The Burgess Shale

Media: 2D Model

Diraphora bellicostata

3D animation of Diraphora bellicostata and other brachiopods (Acrothyra gregaria, Micromitra burgessensis, Nisusia burgessensis, and Paterina zenobia).

Animation by Phlesch Bubble © Royal Ontario Museum

Taxonomy:

Kingdom: 2D Model
Phylum: 2D Model
Higher Taxonomic assignment: Rhynchonellata (Order: Orthida)
Species name: Diraphora bellicostata
Remarks:

Diraphora belongs to the Family Bohemiellidae.

Described by: Walcott
Description date: 1924
Etymology:

Diraphora – from the Greek deiras, “ridge,” and phoras, “bearing.”

bellicostata – from the Latin bellus, “beautiful,” and costatus, “ribbed.”

Type Specimens: Syntypes –USNM69731-69737 in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
Other species:

Burgess Shale and vicinity: none to date. The Burgess Shale brachiopods in particular from the Trilobite Beds on Mount Stephen need to be re-examined (see also Brief history of research).

Other deposits: Several species are known in North America and Australia.

Age & Localities:

Age:
Middle Cambrian, Bathyuriscus-Elrathina Zone (approximately 505 million years ago).
Principal localities:

The Walcott Quarry on Fossil Ridge.

History of Research:

Brief history of research:

Originally assigned to Eoorthis by Walcott (1924), this species was subsequently reassigned by Bell as the type species of a new genus, Diraphora (Bell, 1941). Diraphora bellicostata has not been studied since its original description by Walcott in 1924. Walcott’s description is cursory, inadequately diagnosing the specimen, and no types were designated. The species needs to be redescribed.

Description:

Morphology:

Diraphora bellicostata possesses sharp ornamental lines (costae) radiating on its surface from the hinge. The shells would have been articulated with short and small teeth, like in Nisusia, a comparable form from the Burgess Shale. No preserved soft parts are known and the shell was originally mineralized.

Abundance:

Diraphora bellicostata is known from several hundred specimens in the Walcott Quarry and is the most abundant of all brachiopods but still represents a relatively small fraction of the entire fauna (<1.3%) (Caron and Jackson, 2008).

Maximum Size:
10 mm

Ecology:

Life habits: 2D Model
Feeding strategies: 2D Model
Ecological Interpretations:

It is likely that Diraphora had a short, stout pedicle from which it was attached to the substrate. Some specimens are attached to spicules of sponges in particular of Pirania. Other organisms (for example Mackenzia) attached themselves on isolated valves of Diraphora (representing dead individuals), which they used as anchors. Extraction of food particles from the water would have been possible thanks to a filter-feeding apparatus (located between the shells) called a lophophore.

References:

BELL, C. W. 1941. Cambrian Brachiopoda from Montana. Journal of Paleontology, 15: 193-255.

CARON, J.-B. AND D. A. JACKSON. 2008. Paleoecology of the Greater Phyllopod Bed community, Burgess Shale. Palaeogeography, Palaeoclimatology, Palaeoecology, 258: 222-256.

WALCOTT, C. D. 1924. Cambrian and Ozarkian Brachiopoda. Cambrian Geology and Paleontology IV. Smithsonian Miscellaneous Collections, 67: 477-554.

Other Links:

None

Dinomischus isolatus

Reconstruction of Dinomischus isolatus.

© Marianne Collins

Taxonomy:

Kingdom: 2D Model
Phylum: 2D Model
Higher Taxonomic assignment: Non applicable
Species name: Dinomischus isolatus
Remarks:

Although it has been suggested that Dinomischus may be related to the ectoprocts (Conway Morris, 1977), its unusual morphology has not yet been conclusively related to a known phylum and as such its affinities remain unclear.

Described by: Conway Morris
Description date: 1977
Etymology:

Dinomischus – from the Greek dinos, “goblet,”, and michos, “stalk or stem.” The name refers to the wine glass-shape of the animal.

isolatus – from the Latin insula, “island.” The name refers to the non-gregarious life habit of this animal.

Type Specimens: Holotype –USNM198735 in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
Other species:

Burgess Shale and vicinity: none.

Other deposits: D. venutus Chen, Hou and Lu, 1989 from the Lower Cambrian Chengjiang fauna.

Age & Localities:

Age:
Middle Cambrian, Bathyuriscus-Elrathina Zone (approximately 505 million years ago).
Principal localities:

Burgess Shale and vicinity: Walcott Quarry, Raymond Quarry, Tulip Beds (S7)

Other deposits: A single specimen of D. isolatus was also reported from the Middle Cambrian Kaili Formation (Peng et al., 2006).

History of Research:

Brief history of research:

D. isolatus was among the original fossils collected by Walcott, although it was not formally described until 1977 by Conway Morris. The original description was based on three specimens. A second species was added by Chen et al. (1989) based on material from the Chengjiang in China. Further specimens have been collected by the Royal Ontario Museum from sites on both Fossil Ridge and Mount Stephen.

Description:

Morphology:

Dinomischus consists of a cup-shaped calyx supported by a long stem that terminates in a bulbous swelling. A circle of 20 stiff bracts up to 4.5 mm in length surround the upper margin of the calyx. These point upward and project beyond the level of the anus and the mouth and are interpreted as part of a filter feeding apparatus. Reflective material in the central part of the calyx has been interpreted as a U-shaped gut, with a large sac-like stomach positioned centrally and a mouth and anus on the upper surface. The stem appears to be a rigid structure and the bulbous termination is interpreted as an attachment structure.

Abundance:

Dinomischus is very rare. Only three specimens were originally described from the Burgess Shale. A few additional specimens are known in the Burgess Shale collections of the Royal Ontario Museum.

