Australia: The Land Where Time Began

A biography of the Australian continent 

Acute Vision in Anomalocaris – Origin of compound eyes

Intimate details of the optical design of non-biomineralised arthropod eyes remained elusive until recently in deposits of Cambrian Burgess Shale type, though there had been exceptional preservation of soft-part anatomy in such Konservat-Lageretätten. According to the authors¹ a single origin some time prior to the latest common ancestor of crown-group arthropods is supported by the development and structure of ommatidia of arthropod compound eyes, though the earliest appearance of compound eyes has been poorly constrained due to the lack of adequate fossils. In this paper the authors¹ report the discovery of 2-3-cm paired eyes from the Emu Bay Shale, Kangaroo Island, South Australia that dates to the Early Cambrian, about 515 Ma, that has been assigned to Anomalocaris, the apex predator of the Cambrian.  There are at least 16,000 ommatidia lenses (in a single eye) that are hexagonally packed, which the authors¹ suggest rivals the most acute compound eyes in extant arthropods. There are 2 distinct taphonomic modes shown by the specimens, preserved as iron oxide (after pyrite) and calcium phosphate, which demonstrates that the same type of extracellular tissue (i.e. cuticle) can be replicated by disparate styles of early diagenetic mineralisation within a single deposit of Burgess Shale-type. Compelling evidence of the arthropod affinity of anomalocaridids is provided by these fossils, which moves the origin of compound eyes deeper down the stem lineage of arthropods, the authors¹ suggesting that compound eyes developed earlier than such features as a hardened skeleton. The inferred acuity of the eyes of anomalocaridids is consistent with other evidence that suggests these animals were visual predators in the water column that were highly mobile. The escalatory ‘arms race’ that began more than 500 Ma was probably helped to accelerate by the presence of large macrophagous nektonic predators with sharp vision, such as Anomalocaris within the ecosystem of the Early Cambrian.

 Sources & Further reading

1. Paterson, John R., Diego C. Garcia-Bellido, Michael S. Y. Lee, Glenn A. Brock, James B. Jago, and Gregory D. Edgecombe. "Acute Vision in the Giant Cambrian Predator Anomalocaris and the Origin of Compound Eyes." Nature 480, no. 7376 (12/08/print 2011): 237-40.