III.—The Ventral Integument of Trilobites

Trilobites

Avery’s purification of transforming principle and Kornberg’s purification of the first DNA polymerase, the experiments I have described were of a new type where what might be called the chemical behaviour of genetic material was being analysed without the benefit of purification. And this has become the new style in biology, inaugurated in the late 1950s by Taylor, Meselson and Stahl. It was, ...

The Lifestyles of the Trilobites

Phylogenetic and Biogeographic Analysis of Sphaerexochine Trilobites

BACKGROUND Sphaerexochinae is a speciose and widely distributed group of cheirurid trilobites. Their temporal range extends from the earliest Ordovician through the Silurian, and they survived the end Ordovician mass extinction event (the second largest mass extinction in Earth history). Prior to this study, the individual evolutionary relationships within the group had yet to be determined uti...

Water relations of tetrapod integument.

The vertebrate integument represents an evolutionary compromise between the needs for mechanical protection and those of sensing the environment and regulating the exchange of materials and energy. Fibrous keratins evolved as a means of strengthening the integument while simultaneously providing a structural support for lipids, which comprise the principal barrier to cutaneous water efflux in t...

Developmental trait evolution in trilobites.

We performed a tree-based analysis of trilobite postembryonic development in a sample of 60 species for which quantitative data on segmentation and growth increments between putative successive instars are available, and that spans much of the temporal, phylogenetic, and habitat range of the group. Three developmental traits were investigated: the developmental mode of trunk segmentation, the a...