Susan Evans
University College London, Cell and Developmental Biology, Faculty Member
- Paleontology, Herpetology, Vertebrate Evolution, Vertebrate Palaeontology, Comparative Anatomy, Skeletal Biology, and 12 moreEvolutionary Developmental Biology, Phylogeny/phylogenetics, Systematics, Macroevolution, Embryology, Evolutionary Biomechanics, Human Anatomy (Biology), Evolutionary Anatomy, Herpetofauna, Morphogenesis, Variation (Inter and Intraspeciific), and Biologyedit
Research Interests: Orthodontics, Biomechanics, Medicine, Anatomy, Skull, and 5 moreMastication, Incisor, Rostrum, Biting, and Molar
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Lepidosauria is a speciose clade with a long evolutionary history, but there have been few attempts to explore its taxon richness through time. Here we estimate patterns of terrestrial lepidosaur genus diversity for the... more
Lepidosauria is a speciose clade with a long evolutionary history, but there have been few attempts to explore its taxon richness through time. Here we estimate patterns of terrestrial lepidosaur genus diversity for the Triassic–Palaeogene (252–23 Ma), and compare observed and sampling-corrected richness curves generated using Shareholder Quorum Subsampling and classical rarefaction. Generalized least-squares regression (GLS) is used to investigate the relationships between richness, sampling and environmental proxies. We found low levels of richness from the Triassic until the Late Cretaceous (except in the Kimmeridgian–Tithonian of Europe). High richness is recovered for the Late Cretaceous of North America, which declined across the K–Pg boundary but remained relatively high throughout the Palaeogene. Richness decreased following the Eocene–Oligocene Grande Coupure in North America and Europe, but remained high in North America and very high in Europe compared to the Late Cretaceous; elsewhere data are lacking. GLS analyses indicate that sampling biases (particularly, the number of fossil collections per interval) are the best explanation for long-term face-value genus richness trends. The lepidosaur fossil record presents many problems when attempting to reconstruct past diversity, with geographical sampling biases being of particular concern, especially in the Southern Hemisphere.
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The role of soft tissues in skull biomechanics remains poorly understood. Not least, the chondrocranium, the portion of the braincase which persists as cartilage with varying degrees of mineralization. It also remains commonplace to... more
The role of soft tissues in skull biomechanics remains poorly understood. Not least, the chondrocranium, the portion of the braincase which persists as cartilage with varying degrees of mineralization. It also remains commonplace to overlook the biomechanical role of sutures despite evidence that they alter strain distribution. Here, we examine the role of both the sutures and the chondrocranium in the South American tegu lizard <i>Salvator merianae</i>. We use multi-body dynamics analysis (MDA) to provide realistic loading conditions for anterior and posterior unilateral biting and a detailed finite-element model to examine strain magnitude and distribution. We find that strains within the chondrocranium are greatest during anterior biting and are primarily tensile; also that strain within the cranium is not greatly reduced by the presence of the chondrocranium unless it is given the same material properties as bone. This result contradicts previous suggestions that the anterior portion (the nasal septum) acts as a supporting structure. Inclusion of sutures to the cranium model not only increases overall strain magnitudes but also leads to a more complex distribution of tension and compression rather than that of a beam under sagittal bending.
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The Lower Cretaceous beds of the Wessex Formation of the Isle of Wight are renowned worldwide for their dinosaur fauna, but traces of associated small tetrapods have been harder to find. Here we report the first definitive records, albeit... more
The Lower Cretaceous beds of the Wessex Formation of the Isle of Wight are renowned worldwide for their dinosaur fauna, but traces of associated small tetrapods have been harder to find. Here we report the first definitive records, albeit fragmentary, of lizards and terrestrial amphibians (frogs, albanerpetontids) recovered by screen-washing sediments from the type locality of the theropod dinosaur Neovenator.
