The Burgess Shale

Ptychagnostus praecurrens

Ptychagnostus praecurrens (USNM 116212). Complete individual originally interpreted as the holotype of Triplagnostus burgessensis by Rasetti (1951). Specimen length = 8 mm. Specimen dry – direct light. Walcott Quarry.

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

Taxonomy:

Kingdom: Arthropoda
Phylum: Arthropoda
Higher Taxonomic assignment: Trilobita (Order: Agnostida)
Species name: Ptychagnostus praecurrens
Remarks:

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

Described by: Westergård
Description date: 1936
Etymology:

Ptychagnostus – from the Greek ptycho, “pleated” (some species have pleat-like furrows on the cephalon), and agnostos, for “unknown” or “unknowable.”

praecurrens – from the Latin prae, “before,” and currens, “to run,” in reference to the old age of this fossil

Type Specimens: Holotype – SGU611; in the Geological Survey of Sweden (Sveriges geologiska undersökning – SGU), Uppsala, Sweden (Westergård, 1936)
Other species:

Burgess Shale and vicinity: none.

Other deposits: other species occur throughout the world in Middle Cambrian rocks.

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:

Trilobites currently assigned to this genus and species have been described under several name combinations. Originally, Rasetti (1951) described it as Triplagnostus burgessensis, but subsequently (Rasetti, 1967) considered T. burgessensis to be a synonym of Ptychagnostus praecurrens (Westergård, 1936), a name retained by Peng and Robison (2000), despite numerous interim variations.

Description:

Morphology:

Hard parts: adult dorsal exoskeletons reach about 8 mm in length. The semicircular cephalon has a narrow marginal rim around the front and sides and sharply rounded the genal angles. There are no dorsal eyes and no facial sutures. The narrow glabella comes to an ogival point, with a median furrow extending across the short preglabellar field to the anterior margin; a transverse furrow crosses the glabella just in front of a low tubercle located behind the midpoint. Two short thoracic segments carry lateral nodes on the axial rings. A narrowly rimmed pygidium, the same size and general shape as the cephalon, has abruptly angled anterolateral corners. The pygidial axis is broader than the glabella, but of similar outline, with a median tubercle between two transverse furrows. The pointed tip of the axis reaches almost to the rim posteriorly, without a median furrow.

Unmineralized anatomy: not known

Abundance:

Very common in the Walcott Quarry on Fossil Ridge, where it is the most abundant trilobite (Caron and Jackson, 2008).

Maximum Size:
10 mm

Ecology:

Life habits: Arthropoda
Feeding strategies: Arthropoda
Ecological Interpretations:

Adult agnostine trilobites have often been regarded as pelagic organisms that swam or drifted in the water column. Evidence now suggests that most were members of the mobile benthic epifauna, possibly micrograzers or particle feeders, preferentially occupying colder, deeper, offshore waters.

References:

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

PENG, S. C. AND ROBISON, R. A. 2000. Agnostoid biostratigraphy across the middle-upper Cambrian boundary in Hunan, China. Paleontological Society Memoir, no. 53 (supplement to Journal of Paleontology), 74(4), 104 pp.

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

RASETTI, F. 1967. Lower and Middle Cambrian trilobite faunas from the Taconic Sequence of New York. Smithsonian Miscellaneous Collections, 152(4): 112 pp.

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.

WESTERGÅRD, A. H. 1936. Paradoxides oelandicus beds of Oland: with the account of a diamond boring through the Cambrian at Mossberga. Sveriges Geologiska Undersökning. Series C, no. 394, Årsbok 30, no. 1: 1-66.

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Kootenia burgessensis

Kootenia burgessensis (ROM 60761). Disarticulated specimen. Specimen dry – direct light (left) and coated with ammonium chloride sublimate to show details (right). Specimen length = 44 mm. Walcott Quarry.

