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  • The Royal Society  (5)
  • Cambridge University Press  (2)
  • 1
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    Rediagnosis and redescription of Mosasaurus hoffmannii (Squamata: Mosasauridae) and an assessment of species assigned to the genus Mosasaurus (2016)
    Cambridge University Press
    Details
    Publication Date: 2016-05-13
    Description: The large Late Cretaceous marine reptile Mosasaurus has remained poorly defined, in part owing to the unorthodox (by today's nomenclatural standards) manner in which the name was erected. The lack of a diagnosis accompanying the first use of either the genus or species names allowed the genus to become a catchall taxon, and subsequent diagnoses did little to refine the concept of Mosasaurus. We herein present emended diagnoses for both Mosasaurus and the type species M. hoffmannii, based solely on personal examination of the holotype, and a description of the type species based on personal examination of many specimens. Mosasaurus exhibits a premaxilla with a short, conical edentulous rostrum, a maxilla with little to no dorsal excavation for the external naris, posteromedial processes of the frontal that deeply invade the parietal, a quadrate taller than long with a short suprastapedial process and the stapedial pit dorsal to the mid-height of the shaft, an angular that is laterally visible for only a short length of the post-dentary unit, a very tall surangular, a humerus with the postglenoid process robust and offset and a distal width greater than the length, and a pubis with an anteriorly projecting tubercle. M. hoffmannii is distinguished from other species assignable to the genus by the anteroventral corner formed on the tympanic rim of the quadrate, the asymmetric carinae of the anterior marginal teeth dividing the tooth circumference into short labial and long lingual segments, and the proximal and distal expansion of the femur.
    Print ISSN: 0016-7568
    Electronic ISSN: 1469-5081
    Topics: Geosciences
    Published by Cambridge University Press
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  • 2
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    The first ophthalmosaurid ichthyosaur from the Upper Jurassic of the Umbrian–Marchean Apennines (Marche, Central Italy) (2016)
    Cambridge University Press
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    Publication Date: 2016-07-11
    Description: The first ophthalmosaurid ichthyosaur from the Upper Jurassic deposits of the Central–Northern Apennines (Marche, Italy) is here described for the first time. The specimen is relatively complete and is referred to Gengasaurus nicosiai gen. et sp. nov. based on a unique combination of characters, including a peculiar condition of the preaxial accessory facet on the humerus. The faunal association of the ichthyosaur-bearing level indicates a late Kimmeridgian – earliest Tithonian age, and its finding contributes significantly to our knowledge of the diversity of Late Jurassic ichthyosaurs from the Western Tethys. Two shark teeth assigned to the order Hexanchiformes were also recovered in association with the ichthyosaur specimen, suggesting that scavenging of the carcass might have occurred. Gengasaurus can be referred to Ophthalmosauridae based on the reduced extracondylar area of the basioccipital, and the presence of a preaxial digit. It differs from Ophthalmosaurus spp. in several respects, including the shape of the posterior basisphenoid, the shape of the supraoccipital, the anteriorly deflected preaxial facet of the humerus, and a proximodistally shortened ulna. The new taxon actually shares diagnostic characters with both members of the two main lineages recovered in previous phylogenetic analyses, more nested within Ophthalmosauridae. The affinities of Gengasaurus to genera from both the northern and southern hemispheres also suggest that connectivity between pelagic habitats was high during the early Late Jurassic, allowing dispersal of some forms, followed by local, endemic divergence.
    Print ISSN: 0016-7568
    Electronic ISSN: 1469-5081
    Topics: Geosciences
    Published by Cambridge University Press
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  • 3
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    Cranial ontogeny of Thamnophis radix (Serpentes: Colubroidea) with a re-evaluation of current paradigms of snake skull evolution (2019)
    The Royal Society
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    Publication Date: 2019-08-01
    Description: Accurate knowledge of skeletal ontogeny in extant organisms is crucial in understanding important morpho-functional systems and in enabling inferences of the ontogenetic stage of fossil specimens. However, detailed knowledge of skeletal ontogeny is lacking for most squamates, including snakes. Very few studies have discussed postnatal development in snakes, with none incorporating data from all three major ontogenetic stages—embryonic, juvenile and adult. Here, we provide the first analysis encompassing these three ontogenetic stages for any squamate, using the first complete micro-computed tomography (micro-CT)-based segmentations of any non-adult snake, based on fresh specimens of Thamnophis radix . The most significant ontogenetic changes involve the feeding apparatus, with major elongation of the tooth-bearing elements and jaw suspensorium causing a posterior shift in the jaw articulation. This shift enables macrostomy (large-gaped feeding in snakes) and occurs in T. radix via a different developmental trajectory than in most other macrostomatans, indicating that the evolution of macrostomy is more complex than previously thought. The braincase of T. radix is also evolutionarily unique among derived snakes in lacking a crista circumfenestralis, a phenomenon considered herein to represent paedomorphic retention of the embryonic condition. We thus present numerous important challenges to current paradigms regarding snake cranial evolution.
