capable of reproduction without sperm.
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Rudimentary eyes of squamate fossorial reptiles (amphisbaenia and serpentes). John Wiley & Sons, Hoboken, NJ. 293(2): 351–7. The body is elongated, and the tail truncates in a manner that vaguely resembles the head. Their name is derived from Amphisbaena, a mythical serpent with a head at each end—referencing both the manner in which their tail truncates, and their ability to move just as well in reverse as forwards.
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Nordenosaurus is an extinct genus of crocodilian. When first named in 1973 the genus was thought to be a squamate and was assigned to the family Xenosauridae. A single frontal bone was found from the Norden Bridge locality of the lower Valentine Formation in Brown County, Nebraska, thought to date back to the late Miocene. The size of the bone was initially taken as evidence that it was a giant xenosaurid.
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A suggested theory for the evolution of squamate vision is that corneal accommodation and monocular depth perception are "primitive" mechanisms in comparison to binocular vision and stereopsis. Chameleons use an alternative strategy to stereopsis in functional coupling of the eyes immediately before the tongue shot. This differs from stereopsis in that the images from both eyes are not reconciled into one. However, it is possible that this was first used for neural static reduction.
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Vestigial forelimbs and axial elongation in a 95 million-year-old non-snake squamate. Journal of Vertebrate Paleontology, 27(1), 1-7. However, the validity of Pythonomorpha is still debated; indeed, there is no consensus about the relationships of snakes or mosasaurs to each other, or to the rest of the lizards. An analysis by Conrad (2008) placed mosasaurs with varanoid lizards, and snakes with skinks, while an analysis by Gauthier et al.
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Schematic skull of a squamate showing the location of major dermal bones Extant reptiles are in the clade Diapsida, named for a pair of temporal fenestrations on each side of the skull. Until recently, Diapsida was said to be composed of Lepidosauria and their sister taxa Archosauria. The subclass Lepidosauria is then split into Squamata and Rhynchocephalia. More recent morphological studies and molecular studies or, more commonly, as a sister group to extant archosaurs.
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Ophidiomorpha is a clade composed of snakes and their primitive and early relatives proposed by Palci and Caldwell (2007)Palci, A., & Caldwell, M. W. (2007). Vestigial forelimbs and axial elongation in a 95 million-year-old non- snake squamate. Journal of Vertebrate Paleontology, 27(1), 1-7. The clade was defined as a node-based clade containing the most recent common ancestor of dolichosaurs, adriosaurs, Aphanizocnemus, and fossil and extant Ophidia and all of its descendants.
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Parthenogenesis is a mode of asexual reproduction in which offspring are produced by females without the genetic contribution of a male. Among all the sexual vertebrates, the only examples of true parthenogenesis, in which all- female populations reproduce without the involvement of males, are found in squamate reptiles (snakes and lizards). There are about 50 species of lizard and 1 species of snake that reproduce solely through parthenogenesis (obligate parthenogenesis).Vitt, Laurie J., and Janalee P. Caldwell.
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Lizards are a widespread group of squamate reptiles, with over 6,000 species,Reptile Database. Retrieved on 2012-04-22 ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic as it excludes the snakes and Amphisbaenia; some lizards are more closely related to these two excluded groups than they are to other lizards. Lizards range in size from chameleons and geckos a few centimeters long to the 3 meter long Komodo dragon.
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Ardeosaurus is an extinct genus of basal lizards, known from fossils found in the Late Jurassic Solnhofen Plattenkalk of Bavaria, southern Germany. It was originally thought to have been a species of Homeosaurus. Life restoration Ardeosaurus was originally considered to be a distant relative to modern geckos, and had a similar physical appearance. Evans and colleagues, however, showed it in 2005 to be a basal squamate outside the crown group of all living lizards and snakes.
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Slavoia darevskii, a fossil squamate Squamates are a monophyletic sister group to the rhynchocephalians, members of the order Rhynchocephalia. The only surviving member of Rhynchocephalia is the tuatara. Squamata and Rhynchocephalia form the subclass Lepidosauria, which is the sister group to Archosauria, the clade that contains crocodiles and birds, and their extinct relatives. Fossils of rhynchocephalians first appear in the Early Triassic, meaning that the lineage leading to squamates must have also existed at the time.
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This process leads to genome wide homozygosity, expression of deleterious recessive alleles and often to developmental abnormalities. Both captive-born and wild- born A. contortrix and A. piscivorus appear to be capable of this form of parthenogenesis. Reproduction in squamate reptiles is ordinarily sexual, with males having a ZZ pair of sex determining chromosomes, and females a ZW pair. However, the Colombian Rainbow boa, Epicrates maurus, can also reproduce by facultative parthenogenesis resulting in production of WW female progeny.