© Royal Ontario Museum. Photo: Jean-Bernard Caron

Taxonomy:

Kingdom: Arthropoda
Phylum: Arthropoda
Higher Taxonomic assignment: Trilobita (Order: Corynexochida)
Species name: Kootenia burgessensis
Remarks:

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

Described by: Resser
Description date: 1942
Etymology:

Kootenia – unspecified, but almost certainly for the Kootenay region of southeast British Columbia, or the derivative Kootenay River, both based upon the Ktunaxa or Kutenai First Nation of the same area.

burgessensis – from the Burgess Shale.

Type Specimens: Holotype (K. burgessensis) – USNM65511 in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA (Resser, 1942); Type status under review – (K. dawsoni), University of Michigan Museum of Paleontology, Ann Arbor, Michigan, USA.
Other species:

Burgess Shale and vicinity: Kootenia dawsoni; Olenoides serratus. (Species of Kootenia are no longer considered different enough from those in Olenoides to warrant placement in a separate genus, but Kootenia is retained here for ease of reference to historical literature).

Other deposits: other species attributed to Kootenia are widespread in the Cambrian of North America, and have been recorded in Greenland, China, Australia, and elsewhere.

Age & Localities:

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

The Walcott Quarry on Fossil Ridge, and nearby localities on Mount Field; K. dawsoni is known from the Trilobite Beds and elsewhere on Mount Stephen.

History of Research:

Brief history of research:

Kootenia burgessensis was established by Charles Resser based on material Walcott included in K. dawsoni. Kootenia originally appeared as a subgenus of Bathyuriscus in Walcott’s 1889 paper revising many of Rominger’s Mount Stephen trilobite identifications. Walcott named B. (Kootenia) dawsoni after G. M. Dawson of the Geological Survey of Canada as a replacement for what Rominger had illustrated as Bathyurus (?) in 1887.

In 1908, Walcott followed G. F. Matthew (1899) in calling this Dorypyge (Kootenia) dawsoni, but regarded Kootenia as a full genus in 1918. Harry Whittington included Kootenia burgessensis in his 1975 redescription of Burgess Shale appendage-bearing trilobites, illustrating a single specimen showing biramous thoracic limbs on one side. In 1994, Melzak and Westrop concluded that Kootenia could not be consistently discriminated from Olenoides using traditional characters of the spinose pygidium.

Description:

Morphology:

Hard parts: adult dorsal exoskeletons may reach 5.5 cm in length and are broadly oval in outline. In most general features, Kootenia burgessensis resembles the co-occurring Olenoides serratus, with a semi-circular cephalon bearing genal spines, a thorax of seven segments, and a semi-circular pygidium. In Kootenia, however, spines on the thoracic pleural tips and shorter and blunter, as are those around the margin of the pygidium; interpleural furrows on the pygidium are absent to very faint.

Unmineralized anatomy: based on evidence from just a few specimens, Kootenia burgessensis, like Olenoides serratus, had a pair of flexible, multi-jointed “antennae” followed by three pairs of biramous limbs on the cephalon. Pairs of similar biramous appendages were attached under each thoracic segment, with a smaller number under the pygidium. No specimens, however, show any evidence of posterior antenna-like cerci as in Olenoides.

Abundance:

Kootenia burgessensis is moderately common in the Walcott Quarry section on Fossil Ridge, as is Kootenia dawsoni in the Mount Stephen Trilobite Beds.

Maximum Size:
55 mm

Ecology:

Life habits: Arthropoda
Feeding strategies: Arthropoda
Ecological Interpretations:

Adult Kootenia burgessensis walked along the sea bed, possibly digging shallow furrows to locate small soft-bodied and weakly-shelled animals or carcasses. Kootenia could probably swim just above the sea bed for short distances. Tiny larvae and early juveniles probably swam and drifted in the water column.

References:

MATTHEW, G. F. 1899. Studies on Cambrian faunas, No. 3. Upper Cambrian Fauna of Mount Stephen, British Columbia: The trilobites and worms. Transactions of the Royal Society of Canada, Series 2, Vol. 5, Section IV:39-66.

