Evolutionary changes in the orbits and palatal openings of early tetrapods, with emphasis on temnospondyls

Witzmann, Florian and Ruta, Marcello (2018) Evolutionary changes in the orbits and palatal openings of early tetrapods, with emphasis on temnospondyls. Earth and Environmental Science Transactions of the Royal Society of Edinburgh . pp. 1-18. ISSN 10.1017/S1755691018000919

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Evolutionary changes in the orbits and palatal openings of early tetrapods, with emphasis on temnospondyls

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Abstract

Open palates with large interpterygoid vacuities are a diagnostic characteristic of
temnospondyl amphibians, the most species-rich group of early tetrapods. Aside from their functional
roles, several other aspects of such vacuities, such as their variation and spatial relationships
relative to the orbits, have received only scarce attention. The present work examines patterns of
shape and size changes in the orbits and vacuities of temnospondyls using a time-calibrated phylogeny
of 69 temnospondyl taxa and 13 additional early tetrapod ‘outgroups’ (colosteids, an embolomere,
‘microsaurs’ and nectrideans). Orbit and vacuity outlines are quantified in a comparative framework
using standard eigenshape analyses. In addition, we employ a series of ratios of linear measurements
of both orbits and vacuities, and subject them to a phylogenetic principal component analysis in
order to evaluate their proportional changes relative to the skull and to one another. Finally, we
examine rates of evolutionary change and their associated shifts for shape and size for both structures,
and assess the strength and significance of the correlations between these two variables using
phylogenetic generalised least squares analyses. Although orbits and vacuities have fairly simple outlines,
they both reveal complex models of proportional change across the temnospondyl phylogeny.
These changes exhibit strong phylogenetic signal, that is, trait covariance among taxa is predicted by
tree topology. We discuss the hypothesis that, early in tetrapod evolution, the functional role of the
vacuities was related to the accommodation of the anterior jaw muscles. Only later in evolution did
such vacuities serve to accommodate the eye muscles only.

Keywords:amphibians, interpterygoid vacuities, orbit openings, shape, sizes, spatial relationships
Subjects:F Physical Sciences > F641 Palaeontology
C Biological Sciences > C300 Zoology
C Biological Sciences > C181 Biodiversity
C Biological Sciences > C182 Evolution
Divisions:College of Science > School of Life Sciences
ID Code:34402
Deposited On:23 Jan 2019 17:06

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