3D animation of Odaraia alata.
ANIMATION BY PHLESCH BUBBLE © ROYAL ONTARIO MUSEUM
Odaraia was originally considered a crustacean (Walcott 1912; Briggs 1981; Briggs and Fortey 1989; Hou and Bergstrom 1997; Wills et al. 1998), following previous interpretations on the affinities of other bivalved arthropods (hymenocarines), like Branchiocaris (Briggs 1976) or Canadaspis (Briggs 1978). In the early 2000s, the affinities of Odaraia were re-evaluated and placed in the stem lineage of arthropods (Budd 2002, 2008). Following the discovery of mandibles in several hymenocarines and the re-interpretation of this group as early mandibulate arthropods (which include myriapods, crustaceans and insects), Odaraia was moved to the stem of mandibulates (Aria and Caron 2017; Vannier et al. 2018), and was perhaps even more closely related to myriapods (Aria et al. 2021). Odaraia gives its name to the family Odaraiidae, a group of hymenocarines with highly multisegmented bodies, reduced or absent antennulae and highly multisegmented legs, which includes other Burgess Shale taxa such as Nereocaris or Fibulacaris.
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.
Burgess Shale and vicinity: none.
Other deposits: none.
The Walcott and Raymond Quarries on Fossil Ridge.
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). New morphological features of the head were later incorporated, including a sclerite (Budd 2008) and nervous tissue (Ortega-Hernández 2015). A triad of organs or simple eyes at the front of the head have been associated with a sclerite known in other early arthropods (Ortega-Hernández 2015). The legs of Odaraia have been redescribed, highlighting a potential differentiation between the proximal and distal part (Aria and Caron 2017), a study which also illustrated the sternites (ventral segments) of the animal. Several closely related species to Odaraia, Jugatacaris agilis and different species of Pectocaris (Hou et al. 2004; Jin et al. 2021) have been discovered from the Lower Cambrian Chengjiang in China (Fu and Zhang 2011). The family Odaraidae was originally defined by Simonetta and Delle Cave, 1975. Since then, it has not been formally re-defined, but many other hymenocarines probably belong to this group.
Much of the body of Odaraia is contained within a prominent bivalved carapace in which the valves extend and meet on the ventral surface, similar to Nereocaris briggsi. The carapace forms a tube open at the front and back. The anteriormost, visible part of the head, protruding from the front of the carapace, consists of a rounded projection housing three organs or small eyes arranged triangularly, covered by a possible sclerite, and to which is attached pair of large, spherical eyes. Behind the head, the body consisted of approximately 47 narrow segments, each bearing a pair of appendages. Each limb is biramous, and has a segmented inner branch (endopod) and a paddle-like outer branch (exopod). The tail or telson has three blades or flukes, two of which extend laterally and the third of which extends vertically into a fin-like structure. The gut is typically straight with phosphatized 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 difficult 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 outer branches of its biramous appendages, although this does not rule out interactions with other organisms on the sea floor. The large eyes and phosphatized gut glands (Butterfield 2002) suggest that Odaraia was a predator, seeking out floating or swimming organisms and sieving them out the water as the current passed through the tubular carapace. However, the lack of prehensile or sensory appendages also suggest Odaraia might have been a suspension feeder. To minimize the drag created by its dorsal hinge, it was proposed that Odaraia swam on its back, similar to horseshoe crabs, and the related hymenocarine Fibulacaris. 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.
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