Morphological variation within species is a raw material subject to natural selection. However, temporal change in morphological diversity has usually been studied in terms of variation among rather than within species. The distribution of polymorphic traits in cladistic character-taxon matrices reveals that the frequency and extent of morphological variation in 982 trilobite species are greate...

The function of the central core in lenses of certain schizochroal-eyed trilobites is unknown. To understand the possible optical function(s) of this central core, we performed computational ray-tracing on the lens in the schizochroal compound eyes of a Silurian Dalmanites trilobite. We computed the intensity of light focused by the lens versus the distance from the lower lens surface along the...

The Cambrian 'Orsten' fauna comprises exceptionally preserved and phosphatised microscopic arthropods. The external morphology of these fossils is well known, but their internal soft-tissue anatomy has remained virtually unknown. Here, we report the first non-biomineralised tissues from a juvenile polymerid trilobite, represented by digestive structures, glands, and connective strands harboured...