Maximum Size:
28 mm

Ecology:

Life habits: 2D Model
Feeding strategies: 2D Model
Ecological Interpretations:

Dinomischus was a stalked filter feeder that lived anchored to the sea floor. Its ring of bracts would have captured food particles from passing water and moved them to the mouth.

References:

CONWAY MORRIS, S. 1977. A new entoproct-like organism from the Burgess Shale of British Columbia. Palaeontology, 20(4): 833-845.

CHEN, J. HOU, X. AND H. LU. 1989. Early Cambrian hock glass-like rare sea animal Dinomischus (Entoprocta) and its ecological features. Acta Palaeontologica Sinica., 28 (1): 58-71.

PENG, J., Y. L. ZHAO AND J. P. LIN. 2006. Dinomischus from the Middle Cambrian Kaili Biota, Guizhou, China. Acta Geologica Sinica-English Edition, 80: 498-501.

Other Links:

None

Ottoia prolifica

3D animation of Ottoia prolifica.

ANIMATION BY PHLESCH BUBBLE © ROYAL ONTARIO MUSEUM

Taxonomy:

Kingdom: 2D Model
Phylum: 2D Model
Higher Taxonomic assignment: Unranked clade (stem group priapulids)
Species name: Ottoia prolifica
Remarks:

Ottoia has been compared to the nemathelminth worms (Maas et al., 2007), but most analyses support a relationship with the priapulids at a stem-group level (Harvey et al., 2010; Wills, 1998).

Described by: Walcott
Description date: 1911
Etymology:

Ottoia – from Otto Pass (2,106 m), a few kilometres north-west of the Burgess Shale. The pass was named after Otto Klotz, an astronomer working for the Department of the Interior along the Canadian Pacific Railroad (read about Otto Klotz in the section “First Discoveries”)

prolifica – from the Latin proles, “offspring,” and ferax, “rich, fruitful,” in reference to the great number of specimens discovered.

Type Specimens: Lectotype –USNM57619 in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
Other species:

Burgess Shale and vicinity: none

Other deposits: Ottoia sp. from the Lower Cambrian Pioche Shale, Nevada (Lieberman, 2003).

Age & Localities:

Age:
Middle Cambrian, Bathyuriscus-Elrathina Zone to Ptychagnostus punctuosus Zone (approximately 505 million years ago).
Principal localities:

Burgess Shale and vicinity: The Walcott and Raymond Quarries on Fossil Ridge, the Collins Quarry, the Tulip Beds (S7) and smaller localities on Mount Stephen. Smaller localities on Mount Field, Mount Odaray and Monarch Cirque.

Other deposits: The same species also occurs in the Middle Cambrian Spence Shale and Marjum Formations, Utah (Conway Morris and Robison, 1986).

History of Research:

Brief history of research:

Charles Walcott (1911) first described Ottoia as a tentative member of the now-dismantled grouping of worms called the Gephyrea, which included the priapulids as well as the sipunculans and echiurans. He emphasized a comparison with the sipunculans, leading some subsequent authors to consider it as a member of this phylum; others, however, suggested affinities with the parasitic acanthocephalans, or the priapulids (Banta and Rice, 1970). A re-analysis of the fossil material itself was not conducted until the 1970s, with work by Banta and Rice (1970) and Conway Morris (1977) supporting a relationship with the priapulids, which was later demonstrated to be at a stem-group level (Wills, 1998). Other work has focussed on the ecology of the Burgess Shale representatives (Bruton, 2001; Vannier, 2009; Vannier et al., 2010).

Description:

Morphology:

Ottoia is a priapulid worm with a tooth-lined mouthpart (proboscis) that could be inverted into the trunk; a short posterior tail extension could also be inverted. Ottoia reached 15 cm in length; the smallest specimens – presumably juveniles, but identical to adults – were just 1 cm long. The proboscis was adorned with 28 rows of hooks interspersed with a variety of spines. The worms are usually found curved into a U-shape, with their sediment-filled guts often visible running down the centre of the organism. The trunk was annulated, and bore two sets of four hooks arranged in a ring towards the rear end; these are the only traces of bilateral symmetry, with a radial symmetry superimposed on the organism. Ottoiaperiodically shed its cuticle to allow growth.

Abundance:

Ottoia is one of the more abundant Burgess Shale organisms, accounting for over 80% of the Walcott Quarry priapulids (Conway Morris, 1977) and over 1.3% of the entire Walcott Quarry community (Caron and Jackson, 2008); thousands of specimens are known.

Maximum Size:
150 mm

Ecology:

Life habits: 2D Model
Feeding strategies: 2D Model
Ecological Interpretations:

Specimens of Haplophrentis carinatus preserved in the gut indicate that this hyolith was a staple of the Ottoia diet (Conway Morris, 1977). One fossil slab also shows nine specimens feeding on a recently-dead Sidneyia carcass (Bruton, 2001).

References:

BANTA, W. C. AND M. E. RICE. 1970. A restudy of the Middle Cambrian Burgess Shale fossil worm, Ottoia prolifica. International Symposium on the Biology of the Sipuncula and Echiura 2, Kotor: 79-90.

BRUTON, D. L. 2001. A death assemblage of priapulid worms from the Middle Cambrian Burgess Shale. Lethaia, 34(2):163-167.

CARON, J.-B. AND D. A. JACKSON. 2008. Paleoecology of the Greater Phyllopod Bed community, Burgess Shale. Palaeogeography, Palaeoclimatology, Palaeoecology, 258: 222-256.

CONWAY MORRIS, S. 1977. Fossil priapulid worms. Special Papers in Palaeontology, 20: 1-95.

