Aegirocassis
Aegirocassis is an extinct genus of radiodont arthropod belonging to the family Hurdiidae that lived 480 million years ago during the early Ordovician. It is known by a single species, Aegirocassis benmoulai.[note 1] Van Roy initiated scientific study of the fossil,[3] the earliest known of a "giant" filter-feeder discovered to date.[4] Aegirocassis is considered to have evolved from early predatory radiodonts.[5]
At the time of its existence, A. benmoulai was possibly the largest animal in the world.[6] The length was described as exceeding 2.0 metres (6.6 ft) in the scientific journal Nature.[1]
The fossil was preserved with exceptional three-dimensional detail, unlike most other radiodont fossils, in which the animals are flattened.[7] 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.[1][8]
A fossil of A. benmoulai from the Fezouata biota, Morocco was discovered by and named after Mohamed Ben Moula, a fossil collector who recognized its rare characteristics and brought it to the notice of a professional paleontologist, Peter Van Roy, at the Ghent University in Belgium.[6]
