Hurdia
Hurdia is an extinct genus of hurdiid radiodont that lived 505 million years ago during the Cambrian Period. As a radiodont like Peytoia and Anomalocaris, it is part of the ancestral lineage that led to euarthropods.[1]
Hurdia was one of the largest organisms in the Cambrian oceans, reaching approximately 20 cm (8 inches) in length.[1] Its head bore a pair of rake-like frontal appendages which shovelled food into its pineapple-ring-like mouth (oral cone). Like other hurdiids, Hurdia bore a large frontal carapace protruding from its head composed of three sclerites: a central component known as the H-element and two lateral components known as P-elements. The function of this organ remains mysterious; it cannot have been protective as there was no underlying soft tissue.[2] Body flaps ran along the sides of the organisms, from which large gills were suspended.
Hurdia was a predator, or possibly a scavenger. Its frontal appendages are flimsier than those of Anomalocaris, suggesting that it fed on less robust prey. It displayed a cosmopolitan distribution; it has been recovered from the Burgess shale as well as sites in the US, China and Europe.[1]
Hurdia was named in 1912 by Charles Walcott, with two species, the type species H. victoria and a referred species, H. triangulata.[3] The genus name refers to Mount Hurd.[3] It is possible that Walcott had described a specimen the year prior as Amiella, but the specimen is too fragmentary to identify with certainty, so Amiella is a nomen dubium.[4] Walcott's original specimens consisted only of H-elements of the frontal carapace, which he interpreted as being the carapace of an unidentified type of crustacean. P-elements of the carapace were described as a separate genus, Proboscicaris, in 1962.
In 1996, then-curator of the Royal Ontario Museum Desmond H. Collins erected the taxon Radiodonta to encompass Anomalocaris and its close relatives, and included both Hurdia and Proboscicaris in the group.[5] He subsequently recognized that Proboscicaris and Hurdia were based on different parts of the same animal, and recognized that a specimen previously assigned to Peytoia was also a specimen of the species.[4] He presented his ideas in informal articles,[6][7] and it was not until 2009, after three years of painstaking research, that the complete organism was reconstructed.[1][8][9][10]
Sixty-nine specimens of Hurdia are known from the Greater Phyllopod bed, where they comprise 0.13% of the community.[11]
