Body segmentation in arthropods has been an abiding theme of developmental biology since the 19th century. In recent years, there has been a renaissance of studies of the evolution of these developmental patterns, in parallel with the increasing knowledge of the underlying genetics and cell biology.
Fusco et al. take advantage of the exceptional fossil record of one of the early segmented animals--the trilobite--to investigate developmental evolution. Mature individuals of the trilobite Aulacopleura konincki, from Silurian deposits in the Czech Republic, show variation in the number of thoracic segments. Abundant fossil material at all post-hatching developmental stages enabled a detailed analysis of growth and segmentation in this species, and an assessment of whether the number of segments was determined early or late in development. Morphometric analyses suggested that segment number was under tight control early in the developmental process, as is also the case in modern arthropods, such as centipedes. Thus, fossil material can be used successfully to compare developmental processes in extinct and existing organisms. -- AMS
Am. Nat. 163, 167 (2004).
