Comparative analysis of a unique specimen of a new species of Anomalocaris from the Kinzers Formation of Lancaster County yields a reassessment of the feeding habits of the genus
On account of its large size and morphology, Anomalocaris has come to be regarded as the top predator among the mainly soft-bodied and lightly skeletonized marine organisms of the Early to Middle Cambrian. Anomalocaris has regularly been depicted as preying on abundant trilobites, but now the morphology of its mouth is increasingly being interpreted as incapable of breaking through the carapace even of an Early Cambrian trilobite. Worms were newly abundant and large, and the mouth of Anomalocaris was flexible and circular, so it is much more likely that worms were their preferred prey. This interpretation is also endorsed by the nature of the frontal appendages (so‐called ‘great claws’) of Anomalocaris, which are not well designed for crushing and manipulating prey. Consuming worms would not have required such mechanisms. It is much more likely that the flexible frontal appendages of Anomalocaris were used to search for prey. Four species of Anomalocaris have previously been identified as members of Cambrian faunas around the world, most notably from the Burgess Shale of British Columbia, the Maotianshan Shales of Chengjiang, and the Emu Bay Shale of South Australia. Anomalocaris also occurs in the Kinzers Formation of south‐eastern Pennsylvania, including the recent discovery of a previously unidentified species. This new specimen is of particular interest on account of the nature of the ventral spines on its frontal appendages. These ventral spines are longer in relation to the size of the animal than those of any previously identified species of Anomalocaris, and they lack any evidence of branching auxiliary spines. 2 Variation in morphology of the ventral spines suggests a spectrum of claw actions. Long, somewhat flexible spines would have been ideal for sweeping loose sediment away, exposing buried prey. Short, rigid and often branching spines were potentially more attuned to probing through coarser, stiffer, or more cohesive materials. The unique new specimen from the Kinzers Formation is an end member on this spectrum of adaptations, bearing long, flexible ventral spines on its frontal appendages, whereas previously identified species of the genus represent forms in the middle and at the opposite end of the spectrum. The new specimen of Anomalocaris also potentially represents a transitional form between predators adapted for bottom feeding and those adapted for suspension feeding. This inference is prompted by the recent discovery of Tamisiocaris, and its interpretation as a nektonic, suspension-feeding anomalocaridid. The new species from the Kinzers Formation is intermediate in form and function between other bottom‐feeding species of Anomalocaris and Tamisiocaris. As an end member of one series of adaptations and as a transitional form in relation to a different mode of life, the new species provides a key for identifying and analyzing the functions of different ventral spine morphologies and their relationships to the specific environments to which they were adapted.
Franklin and Marshall College Archives, Undergraduate Honors Thesis 2014
- F&M Theses Collection