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A phylogenetic analysis published alongside the original 2015 description of Tetrapodophis places it as a close relative of other early snakes such as Coniophis, Dinilysia, and Najash, but outside the crown group Serpentes, meaning that it branched off before the most recent common ancestor of all living snakes. Below is a cladogram from that analysis: The interpretation of Tetrapodophis amplectus as an early fossorial snake was challenged by Caldwell et al. (2016), who considered it more likely to be a dolichosaurid squamate.
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De Queiroz’s research has focused primarily on the phylogeny and evolutionary biology of squamate reptiles, including his Master’s research on the phylogeny of iguanine lizards and his Ph.D. research on the phylogeny of phrynosomatine sand lizards. He worked with his mentors Richard Estes and Richard Etheridge on the phylogeny of Squamata Estes, R., K. de Queiroz, and J. A. Gauthier. (1988) “Phylogenetic relationships within Squamata.” Pp. 119-281 in ‘’Phylogenetic Relationships of the Lizard Families’’, R. Estes and G. Pregill (eds.), Stanford Univ.
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The tessellated gecko was first described by a German- born British zoologist, ichthyologist, and herpetologist Albert Gunther in 1875. Diplodactylus tessellates is a species of geckos of the genus Diplodactylus within the family Diplodactylidae. Australian diplodactyline geckos are the only extant squamate group thought to have been in Australia before its separation from other east Gondwanan landmasses. D. tessellatus is thought to have speciated from Diplodactylus vittatus between 12–20 million years ago during the Miocene Epoch of the Neogene period.
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Tod W. Reeder, Ted M. Townsend, Daniel G. Mulcahy, Brice P. Noonan, Perry L. Wood Jr., Jack W. Sites Jr., and John J. Wiens. (2015). "Integrated analyses resolve conflicts over Squamate reptile phylogeny and reveal unexpected placements for fossil taxa" PLoS ONE 10(3): e0118199. Another primitive Mosasauroid, Opetiosaurus, was suggested to represent a second species of Aigialosaurus in 2009, "Aigialosaurus bucchichi",Dutchak, Alex R.; and Caldwell, Michael W. (2009)."A redescription of Aigialosaurus (= Opetiosaurus) bucchichi (Kornhuber, 1901) (Squamata: Aigialosauridae) with comments on mosasauroid systematics".
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The hemipenis is the intromittent organ of squamata, which is the second largest order of vertebrates with over 9000 species distributed around the world. They differ from the intromittent organs of most other amniotes such as mammals, archosaurs and turtles that have a single genital tubercle, as squamates have the paired genitalia remaining separate. Squamate hemipenes also develop from a different cell origin, originating from the same embryonic cells that produce the limbs, whereas mammalian penises arise from the embryonic cells that develop the tail.
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The combination of small eggs and the absence of a larval stage, where posthatching growth occurs in anamniotic tetrapods before turning into juveniles, would limit the size of the adults. This is supported by the fact that extant squamate species that lay eggs less than 1 cm in diameter have adults whose snout-vent length is less than 10 cm. The only way for the eggs to increase in size would be to develop new internal structures specialized for respiration and for waste products.
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There are no records of vicious fights between snakes and Eurasian eagle-owls as there are with the great horned owl, with the horned owl sometimes losing its life after attacking a snake. Perhaps with their larger size and greater power, the eagle-owl can more easily overpower any snakes they encounter, although most snakes in Europe and temperate Asia are not particularly large.Olalla‐Tárraga, M. Á., Rodríguez, M. Á., & Hawkins, B. A. (2006). Broad‐scale patterns of body size in squamate reptiles of Europe and North America. Journal of Biogeography, 33(5), 781-793.
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In biology, placentation refers to the formation, type and structure, or arrangement of the placenta. The function of placentation is to transfer nutrients, respiratory gases, and water from maternal tissue to a growing embryo, and in some instances to remove waste from the embryo. Placentation is best known in live-bearing mammals (theria), but also occurs in some fish, reptiles, amphibians, a diversity of invertebrates, and flowering plants. In vertebrates, placentas have evolved more than 100 times independently, with the majority of these instances occurring in squamate reptiles.
