The Cambrian Information Revolution  

During the Ediacaran, mobile organisms were confined to an essentially two-dimensional world, conscribed by biomats.  In contrast, the early Cambrian world was recognizably three-dimensional, with both an incipient infauna and pelagic eumetazoans.  We suggest that these changes in the spatial organization of the environment produced a “Cambrian Information Revolution”, a co-evolutionary increase in the potential information content of the marine environment, and in the ability and necessity for organisms to obtain and process this information.

Organisms emit, detect, and respond to a huge array of environmental signals.The distribution of a given signal is dependent, first of all, upon the original spatial distribution of signal sources, the source landscape. The signal sources can be fixed or moving, and their output can be stable or ephemeral.The emitted signals are modified by relevant transport processes, which are often strongly scale- and environment-dependent.  Chemical signals, for example, are propagated by diffusion and turbulence.  The complex and dynamic three-dimensional distribution of signals which results is the signal landscape: the environment of potentially available information in which sensory systems function and have evolved.

Organisms also differ widely in which signals they can actually detect; the distribution of signals that an organism can potentially respond to is its information landscape. Although increasing the kinds and specificity of signals that can be detected and processed can lead to improved decision making, it almost always comes at an increased cost.The greater the spatial and temporal complexity of the environment, the greater are the costs of incomplete information — and the more advantageous is the development of improved information gathering capabilities. 

Information landscapes and the corresponding sensory systems should have evolved in concert with major transitions in the history of life.  We suggest that the appearance and evolution of macroscopic sense organs in mobile bilaterians during the Ediacaran–Cambrian bilaterian radiation was driven by an increased spatial complexity relative to the scale of mobile organisms. 

The evolution of sense organs is part of a wider picture of the development of neurological systems and behaviour during the Cambrian radiation.  Detailed examination of sensory organ distribution and morphology in Cambrian animals should elucidate how sensory organ evolution took place in early animals, and its contribution to the ecological feedbacks that fuelled the Cambrian radiation.  Understanding the history of the interactions between the changing landscape of spatial signals and the ability of organisms to detect and react to this variability should give new insights into both the body and trace fossil record during this interval.