MELZAK, A. AND S. R. WESTROP. 1994. Mid-Cambrian (Marjuman) trilobites from the Pika Formation, southern Canadian Rocky Mountains, Alberta. Canadian Journal of Earth Sciences, 31:969-985.

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

RESSER, C. E. 1942. Fifth contribution to nomenclature of Cambrian trilobites. Smithsonian Miscellaneous Collections, 101 (15): 1-58.

RESSER, C. E. 1942. Fifth contribution to nomenclature of Cambrian trilobites. Smithsonian Miscellaneous Collections, 101 (15): 1-58.

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.

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. 1889. Description of new genera and species of fossils from the Middle Cambrian. United States National Museum, Proceedings for 1888:441-446.

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

WALCOTT, C. 1918. Cambrian Geology and Paleontology IV. Appendages of trilobites. Smithsonian Miscellaneous Collections, 67(4): 115-216.

WHITTINGTON, H. B. 1975. Trilobites with appendages from the Middle Cambrian, Burgess Shale, British Columbia. Fossils and Strata, No. 4: 97-136.

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Isoxys acutangulus

3D animation of Isoxys carinatus.

Animation by Phlesch Bubble © Royal Ontario Museum

Taxonomy:

Kingdom: Arthropoda
Phylum: Arthropoda
Higher Taxonomic assignment: Unranked clade (stem group arthropods)
Species name: Isoxys acutangulus
Remarks:

The affinity of Isoxys is uncertain because for a long time it was known only from empty carapaces. Recent descriptions of soft parts show that the frontal appendage is similar to that of some megacheiran, or “great appendage,” taxa such as Leanchoilia, Alalcomenaeus, and Yohoia (Vannier et al., 2009; García-Bellido et al., 2009a). The affinity of Megacheira as a whole is uncertain, but it has been suggested that they either sit within the stem-lineage to the euarthropods (Budd, 2002) or they are stem-lineage chelicerates (Chen et al., 2004; Edgecombe, 2010).

Described by: Walcott
Description date: 1908
Etymology:

Isoxys – from the Greek isos, “equal,” and xystos, “smooth surface”; thus referring to the pair of smooth valves.

acutangulus – from the Latin acutus, “sharp, pointed,” and angulus, “angle”; thus referring to the acute angle of the cardinal spines.

Type Specimens: Type status under review –USNM56521 (I. acutangulus) and Holotype –USNM189170 (I. longissimus) in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
Other species:

Burgess Shale and vicinity: I. longissimus from Walcott, Raymond and Collins Quarries on Fossil Ridge.

Other deposits: I. chilhoweanus from the Chilhowee Group, Tennessee, USA; I. auritus, I. paradoxus and I. curvirostratus from the Maotianshan Shale of China; I. bispinatus from the Shuijingtuo Formation, Hubei, China; I. wudingensis from the Guanshan fauna of China; I. communis and I. glaessneri from the Emu Bay Shale of Australia; I. volucris from the Buen Formation, Sirius Passet in Greenland; I. carbonelli from the Sierro Morena of Spain, and I. zhurensis from the Profallotaspis jakutensis Zone of Western Siberia. Undescribed species from Canada; Mount Cap Formation in the Mackenzie Mountains, Northwest Territories and the Eager Formation near Cranbrook. Other undescribed species in the Kaili Formation, Guizhou Province, China and the Kinzers Formation, Pennsylvania, USA. See references in Briggs et al., 2008; García-Bellido et al., 2009a,b; Stein et al., 2010; Vannier and Chen, 2000.

Age & Localities:

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

The Walcott, Raymond and Collins Quarries on Fossil Ridge. Additional localities are known on Mount Field, Mount Stephen – Tulip Beds (S7) and the Trilobite Beds, and near Stanley Glacier.

