Home > Canadaspis perfecta
3D animation of Canadaspis perfecta.
Animation by Phlesch Bubble © Royal Ontario Museum
3D model of Canadaspis perfecta.
Animation by Phlesch Bubble © Royal Ontario Museum
Reconstruction of Canadaspis perfecta.
© Marianne Collins
Canadaspis perfecta (GSC 45261). Isolated valves, frontal view. Specimen length = 35 mm. Specimen dry – polarized light. Walcott Quarry.
© Geological Survey of Canada. Photo: Jean-Bernard Caron
Canadaspis perfecta (GSC 45279). Complete juvenile specimen, dorsal view. Specimen length = 18 mm. Specimen dry – polarized light. Walcott Quarry.
© Geological Survey of Canada. Photo: Jean-Bernard Caron
Canadaspis perfecta (ROM 56954). Slab with dozens of specimens associated with the priapulid worm Ottoia prolifica and the trilobite Elrathina cordillerae (bottom of slab). Right, close up of part of the same slab showing empty carapaces and specimens preserved with appendages. Slab width = 432 mm. Specimen dry – polarized light (left), wet – polarized light (right). Walcott Quarry.
© Royal Ontario Museum. Photos: Jean-Bernard Caron
Canadaspis perfecta (ROM 61119) – Part and counterpart. Complete specimen showing phosphatized gut diverticulae and posterior dark stain (probably representing decay fluids), lateral view. Left images, complete slab (part) showing associated species; Yohoia tenuis (bottom right), Waptia fieldensis (left, partially covered by a disarticulated carapace of Canadaspis), Burgessia bella (far left). Right images, details of the counterpart. Specimen length = 72 mm. Specimen dry – direct light (top row), dry – polarized light (bottom left), wet – polarized light (bottom right). Walcott Quarry.
© Royal Ontario Museum. Photos: Jean-Bernard Caron
Canadaspis perfecta (USNM 57703) – Lectotype. Complete specimen, lateral view. Specimen length = 47 mm. Specimen dry – polarized light. Walcott Quarry.
© Smithsonian Institution – National Museum of Natural History. Photo: Jean-Bernard Caron
Canadaspis was originally classified as a Malacostracan crustacean (Walcott, 1912; Briggs, 1978), but this has been widely debated (e.g. Hou and Bergström, 1997; Boxshall, 1998; Walossek, 1999; Butterfield, 2002). It has also been placed in the upper euarthropod stem-lineage (Edgecombe, 2010), forming a clade with other bivalved arthropods such as Perspicaris (Bergström and Hou, 1998; Waloszek et al., 2007), and possibly including Fuxianhuia (Budd, 2002; Budd and Telford, 2009).
Canadaspis – from the country Canada, whose name derives from the Saint-Lawrence Iroquoian kanata, “settlement” or “land,” and the Greek aspis, “ shield.”
perfecta – from the Latin perfectus, “complete.”
Burgess Shale and vicinity: none.
Other deposits: C. laevigata from the Lower Cambrian Chengjiang biota (Hou and Bergström, 1991, 1997). Further material of Canadaspis cf. perfecta has been recovered from additional localities in the USA (Robison and Richards, 1981; Lieberman, 2003; Briggs et al., 2008).
The Walcott Quarry on Fossil Ridge.
Originally referred to as Hymenocaris by Charles Walcott (1912), the genus Canadaspis was erected by Novozhilov (1960). Four species were designated by Simonetta and delle Cave (1975), but two of them, Canadaspis ovalis and Canadaspis dictynna have since been redescribed within Perspicaris dictynna (Briggs, 1977). A third species, Canadaspis obesa was redescribed within Canadaspis perfecta (Briggs, 1978). A full study of the fourth and only valid species, Canadaspis perfecta was published by Briggs (1978), who posited a crustacean affinity. This was rebuffed by later workers (Hou and Bergström, 1997; Boxshall, 1998; Walossek, 1999), and a close relationship with other bivalved Burgess Shale taxa in the arthropod stem lineage, including Branchiocaris, Perspicaris and Odaraia, was suggested (Budd, 2002; Budd, 2008).
Canadaspis is composed of a bivalved carapace covering a body with an appendage-bearing head region, an abdomen of 8 segments with associated limbs that are segmented and branch into two (biramous), and a thorax of 7 segments with a spiny telson or tail. The length of the bivalved carapaces ranges in size from 0.8-5.2 cm. The carapace valves are suboval in outline and taper towards the anterior, with a straight hinge line connecting them towards the back of the upper surface (dorsally).
The head has two pairs of antennae, small eyes, spiny mouth parts and two pairs of biramous appendages. The first antennae are short and unsegmented, while the second antennae are much longer, have at least 12 segments and are fringed with long spines. The small eyes were borne on short, blunt stalks. A series of spines behind the antennae are interpreted as mandibles, arthropod mouth parts used for cutting food. The ten pairs of biramous limbs of the head and abdomen consist of a segmented inner walking limb, and a large outer flap with lamellae, interpreted to be gills. The segmented abdomen does not bear appendages, and ends in a spiny telson. The gut of Canadaspis is sometimes preserved, with mid-gut glands giving it a segmented appearance (Butterfield, 2002).
Canadaspsis is abundant, with over 5,000 specimens known; it comprises 8.6% of the Walcott Quarry community (Caron and Jackson, 2008).
Canadaspis was likely to have lived on the sea floor, walking on its biramous appendages by moving them in a rippling motion. This would also waft water past the gills that form the outer branches of its biramous limbs, allowing for respiration. This movement may also propelled Canadaspis through the water column. The biramous appendages on Canadapsis’ head are tipped with a pair of claws that were probably used in feeding. The inner surfaces of its legs were covered with spines that would have assisted in feeding by directing food particles to the organism’s mouth. The mandibles would have been used to help consume the coarse particles found on the sediment surface. Canadapsis’ spiny head-shield probably protected it from predators.
BERGSTRÖM, J. AND X. HOU. 1998. Chengjiang arthropods and their bearing on early arthropod evolution, p. 151-184. In G. D. Edgecombe (ed.), Arthropod Fossils and Phylogeny. Columbia University Press, New York.
BOXSHALL, G. 1998. Comparative limb morphology in major crustacean groups: the coax-basis joint in postmandibular limbs, p. 155-167. In R. A Fortey and R. Thomas (eds.), Arthropod phylogeny. Chapman & Hall, London.
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BRIGGS, D. E. G. 1978. The morphology, mode of life, and affinities of Canadaspis perfecta (Crustacea: Phyllocarida), Middle Cambrian, Burgess Shale, British Columbia. Philosophical Transactions of the Royal Society of London, Series B, 281(984): 439-487.
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