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Cranial morphology in lepidosaurs is highly disparate and characterised by the frequent loss or reduction of bony elements. In varanids and geckos, the loss of the postorbital bar is associated with changes in skull shape, but the... more
Cranial morphology in lepidosaurs is highly disparate and characterised by the frequent loss or reduction of bony elements. In varanids and geckos, the loss of the postorbital bar is associated with changes in skull shape, but the mechanical principles underlying this variation remain poorly understood. Here, we sought to determine how the overall cranial architecture and the presence of the postorbital bar relate to the loading and deformation of the cranial bones during biting in lepidosaurs. Using computer-based simulation techniques, we compared cranial biomechanics in the varanid Varanus niloticus and the teiid Salvator merianae, two large, active foragers. The overall strain magnitude and distribution across the cranium were similar in the two species, despite lower strain gradients in V. niloticus. In S. merianae, the postorbital bar is important for resistance of the cranium to feeding loads. The postorbital ligament, which in varanids partially replaces the postorbital bar,...
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Osteoderms (OD) are mineralised dermal structures consisting mainly of calcium phosphate and collagen. The sheer diversity of OD morphologies and their distribution within the skin of lizards makes these reptiles an ideal group in which... more
Osteoderms (OD) are mineralised dermal structures consisting mainly of calcium phosphate and collagen. The sheer diversity of OD morphologies and their distribution within the skin of lizards makes these reptiles an ideal group in which to study ODs. Nonetheless, our understanding of the structure, development, and function of lizard ODs remains limited. The specific aims of this study were: (1) to carry out a detailed morphological characterisation of ODs in three lizard species; (2) to design and manufacture biomimetic sheets of ODs corresponding to the OD arrangement in each species; and (3) to evaluate the impact resistance of the manufactured biomimetic sheets under a drop weight test. Skin samples of the anguimorphs H. suspectum and O. ventralis, and the skink C. zebrata were obtained from frozen lab specimens. Following a series of imaging and image characterisations, 3D biomimetic models of the ODs were developed. 3D models were then printed using additive manufacturing tech...
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Oculudentavis khaungraae was described based on a tiny skull trapped in amber. The slender tapering rostrum with retracted osseous nares, large eyes, and short vaulted braincase led to its identification as the smallest avian dinosaur on... more
Oculudentavis khaungraae was described based on a tiny skull trapped in amber. The slender tapering rostrum with retracted osseous nares, large eyes, and short vaulted braincase led to its identification as the smallest avian dinosaur on record, comparable to the smallest living hummingbirds. Despite its bird-like appearance, Oculudentavis showed several features inconsistent with its original phylogenetic placement. Here we describe a more complete, specimen that demonstrates Oculudentavis is actually a bizarre lizard of uncertain position. The new interpretation and phylogenetic placement highlights a rare case of convergent evolution rarely seen among reptiles. Our results re-affirm the importance of Myanmar amber in yielding unusual taxa from a forest ecosystem rarely represented in the fossil record.
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The braincase of Youngina capensis is described and illustrated. The investigation highlights the generally primitive bature of the younginid braincase. In some characters, however, including the size of the stapes and paroccipital... more
The braincase of Youngina capensis is described and illustrated. The investigation highlights the generally primitive bature of the younginid braincase. In some characters, however, including the size of the stapes and paroccipital processes, and the structure of the exoccipital, Youngina appears to be more derived than members of the Tangasauridae (sensu Currie 1982)
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Research Interests: Herpetology, Geology, Paleontology, Crustacea, Biology, and 5 moreCretaceous, Squamata, Lizard, Crayfish, and Integumentary System
In vivo bone strain data provide direct evidence of strain patterns in the cranium during biting. Compared to mammals, in vivo bone strains in lizard skulls are poorly documented. This paper presents strain data from the skulls of Anolis... more
In vivo bone strain data provide direct evidence of strain patterns in the cranium during biting. Compared to mammals, in vivo bone strains in lizard skulls are poorly documented. This paper presents strain data from the skulls of Anolis equestris, Gekko gecko, Iguana iguana and Salvator merianae during transducer biting. Analysis of variance was used to investigate effects of bite force, bite point, diet, cranial morphology and cranial kinesis on strain magnitudes. Within individuals the most consistent determinants of variance in bone strain magnitudes are gage location and bite point, with the importance of bite force varying between individuals. Inter-site variance in strain magnitudes—strain gradient—is present in all individuals, and varies with bite point. Between individuals within species, variance in strain magnitude is driven primarily by variation in bite force, not gage location or bite point, suggesting that inter-individual variation in patterns of strain magnitude is...