    Electronic ISSN: 2054-5703
    Topics: Natural Sciences in General
    Published by The Royal Society
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  • 4
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    Palaeoecological inferences for the fossil Australian snakes Yurlunggur and Wonambi (Serpentes, Madtsoiidae) (2018)
    The Royal Society
    Details
    Publication Date: 2018-03-01
    Description: Madtsoiids are among the most basal snakes, with a fossil record dating back to the Upper Cretaceous (Cenomanian). Most representatives went extinct by the end of the Eocene, but some survived in Australia until the Late Cenozoic. Yurlunggur and Wonambi are two of these late forms, and also the best-known madtsoiids to date. A better understanding of the anatomy and palaeoecology of these taxa may shed light on the evolution and extinction of this poorly known group of snakes and on early snake evolution in general. A digital endocast of the inner ear of Yurlunggur was compared to those of 81 species of snakes and lizards with known ecological preferences using three-dimensional geometric morphometrics. The inner ear of Yurlunggur most closely resembles both that of certain semiaquatic snakes and that of some semifossorial snakes. Other cranial and postcranial features of this snake support the semifossorial interpretation. While the digital endocast of the inner ear of Wonambi is too incomplete to be included in a geometric morphometrics study, its preserved morphology is very different from that of Yurlunggur and suggests a more generalist ecology. Osteology, palaeoclimatic data and the palaeobiogeographic distribution of these two snakes are all consistent with these inferred ecological differences.
    Electronic ISSN: 2054-5703
    Topics: Natural Sciences in General
    Published by The Royal Society
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  • 5
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    A new fossil marine lizard with soft tissues from the Late Cretaceous of southern Italy (2018)
    The Royal Society
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    Publication Date: 2018-06-01
    Description: A new marine lizard showing exceptional soft tissue preservation was found in Late Cretaceous deposits of the Apulian Platform (Puglia, Italy). Primitivus manduriensis gen. et sp. nov. is not only the first evidence of the presence of dolichosaurs in a southern Italian Carbonate Platform, filling a palaeogeographic gap in the Mediterranean Tethys, but also extends the range of this group to the upper Campanian–lower Maastrichtian. Our parsimony analysis recovers a monophyletic non-ophidian pythonomorph clade, including Tetrapodophis amplectus at the stem of Mosasauroidea + Dolichosauridae, which together represent the sister group of Ophidia (modern and fossil snakes). Based on Bayesian inference instead, Pythonomorpha is monophyletic, with Ophidia representing the more deeply nested clade, and the new taxon as basal to all other pythonomorphs. Primitivus displays a fairly conservative morphology in terms of both axial elongation of the trunk and limb reduction, and the coexistence of aquatic adaptations with features hinting at the retention of the ability to move on land suggests a semi-aquatic lifestyle. The exceptional preservation of mineralized muscles, portions of the integument, cartilages and gut content provides unique sources of information about this extinct group of lizards. The new specimen may represent local persistence of a relict dolichosaur population until almost the end of the Cretaceous in the Mediterranean Tethys, and demonstrates the incompleteness of our knowledge of dolichosaur temporal and spatial distributions.
    Electronic ISSN: 2054-5703
    Topics: Natural Sciences in General
    Published by The Royal Society
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  • 6
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    The morphology of the inner ear of squamate reptiles and its bearing on the origin of snakes (2017)
    The Royal Society
    Details
    Publication Date: 2017-08-01
    Description: The inner ear morphology of 80 snake and lizard species, representative of a range of ecologies, is here analysed and compared to that of the fossil stem snake Dinilysia patagonica , using three-dimensional geometric morphometrics. Inner ear morphology is linked to phylogeny (we find here a strong phylogenetic signal in the data that can complicate ecological correlations), but also correlated with ecology, with Dinilysia resembling certain semi-fossorial forms ( Xenopeltis and Cylindrophis ), consistent with previous reports. We here also find striking resemblances between Dinilysia and some semi-aquatic snakes, such as Myron (Caenophidia, Homalopsidae). Therefore, the inner ear morphology of Dinilysia is consistent with semi-aquatic as well as semi-fossorial habits: the most similar forms are either semi-fossorial burrowers with a strong affinity to water ( Xenopeltis and Cylindrophis ) or amphibious, intertidal forms which shelter in burrows ( Myron). Notably, Dinilysia does not cluster as closely with snakes with exclusively terrestrial or obligate burrowing habits (e.g. scolecophidians and uropeltids). Moreover, despite the above similarities, Dinilysia also occupies a totally unique morphospace, raising issues with linking it with any particular ecological category.
    Electronic ISSN: 2054-5703
    Topics: Natural Sciences in General
    Published by The Royal Society
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  • 7
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    Skin of the Cretaceous mosasaur Plotosaurus : implications for aquatic adaptations in giant marine reptiles (2009)
    The Royal Society
    Details
    Publication Date: 2009-04-08
    Description: The physical nature of water and the environment it presents to an organism have long been recognized as important constraints on aquatic adaptation and evolution. Little is known about the dermal cover of mosasauroids (a group of secondarily aquatic reptiles that occupied a wide array of predatory niches in the Cretaceous marine ecosystems 92–65 Myr ago), a lack of information that has hindered inferences about the nature and level of their aquatic adaptations. A newly discovered Plotosaurus skeleton with integument preserved in three dimensions represents not only the first documented squamation in a mosasaurine mosasaur but also the first record of skin in an advanced member of the Mosasauroidea. The dermal cover comprises keeled and possibly osteoderm-reinforced scales that presumably contributed to an anterior–posterior channelling of the water flow and a reduction of microturbulent burst activities along the surface of the skin. Thus, hydrodynamic requirements of life in the water might have influenced the evolution of multiple-keeled body scales in advanced mosasauroids.
    Print ISSN: 1744-9561
    Electronic ISSN: 1744-957X
    Topics: Biology
    Published by The Royal Society
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