History of Research:

Brief history of research:

Walcott gave the name Isoxys to specimens from the lower Cambrian Chilhowee Group of Tennessee, USA, in 1890. He then later designated the first species from the Trilobite Beds on Mount Stephen, Anomalocaris? acutangulus (Walcott, 1908), although he placed it erroneously in the genus Anomalocaris. Simonetta and Delle Cave (1975) renamed it Isoxys acutangulus and discovered a second Burgess Shale species, I. longissimus. The original designations were based on carapaces only, making research on the ecology and affinity of Isoxys difficult. Soft parts have recently been described from the Burgess Shale taxa (Vannier et al. 2009, García-Bellido et al. 2009a).

Description:

Morphology:

The most prominent feature of Isoxys is the non-mineralized carapace, which ranged in length from 1 cm to almost 4 cm, and covered most of the body. It was folded to give two equal hemispherical valves, and had pronounced spines at the front and back. A pair of bulbous, spherical eyes protrudes forward and laterally from under the carapace. They are attached to the head by very short stalks. A pair of frontal appendages that are segmented and non-branching (uniramous) is adjacent to the eyes. The flexible appendages are curved with a serrated outline and five segments in total, including a basal part, three segments with stout outgrowths, and a pointed terminal segment.

The trunk of the body has 13 pairs of evenly spaced appendages that are segmented and branch into two (biramous), with slender, unsegmented walking limbs and large, paddle-like flaps fringed with long setae. The telson has a pair of lateral flaps. A cylindrical gut passes from the head to the ventral terminus of the telson, and is lined by paired, lobate gut glands. I. longissimus is distinguished from I. acutangulus by the presence of extremely long spines and an elongated body shape.

Abundance:

Isoxys is known from hundreds of specimens collected on Fossil Ridge. In the Walcott Quarry, Isoxys acutangulus is relatively common and represents about 0.35% of the community whereas Isoxys longissimus is extremely rare (Caron and Jackson, 2008).

Maximum Size:
40 mm

Ecology:

Life habits: Arthropoda
Feeding strategies: Arthropoda
Ecological Interpretations:

The streamlined body, thin carapace, and the presence of large paddle-shaped flaps in the appendages all suggest that Isoxys was a free-swimming animal. The spines and wide telson would have been use for steering and stability in the water column. A predatory lifestyle is indicated by the large eyes, frontal appendage, and gut glands. Isoxys would have swum just above the sea floor, seeking out prey in the water column and at the sediment-water interface.

References:

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

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

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

CHEN, J. Y., D. WALOSZEK AND A. MAAS. 2004. A new ‘great-appendage’ arthropod from the Lower Cambrian of China and homology of chelicerate chelicerae and raptorial antero-ventral appendages. Lethaia, 37: 3-20.

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.

GARCÍA-BELLIDO, D. C., J. VANNIER AND D. COLLINS. 2009a. Soft-part preservation in two species of the arthropod Isoxys from the middle Cambrian Burgess Shale of British Columbia, Canada. Acta Palaeontologica Polonica, 54: 699-712.

GARCÍA-BELLIDO, D. C., J. R. PATERSON, G. D. EDGECOMBE, J. B. JAGO, J. G. GEHLING AND M. S. Y. LEE. 2009b. The bivavled arthropods Isoxys and Tuzoia with soft-part preservation from the lower Cambrian Emu Bay Shale Lagerstätte (Kangaroo Island, Australia). Palaeontology, 52: 1221-1241.

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.

STEIN, M., J. S. PEEL, D. J. SIVETER AND M. WILLIAMS. 2010. Isoxys (Arthropoda) with preserved soft anatomy from the Sirius Passet Lagerstätte, lower Cambrian of North Greenland. 2010. Lethaia, 43: 258-265.

VANNIER, J. AND J.-Y. CHEN. 2000. The Early Cambrian colonization of pelagic niches exemplified by Isoxys (Arthropoda). Lethaia, 35: 107-120.