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The Mesozoic lizard fauna of Gondwana is virtually unknown. We report here on a lizard assemblage from the Upper Member of the Kota Formation of peninsular India, usually considered to be of Early–Middle Jurassic age. The dominant form,... more
The Mesozoic lizard fauna of Gondwana is virtually unknown. We report here on a lizard assemblage from the Upper Member of the Kota Formation of peninsular India, usually considered to be of Early–Middle Jurassic age. The dominant form, Bharatagama rebbanensis, gen. et sp. nov., has a predominantly acrodont dentition. Comparison with living and extinct taxa suggests that this new genus is a primitive acrodont iguanian
distinct from the Cretaceous priscagamids. It predates known records of iguanian lizards by some 80 Ma, and provides evidence that iguanians had begun to diversify before the break-up of Pangea. A second fully pleurodont taxon is known from the same deposit. It is tentatively attributed to the Squamata but is too fragmentary for further determination.
distinct from the Cretaceous priscagamids. It predates known records of iguanian lizards by some 80 Ma, and provides evidence that iguanians had begun to diversify before the break-up of Pangea. A second fully pleurodont taxon is known from the same deposit. It is tentatively attributed to the Squamata but is too fragmentary for further determination.
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The Lower Cretaceous (Albian age) locality of Pietraroia, near Benevento in southern Italy, has yielded a diverse assemblage of fossil vertebrates, including at least one genus of rhynchocephalian (Derasmosaurus) and two named lizards... more
The Lower Cretaceous (Albian age) locality of Pietraroia, near Benevento in southern Italy, has yielded a diverse assemblage of fossil vertebrates, including at least one genus of rhynchocephalian (Derasmosaurus) and two named lizards
(Costasaurus and Chometokadmon), as well as the exquisitely preserved small dinosaur, Scipionyx. Here we describe material pertaining to a new species of the fossil lizard genus Eichstaettisaurus (E. gouldi sp. nov.). Eichstaettisaurus was
first recorded from the Upper Jurassic (Tithonian age) Solnhofen Limestones of Germany, and more recently from the basal Cretaceous (Berriasian) of Montsec, Spain. The new Italian specimen provides a significant extension to the tempo−
ral range of Eichstaettisaurus while supporting the hypothesis that the Pietraroia assemblage may represent a relictual island fauna. The postcranial morphology of the new eichstaettisaur suggests it was predominantly ground−living. Further
skull material of E. gouldi sp. nov. was identified within the abdominal cavity of a second new lepidosaurian skeleton from the same locality. This second partial skeleton is almost certainly rhynchocephalian, based primarily on foot and
pelvic structure, but it is not Derasmosaurus and cannot be accommodated within any known genus due to the unusual morphology of the tail vertebrae.
(Costasaurus and Chometokadmon), as well as the exquisitely preserved small dinosaur, Scipionyx. Here we describe material pertaining to a new species of the fossil lizard genus Eichstaettisaurus (E. gouldi sp. nov.). Eichstaettisaurus was
first recorded from the Upper Jurassic (Tithonian age) Solnhofen Limestones of Germany, and more recently from the basal Cretaceous (Berriasian) of Montsec, Spain. The new Italian specimen provides a significant extension to the tempo−
ral range of Eichstaettisaurus while supporting the hypothesis that the Pietraroia assemblage may represent a relictual island fauna. The postcranial morphology of the new eichstaettisaur suggests it was predominantly ground−living. Further
skull material of E. gouldi sp. nov. was identified within the abdominal cavity of a second new lepidosaurian skeleton from the same locality. This second partial skeleton is almost certainly rhynchocephalian, based primarily on foot and
pelvic structure, but it is not Derasmosaurus and cannot be accommodated within any known genus due to the unusual morphology of the tail vertebrae.