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Skin of a sand lizard, showing squamate reptiles iconic Scales A white-headed dwarf gecko with shed tail Reptiles are tetrapod animals in the class Reptilia, comprising today's turtles, crocodilians, snakes, amphisbaenians, lizards, tuatara, and their extinct relatives. The study of these traditional reptile orders, historically combined with that of modern amphibians, is called herpetology. List of reptiles lists the vertebrate class of reptiles by family, spanning two subclasses. 'Reptile' here is taken in its traditional (paraphyletic) sense, and thus birds are not included (although birds are considered reptiles in the cladistic sense).
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Squamates, the group containing modern lizards and snakes, also lack a quadratojugal, but early squamate relatives such as Marmoretta do retain the bone. Ichthyosaurs, a group without a lower temporal bar, have a quadratojugal that is taller than it is long, stretching above (rather than below) the open infratemporal fenestra to contact the postorbital bone (rather than the jugal). Early turtles such as Proganochelys also have a tall quadratojugal, which contacts the jugal without any trace of the infratemporal fenestra. dromaeosaurid dinosaur Dromaeosaurus, with the quadratojugal (light blue) labelled.
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They are separated by a narrow channelled suture. The upper whorls are slightly worn, with 3 and 4 spiral lirae, which increase to 5 in number on the last 4 or 5 whorls. They are crossed by slightly undulating ribs, with beads where they cross each other, the lowest of the lirae forming the peripheral keel is the largest, and on this one the beads have a tendency to become squamate, (but not so much as in the preceding species). The body whorl descends in front and here the ribs form irregular lamellae.
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It does > mean, however, that we need to re-evaluate the relative danger of non- > venomous snakes. This prompted further research, which led to the discovery of venom (and venom genes) in species from groups which were not previously known to produce it, e.g. in Iguania (specifically Pogona barbata from the family Agamidae) and Varanidae (from Varanus varius). It is thought that this was the result of descent from a common venom-producing squamate ancestor; the hypothesis was described simply as the "venom clade" when first proposed to the scientific community.
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Numerous theropods are known from the Violante Farm fossil site, including Gualicho and Aoniraptor (which may or may not represent the same megaraptoran); the carcharodontosaurid Taurovenator; a coelurosaur (identified by Cerroni and colleagues as an unenlagiine) and another carcharodontosaurid that remain unnamed, but are likely distinct species; and another indeterminate megaraptoran. Other dinosaurs also include a titanosaurian sauropod and an ornithopod. Additional vertebrates from the Violante Farm site include the eilenodontid rhynchocephalian Patagosphenos; a crocodyliform, possibly belonging to the Neosuchia; a squamate; a chelid turtle; and a fish referred to Lepidotes.
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Dimetrodon grandis in an upright posture based on Dimetropus tracks, with scaleless skin and scutes on its underside No fossil evidence of Dimetrodon's skin has yet been found. Impressions of the skin of a related animal, Estemmenosuchus, indicate that it would have been smooth and well-provided with glands, however this form of skin may not have applied to Dimetrodon as its lineage is fairly distant. Dimetrodon also may have had large scutes on the underside of its tail and belly, as other synapsids did. Evidence from the varanopid Ascendonanus suggests that some early synapsids may have had squamate-like scales.
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Retrieved on 25 May 2009. Other scientists have stated that this allegation of venom glands "has had the effect of underestimating the variety of complex roles played by oral secretions in the biology of reptiles, produced a very narrow view of oral secretions and resulted in misinterpretation of reptilian evolution". According to these scientists "reptilian oral secretions contribute to many biological roles other than to quickly dispatch prey". These researchers concluded that, "Calling all in this clade venomous implies an overall potential danger that does not exist, misleads in the assessment of medical risks, and confuses the biological assessment of squamate biochemical systems".
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Recent research suggests that the evolutionary origin of venom may exist deep in the squamate phylogeny, with 60% of squamates placed in this hypothetical group called Toxicofera. Venom has been known in the clades Caenophidia, Anguimorpha, and Iguania, and has been shown to have evolved a single time along these lineages before the three groups diverged, because all lineages share nine common toxins. The fossil record shows the divergence between anguimorphs, iguanians, and advanced snakes dates back roughly 200 Mya to the Late Triassic/Early Jurassic. But the only good fossil evidence is from the Jurassic.
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Iguania is an infraorder of squamate reptiles that includes iguanas, chameleons, agamids, and New World lizards like anoles and phrynosomatids. Consisting of nearly 13,000 named species. T Using morphological features as a guide to evolutionary relationships, the Iguania are believed to form the sister group to the remainder of the Squamata. However, molecular information has placed Iguania well within the Squamata as sister taxa to the Anguimorpha and closely related to snakes.. The order has been under debate and revisions after being classified by Charles Lewis Camp in 1923 due to difficulties finding adequate synapomorphic morphological characteristics.
