© Smithsonian Institution – National Museum of Natural History. Photo: Jean-Bernard Caron
Trilobites are extinct euarthropods, probably stem lineage representatives of the Mandibulata, which includes crustaceans, myriapods, and hexapods (Scholtz and Edgecombe, 2006).
Chancia – unspecified.
palliseri – unspecified, but probably in reference to the Palliser Range of the Canadian Rockies (near Banff, AB), named by the Palliser Expedition (British North American Exploring Expedition, 1857-1860), led by John Palliser.
Burgess Shale and vicinity: Chancia bigranulosa, C. latigena, C. odarayensis, and C. stenometopa have been described from rocks that are slightly older and slightly younger at nearby sites on Mount Stephen and Mount Odaray.
Other deposits: Other species of Chancia occur in Cambrian rocks of western North America.
The Trilobite Beds and additional localities on Mount Stephen. The Walcott and Raymond Quarries on Fossil Ridge.
Although this rare species was named and illustrated as Ptychoparia palliseri by Walcott in 1908 and reassigned to Elrathia by Resser in 1937, it wasn’t formally described until Rasetti placed it in the genus Chancia in 1951! Interestingly, Walcott had established Chancia in 1924 for a very similar species (C. ebdome) in the Spence Shale of Utah and Idaho.
Hard parts: adult dorsal exoskeletons may be up to 4 cm long. The semicircular cephalon occupies about 30% the length of the entire dorsal shield; it is bordered by a low narrow rim, and bears short thorn-like genal spines. Elevated transverse ridges extend across the broad fixed cheeks to small prominent eyes located forward of the mid-glabellar length. The convex and narrowly conical glabella has three pairs of lateral furrows angled sharply backwards. A markedly broad, flat preglabellar field is about one-quarter the length of the cephalon, measured on the midline. The thorax of 20 parallel-sided segments has a narrow axis; the wide pleural lobes are gently flexed ventrally two-thirds of their length from the axial furrow. The thorax narrows in a wide smooth curve backwards to a very short, broadly triangular pygidium with three poorly defined axial rings and a terminal piece.
Unmineralized anatomy: not known.
Relatively rare at the Mount Stephen Trilobite Beds, rarer still on Fossil Ridge.
Like other rather similar-looking Cambrian ptychoparioid trilobites, C. palliseri may have been adapted to very low oxygen levels, feeding on particulate matter on the sea bed.
RASETTI, F. 1951. Middle Cambrian stratigraphy and faunas of the Canadian Rocky Mountains. Smithsonian Miscellaneous Collections, 116 (5): 277 p.
RESSER, C. E. 1937. Third contribution to nomenclature of Cambrian trilobites. Smithsonian Miscellaneous Collections, 95 (22): 29 p.
SCHOLTZ, G. AND G, D, EDGECOMBE. 2006. The evolution of arthropod heads: reconciling morphological, developmental and palaeontological evidence. Development Genes and Evolution, 216: 395-415.
WALCOTT, C. D. 1908. Mount Stephen rocks and fossils. Canadian Alpine Journal, 1: 232-248.
WALCOTT, C. D. 1924. Cambrian and Lower Ozarkian trilobites. Smithsonian Miscellaneous Collections, 75(2): 53-60.