CONWAY MORRIS, S. AND J. S. PEEL. 2009. New Palaeoscolecidan Worms from the Lower Cambrian: Sirius Passet, Latham Shale and Kinzers Shale. Acta Palaeontologica Polonica, 55(1): 141-156.

HARVEY, T. H. P., X. DONG AND P. C. J. DONOGHUE. 2010. Are palaeoscolecids ancestral ecdysozoans? Evolution & Development, 12(2): 177-200.

MAAS, A., D. HUANG, J. CHEN, D. WALOSZEK AND A. BRAUN. 2007. Maotianshan-Shale nemathelminths – Morphology, biology, and the phylogeny of Nemathelminthes. Palaeogeography, Palaeoclimatology, Palaeoecology, 254(1-2): 288-306.

WALCOTT, C. 1911. Cambrian Geology and Paleontology II. Middle Cambrian annelids. Smithsonian Miscellaneous Collections, 57(5): 109-145.

Other Links:

http://paleobiology.si.edu/burgess/ottoia.html

Orthrozanclus reburrus

Taxonomy:

3D animation of Orthrozanclus reburrus.

ANIMATION BY PHLESCH BUBBLE © ROYAL ONTARIO MUSEUM

Kingdom: 2D Model
Phylum: 2D Model
Higher Taxonomic assignment: Unranked clade halwaxiids (stem group molluscs)
Species name: Orthrozanclus reburrus
Remarks:

The classification of this animal remains ambiguous but is thought to belong to the halwaxiids, a group including Wiwaxia and halkierids (Conway Morris and Caron, 2007). Two alternative positions were proposed for the halwaxiids, as either stem-group lophotrochozoans (a group which includes molluscs, annelids, and brachiopods) or as stem-group molluscs (see also Sigwart and Sutton, 2007).

Described by: Conway Morris and Caron
Description date: 2007
Etymology:

Orthrozanclus – from the Greek orthros, “dawn,” referring to its ancestral position, and zanclon, “sickle-like,” in reference to its long sclerites.

reburrus – from the Latin reburrus, “with bristling hair,” in reference to its hairy appearance.

Type Specimens: Holotype –ROM57197 in the Royal Ontario Museum, Toronto, Canada.
Other species:

Burgess Shale and vicinity: none.

Other deposits: none.

Age & Localities:

Age:
Middle Cambrian, Bathyuriscus-Elrathina Zone (approximately 505 million years ago).
Principal localities:

The Walcott Quarry on Fossil Ridge.

History of Research:

Brief history of research:

Two specimens were collected by Walcott but were never described. Between 1994 and 2000, the Royal Ontario Museum collected nine additional specimens from the Walcott Quarry. These were recognized as an unknown sclerite-bearing animal (Type C, Caron and Jackson 2006) allowing for a formal description of this new species (Conway Morris and Caron, 2007).

Description:

Morphology:

Specimens vary from 6 mm to 11.3 mm in length. The ventral side is flat, whereas the dorsal surface is rounded in cross-section, bearing three zones of sclerites and one anterior shell. A set of relatively small sclerites is present around the margins of the body. These appear flat and slightly curved in one direction. Above this marginal set is a second set of much longer sclerites that seem to originate from a narrow zone along the entire length of the body. These are circular in cross section, appear to have a larger base, and tend to be curved and pointing upwards; they are probably hollow and bear one or two ridges. The presence of kinked sclerites suggests a lack of mineralization. A third set of much smaller sclerites covers the convex dorsal side of the body, but these are not clearly preserved. The shell, which was presumably mineralized, is triangular in outline with the pointed end towards the front. Fine striations along the shell are probably growth lines, indicating that growth occurred from the front to the back.

Abundance:

Very rare; all 11 known specimens come from the Walcott Quarry only, where it represents a tiny fraction of the community (0.02%) (Caron and Jackson, 2008).

Maximum Size:
11 mm

Ecology:

Life habits: 2D Model
Feeding strategies: 2D Model
Ecological Interpretations:

Orthrozanclus is similar in overall aspect and probably in ecology to the better known Wiwaxia corrugata.Orthrozanclus, like Wiwaxia, was probably herbivorous and would have crept along the seafloor in search for food.

References:

CARON, J.-B. AND D. A. JACKSON. 2008. Paleoecology of the Greater Phyllopod Bed community, Burgess Shale. Palaeogeography, Palaeoclimatology, Palaeoecology, 258: 222-256.

CONWAY MORRIS, S. AND J.-B. CARON. 2007. Halwaxiids and the early evolution of the lophotrochozoans. Science, 315: 1255-1258.

SIGWART, J. D. AND M. D. SUTTON. 2007. Deep molluscan phylogeny: synthesis of palaeontological and neontological data. Proceedings of the Royal Society B: Biological Sciences, 274: 2413-2419.

Other Links:

http://www.sciencemag.org/content/315/5816/1255

Opabinia regalis

3D animation of Opabinia regalis.

ANIMATION BY PHLESCH BUBBLE © ROYAL ONTARIO MUSEUM

Taxonomy:

Kingdom: 2D Model
Phylum: 2D Model
Higher Taxonomic assignment: Dinocarida (Order: Radiodonta, stem group arthropods)
Species name: Opabinia regalis
Remarks:

Opabinia is an anomalocaridid. Anomalocaridids have been variously regarded as basal stem-lineage euarthropods (e.g., Budd, 1996; Zhang and Briggs, 2007, Daley et al., 2009), basal members of the arthropod group Chelicerata (e.g., Chen et al., 2004), and as a sister group to the arthropods (e.g., Hou et al., 2006)

Described by: Walcott
Description date: 1912
Etymology:

Opabinia – from Opabin Pass (2,606 m) between Mount Hungabee and Mount Biddle in Yoho National Park. From the Stoney First Nation Nakoda word for “rocky,” a descriptive name for the pass given by Samuel Allen in 1894.

regalis – from the Latin regalis, “royal, or regal.”

