The Middle Cambrian Burgess Shale fauna from British Columbia, Canada preserves many soft-bodied fossils similar to those of the Chengjiang fauna, indicating that these forms were widespread and persisted for many millions of years. These faunas serve to emphasize the spectacular morphologic breadth that was achieved so early in animal history. This fossil record raises many questions as to how new body plans evolve and just how rapidly such novel evolutionary innovations may be produced. Answering these questions requires information from the field of evolutionary developmental biology. Ancient Developmental Systems One of the most remarkable discoveries of the past few years is that the major elements controlling animal development are quite similar across a wide range of body plans.
Most animals start from a single cell, the fertilized egg or zygote.
However, during development their cells multiply and differentiate into specialized cell types that make up muscles, nerves, glands and all the other tissues and organs. Unlike their unicellular ancestors, multicellular animals need a genetic regulatory system to specify different gene activities in the different cell types as development unfolds to produce an adult body plan. Thus the striking changes in body plans have been accompanied by relatively modest tinkering with the machinery of early development of that long-extinct precursor. Developmental regulation proceeds through the sequential activation of a series of regulatory switches that in turn activate networks of other genes. In general, the regulatory genes produce proteins that bind to and influence the activity of other genes.