Australia: The Land Where Time Began

A biography of the Australian continent 

New Anatomical Information on Anomalocaris – Emu Bay Shale, South Australia

In the Emu Bay Shale, Big Gully, Kangaroo Island, South Australia (Cambrian Series 2 Stage 4), there are 2 species of Anomalocaris that co-occur. The more common of the 2 is Anomalocaris briggsi Nedin, 1995, and the less common species is Anomalocaris cf. Canadensis Whiteaves, 1892, recovered from a quarry inland of the wave-cut platform site from which these species were originally described. An oral cone that has 3 large node-bearing plates that were recently documented for Anomalocaris Canadensis, which the authors¹ suggest confirms the lack in Anomalocaris of a tetraradial ‘Peytoia’ oral cone and strengthens the case for the identity of the Australian specimens being Anomalocaris. Disarticulated body flaps of anomalocaridids are more common in the Emu Bay Shale than at other sites, and they preserve anatomical details that have not been recognised elsewhere. There are transverse lines on the anterior part of the flaps that have previously been interpreted as strengthening rays or veins in descriptions of anomalocaridids, have been found in the Emu Bay Shale specimens to be associated with internal structures that consist of a well-bounded, stratified block of bars. According to the authors¹ their structure is consistent with a structural function that imparts strength to the body flaps. Setal structures that consist of a series of lanceolate blades are similar to those present in other anomalocaridids and are found either in isolation or associated with body flaps. Putative gut diverticula have also been preserved in a single specimen. It appears to have been an active predator, as suggested by the morphology of the appendages, oral cone, gut diverticula and compound eyes of Anomalocaris, as well as its large size, and specimens of coprolites that contain trilobite fragments and trilobites with prominent injuries have been cited as evidence of predation on trilobites by anomalocaridids. Anomalocaris briggsi is inferred to have preyed exclusively on soft-bodied animals based on the morphology of the frontal appendages, and only Anomalocaris cf. Canadensis may have been capable of durophagous predation on trilobites, though predation, including possible cannibalism, by Redlichia could also be an explanation for the coprolites and damage to trilobite exoskeletons found in the Emu Bay Shale.

Sources & Further reading

1. Daley, Allison C., John R. Paterson, Gregory D. Edgecombe, Diego C. García-Bellido, and James B. Jago. "New Anatomical Information on Anomalocaris from the Cambrian Emu Bay Shale of South Australia and a Reassessment of Its Inferred Predatory Habits." Palaeontology 56, no. 5 (2013): 971-90.