VANNIER, J., D. C. GARCÍA-BELLIDO, S. X. HU AND A. L. CHEN. 2009. Arthropod visual predators in the early pelagic ecosystem: evidence from the Burgess Shale and Chengjiang biotas. Proceedings of the Royal Society of London Series B, 276: 2567-2574.

WALCOTT, C. D. 1890. The fauna of the Lower Cambrian or Olenellus Zone. Reports of the U.S. Geological Survey, 10: 509-763.

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

WILLIAM, M., D. J. SIVETER AND J. S. PEEL. 1996. Isoxys (Arthropoda) from the early Cambrian Sirius Passet Lagerstätte, North Greenland. Journal of Paleontology, 70: 947-954.

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Hurdia victoria

3D animation of Hurdia victoria.

Animation by Phlesch Bubble © Royal Ontario Museum

Taxonomy:

Kingdom: Arthropoda
Phylum: Arthropoda
Higher Taxonomic assignment: Dinocarida (Order: Radiodonta, stem group arthropods)
Species name: Hurdia victoria
Remarks:

Hurdia is an anomalocaridid, and is usually considered to represent either a basal stem-lineage euarthropod (e.g. Daley et al., 2009), a member of the crown-group arthropods (e.g. Chen et al., 2004), or a sister group to the arthropods (Hou et al., 2006).

Described by: Walcott
Description date: 1912
Etymology:

Hurdia – from Mount Hurd (2,993 m), a mountain northeast of the now defunct Leanchoil railway station on the Canadian Pacific Railway in Yoho National Park. The peak was named by Tom Wilson for Major M. F. Hurd, a CPR survey engineer who explored the Rocky Mountain passes starting in the 1870s.

victoria – unspecified; perhaps from Mount Victoria (3,464 m) on the border of Yoho and Banff National Parks, named by Norman Collie in 1897 to honour Queen Victoria.

Type Specimens: Lectotypes –USNM57718 (H. victoria) andUSNM57721 (H. triangulata) in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
Other species:

Burgess Shale and vicinity: Hurdia triangulata.

Other deposits: Potentially other species are represented in Utah (Wheeler Formation) (Briggs et al., 2008), the Jince Formation in the Czech Republic (Chlupáč and Kordule 2002) and the Shuijingtuo Formation in Hubei Province, China (Cui and Huo, 1990) and possibly Nevada (Lieberman, 2003).

Age & Localities:

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

The Walcott, Raymond and Collins Quarries on Fossil Ridge. Also known from other localities on Mount Field, Mount Stephen – Tulip Beds (S7) – and near Stanley Glacier.

History of Research:

Brief history of research:

Hurdia is a relative newcomer to the anomalocaridids. Although isolated parts of its body were first identified in the early 1900s, no affinity could be determined until the description of whole body specimens by Daley et al. in 2009. Hurdia victoria was the name originally given to an isolated triangular carapace that Walcott (1912) suggested belonged to an unknown arthropod. Proboscicaris, another isolated carapace, was originally described as a phyllopod arthropod (Rolfe, 1962). Hurdia’s frontal appendages were first described by Walcott (1911a) as the feeding limbs of Sidneyia, but were later removed from this genus and referred to as “Appendage F” with unknown affinity (Briggs, 1979).

Like other anomalocaridids, the mouth parts were first described as the jellyfish Peytoia nathorsti (Walcott, 1911b). When Whittington and Briggs (1985) discovered the first whole body specimens of Anomalocaris, the mouth part identity of Peytoia was recognized and “Appendage F” was determined to be the frontal appendage of Anomalocaris nathorsti (later renamed Laggania cambria by Collins (1996). When describing Anomalocaris, Whittington and Briggs (1985) also figured a mouth apparatus with extra rows of teeth.

After two decades of collecting at the Burgess Shale, Desmond Collins from the Royal Ontario Museum (ROM) discovered that this extra-spiny mouth part actually belonged to a third type of anomalocaridid, which also had an “Appendage F” pair and a frontal carapace structure consisting of one Hurdia carapace and two Proboscicaris carapaces (Daley et al., 2009). This is the Hurdia animal. ROM specimens of “Appendage F” showed that it has three distinct morphologies, two of which belongs to the Hurdia animal (known from two species, victoria and triangulata) and one to Laggania cambria.

