At First Sight – Functional Analysis of Lower Cambrian Eye Systems  

Over the last 35 years, more than 200 species have been described from the Lower Cambrian Chengjiang lagerstätte.  The body plans typical of that time may continue an evolutionary sequence with hidden Precambrian origins; many related forms are still represented in the Middle Cambrian, in the Burgess Shale. 

Although the Chengjiang fossils are flattened, their exquisite preservation allows the detailed analysis of features such as cuticular structures, and especially the morphology of eyes.  Many of the different eye systems known in recent animals are already present in the Chengjiang fauna.  The arthropods that bore these eyes were all adapted to particular life habitats, while the design of visual systems is conditioned by the availability of light and the need for acute vision.  All visual systems have to obey the same physical rules in the same way, and an analysis of the structure of fossilized eyes, in comparison to those of marine arthropods living today may reveal how, and under which conditions the now fossilized visual organs may have worked.  The result of the investigations presented here is that some of the Lower Cambrian arthropods of the Chengjiang Fauna show “experimental” designs, some of which failed and are no longer present, while others are still represented today.  These arthropods may be confidently assigned to a life habitat at a water depth of c. 120 m, which is consistent with the geological interpretation of the Kunming area during the early Cambrian. 

The analysis of the stalked eyes of Leanchoilia, which was thought for a long time to be blind, has shown that the acuity of the eye is far too low to support the idea that this animal was an active free-swimming predator, locating its prey with its eyes.  Such optical tracking of prey, however, was possible for the greatest predator of the Cambrian – Anomalocaris. It swam with its bulbous eyes extended laterally.  The majority of its lenses pointed downwards, and were adapted to vision under dim light condtions as to faster velocities.  They were able to scan the world below until they detected a moving target – potential prey.  The lateral-most/outermost tip of the eye has smaller lenses but a lower acuity, and is to be interpreted as a zone of growth.  A functional analysis of other Chengjiang arthropods is also presented, with a discussion of the relevance of these functions to ecology.