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Bellairsia Gracilis
''Bellairsia'' is an extinct genus of stem-squamate known from a single species, ''Bellairsia gracilis'', from the Middle Jurassic (Bathonian) of England and Scotland. It is amongst the oldest squamates known. It was originally described in 1998 by Susan E. Evans from disarticulated individual bones, including the holotype dentary, collected from the Forest Marble Formation in Kirtlington Quarry, Oxfordshire, England. It was named in honor of British herpetologist and vertebrate anatomist Angus Bellairs. In 2022, a partial 70% complete skeleton was described from the equivalently aged Kilmaluag Formation of the Isle of Skye, Scotland. The partial skeleton had an estimated snout-vent length of around . While originally considered a member of Scincomorpha, the 2022 study recovered it to be a stem-group squamate, with the phylogeny recovering it as part of a weakly supported clade also containing ''Huehuecuetzpalli'' and '' Oculudentavis''. Classification Phylogeny A phyloge ...
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Middle Jurassic
The Middle Jurassic is the second Epoch (geology), epoch of the Jurassic Period (geology), Period. It lasted from about 174.1 to 161.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relatively rare, but geological formations containing land animal fossils include the Forest Marble Formation in England, the Kilmaluag Formation in Scotland,British Geological Survey. 2011Stratigraphic framework for the Middle Jurassic strata of Great Britain and the adjoining continental shelf: research report RR/11/06 British Geological Survey, Keyworth, Nottingham. the Calcaire de Caen of France, the Daohugou Beds in China, the Itat Formation in Russia, the Tiouraren Formation of Niger, and the Isalo III Formation of western Madagascar. Rocks of the Middle Jurassic were formerly (until about 1980s) in Europe called ''Dogger'' or ''Brown Jurassic''. Paleogeography During the Middle Jurassic Epoch, Pangaea began to separate into Laurasia and Gond ...
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Phylogeny
A phylogenetic tree or phylogeny is a graphical representation which shows the evolutionary history between a set of species or Taxon, taxa during a specific time.Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA. In other words, it is a branching diagram or a tree (graph theory), tree showing the evolutionary relationships among various biological species or other entities based upon similarities and differences in their physical or genetic characteristics. In evolutionary biology, all life on Earth is theoretically part of a single phylogenetic tree, indicating common ancestry. Phylogenetics is the study of phylogenetic trees. The main challenge is to find a phylogenetic tree representing optimal evolutionary ancestry between a set of species or taxa. computational phylogenetics, Computational phylogenetics (also phylogeny inference) focuses on the algorithms involved in finding optimal phylogenetic tree in the phylogenetic landscape. Phylogene ...
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Jurassic Reptiles
The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. The Jurassic constitutes the second and middle period of the Mesozoic, Mesozoic Era as well as the eighth period of the Phanerozoic, Phanerozoic Eon and is named after the Jura Mountains, where limestone strata from the period were first identified. The start of the Jurassic was marked by the major Triassic–Jurassic extinction event, associated with the eruption of the Central Atlantic magmatic province, Central Atlantic Magmatic Province (CAMP). The beginning of the Toarcian Age started around 183 million years ago and is marked by the Toarcian Oceanic Anoxic Event, a global episode of Anoxic event, oceanic anoxia, ocean acidification, and elevated global temperatures associated with extinctions, likely caused by the eruption of the Kar ...
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Squamata
Squamata (, Latin ''squamatus'', 'scaly, having scales') is the largest Order (biology), order of reptiles; most members of which are commonly known as Lizard, lizards, with the group also including Snake, snakes. With over 11,991 species, it is also the second-largest order of Neontology, extant (living) vertebrates, after the Perciformes, perciform fish. Squamates are distinguished by their skins, which bear horny scale (zoology), scales or shields, and must periodically engage in molting. They also possess movable quadrate bones, making possible movement of the Maxilla, upper jaw relative to the neurocranium. This is particularly visible in snakes, which are able to open their mouths very widely to accommodate comparatively large prey. Squamates are the most variably sized living reptiles, ranging from the Sphaerodactylus ariasae, dwarf gecko (''Sphaerodactylus ariasae'') to the reticulated python (''Malayopython reticulatus''). The now-Extinction, extinct mosasaurs reached ...
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Stem Group
In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. It is thus a way of defining a clade, a group consisting of a species and all its extant or extinct descendants. For example, Neornithes (birds) can be defined as a crown group, which includes the most recent common ancestor of all modern birds, and all of its extant or extinct descendants. The concept was developed by Willi Hennig, the formulator of phylogenetic systematics, as a way of classifying living organisms relative to their extinct relatives in his "Die Stammesgeschichte der Insekten", and the "crown" and "stem" group terminology was coined by R. P. S. Jefferies in 1979. Though formulated in the 1970s, the term was not commonly used until its reintroduction in 2000 by Graham Budd and Sören Jensen. Contents of the crown ...
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Rhynchocephalia
Rhynchocephalia (; ) is an order of lizard-like reptiles that includes only one living species, the tuatara (''Sphenodon punctatus'') of New Zealand. Despite its current lack of diversity, during the Mesozoic rhynchocephalians were a speciose group with high morphological and ecological diversity. The oldest record of the group is dated to the Middle Triassic around 238 to 240 million years ago, and they had achieved global distribution by the Early Jurassic. Most rhynchocephalians belong to the group Sphenodontia ('wedge-teeth'). Their closest living relatives are lizards and snakes in the order Squamata, with the two orders being grouped together in the superorder Lepidosauria. Rhynchocephalians are distinguished from squamates by a number of traits, including the retention of rib-like gastralia bones in the belly, as well as most rhynchocephalians having acrodont teeth that are fused to the crests of the jaws (the latter also found among a small number of modern lizard grou ...