Description:

Morphology:

Hurdia has a bilaterally symmetrical body that is broadly divisible into two sections of equal lengths. The anterior region is a complex of non-mineralized carapaces consisting of one dorsal triangular H-element (previously called Hurdia) and two lateral subrectangular P-elements (or Proboscicaris). This complex is hollow and open ventrally. It attaches near the anterior margin of the head and protrudes forward. The surfaces of the H- and P-elements are covered in a distinctive polygonal pattern similar to that seen on Tuzoia carapaces. A pair of oval eyes on short stalks protrudes upwards through dorsal-lateral notches in the overlapping posterior corners of the H- and P-elements.

Mouth parts are on the ventral surface of the head, and consist of a circlet of 32 tapering and overlapping plates, 4 large and 28 small, with spines lining the square inner opening. Within the central opening are up to five inner rows of toothed plates. A pair of appendages flanks the mouth part, each with nine thin segments with short dorsal spines and seven elongated ventral spines. The posterior half of the body consists of a series of seven to nine reversely imbricated lateral lobes that extend ventrally into triangular flaps. Dorsal surfaces of the lateral lobes are covered in a series of elongated blades interpreted to be gill structures. The body terminates abruptly in two rounded lobes, and lacks a tailfan. Complete specimens are up to 20 cm in length, although disarticulated fragments may suggest a larger body size up to 50 cm long. Hurdia triangulata differs from Hurdia victoria by having a wider and shorter H-element.

Abundance:

Over 700 specimens of Hurdia have been identified, most of which are disarticulated. Hurdia is found in all Burgess Shale quarries on Fossil Ridge, and is particularly abundant in Raymond Quarry, where it makes up almost 1% of the community (240 specimens). A total of 7 complete body specimens exist.

Maximum Size:
500 mm

Ecology:

Life habits: Arthropoda
Feeding strategies: Arthropoda
Ecological Interpretations:

Hurdia was likely nektonic, since there are no trunk limbs for walking, and the numerous gills suggest an active swimming lifestyle. The animal propelled itself through the water column by waving its lateral lobes and gills. The large eyes, prominent appendages and spiny mouth parts suggest that Hurdia actively sought out moving prey items. Although the function of the frontal carapace remains unknown, it may have played a role in prey capture. If Hurdia were swimming just above the sea floor, it could have used the tip of its frontal carapace to stir up sediment and dislodge prey items, which would then be trapped beneath its frontal carapace. Prey items were funneled towards the mouth by a sweeping motion of the long ventral blades of the frontal appendages, which formed a rigid net or cage. Like other anomalocaridids, Hurdia likely ingested soft-bodied prey.

References:

BRIGGS, D. E. G. 1979. Anomalocaris, the largest known Cambrian arthropod. Palaeontology, 22: 631-663.

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

CHEN, J. Y., D. WALOSZEK AND A. MAAS. 2004. A new ‘great-appendage’ arthropod from the Lower Cambrian of China and homology of chelicerate chelicerae and raptorial antero-ventral appendages. Lethaia, 37: 3-20.

CHLUPÁČ, I. AND V. KORDULE. 2002. Arthropods of Burgess Shale type from the Middle Cambrian of Bohemia (Czech Republic). Bulletin of the Czech Geological Survey, 77: 167-182.

COLLINS, D. 1996. The “evolution” of Anomalocaris and its classification in the arthropod class Dinocarida (nov) and order Radiodonta (nov). Journal of Paleontology, 70: 280-293.

CUI, Z. AND S. HUO. 1990. New discoveries of Lower Cambrian crustacean fossils from Western Hubei. Acta Palaeontologica Sinica, 29: 321-330.

