A New Anomalocaridid from the Chengjiang Biota  

The spinose great appendages of anomalocaridids are usually preserved in isolation, and it is therefore postulated that they were composed of more skeletonized cuticle, in comparison to the rest of the body, making the spines harder and more suitable for predation.  Functionally, the spine patterns of anomalocaridid great appendages can be grouped into two types.  The first is that of Anomalocaris, Amplectobelua and Parapeytoia, with rigid spines which might have functioned to impale, subdue and immobilize their prey.  When curved, the appendage would have squeezed and torn the prey.  The second type is comb-like spine pattern, such as those of Laggnia and Cassubia. Their auxiliary spines (AS) are also comb-like.  This type of appendage probably functioned to sieve water and sediment in search of food, rather than attacking prey directly. 

Here we report another unique type of great appendage belonging to a new anomalocaridid from the Chengjiang Biota.  This type of appendage is characterized by a reduction in the number of spines (and possibly the number of appendage segments) and differentiation of proximal and distal spines.  There are eight pairs of spines of this new type.  The three most proximal pairs are very stout and almost equally wide from proximal to distal ends, along which at least six pairs of AS are present.  The proximal AS are short and slender, while the two most distal pairs are relatively longer and stronger.  The other five pairs of spines are very simple and have no AS. 

This unique spine pattern shows that the proximal spines of the new anomalocaridid are greatly specialized, and the distal ones are relatively simplified (compared to the normal spine structure which usually has AS). The differentiation of spines indicates that the new animal must have a feeding habit that differs from other anomalocaridids.  The edge between the two kinds of spines is greatly curved, which indicates that the new animal might only use the distal five simple spines for predation, with the prey being transferred to the three pairs of proximal spines for tearing.  After tearing, the prey would be carried to the mouth by the spines, because they show some kind of flexibility, e.g. curving at varying degree.  Together with the four genera (five species) previously described, the new anomalocaridid from Chengjiang Biota reveals the morphological diversity and disparity of the anomalocaridid feeding apparatus, the great appendage, and indicates the diversification of predation strategy in the Early Cambrian.