Type Specimens: Lectotype –USNM57683 in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
Other species:

Burgess Shale and vicinity: none.

Other deposits: none.

Age & Localities:

Age:
Middle Cambrian, Bathyuriscus-Elrathina Zone (approximately 505 million years ago).
Principal localities:

The Walcott and Raymond Quarries on Fossil Ridge.

History of Research:

Brief history of research:

Opabinia regalis was first described by Walcott (1912) as the most primitive of all Burgess Shale arthropods. Owing to its unique morphology with a bizarre frontal “nozzle,” Opabinia became a flagship fossil for the Burgess Shale, leading to much speculation on its affinity and lifestyle. One famous reconstruction shows the animal swimming upside down as an anostracan crustacean (Hutchinson, 1930).

It wasn’t until the major redescription by Whittington (1975) that the morphology of Opabinia was revealed to be truly one of the most enigmatic of all fossils. It was so unusual, in fact, that when Whittington showed an early version of his reconstruction in a meeting of palaeontologists in 1972, the whole room burst out laughing!

Further work by Bergström (1986) identified similarities between Opabinia and the recently discovered whole-body specimens of Anomalocaris (Whittington and Briggs, 1985), and updated the morphology of the gills and frontal proboscis. Budd (1996) was the first to place Opabinia in the stem lineage of the euarthropods (just below the anomalocaridids), and also suggested the animal had trunk limbs, though this idea was contested by Zhang and Briggs (2007). The issue of whether Opabinia had trunk limbs remains controversial (Budd and Daley, 2011).

Description:

Morphology:

Opabinia has five eyes, a frontal “nozzle,” or proboscis, a body with serially repeated lateral lobes and gills, and a prominent tail fan. The whole body length ranges between 4.3 and 7.0 cm (excluding proboscis). The head has a rounded anterior margin, with five bulbous compound eyes on short stalks clustered on the dorsal surface of the head. The annulated frontal proboscis is four times longer than the head. It is highly flexible, and has a fused pair of appendages at the distal end, consisting of two opposing claws with five or six spines each. The mouth was ventral and faced to the rear.

The trunk was divided into 15 segments, each bearing a pair of lateral lobes in association with gill structures consisting of a series of lanceolate blades. There is some controversy as to the exact location of the gills (dorsal, ventral or posterior) relative to the lobes. The tail fan consists of three pairs of upward-directed flaps. The central region of the body shows an outline of the main body cavity, and a dark line representing a trace of the gut runs along the length of the body, starting with a U-shaped bend near the rearward opening ventral mouth. Paired spherical structures next to the alimentary canal could represent gut glands. There are also controversial triangular features in the central region of the body, which have alternatively been interpreted as lobopod-like walking limbs (Budd, 1996), or as undifferentiated diverticula or extensions of the gut (Whittington, 1975; Zhang and Briggs, 2007).

Abundance:

Opabinia is rare, with only 42 specimens known from all collections. In the Walcott Quarry, Opabinia represents only 0.006% of the community (Caron and Jackson, 2008).

Maximum Size:
101 mm

Ecology:

Life habits: 2D Model
Feeding strategies: 2D Model
Ecological Interpretations:

Opabinia was a swimmer. Undulatory waves along its lateral lobes propelled it forward, while it used its tail fan to steer. Opabinia probably employed the distal claws on its flexible nozzle to grasp soft food items and carry them towards its ventral mouth.

References:

BERGSTRÖM, J. 1986. Opabinia and Anomalocaris, unique Cambrian ‘arthropods.’ Lethaia, 19: 241-46.

BUDD, G.E. 1996: The morphology of Opabinia regalis and the reconstruction of the arthropod stem group. Lethaia, 29: 1-14.

BUDD, G.E. AND A. DALEY. 2011. The lobes and lobopods of Opabinia regalis from the middle Cambrian Burgess Shale. Lethaia, DOI: 10.1111/j.1502-3931.2011.00264.x.

CARON, J.-B. AND D. A. JACKSON. 2008. Paleoecology of the Greater Phyllopod Bed community, Burgess Shale. Palaeogeography, Palaeoclimatology, Palaeoecology, 258: 222-256.

HUTCHINSON, G.E. 1930. Restudy of some Burgess Shale fossils. Proceedings of the U.S. National Museum, 78: 1-11.

WALCOTT, C. D. 1912. Middle Cambrian Branchiopoda, Malacostraca, Trilobita and Merostomata. Smithsonian Miscellaneous Collections, 57: 145-228.

WHITTINGTON, H.B. 1975. The enigmatic animal Opabinia regalis, Middle Cambrian, Burgess Shale, British Columbia. Philosophical Transactions of the Royal Society of London, Series B: Biological Sciences, 271: 1-43.

WHITTINGTON, H. B. AND D. E. G. BRIGGS. 1985. The largest Cambrian animal, Anomalocaris, Burgess Shale, British Columbia. Philosophical Transactions of the Royal Society of London Series B-Biological Sciences, 309: 569-609.

ZHANG, X.-G. AND D. E. G. BRIGGS. 2007: The nature and significance of the appendages of Opabinia from the Middle Cambrian Burgess Shale. Lethaia, 40: 161-173.

Other Links:

http://paleobiology.si.edu/burgess/opabinia.html

Canadia spinosa

3D animation of Canadia spinosa.