DALEY, A. C., G. E. BUDD, J. B. CARON, G. D. EDGECOMBE AND D. COLLINS. 2009. The Burgess Shale anomalocaridid Hurdia and its significance for early euarthropod evolution. Science, 323: 1597-1600.

HOU, X., J. BERGSTRÖM AND P. AHLBERG. 1995. Anomalocaris and other large animals in the Lower Cambrian Chengjiang fauna of Southwest China. GFF, 117: 163-183.

HOU, X., J. BERGSTRÖM AND Y. JIE. 2006. Distinguishing anomalocaridids from arthropods and priapulids. Geological Journal, 41: 259-269.

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

ROLFE, W. D. I. 1962. Two new arthropod carapaces from the Burgess Shale (Middle Cambrian) of Canada. Breviora Museum of Comparative Zoology, 60: 1-9.

WALCOTT, C. D. 1911a. Middle Cambrian Merostomata. Cambrian Geology and Paleontology II. Smithsonian Miscellaneous Collections, 57: 17-40.

WALCOTT, C. D. 1911b. Middle Cambrian holothurians and medusae. Cambrian Geology and Paleontology II. Smithsonian Miscellaneous Collections, 57: 41-68.

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

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.

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Hanburia gloriosa

Hanburia gloriosa (ROM 48468). Complete individual (external mold). Specimen length = 26 mm Specimen coated with ammonium chloride sublimate to show details. Trilobite Beds on Mount Stephen.

© Royal Ontario Museum. Photo: Jean-Bernard Caron

Taxonomy:

Kingdom: Arthropoda
Phylum: Arthropoda
Higher Taxonomic assignment: Trilobita (Order: Corynexochida?)
Species name: Hanburia gloriosa
Remarks:

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

Described by: Walcott
Description date: 1916
Etymology:

Hanburia – unspecified, but probably after Hanbury Peak or Hanbury Glacier in the Canadian Rockies, in turn named for David T. Hanbury (1864-1910), a British explorer of the Canadian Northwest Territories.

gloriosa – from the Latin gloriosus, meaning “glorious” or “boastful,” perhaps in allusion to the unusual cephalic morphology of this rare species.

Type Specimens: Lectotype –USNM61724, 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, Glossopleura to Bathyuriscus-Elrathina Zones (approximately 505 million years ago).
Principal localities:

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

History of Research:

Brief history of research:

Walcott’s three original specimens of Hanburia gloriosa were found over the course of five years of quarrying the Phyllopod Bed on Fossil Ridge (Walcott, 1916); two more from this locality are also in theUSNMcollections. A singleUSNMspecimen was later found by Charles Resser, supposedly from the “Ogygopsis shale” on Mount Stephen (Rasetti, 1951), but this is almost certainly an error. Harry Whittington reassessed this odd trilobite in 1998.

Description:

Morphology:

Hard parts: the few known specimens of Hanburia gloriosa range in length from 4 mm (for a juvenile stage) to 35 mm. Dorsal shields are broadly ovate to subcircular in outline and all specimens are considerably flattened by compression of the thin exoskeleton. The cephalon is semicircular with a weak, shallow border furrow along the posterior and lateral margins, fading out towards the anterior corners of the glabella. The glabella in small specimens expands forwards and shows two pairs of faint bulbous lateral lobes; in larger specimens, the glabella is parallel-sided and the lobes are subdued. There are no apparent eyes located laterally on the cephalon, and there is no sign of dorsal facial suture. In these two features, Hanburia is unique among the non-agnostoid trilobites of the Burgess Shale.

Whittington (1998) has suggested that the facial suture might run along the outside edge of the cephalon, or ventrally, crossing to the dorsal side only at the genal angles, which in all specimens appear to be rounded. Larger individuals show six or seven segments in the comparatively short thorax, and a single known (presumed) juvenile stage shows four; the distal tips of the pleurae are rounded. The semicircular pygidium lacks a defined border, and is approximately the same width and length as the cephalon. Seven or eight axial rings and a terminal piece make up the pygidial axis, which ends short of the posterior margin. Eight or nine pairs of well-marked pygidial pleurae radiate out and back from the axis.