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Research Interests: Engineering, Computer Science, Imaging, Anatomy, Sphenodon, and 7 moreTuatara, MDA, Jaw Muscles, Head, Neck, D, and Schematic
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Research Interests: Evolutionary Biology, Geology, Paleontology, Ecology, China, and 5 moreCretaceous, Mesozoic, Aptian, Genus, and Taxon
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We here report on a well-preserved juvenile lizard specimen in Albian amber (ca. 110 mya) from the Hkamti site in Myanmar. This new taxon, Retinosaurus hkamtiensis gen. et sp. nov., is represented by an articulated skull and the anterior... more
We here report on a well-preserved juvenile lizard specimen in Albian amber (ca. 110 mya) from the Hkamti site in Myanmar. This new taxon, Retinosaurus hkamtiensis gen. et sp. nov., is represented by an articulated skull and the anterior portion of the trunk, including the pectoral girdle and forelimbs. The ocular skeleton (scleral ossicles) and eyelid are also visible, and the specimen exhibits pristine detail of the integument (of both head and body). In a combined molecular and morphological analysis, Retinosaurus was consistently recovered as a scincoid lizard (i.e. Scinciformata), as the sister taxon to the Mexican Cretaceous genus Tepexisaurus + Xantusiidae. However, the phylogenetic position of Retinosaurus should be interpreted with caution. We cannot not rule out the possibility that Retinosaurus represents a separate lineage of uncertain phylogenetic position, as it is the case for many Jurassic and Cretaceous taxa. Nonetheless, this fossil offers a rare opportunity to gli...
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The falx cerebri and the tentorium cerebelli are two projections of the dura mater in the cranial cavity which ossify to varying degrees in some mammalian species. The idea that the ossification of these structures may be necessary to... more
The falx cerebri and the tentorium cerebelli are two projections of the dura mater in the cranial cavity which ossify to varying degrees in some mammalian species. The idea that the ossification of these structures may be necessary to support the loads arising during feeding has been proposed and dismissed in the past, but never tested quantitatively. To address this, a biomechanical model of a domestic cat ( Felis silvestris catus ) skull was created and the material properties of the falx and tentorium were varied for a series of loading regimes incorporating the main masticatory and neck muscles during biting. Under these loading conditions, ossification of the falx cerebri does not have a significant impact on the stress in the cranial bones. In the case of the tentorium, however, a localized increase in stress was observed in the parietal and temporal bones, including the tympanic bulla, when a non-ossified tentorium was modelled. These effects were consistent across the differ...
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Research Interests: Evolutionary Biology, Geology, Biology, Ecology, Cretaceous, and 3 moreSquamata, Iguanidae, and Lizard
Research Interests: Engineering, Mechanical Engineering, Biophysics, Biomedical Engineering, Rehabilitation, and 15 moreBiomechanics, Motion control, Medicine, Bite force, Anatomy, Computer Model, Lizards, Animals, Multibody Dynamics, Bites and Stings, Computer Modelling, Muscle Force, Ligaments, Orthopedics and Sports Medicine, and Biting
The skull is composed of many bones that come together at sutures. These sutures are important sites of growth, and as growth ceases some become fused while others remain patent. Their mechanical behaviour and how they interact with... more
The skull is composed of many bones that come together at sutures. These sutures are important sites of growth, and as growth ceases some become fused while others remain patent. Their mechanical behaviour and how they interact with changing form and loadings to ensure balanced craniofacial development is still poorly understood. Early suture fusion often leads to disfiguring syndromes, thus is it imperative that we understand the function of sutures more clearly. By applying advanced engineering modelling techniques, we reveal for the first time that patent sutures generate a more widely distributed, high level of strain throughout the reptile skull. Without patent sutures, large regions of the skull are only subjected to infrequent low-level strains that could weaken the bone and result in abnormal development. Sutures are therefore not only sites of bone growth, but could also be essential for the modulation of strains necessary for normal growth and development in reptiles.