Animation by Phlesch Bubble © Royal Ontario Museum

Taxonomy:

Kingdom: 2D Model
Phylum: 2D Model
Higher Taxonomic assignment: Unranked clade (stem group polychaetes)
Species name: Canadia spinosa
Remarks:

Canadia was briefly compared to modern chrysopetalids (Family: Palmyridae) but the similarities were thought to be too general to allow the inclusion of this species to this group (Conway Morris, 1979). Canadia is now regarded as a stem-group polychaete (Eibye-Jacobsen, 2004).

Described by: Walcott
Description date: 1911
Etymology:

Canadia – from Canada, the country where the Burgess Shale is located.

spinosa – from the Latin spinosus, “full of spines,” reflecting its spiny appearance.

Type Specimens: Lectotype –USNM57654 in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
Other species:

Burgess Shale and vicinity: none.

Other deposits: One specimen known from the Spence Shale (Middle Cambrian of Utah) and described as Canadia sp. (Robison, 1969).

Age & Localities:

Age:
Middle Cambrian, Bathyuriscus-Elrathina Zone (approximately 505 million years ago).
Principal localities:

The Walcott Quarry on Fossil Ridge.

History of Research:

Brief history of research:

Walcott (1911) described two different species of Canadia (C. setigera and C. spinosa) in his initial census of the Burgess Shale, and a more detailed description was produced from his notes after his death by Resser (Walcott, 1931) adding several additional species (C. grandis, C. irregularis, C. sparsa, C. dubia, and C. simplex). Conway Morris (1979) synonymised C. irregularis and C. grandis with C. spinosa, while the other species have all been reinterpreted as different genera. Nick Butterfield (1990) succeeded in isolating individual scales by dissolving fossils in acid. These scales were compared with the sclerites of Wiwaxia, suggesting a possible affinity between the two taxa. Wiwaxia is now regarded as a primitive mollusc (Caron et al., 2006) implying the scales of Canadia and sclerites of Wiwaxia are probably convergent. Like Burgessochaeta, Canadia has proven useful in calculating the extent of decay in fossil assemblages (Caron and Jackson, 2006).

Description:

Morphology:

Canadia is a bristled worm around 2 to 4 cm long and slightly dorsoventrally flattened. A long pair of smooth, tentacles protrudes from the front of its head. The variation in shape seen among these tentacles suggests that the organism could contract and extend them. The rest of the body consists of 20 to 22 trunk segments, each bearing a pair of lateral projections called parapodia. On the first segment the parapodia are simple (uniramous), while all the other segments have biramous parapodia (divided into two sections). All parapodia bear bristles called setae. In the second segment through to the last segment they form two main bundles, the notosetae (dorsal) and the neurosetae (lateral). Gills (branchiae) are situated between these two bundles of setae. The notosetae cover the organism asymmetrically, with the longest, widest setae closest to the midline. The lateral surface of the larger setae is serrated, and all the setae bear a finely spaced patterning of ridges, which may have given Canadia an iridescent lustre in life (Parker, 1998). The animal had a straight gut, and an eversible soft proboscis.

Abundance:

Canadia is relatively rare in the Walcott Quarry representing only 0.05% of the specimens counted in the community (Caron and Jackson, 2008).

Maximum Size:
45 mm

Ecology:

Life habits: 2D Model
Feeding strategies: 2D Model
Ecological Interpretations:

Canadia probably lived close to the seafloor and could have swum by using its bristle-fans as paddles and by undulating its body. It would have used its tentacles primarily as sensory organs, and its proboscis for feeding on live or dead organisms.

References:

BUTTERFIELD, N. J. 1990. A reassessment of the enigmatic Burgess Shale fossil Wiwaxia corrugata (Matthew) and its relationship to the polychaete Canadia spinosa Walcott. Paleobiology, 16(3): 287-303.

CARON, J.-B. AND D. A. JACKSON. 2006. Taphonomy of the Greater Phyllopod Bed Community, Burgess Shale. PALAIOS, 21: 451-465.

CARON, J.-B., A. H. SCHELTEMA, C. SCHANDER, AND D. RUDKIN. 2006. A soft-bodied mollusc with radula from the Middle Cambrian Burgess Shale. Nature, 442: 159-163.

CARON, J.-B. AND D. A. JACKSON. 2008. Paleoecology of the Greater Phyllopod Bed community, Burgess Shale. Palaeogeography, Palaeoclimatology, Palaeoecology, 258: 222-256.

CONWAY MORRIS, S. 1979. Middle Cambrian polychaetes from the Burgess Shale of British Columbia. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences, 285(1007): 227-274.

EIBYE-JACOBSEN, D. 2004. A reevaluation of Wiwaxia and the polychaetes of the Burgess Shale. Lethaia, 37: 317-335.

PARKER, A. R. 1998. Colour in Burgess Shale animals and the effect of light on evolution in the Cambrian. Proceedings of the Royal Society of London, Biological Sciences. 265: 967-972.

ROBISON, R. A. 1969. Annelids from the Middle Cambrian Spence Shale of Utah. Journal of Paleontology, 43: 1169-1173.

WALCOTT, C. D. 1911. Middle Cambrian annelids. Smithsonian Miscellaneous Collections, 57(2): 109-144.

WALCOTT, C. 1931. Addenda to descriptions of Burgess Shale fossils. Smithsonian Miscellaneous Collections, 85(3): 1-46.

Other Links:

http://paleobiology.si.edu/burgess/canadia.html

Canadaspis perfecta

3D animation of Canadaspis perfecta.

Animation by Phlesch Bubble © Royal Ontario Museum

Taxonomy:

Kingdom: 2D Model
Phylum: 2D Model
Higher Taxonomic assignment: Unranked clade (stem group arthropods)
Species name: Canadaspis perfecta
Remarks:

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).

