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Crown Group Lizards (Reptilia, Squamata) from the Middle Jurassic of the British Isles

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Susan E. Evans at University College London
Susan E. Evans
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Abstract

An assemblage of crown-group lizards is described from a middle Jurassic (Bathonian) horizon in the British Isles (Kirlington Quarry, Oxfordshire). These are amongst the earliest true lizards on record. At least five distinct genera (four of them new) are represented with three scincomorphs, an anguimorph (probably varanoid) and possible gekkotans. The assemblage resembles that of later Jurassic and early Cretaceous localities in being dominated by scincomorphs. These include one or more paramacellodids and a highly derived form which was apparently long-bodied with reduced limbs. The taxonomic diversity of the assemblage supports the view that the radiation of true squamates had begun by at least the early Jurassic, despite the absence of any reliable Triassic or early Jurassic record. Taxonomic and palaeogeographic implications are discussed.
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... The Gekkonomorpha, including †Eichstaettisaurus schroederi [40], lie more basally, in a polytomy with †Hongshanxi xeie [39] and †Scandensia ciervensis [38]. This grouping is at the base of the Squamata but is crownwards of the pan-squamates †Oculudentavis khaungraae [10], †Bellairsia [41] and †Huehuequetzpalli mixtecus [42]. ...
... When the same matrix is processed using the molecular constraints and methodology of [10], and removing †Vellbergia and †Scandensia as rogue taxa, †Cryptovaranoides is in a poorly resolved polytomy of unidentatan and gekkonomorph crown squamates (figure 7b). This includes †Hongshanxi xiei [39], †Ardeosaurus brevipes [37] and †Eichstaettisaurus schroederi [40] but all are crownward of †Oculudentavis khaungraae [10], †Bellairsia [41] and †Huehuequetzpalli mixtecus [42]. In these analyses based on morphology only and morphology with molecular constraints, †Cryptovaranoides is therefore certainly the oldest described crown squamate, as we have previously stated [1] and when better resolved is positioned as a unidentatan, crownwards of the Gekkonomorpha. ...
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Article
Full-text available
  • Nov 2024
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Article
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Article
Full-text available
  • Mar 2025
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Article
Full-text available
  • Nov 2024
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Article
Full-text available
  • Oct 2022
  • NATURE
Squamates (lizards and snakes) include more than 10,000 living species, descended from an ancestor that diverged more than 240 million years ago from that of their closest living relative, Sphenodon. However, a deficiency of fossil evidence1–7, combined with serious conflicts between molecular and morphological accounts of squamate phylogeny8–13 (but see ref. ¹⁴), has caused uncertainty about the origins and evolutionary assembly of squamate anatomy. Here we report the near-complete skeleton of a stem squamate, Bellairsia gracilis, from the Middle Jurassic epoch of Scotland, documented using high-resolution synchrotron phase-contrast tomography. Bellairsia shares numerous features of the crown group, including traits related to cranial kinesis (an important functional feature of many extant squamates) and those of the braincase and shoulder girdle. Alongside these derived traits, Bellairsia also retains inferred ancestral features including a pterygoid–vomer contact and the presence of both cervical and dorsal intercentra. Phylogenetic analyses return strong support for Bellairsia as a stem squamate, suggesting that several features that it shares with extant gekkotans are plesiomorphies, consistent with the molecular phylogenetic hypothesis that gekkotans are early-diverging squamates. We also provide confident support of stem squamate affinities for the enigmatic Oculudentavis. Our findings indicate that squamate-like functional features of the suspensorium, braincase and shoulder girdle preceded the origin of their palatal and vertebral traits and indicate the presence of advanced stem squamates as persistent components of terrestrial assemblages up to at least the middle of the Cretaceous period.
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Article
Full-text available
Lepidosaurs are an ecologically diverse and speciose group with more than 11 000 living species (squamates and the tuatara). Stem lepidosaurs are known from the Early Triassic onwards, but primarily from very incomplete specimens. Therefore, we have little information on their ecological diversity or the ecological context of deep evolutionary divergences of Lepidosauria. Marmoretta oxoniensis, from the Middle Jurassic of the UK, is one of the most completely known candidate stem lepidosaurs. Previous studies proposed that it may have been semi-aquatic, based primarily on its abundance in marginal marine rocks. We show here that Marmoretta was adapted for climbing, based on the post-cranial anatomy of a partial skeleton, visualized using micro-computed tomography (µCT)—in particular, the steep angles of thoracic zygapophyses, ungual phalanx morphology and elongate penultimate manual phalanges that curve distoventrally along their lengths. Linear discriminant analysis of the partial hand, using a training dataset of hand skeleton measurements and habitat use in extant squamates, returns strong evidence for clinging arboreality and Marmoretta clusters among scansorial/arboreal iguanians in manus shape space. Evidence of arboreality in Marmoretta provides the first information about habitat use in a probable stem lepidosaur and illuminates the vertical structure of ecological communities of the mid-Mesozoic.
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Fossil-informed biogeographic analysis suggests Eurasian regionalization in crown Squamata during the early Jurassic
Article
Full-text available
  • Apr 2024
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Article
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Full-text available
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  • Neues Jahrbuch Geol Palaontol Monatsh
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Article
  • Jan 1991
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Article
  • Jul 1980
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Article
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Article
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