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Juvenile Iguana heart bisected through the ventricle, bisecting the left and right atrium For example, Iguana hearts, like the majority of the squamates hearts, are composed of three chambers with two aorta and one ventricle, cardiac involuntary muscles. The main structures of the heart are the sinus venosus, the pacemaker, the left atrium, the right atruim, the atrioventricular valve, the cavum venosum, cavum arteriosum, the cavum pulmonale, the muscular ridge, the ventricular ridge, pulmonary veins, and paired aortic arches. Some squamate species (e.g., pythons and monitor lizards) have three-chambered hearts that become functionally four-chambered hearts during contraction.
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Parthenogenesis is a natural form of reproduction in which growth and development of embryos occur without fertilization. Reproduction in squamate reptiles is ordinarily sexual, with males having a ZZ pair of sex determining chromosomes, and females a ZW pair. However, various species, including the Colombian Rainbow boa (Epicrates maurus), Agkistrodon contortrix (copperhead snake) and Agkistrodon piscivorus (cotton mouth snake) can also reproduce by facultative parthenogenesis—that is, they are capable of switching from a sexual mode of reproduction to an asexual mode—resulting in production of WW female progeny. The WW females are likely produced by terminal automixis.
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Characteristic dinosaur taxa include the ceratopsian Torosaurus utahensis, the titanosaurid sauropod Alamosaurus sanjuanensis, and the theropod Tyrannosaurus;Sampson, S.D., Loewen, M.A.(2005). Tyrannosaurus from the Upper Cretaceous (Maastrichtian) North Horn Formation of Utah: biogeographic and paleoecologic implications. Journal of Vertebrate Paleontology 25:2, 469-472 however, the most frequently occurring taxon in the Cretaceous strata of the North Horn Formation is the Polyglyphanodont squamate Polyglyphanodon. Fauna recorded from Paleocene strata within the formation appear to be far more diverse and over 70 different taxa have been identified, including frogs, numerous multituberculate, protoeutherians, periptychids, arctocyonids and phenacodontid mammals, crocodyliforms, choristoderes, trace fossils, and palynomorphs.
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One found Eichstaettisaurus as the sister group of a group containing Xantusiidae, Gekkonidae, Pygopodidae, and Amphisbaenia, with Ardeosaurus being close to Lacertidae and Teiioidea; the other united Eichstaettisaurus with Dalinghosaurus and the Xenosauridae in the Anguimorpha, with Ardeosaurus as the sister group of Iguania. After Evans, Wang, and Chun Li added Yabeinosaurus to the same analyses, one found Eichstaettisaurus, Ardeosaurus, Yabeinosaurus, and Parviraptor to form the sister group to the Scleroglossa, while the other recovered Ardeosaurus as a stem-squamate and Eichstaettisaurus, Hoyalacerta, Parviraptor, and Scandensia to form a group among Scleroglossa. A 2006 phylogenetic analysis by Jack Conrad and Mark Norell likewise found Eichstaettisaurus as close to the Scleroglossa.
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Purbicella is a genus of extinct squamate from the Early Cretaceous of southern England (Lulworth Formation). The type and only species is Purbicella ragei, which was described by Susan E. Evans and colleagues in 2012 for a mostly complete and articulated skull from the Berriasian Lulworth Formation of Dorset. The generic name described the region of Purbeck where the fossil was found, while the species name honours paleoherpetologist Jean-Claude Rage. Purbicella has the most complete skull of any British fossil lizard, British Geological Survey (BGS) specimen GSb581, which was originally collected prior to 1911, but then remained in BGS storage until it was rediscovered and described by Evans and colleagues.
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In general, avian predators are liable to steer clear of an alert great kiskadee, lest their hunting success be spoiled, and will hunt the great kiskadee itself - though it is as meaty as a fat thrush - only opportunistically. Zooming straight in mid-air Myiozetetes similis To mammalian and squamate predators that can sneak up to nesting or sleeping birds, it is more vulnerable however. Even omnivorous mammals as small as the common marmoset (Callithrix jacchus) will try to plunder great kiskadee nests - at least during the dry season when fruits are scarce - despite the birds' attempts to defend their offspring.de Lyra-Neves et al.