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<p>A, <i>Anoualerpeton priscum</i> (Middle Jurassic, UK); B, <i>An</i>. <i>unicum</i> (Early Cretaceous, Morocco); C, <i>Shirerpeton isajii</i> (Early Cretaceous, Japan); D,... more
<p>A, <i>Anoualerpeton priscum</i> (Middle Jurassic, UK); B, <i>An</i>. <i>unicum</i> (Early Cretaceous, Morocco); C, <i>Shirerpeton isajii</i> (Early Cretaceous, Japan); D, <i>Wesserpeton evansae</i> (Early Cretaceous, UK); E, <i>Albanerpeton arthridion</i> (Early Cretaceous, North America); F, <i>Albanerpeton gracile</i> (Late Cretaceous, North America); G, <i>Albanerpeton nexuosum</i> (Late Cretaceous, North America); H, <i>Albanerpeton galaktion</i> (Late Cretaceous, North America); I, <i>Albanerpeton inexpectatum</i> (Miocene, France); J, <i>Albanerpeton pannonicum</i> (Pliocene, Hungary). Outlines redrawn or reconstructed from: A-B [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0189767#pone.0189767.ref020" target="_blank">20</a>]; C, original, SBEI 2459; D [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0189767#pone.0189767.ref034" target="_blank">34</a>]; E [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0189767#pone.0189767.ref026" target="_blank">26</a>]; F-H [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0189767#pone.0189767.ref029" target="_blank">29</a>]; I [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0189767#pone.0189767.ref072" target="_blank">72</a>]; J [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0189767#pone.0189767.ref016" target="_blank">16</a>]. Images C-H have been "mirror-imaged" for ease of comparison.</p
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Research Interests: Herpetology, Geology, Anurans, China, Palaeoecology, and 7 moreCretaceous, Mesozoic frogs, Frog, FROGS, Limb Proportions, Jehol Biota, and Saltation
The Cambridge Greensand has yielded a diverse fauna of terrestrial and marine vertebrates, including various fish, birds, dinosaurs and marine reptiles. However, this important late Early Cretaceous biome has been severely neglected and... more
The Cambridge Greensand has yielded a diverse fauna of terrestrial and marine vertebrates, including various fish, birds, dinosaurs and marine reptiles. However, this important late Early Cretaceous biome has been severely neglected and the taxonomy and systematics of most of these animals are in need of urgent revision. The small reptile &amp;amp;amp;amp;#x27;Patricosaurus merocratus&amp;amp;amp;amp;#x27; was named on the basis of a partial femur and sacral vertebra and referred to the Squamata. Re-examination of the type material indicates that &amp;amp;amp;amp;#x27; ...
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Albanerpetontids are an enigmatic fossil amphibian group known from deposits of Middle Jurassic to Pliocene age. The oldest and youngest records are from Europe, but the group appeared in North America in the late Early Cretaceous and... more
Albanerpetontids are an enigmatic fossil amphibian group known from deposits of Middle Jurassic to Pliocene age. The oldest and youngest records are from Europe, but the group appeared in North America in the late Early Cretaceous and radiated there during the Late Cretaceous. Until now, the Asian record has been limited to fragmentary specimens from the Late Cretaceous of Uzbekistan. This led to speculation that albanerpetontids migrated into eastern Asia from North America in the Albian to Cenomanian interval via the Beringian land bridge. However, here we describe albanerpetontid specimens from the Lower Cretaceous Kuwajima Formation of Japan, a record that predates their first known occurrence in North America. One specimen, an association of skull and postcranial bones from a single small individual, permits the diagnosis of a new taxon. High Resolution X-ray Computed Microtomography has revealed previously unrecorded features of albanerpetontid skull morphology in three dimens...
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Research Interests: Geology and Cretaceous
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Lepidosauria is a speciose clade with a long evolutionary history, but there have been few attempts to explore its taxon richness through time. Here we estimate patterns of terrestrial lepidosaur genus diversity for the... more
Lepidosauria is a speciose clade with a long evolutionary history, but there have been few attempts to explore its taxon richness through time. Here we estimate patterns of terrestrial lepidosaur genus diversity for the Triassic-Palaeogene (252-23 Ma), and compare observed and sampling-corrected richness curves generated using Shareholder Quorum Subsampling and classical rarefaction. Generalized least-squares regression (GLS) is used to investigate the relationships between richness, sampling and environmental proxies. We found low levels of richness from the Triassic until the Late Cretaceous (except in the Kimmeridgian-Tithonian of Europe). High richness is recovered for the Late Cretaceous of North America, which declined across the K-Pg boundary but remained relatively high throughout the Palaeogene. Richness decreased following the Eocene-Oligocene Grande Coupure in North America and Europe, but remained high in North America and very high in Europe compared to the Late Cretace...