Patterns of Variation in the Cranial Osteology of Three Species of Endemic Australian Lizards (Ctenophorus: Squamata: Agamidae): Implications for the Fossil Record and Morphological Analyses made with Limited Sample Sizes

Stilson, Kelsey T.; Bell, Christopher J.; Mead, Jim I.

doi:10.1670/16-152

Cited by 6 publications

(3 citation statements)

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“…[32]); its role in supporting sensory structures, in food gathering, for social signalling and as a weapon, mean that it must be responsive to multiple selective pressures. Amphibolurinae includes some markedly varied and specialised skull shapes [33, 34], but apart from one recent limited study [35], there has been little examination of cranial growth patterns among different species.…”

Section: Introductionmentioning

confidence: 99%

Changes in ontogenetic patterns facilitate diversification in skull shape of Australian agamid lizards

et al. 2019

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BackgroundMorphological diversity among closely related animals can be the result of differing growth patterns. The Australian radiation of agamid lizards (Amphibolurinae) exhibits great ecological and morphological diversity, which they have achieved on a continent-wide scale, in a relatively short period of time (30 million years). Amphibolurines therefore make an ideal study group for examining ontogenetic allometry. We used two-dimensional landmark-based geometric morphometric methods to characterise the postnatal growth patterns in cranial shape of 18 species of amphibolurine lizards and investigate the associations between cranial morphology, and life habit and phylogeny.ResultsFor most amphibolurine species, juveniles share a similar cranial phenotype, but by adulthood crania are more disparate in shape and occupy different sub-spaces of the total shape space. To achieve this disparity, crania do not follow a common post-natal growth pattern; there are differences among species in both the direction and magnitude of change in morphospace. We found that these growth patterns among the amphibolurines are significantly associated with ecological life habits. The clade Ctenophorus includes species that undergo small magnitudes of shape change during growth. They have dorsoventrally deep, blunt-snouted skulls (associated with terrestrial lifestyles), and also dorsoventrally shallow skulls (associated with saxicolous lifestyles). The sister clade to Ctenophorus, which includes the bearded dragon (Pogona), frill-neck lizard (Chlamydosaurus), and long-nosed dragon (Gowidon), exhibit broad and robust post-orbital regions and differing snout lengths (mainly associated with scansorial lifestyles).ConclusionsAustralian agamids show great variability in the timing of development and divergence of growth trajectories which results in a diversity of adult cranial shapes. Phylogenetic signal in cranial morphology appears to be largely overwritten by signals that reflect life habit. This knowledge about growth patterns and skull shape diversity in agamid lizards will be valuable for placing phylogenetic, functional and ecological studies in a morphological context.Electronic supplementary materialThe online version of this article (10.1186/s12862-018-1335-6) contains supplementary material, which is available to authorized users.

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Section: Introductionmentioning

confidence: 99%

Changes in ontogenetic patterns facilitate diversification in skull shape of Australian agamid lizards

et al. 2019

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“…In part, that is because methods for integrating polymorphic characters into phylogenetic analyses are not straightforward. Nevertheless, continued investigations into morphological variation have yielded new insights into phylogenetic relationships and morphological evolution of squamates (e.g., Bhullar, 2011 ; Čerňanský, Smith & Klembara, 2014 ; Díaz-Fernández, Quinteros & Lobo, 2017 ; Stilson, Bell & Mead, 2017 ; Hernández Morales et al, 2019 ). Investigations into other vertebrate clades including turtles ( Joyce & Bell, 2004 ), frogs ( Bever, 2005 ), birds ( Kirchner-Smith, 2015 ), and mammals ( Gould, 2001 ) have also shown that substantial amounts of previously unreported morphological variation exist, some of which alter the diagnostic utility of previously reported features.…”

Section: Discussionmentioning

confidence: 99%

Variation in the skulls of Elgaria and Gerrhonotus (Anguidae, Gerrhonotinae) and implications for phylogenetics and fossil identification

