Unranked clade (stem group arthropods)
The affinity of Odaraia is uncertain because, while it was historically considered as a crustacean (Walcott, 1912; Briggs, 1981; Briggs and Fortey, 1989; Hou and Bergström, 1997; Wills et al., 1998), more recent studies have placed it in the upper stem lineage to the arthropods (Budd, 2002, 2008).
Odaraia – from Odaray Mountain (3,159 m) in Yoho Park, which was named by J. J. McArthur in 1887 from the Stoney First Nation Nakoda expression for “many waterfalls.”
alata – from the Latin ala, “wing,” referring to the wing-like fins of the tail.
Lectotype –USNM57722 (O. alata) in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
Burgess Shale and vicinity: none.
Other deposits: none.
Middle Cambrian, Bathyuriscus-Elrathina Zone (approximately 505 million years ago).
The Walcott and Raymond Quarries on Fossil Ridge.
Brief history of research:
Odaraia was first described by Walcott (1912), and was re-examined briefly by Simonetta and Delle Cave (1975). A major restudy of Odaraia was published by Briggs (1981), and it has since been included in several studies on arthropod evolution (Briggs and Fortey, 1989; Hou and Bergström, 1997; Wills et al. 1998; Budd, 2002). New morphological features of the gut and the head region were described by Butterfield (2002) and Budd (2008) respectively.
Much of the body of Odaraia is contained within a prominent bivalved carapace that, unusually, has its hinge line along the dorsal midline of the animal with the valves meeting on the ventral surface. The carapace forms a tube open at the front and back. The head protrudes from the front of this carapace tube, and consists of a small anterior plate, or sclerite, that bears a pair of large, spherical eyes on short stalks. On the head between the two large eyes are three small, highly reflective spots that have been interpreted as median eyes.
Behind the head, the body consisted of approximately 47 narrow segments, each bearing a pair of appendages. The appendages on the first two body segments are thin, segmented walking branches, but all appendages behind this are segmented and branch into two (biramous). These biramous appendages have a segmented inner branch that has a large spine at its base and splits into two walking branches distally, and an outer branch with filamentous blades. The tail or telson has three blades or flukes, two of which extend laterally and the third of which extends vertically. The gut is typically straight and has paired midgut glands.
Odaraia typically makes up less than 0.5% of the community in Walcott Quarry, from which over 200 specimens have been collected (Caron and Jackson, 2008). About a dozen specimens are known from Raymond Quarry.
The tubular carapace of Odaraia would have enclosed the ventral appendages, making it impossible for the animal to use its appendages for walking on the sea floor. It therefore seems to have swum through the water column by waving the inner segmented branches of its biramous appendages. The outer filamentous branches were likely used for respiration.
The large eyes and gut glands suggest that Odaraia was an active predator, seeking out floating or swimming organisms and sieving them out the water as the current passed through the tubular carapace. To minimize the drag created by its dorsal hinge, it is quite likely that Odaraia swam on its back, similar to the modern horseshoe crab. The large telson would have been used to stabilize the animal while swimming to prevent it from rolling, and to help with steering and braking.