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Sophineta
''Sophineta'' is an extinct genus of basal (phylogenetics), basal lepidosauromorph reptile known from the Early Triassic (late Olenekian age) of Lesser Poland Voivodeship, Małopolska Province, southern Poland. It contains a single species, ''Sophineta cracoviensis''. Discovery ''Sophineta'' was first described and named by Susan E. Evans and Magdalena Borsuk−Białynicka in 2009 in paleontology, 2009, and the type species is ''Sophineta cracoviensis''. It is known from holotype ZPAL RV/175, a nearly complete right maxilla. Many isolated or associated skull and postcranial fragments are referred to the species, representing frontals, parietals, prefrontal, postfrontals, postorbitals, jugals, squamosals, pterygoids, quadrates, maxillae, premaxilla, dentaries, vertebrae and ilia. ''Sophineta'' fossils were discovered ''in situ'' and collected in 1982 by a team (Paszkowski and Wieczorek) from the Institute of Geological Sciences of Jagiellonian University in Kraków. They were ...
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Lepidosauria
The Lepidosauria (, from Greek meaning ''scaled lizards'') is a Order (biology), superorder or Class (biology), subclass of reptiles, containing the orders Squamata and Rhynchocephalia. Squamata also includes Lizard, lizards and Snake, snakes. Squamata contains over 9,000 species, making it by far the most species-rich and diverse order of non-avian reptiles in the present day. Rhynchocephalia was a formerly widespread and diverse group of reptiles in the Mesozoic era, Mesozoic Era. However, it is represented by only one living species: the tuatara (''Sphenodon punctatus),'' a superficially lizard-like reptile native to New Zealand. Lepidosauria is a monophyletic group (i.e. a clade), containing all descendants of the Most recent common ancestor, last common ancestor of squamates and rhynchocephalians. Lepidosaurs can be distinguished from other reptiles via several traits, such as large Keratin, keratinous Scale (anatomy), scales which may overlap one another. Purely in the conte ...
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Crown Group
In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. It is thus a way of defining a clade, a group consisting of a species and all its extant or extinct descendants. For example, Neornithes (birds) can be defined as a crown group, which includes the most recent common ancestor of all modern birds, and all of its extant or extinct descendants. The concept was developed by Willi Hennig, the formulator of phylogenetic systematics, as a way of classifying living organisms relative to their extinct relatives in his "Die Stammesgeschichte der Insekten", and the "crown" and "stem" group terminology was coined by R. P. S. Jefferies in 1979. Though formulated in the 1970s, the term was not commonly used until its reintroduction in 2000 by Graham Budd and Sören Jensen. Contents of the crow ...
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Marmoretta
''Marmoretta'' is an extinct genus of small lepidosauromorph reptile known from the Middle-Late Jurassic of Britain and Portugal. The genus contains two species, ''M. oxoniensis'' and ''M. drescherae''. Discovery and naming ''Marmoretta'' is known from holotype BMNH R.12020, the anterior region of a right maxilla. All specimens are housed in the Natural History Museum. They were collected from the Mammal Bed of the Forest Marble Formation, at Kirtlington Quarry, Oxfordshire, which has yielded a rich assemblage of small vertebrates including mammals, frogs, salamanders and other small reptiles. ''Marmoretta'' is very common in that locality but its remains are fragmentary. In 1994, additional specimens of ''Marmoretta'' were described from the Kilmaluag Formation (previously known as the Ostracod Limestones) of the Great Estuarine Group in Skye. This material of ''Marmoretta'' includes the first associated skull and postcranial remains. They confirm the original descrip ...
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Fraxinisaura
''Fraxinisaura'' is an extinct genus of basal lepidosauromorph reptile known from the Middle Triassic of Germany. The only known species is ''Fraxinisaura rozynekae''. It possessed an elongated snout, unique features of the teeth, and an ilium (upper hip bone) which was intermediate in orientation between sphenodontians (the branch of lepidosaurs including the tuatara) and squamates (the branch including lizards). Based on characteristics of the maxilla, it is considered a close relative of ''Marmoretta'' from the Middle Jurassic of the United Kingdom, resolving a ghost lineage between that genus and other Triassic basal lepidosauromorphs. Discovery Remains of ''Fraxinisaura'' have only been recovered from the Schumann limestone quarry near Vellberg, Germany. Stratigraphically, it hails from the Untere Graue Mergel Layer of the Erfurt Formation, also known as the Lower Keuper. The Lower Keuper preserved a lakeshore environment of Ladinian (late Middle Triassic) age. The holo ...
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Megachirella
''Megachirella'' is an Extinction, extinct genus of lepidosaur, possibly a Crown group#Stem groups, stem-Squamata, squamate that lived about 240 million years ago during the Middle Triassic and contains only one known species, ''Megachirella wachtleri''. It is known from a partial skeleton discovered in the Dolomites of Northern Italy and was described in 2003. Description ''Megachirella'' is known exclusively from a partial skeleton, preserved in anatomical connection. The find includes an almost complete skull, the front half of the body and part of the front legs. The skull, although devoid of the front part of the snout, is rather robust and large; the neck is moderately elongated and the front legs are large and strong. The dimensions do not exceed in length, and the appearance is similar to that of a strong-legged lizard. Classification ''Megachirella'' was discovered in the Dont Formation of the area of Braies, in South Tyrol, and described in 2003. It was classified as a ...
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