Described by: Walcott
Description date: 1912
Etymology:

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.”

Type Specimens: Lectotype –USNM57703 in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
Other species:

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).

Age & Localities:

Age:
Middle Cambrian, Bathyuriscus-Elrathina Zone (approximately 505 million years ago).
Principal localities:

The Walcott Quarry on Fossil Ridge.

History of Research:

Brief history of research:

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).

Description:

Morphology:

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).

Abundance:

Canadaspsis is abundant, with over 5,000 specimens known; it comprises 8.6% of the Walcott Quarry community (Caron and Jackson, 2008).

Maximum Size:
52 mm

Ecology:

Life habits: 2D Model
Feeding strategies: 2D Model
Ecological Interpretations:

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.

References:

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.

BRIGGS, D. E. G. 1977. Bivalved arthropods from the Cambrian Burgess Shale of British Columbia. Palaeontology, 20: 596-612.

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.

BRIGGS, D. E. G., B. S. LIEBERMAN, J. R. HENDRICKS, S. L. HALGEDAHL AND R. D. JARRARD. 2008. Middle Cambrian arthropods from Utah. Journal of Paleontology, 82(2): 238-254.

BUDD, G. E. 2002. A palaeontological solution to the arthropod head problem. Nature, 417(6886): 271-275.

BUDD, G. E. 2008. Head structure in upper stem-group euarthropods. Palaeontology, 51(3): 561-573.

BUDD, G. E. AND M. J. TELFORD. 2009. The origin and evolution of arthropods. Nature, 457(7231): 812-817.

BUTTERFIELD, N. J. 2002. Leanchoilia guts and the interpretation of three-dimensional structures in Burgess Shale-type fossils. Paleobiology, 28(1): 155-171.

CARON, J.-B. and D. A. JACKSON. 2008. Paleoecology of the Greater Phyllopod Bed community, Burgess Shale. Palaeogeography, Palaeoclimatology, Palaeoecology, 258: 222-256.

EDGECOMBE, G. D. 2010. Arthropod phylogeny: An overview from the perspectives of morphology, molecular data and the fossil record. Arthropod Structure & Development, 39: 74-87.

HOU, X. AND J. BERGSTRÖM. 1991. The arthropods of the Lower Cambrian Chengjiang fauna, with relationships and evolutionary significance p. 179-187. In A. M. Simonetta and S. Conway Morris (eds.), The Early Evolution of Metazoa and the Significance of Problematic Taxa. Cambridge University Press, Cambridge.

HOU, X. AND J. BERGSTRÖM. 1997. Arthropods of the Lower Cambrian Chengjiang fauna, southwest China. Fossils and Strata, 45: 1-116.

LIEBERMAN, B. S. 2003. A new soft-bodied fauna: the Pioche Formation of Nevada. Journal of Paleontology, 77(4): 674-690.

NOVOZHILOV. N. I. 1960. Principles of Paleontology: arthropods, trilobites and crustaceans. In Y. A. Orlov (ed.). Gos. Nauchno-Techn. Izdvo, Moscow.

ROBISON, R. A. AND B. C. RICHARDS. 1981. Larger bivalve arthropods from the Middle Cambrian of Utah. The University of Kansas Paleontological Contributions, 106: 1-28.

SIMONETTA, A. M. AND L. DELLE CAVE. 1975. The Cambrian non-trilobite arthropods from the Burgess shale of British Columbia: A study of their comparative morphology, taxonomy and evolutionary significance. Palaeontographia Italica, 69: 1-37.

WALCOTT, C. D. 1912. Middle Cambrian Branchiopoda, Malacostraca, Trilobita, and Merostomata, pp. 145-228, Cambrian Geology and Paleontology, 2.Volume 57 (6). Smithsonian Miscellaneous Collections.

WALOSZEK, D. 1999. On the Cambrian diversity of Crustacea, p. 3-27. In F. R. Schram and J. C. von Vaupel Klein (eds.), Crustaceans and the biodiversity crisis. Volume 1. Brill, Leiden.

WALOSZEK, D. MAAS, A. CHEN, J. AND M. STEIN. 2007. Evolution of cephalic feeding structures and the phylogeny of Arthropoda. Palaeogeography, Palaeoclimatology, Palaeoecology, 254: 273-287.

Other Links:

http://paleobiology.si.edu/burgess/canadaspis.html

Odontogriphus omalus

3D animation of Odontogriphus omalus.

ANIMATION BY PHLESCH BUBBLE © ROYAL ONTARIO MUSEUM

Taxonomy:

Kingdom: 2D Model
Phylum: 2D Model
Higher Taxonomic assignment: Unranked clade halwaxiids (stem group molluscs)
Species name: Odontogriphus omalus
Remarks:

Odontogriphus is an early stem-group mollusc (Caron et al., 2006; Sigwart and Sutton, 2007), or a stem-group to the lophotrochozoans, a group which includes molluscs, annelids, and brachiopods (Conway Morris and Caron, 2007). A relationship to annelids (Butterfield, 2006) has been suggested, but appears less likely (Caron et al., 2007).

Described by: Conway Morris
Description date: 1976
Etymology:

Odontogriphus – from the Greek odontos, “tooth,” and griphos, “puzzle, or riddle,” in reference to its uncertain affinities.

omalus – from the Greek homalos, “flat,” in reference to the animal’s flattened shape.

Type Specimens: Holotype –USNM196169 in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
Other species:

Burgess Shale and vicinity: none.

Other deposits: none.

