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Dryad

Data from: Heterochronic origin of spherical fusulinid foraminifera in the Late Paleozoic

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Sep 25, 2020 version files 1.99 MB

Abstract

Heterochrony describes acceleration, displacement and/or retardation of descendants’ development events compared to ancestral states and has often been cited as an important process to bring about morphological novelty. It was coined one and half centuries ago and has been discussed by both paleobiologists and biologists frequently ever since. Many types of fossil organisms preserve aspects of their development histories in their bones or shells that have been used for heterochrony analyses, with body size being used as a developmental age indicator, despite raised questions regarding this practice. For organisms whose hard structures consist of multiple chambers, or that contain growth lines, age information suggested by these structures independently can facilitate ontogenetic modeling. In this way, relations among size, shape and age can be established in order to document patterns of morphological development.

Morphological analysis of pseudoschwagerine fusulinids, a fossil foraminifera group that developed a morphologically novel spherical shell, along with their presumptive triticitid ancestors illustrates this approach to heterochrony analysis. Ontogenetic trajectory comparisons of four major pseudoschwagerine genera, as well as those of triticitid foraminifera, document relations between their shape, size and developmental ages. A complex of heterochronic patterns including peramorphic pre-displacement, hypermorphosis and acceleration characterize pseudoschwagerine development and appear to be responsible for the novel appearance of large, inflated fusiform and spherical tests in these Late Paleozoic benthic foraminifera. The morphometric approach employed in this investigation could be applied widely in the quantitative morphological studies of development histories in a variety of other fossil groups.