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The articulate snake vertebrate fossils were found and studied in terms of the trunks and vertebral morphological variation has allowed for the deduction of that UNC-CIP 1 can be identified in the Dinilysia genus. Additionally, the ongoing debate of whether snakes evolved on land or in the ocean; certain pieces of evidence point towards oceanic origin based on possible close relationships between snakes and mosasaurs. However, further evidence shows that terrestrial origin is quite possible because of the structure similarities between the inner ear of the Dinilysia and similar burrowing squamate snakes. Based on both the evolutionary and morphological features and similarities that D. Patagonica possess, evidence can be drawn from the features in order to predict the general location of origin.
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Many of their fossils are too fragmentary to be properly identified, but known Turonian taxa include but not limited to Enchodus, Pachyrhizodus, and the ichthyodectids Ichthyodectes and Xiphactinus. While consistent in fauna, the abundance of fish fossils from the Turonian- aged Fairport Chalk and Greenhorn Shale are significantly lower than such from older deposits such as an earlier deposit of the Greenhorn Shale below the Cenomanian-Turonian boundary that has yielded hundreds to thousands of fish fossils. However, this may simply be a case of collecting bias. Of the marine reptiles, plesiosaurs – including the polycotylid Trinacromerum, pliosaurs such as Brachauchenius and Megacephalosaurus itself, and indeterminate elasmosaurs – sea turtles, the crocodylomorph Terminonaris, the marine squamate Coniasaurus, and plioplatecarpine mosasaurs have been found within the Turonian Fairport Chalk and/or Greenhorn Shale.
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The surface of hemipenes is one of the most interesting and unique features, and is often covered in sharp spines and spicules that are organized in formations called rosettes. However, species with relatively smooth hemipene surfaces also exist. For example, the hemipenis of the Siamese spitting cobra (Naja siamensis) is smooth with blunt ends, while that of the many-spotted cat-eyed snake (Boiga multomaculata) is entirely covered in hooked spines and spicules. Yet despite this assortment of hemipenis designs, no association has been found between the design of hemipenes and the disposition or danger of the animal. Rather, it is believed that hemipenes found in the squamate world exhibit such diverse designs to facilitate mating compatibility amongst individuals of the same species, a theory that is referred to as the “lock-and-key mechanism”.
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Variations on the theme in biology are enormous, ranging from trophic eggs to resorption of partly developed embryos in hard times or when they are too numerous for the mother to bring to term, but among the most profoundly advantageous features of viviparity are various forms of physiological support and protection of the embryo, such as thermoregulation and osmoregulation. Since the developing offspring remains within the mother's body, she becomes, in essence, a walking incubator, protecting the developing young from excessive heat, cold, drought, or flood. This offers powerful options for dealing with excessive changes in climate or when migration events expose populations to unfavourable temperatures or humidities. In squamate reptiles in particular, there is a correlation between high altitudes or latitudes, colder climates and the frequency of viviparity.
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Other scientists such as Washington State University biologist Kenneth V. Kardong and toxicologists Scott A. Weinstein and Tamara L. Smith, have stated that the allegation of venom glands found in many of these animals "has had the effect of underestimating the variety of complex roles played by oral secretions in the biology of reptiles, produced a very narrow view of oral secretions and resulted in misinterpretation of reptilian evolution". According to these scientists "reptilian oral secretions contribute to many biological roles other than to quickly dispatch prey". These researchers concluded that, "Calling all in this clade venomous implies an overall potential danger that does not exist, misleads in the assessment of medical risks, and confuses the biological assessment of squamate biochemical systems". More recently, it has been suggested that many of the shared toxins that underlie the Toxicofera hypothesis are in fact not toxins at all.
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His PhD thesis constituted the first major cladistic analysis of Diapsida, as well as arguing for the monophyly of the dinosaurs. He followed this with an important paper on the origin of birds from theropods.Gauthier (1986) This was the first detailed cladistic analysis of the theropod dinosaurs, and initiated a revolution in dinosaur phylogenetics, in which cladistics replaced the Linnaean system in the classification and phylogenetic understanding of the dinosaurs. Gauthier's corpus contributed the foundational phylogenetic studies of Archosauria and Lepidosauria, two major amniote clades; and he was the primary author of the foundational and still widely cited phylogenetic study of AmniotaGauthier, Kluge & Rowe (1988); Gauthier (1994) as a whole. The phylogenetic character sets from his 1984 and 1986 works, the 1988 amniote paper, and the 1988 lepidosaur and squamate papers still form the core of essentially all gross-anatomy-based phylogenetic analyses of these groups, and as such are among the most highly cited papers in amniote morphology and paleobiology.
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