Age & Localities:

Age:
Middle Cambrian, Bathyuriscus-Elrathina Zone (approximately 505 million years ago).
Principal localities:

The Walcott Quarry on Fossil Ridge and the Tulip Beds (S7) on Mount Stephen.

History of Research:

Brief history of research:

Walcott collected the first specimen between 1909 and 1924 but it remained unstudied for more than half a century. Conway Morris “rediscovered” the part and counterpart of this specimen in different sections of the Walcott collection and described it in 1976 as Odontogriphus omalus. The affinities of Odontogriphus remained uncertain until the Royal Ontario Museum discovered 189 new specimens between 1990 and 2000, allowing for a thorough redescription of the animal (Caron et al., 2006).

Description:

Morphology:

This entirely soft-bodied animal is ovoid and dorsoventrally compressed, reaching up to 125 mm in length and 43 mm in width. The front and back are semicircular in outline and of similar size. The mouth is ventral with a radula composed of two primary tooth rows. A muscular foot extends from behind the mouth to the posterior part of the animal and is surrounded by gills (or ctenidia), except at the front. The dorsal surface is smooth and does not bear any shells, spines or plates. Internally, a large stomach is preserved with a narrow and straight intestine ending in a sub-terminal anus.

Abundance:

Most specimens come from the Walcott Quarry, where Odontogriphus represents 0.42% of the community (Caron and Jackson, 2008). A single specimen comes from Mount Stephen (S7 locality).

Maximum Size:
125 mm

Ecology:

Life habits: 2D Model
Feeding strategies: 2D Model
Ecological Interpretations:

The presence of a radula suggests that Odontogriphus was a grazer, using its teeth to rasp and ingest food. Locomotory waves within the large foot would have enabled the animal to crawl along the surface of the mud. Odontogriphus might have fed on benthic, sheet-like masses of the cyanobacterium Morania, since fossils of both are often found associated in the same layers.

References:

BUTTERFIELD, N. J. 2006. Hooking some stem-group “worms”: fossil lophotrochozoans in the Burgess Shale. BioEssays, 28: 1161-1166.

CARON, J.-B., A. H. SCHELTEMA, C. SCHANDER AND D. RUDKIN. 2006. A soft-bodied mollusc with radula from the Middle Cambrian Burgess Shale. Nature, 442: 159-163.

CARON, J.-B., A. H. SCHELTEMA, C. SCHANDER AND D. RUDKIN. 2007. Reply to Butterfield on stem-group “worms:” fossil lophotrochozoans in the Burgess Shale. BioEssays, 29: 200-202.

CONWAY MORRIS, S. 1976. A new Cambrian lophophorate from the Burgess Shale of British Columbia. Palaeontology, 19: 199-222.

SIGWART, J. D. AND M. D. SUTTON. 2007. Deep molluscan phylogeny: synthesis of palaeontological and neontological data. Proceedings of the Royal Society B: Biological Sciences, 274: 2413-2419.

Other Links:

http://www.nature.com/nature/journal/v442/n7099/full/nature04894.html

Odaraia alata

3D animation of Odaraia alata.

ANIMATION BY PHLESCH BUBBLE © ROYAL ONTARIO MUSEUM

Taxonomy:

Kingdom: 2D Model
Phylum: 2D Model
Higher Taxonomic assignment: Unranked clade (stem group arthropods)
Species name: Odaraia alata
Remarks:

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).

Described by: Walcott
Description date: 1912
Etymology:

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.

Type Specimens: Lectotype –USNM57722 (O. alata) in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
Other species:

Burgess Shale and vicinity: none.

Other deposits: none.

Age & Localities:

Age:
Middle Cambrian, Bathyuriscus-Elrathina Zone (approximately 505 million years ago).
Principal localities:

The Walcott and Raymond Quarries on Fossil Ridge.

History of Research:

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.

Description:

Morphology:

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.

Abundance:

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.

Maximum Size:
150 mm

Ecology:

Life habits: 2D Model
Feeding strategies: 2D Model
Ecological Interpretations:

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.

References:

BRIGGS, D. E. G. 1981. The arthropod Odaraia alata Walcott, Middle Cambrian, Burgess Shale, British Columbia. Philosophical Transactions of the Royal Society of London B, 291: 541-582.

BRIGGS, D. E. G. AND R. A. FORTEY. 1989. The early radiation and relationships of the major arthropod groups. Science, 246: 241-243.

BUDD, G. E. 2002. A palaeontological solution to the arthropod head problem. Nature, 417: 271-275.

BUDD, G. E. 2008. Head structures in upper stem-group euarthropods. Palaeontology, 51: 561-573.

CARON, J.-B. AND D. A. JACKSON. 2008. Paleoecology of the Greater Phyllopod Bed community, Burgess Shale. Palaeogeography, Palaeoclimatology, Palaeoecology, 258: 222-256.

HOU, X. AND J. BERGSTRÖM. 1997. Arthropods of the Lower Cambrian Chengjiang fauna, southwest China. Fossils and Strata, 45: 1-116.

SIMONETTA, A. M. AND L. DELLE CAVE. 1975. The Cambrian non-trilobite arthropods from the Burgess shale of British Columbia: A study of their comparative morphology, taxonomy and evolutionary significance. Palaeontographia Italica, 69: 1-37.

WALCOTT, C. D. 1912. Cambrian Geology and Paleontology II. Middle Cambrian Branchiopoda, Malacostraca, Trilobita and Merostomata. Smithsonian Miscellaneous Collections, 57(6): 145-228.

WILLS, M. A., D. E. G. BRIGGS, R. A. FORTEY, M. WILKINSON AND P. H. A. SNEATH. 1998. An arthropod phylogeny based on fossil and recent taxa, p. 33-105. In G. D. Edgecombe (ed.), Arthropod fossils and phylogeny. Columbia University Press, New York.

