Aegirocassis benmoulae

A. benmoulai was the largest known radiodont and the largest known animal that existed in this period, and the length was described as exceeding 2.0 metres (6.6 ft). The fossil was preserved with exceptional three-dimensional detail, unlike most other radiodont fossils, in which the animals are flattened. The quality of three-dimensional preservation has shed light on the nature of radiodont trunk flaps. Each trunk segment of the Aegirocassis benmoulai specimen has both a ventral and a dorsal pair of flaps. Several details seen clearly in the specimen led to a review and reassessment of research of existing specimens and, most importantly, to the conclusion that the ventral pair are homologous with arthropod endopods (limb-like inner branches) and lobopodian limbs (lobopods), and the dorsal pair are homologous with the flaps of gilled lobopodians and exites (gill-like outer branches) of the arthropod biramous limb. This discovery also found that other hurdiid radiodonts like Peytoia and Hurdia had a dorsal pair of flaps as well. Frontal appendages of Aegirocassis had 5 endites, and each endites had around 80 setae-like auxiliary spines. These spines are estimated to have been used as a mesh for filter feeding. It was probably able to consume mesozooplankton roughly the same size as the other filter feeding radiodont, Tamisiocaris, was able to catch. …