Combining geometric morphometric analyses of multiple 2D observation views improves interpretation of evolutionary allometry and shape diversification in monitor lizard (<i>Varanus</i>) crania

Openshaw, Gabrielle H.; D’Amore, Domenic C.; Vidal‐García, Marta; Keogh, J. Scott

doi:10.1111/bij.12899

Cited by 15 publications

(14 citation statements)

References 61 publications

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“…This also highlights the importance of using different views when studying skull shape and interpreting their evolutionary patterns (Openshaw et al . ). Furthermore, when we used a different phylogenetic framework, which essentially rearranged the sampled species into different taxonomic groups (see Method, above), the morphospaces of sebecosuchians (which includes baurusuchids) and other notosuchians remain significantly separated (Godoy et al .…”

Section: Discussionmentioning

confidence: 97%

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Evidence for heterochrony in the cranial evolution of fossil crocodyliforms

et al. 2018

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The southern supercontinent of Gondwana was home to an extraordinary diversity of stem-crocodylians (Crocodyliformes) during the Late Cretaceous. The remarkable morphological disparity of notosuchian crocodyliforms indicates that this group filled a wide range of ecological roles more frequently occupied by other vertebrates. Among notosuchians, the distinctive cranial morphology and large body sizes of Baurusuchidae suggest a role as apex predators in ecosystems in which the otherwise dominant predatory theropod dinosaurs were scarce. Large-bodied crocodyliforms, modern and extinct, are known to have reached large sizes by extending their growth period. In a similar way, peramorphic heterochronic processes may have driven the evolution of the similarly large baurusuchids. To assess the presence of peramorphic processes in the cranial evolution of baurusuchids, we applied a geometric morphometric approach to investigate ontogenetic cranial shape variation in a comprehensive sample of notosuchians. Our results provide quantitative morphological evidence that peramorphic processes influenced the cranial evolution of baurusuchids. After applying size and ancestral ontogenetic allometry corrections to our data, we found no support for the action of either hypermorphosis or acceleration, indicating that these two processes alone cannot explain the shape variation observed in Notosuchia. Nevertheless, the strong link between cranial shape variation and size increase in baurusuchids suggests that peramorphic processes were involved in the emergence of hypercarnivory in these animals. Our findings illustrate the role of heterochrony as a macroevolutionary driver, and stress, once more, the usefulness of geometric morphometric techniques for identifying heterochronic processes behind evolutionary trends.

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Section: Discussionmentioning

confidence: 97%

“…To obtain more detailed interpretations of skull shape variation, we used both lateral and dorsal views for the analyses (Openshaw et al . ), with 19 and 17 landmarks respectively (for the position and description of landmarks, see Godoy et al . , fig.…”

Section: Methodsmentioning

confidence: 99%

Evidence for heterochrony in the cranial evolution of fossil crocodyliforms

et al. 2018

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“…Unfortunately, ontogenetic allometry of the skull has not been documented in varanids, but phylogenetic allometry (sensu Gould 1966) has been (Emerson and Bramble 1993;Openshaw and Keogh 2014;Openshaw et al 2016). Thus, in the genus Varanus, which varies appreciably in size, tooth row length is isometric, whereas skull width and jaw length are positively isometric (Emerson and Bramble 1993).…”

Section: Discussionmentioning

confidence: 99%

Allometric growth in the skull of Tylosaurus proriger (Squamata: Mosasauridae) and its taxonomic implications

Stewart

Mallon

2018

Vert. Anat. Morph. Palaeo.

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Ontogeny—the growth and development of an organism—is among the more poorly understood aspects of the life history of mosasaurs, largely owing to a dearth of fossil material from young individuals. We describe the partial and complete skulls of two subadult individuals of the mosasaurid Tylosaurus proriger from the upper Smoky Hills Chalk Member of the Niobrara Formation in Kansas. We include the more complete of the two specimens in an allometric analysis to better understand proportional changes of the skull through growth. Although our small sample size produces several instances of ‘soft isometry’, we recover the length of the edentulous rostrum as significantly negatively allometric, and quadrate height as significantly positively allometric. In light of our findings, we go on to consider the question of whether T. kansasensis represents an immature ontogimorph of T. nepaeolicus, but find no convincing evidence that this is the case.

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“…This again suggests that the accuracy of 2D data may be influenced by a complex range of factors, that do not only include the magnitude of the differences, but also landmark coplanarity and taxon-specific anatomical variability. Openshaw et al (2017) suggested that "studies restricted to a 2D geometric morphometric analysis of a complex 3D biological structure can combine carefully designed 2D landmark configurations describing alternative planes [e.g., ventral, side and dorsal views] to maximize shape coverage". That may be true, but could also, as in many other cases, be specific to their study.…”

Section: Conclusion: 2d or Not 2d?mentioning

confidence: 99%

How flat can a horse be? Exploring 2D approximations of 3D crania in equids

Cardini

Chiappelli

2019

Preprint

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Quantitative analyses of morphological variation using geometric morphometrics are often performed on 2D photos of 3D structures. It is generally assumed that the error due to the flattening of the third dimension is negligible. However, despite hundreds of 2D studies, few have actually tested this assumption and none has done it on large animals, such as those typically classified as megafauna. We explore this issue in living equids, focusing on ventral cranial variation at both micro-and macro-evolutionary levels. By comparing 2D and 3D data, we found that size is well approximated, whereas shape is more strongly impacted by 2D inaccuracies, as it is especially evident in intra-specific analyses. The 2D approximation improves when shape differences are larger, as in macroevolution, but even at this level precise inter-individual similarity relationships are altered. Despite this, main patterns of sex, species and allometric variation in 2D were the same as in 3D, thus suggesting that 2D may be a source of 'noise' that does not mask the main signal in the data. However, the problem is complex and any generalization premature. Morphometricians should therefore test the appropriateness of 2D using preliminary investigations in relation to the specific study questions in their own samples. We discuss whether this might be feasible using a reduced landmark configuration and smaller samples, which would save time and money. In an exploratory analysis, we found that in equids results seem robust to sampling, but become less precise and, with fewer landmarks, may slightly overestimate 2D inaccuracies.

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Combining geometric morphometric analyses of multiple 2D observation views improves interpretation of evolutionary allometry and shape diversification in monitor lizard (Varanus) crania

Cited by 15 publications

References 61 publications

Evidence for heterochrony in the cranial evolution of fossil crocodyliforms

Evidence for heterochrony in the cranial evolution of fossil crocodyliforms

Allometric growth in the skull of Tylosaurus proriger (Squamata: Mosasauridae) and its taxonomic implications

How flat can a horse be? Exploring 2D approximations of 3D crania in equids

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