Other Links:

None

Bathyuriscus rotundatus

Bathyuriscus rotundatus (USNM 116232b) – Plesiotype. Nearly complete individual with right free cheek in place. Specimen length = 14 mm. Specimen dry – direct light. Trilobite Beds on Mount Stephen.

© Smithsonian Institution – National Museum of Natural History. Photo: Jean-Bernard Caron

Taxonomy:

Kingdom: 2D Model
Phylum: 2D Model
Higher Taxonomic assignment: Trilobita (Order: Corynexochida)
Species name: Bathyuriscus rotundatus
Remarks:

Trilobites are extinct euarthropods, probably stem lineage representatives of the Mandibulata, which includes crustaceans, myriapods, and hexapods (Scholtz and Edgecombe, 2006).

Described by: Rominger
Description date: 1887
Etymology:

Bathyuriscus – a variation of the earlier trilobite genus name Bathyurus, originally based on the Greek bathys, “deep,” and the Greek oura, “tail,” thus, a trilobite with a deep tail.

rotundatus – from the Latin rotundus, “round,” presumably alluding to the rounded outline of the dorsal shield.

Type Specimens: Type status under review – UMMP 4884 (9 specimens), University of Michigan Museum of Paleontology, Ann Arbor, Michigan, USA.
Other species:

Burgess Shale and vicinity: Bathyuriscus adaeus Walcott, 1916, from several localities higher in the Bathyuriscus-Elrathina Zone on Mount Stephen, Mount Odaray, and Park Mountain.

Other deposits: other species of Bathyuriscus have been described from numerous localities elsewhere in the Cambrian of North America.

Age & Localities:

Age:
Middle Cambrian, Bathyuriscus–Elrathina Zone (approximately 505 million years ago).
Principal localities:

The Trilobite Beds and other localities on Mount Stephen. Fossil Ridge in sections stratigraphically below the Walcott Quarry.

History of Research:

Brief history of research:

Bathyuriscus rotundatus was first described in the same 1887 publication as several other important Mount Stephen trilobites. Carl Rominger initially used the name Embolimus rotundata for partial specimens of this trilobite, and named a second similar species in his collection Embolimus spinosa (now known as Zacanthoides romingeri). In 1908, Walcott revised Rominger’s original species name to yield the combination Bathyuriscus rotundatus, still in use today (Walcott, 1908). Along with the co-occurring Elrathina cordillerae, B. rotundatus is a signature fossil for the Middle Cambrian Bathyuriscus-Elrathina Zone in the southern Canadian Rockies.

Description:

Morphology:

Hard parts: adult dorsal exoskeletons may be up to 5 cm long and are narrowly oval in outline, with a semicircular cephalon, a thorax of nine segments ending in blade-like tips with short spines, and a semicircular pygidium without spines.

The long glabella reaches almost to the anterior cephalic border; the posterior portion is narrow and parallel-sided, while the anterior third expands rapidly forward. There are four pairs of lateral glabellar furrows, with the two front pairs angled forward and the posterior pair directed obliquely back. The eyes are relatively long and lie close to the glabella. Broad free cheeks are extended back into short genal spines. The pygidium is slightly smaller than the cephalon, with a well-defined narrow axial lobe of five rings and a terminal piece; four pairs of pygidial ribs are usually visible. The exoskeleton is mostly smooth externally, but very well preserved specimens may show faint anastomosing ridges on the free cheeks.

Unmineralized anatomy: not known.

Abundance:

Extremely common in the Mount Stephen Trilobite Beds, where it rivals Ogygopsis klotzi in abundance.

Maximum Size:
50 mm

Ecology:

Life habits: 2D Model
Feeding strategies: 2D Model
Ecological Interpretations:

Bathyuriscus rotundatus was a mobile epibenthic trilobite. Because we have no direct evidence of limb structure, its feeding habits are uncertain. It may have been a deposit feeder and opportunistic scavenger. Like Ogygopsis, Bathyuriscus may occur as fully intact individuals (probably carcasses), with the free cheeks missing, inverted, or rotated (presumed moults), and as scattered pieces. Some show evidence of healed injuries that may be predation scars (Rudkin, 2009).

References:

RASETTI, F. 1951. Middle Cambrian stratigraphy and faunas of the Canadian Rocky Mountains. Smithsonian Miscellaneous Collections, 116 (5): 1-277.

ROMINGER, C. 1887. Description of primordial fossils from Mount Stephens, N. W. Territory of Canada. Proceedings of the Academy of Natural Sciences of Philadelphia, 1887: 12-19.

RUDKIN, D. M. 2009. The Mount Stephen Trilobite Beds, pp. 90-102. In J.-B. Caron and D. Rudkin (eds.), A Burgess Shale Primer – History, Geology, and Research Highlights. The Burgess Shale Consortium, Toronto.

SCHOLTZ, G. AND EDGECOMBE, G. D. 2006. The evolution of arthropod heads: reconciling morphological, developmental and palaeontological evidence. Development Genes and Evolution, 216: 395-415.

WALCOTT, C. D. 1888. Cambrian fossils from Mount Stephens, Northwest Territory of Canada. American Journal of Science, series 3: 163-166.

WALCOTT, C. D. 1908. Mount Stephen rocks and fossils. Canadian Alpine Journal, 1: 232-248.

WALCOTT, C. D. 1916. Cambrian Geology and Paleontology III. Cambrian Trilobites. Smithsonian Miscellaneous Collections, 64(5): 303-456.

Other Links:

http://www.trilobites.info/ordcorynexochida.htm