Ledesma

Scarpetta

Bell

2021

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Background There are limited data on intra- and interspecific osteological variation for many squamate clades. Those data are relevant for phylogenetic analyses that use osteological characters and for apomorphic identifications of fossils. We investigate whether morphological features in the skulls of extant gerrhonotine lizards can be used to distinguish taxa at the species- and genus-level and assess whether newly discovered intra- and interspecific osteological variation alters the utility of previously reported apomorphic features. We examined skulls of species belonging to the gerrhonotine genera Elgaria and Gerrhonotus. These genera contain 17 extant species, but the cranial osteology of only a few species was previously examined. As a result, intra- and interspecific osteological variation of these gerrhonotines is poorly understood. Methods We employed high-resolution x-ray computed tomography (CT) to scan 25 alcohol-preserved specimens. We provide data on the skulls of all eight species of Elgaria, four for the first time, and five species of Gerrhonotus, three for the first time. We examined 3-D reconstructed skulls of the scanned specimens as well as dry, traditionally prepared skeletons (when they were available). Results We found that the purported diagnostic utility of many previously described morphological features is impacted because of substantial morphological variation between and within species. We present an assessment of osteological differences that may be useful to differentiate species of Elgaria and Gerrhonotus, many of which are present on isolated cranial elements commonly recovered as fossils, including the premaxilla, maxilla, parietal, pterygoid, prootic, dentary, and surangular. We demonstrate the importance of documenting patterns of osteological variation using large sample sizes, and the utility of examining disarticulated cranial elements of the squamate skull to identify diagnostic morphology. This study adds to a growing body of literature suggesting that extensive documentation of morphological variation is needed to further our understanding of the phylogenetic and diagnostic utility of morphological features across vertebrate clades. Efforts in that direction likely will benefit from examination of disarticulated skeletal elements.

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“…They have also developed many strategies for evading predators and catching prey, including speed (Cogger 2014), crypsis (Shoo et al 2008), defensive displays (Throckmorton et al 1985;Shine 1990), and spines (Pianka and Pianka 1970). They exhibit great variation in their skull anatomy (e.g., Siebenrock 1895;Bell et al 2009;Gray et al 2017;Stilson et al 2017;Gray et al 2019a, b). However, their potential to be defined as an "adaptive radiation" has not yet been explicitly investigated.…”

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Evolution of cranial shape in a continental‐scale evolutionary radiation of Australian lizards

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A defining character of adaptive radiations is the evolution of a diversity of morphological forms that are associated with the use of different habitats, following the invasion of vacant niches. Island adaptive radiations have been thoroughly investigated but continental scale radiations are more poorly understood. Here, we use 52 species of Australian agamid lizards and their Asian relatives as a model group, and employ three‐dimensional geometric morphometrics to characterize cranial morphology and investigate whether variation in cranial shape reflects patterns expected from the ecological process of adaptive radiation. Phylogenetic affinity, evolutionary allometry, and ecological life habit all play major roles in the evolution of cranial shape in the sampled lizards. We find a significant association between cranial shapes and life habit. Our results are in line with the expectations of an adaptive radiation, and this is the first time detailed geometric morphometric analyses have been used to understand the selective forces that drove an adaptive radiation at a continental scale.

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Patterns of Variation in the Cranial Osteology of Three Species of Endemic Australian Lizards (Ctenophorus: Squamata: Agamidae): Implications for the Fossil Record and Morphological Analyses made with Limited Sample Sizes

Abstract: BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.

Cited by 6 publications

References 56 publications

Changes in ontogenetic patterns facilitate diversification in skull shape of Australian agamid lizards

Changes in ontogenetic patterns facilitate diversification in skull shape of Australian agamid lizards

Variation in the skulls of Elgaria and Gerrhonotus (Anguidae, Gerrhonotinae) and implications for phylogenetics and fossil identification

Evolution of cranial shape in a continental‐scale evolutionary radiation of Australian lizards

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