Heterochronic origin of spherical fusulinid foraminifera in the Late Paleozoic

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 foram...