Unmineralized anatomy: not known

Abundance:

Very rare in all the Burgess Shale localities.

Maximum Size:
35 mm

Ecology:

Life habits: Arthropoda
Feeding strategies: Arthropoda
Ecological Interpretations:

Due to its unusual cephalic morphology (i.e., no dorsal sutures or lateral compound eyes), rarity, and unique occurrence only in the Burgess Shale, Hanburia gloriosa remains an ecological enigma. Other “blind” Cambrian trilobites with somewhat similar morphologies have been interpreted as inhabiting deeper waters, perhaps below the photic zone (Whittington, 1998).

References:

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

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. 1916. Smithsonian Miscellaneous Collections, 64(3): 157-258.

WHITTINGTON, H. B. 1998. Hanburia gloriosa: rare trilobite from the Middle Cambrian, Stephen Formation, British Columbia, Canada. Journal of Paleontology, 72: 673-677.

Other Links:

None

Habelia? brevicauda

Habelia? brevicauda (USNM 144910) – Holotype. Complete individual preserved without appendages. Total specimen length = 50 mm. Specimen dry – polarized light. Walcott Quarry.

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

Taxonomy:

Kingdom: Arthropoda
Phylum: Arthropoda
Higher Taxonomic assignment: Unranked clade (stem group arthropods)
Species name: Habelia? brevicauda
Affinity:

Habelia? brevicauda is too poorly known to definitively determine its affinities. It has been aligned in some studies with the arachnomorphs (a group including chelicerates and trilobites), and has been suggested to be closely related to lamellipedians such as Naraoia and the trilobites (Briggs and Fortey, 1989), or placed within Megacheira as a close relative of Leanchoilia (Wills et al., 1998).

Described by: Simonetta
Description date: 1964
Etymology:

Habelia – from Mount Habel (3,161 m), today known as Mount Des Poilus, at the head of Yoho Valley, named in 1900 by Norman Collie in honour of Jean Habel, a German mountaineer. The name Mount Habel is now applied to a peak north of Mount Des Poilus.

brevicauda – from the Latin brevis, “short,” and cauda, “tail.”

Type Specimens: Holotype –USNM144910 in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
Other species:

Burgess Shale and vicinity: Habelia optata from Walcott Quarry, Fossil Ridge and The Monarch in Kootenay National Park.

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:

Habelia optata was first described by Walcott in 1912, to which Simonetta added the possible second species Habelia? brevicauda in 1964. This second species was later restudied by Whittington (1981). Phylogenetic analyses suggest a position within the arachnomorphs (Briggs and Fortey, 1989; Wills et al., 1998). If this is confirmed, Habelia probably represent a stem group of the Mandibulata, which includes crustaceans, myriapods, and hexapods (Scholtz and Edgecombe, 2006).

Description:

Morphology:

The body ranges in size from 1.8 – 5.4 cm and consists of a half-circle head shield and a trunk with twelve segments, the last of which bears a posterior spine. The head shield is smooth and featureless. The trunk segments have a broad, convex axial region, with blade-shaped elements (pleura) extending from either side. The pleura are short and round at the anterior of the body, but become progressively wider and have increasingly backward-pointing tips towards the posterior. The short, broad posterior spine tapers with a bluntly rounded tip.

In the type species, Habelia optata, the exoskeleton is covered in small tubercules , and appendages include a pair of antennae, two pairs of head appendages that are segmented and branch into two (biramous), and six pairs of possibly gnathobasic biramous trunk appendages (i.e., with a robust and spiny basal podomere or segment used for crushing food items). Tubercules and appendages have not been described in Habelia? brevicauda, which is why its placement in the genus is uncertain.

Abundance:

Habelia? brevicauda was originally described from fewer than ten specimens.

Maximum Size:
54 mm

Ecology:

Life habits: Arthropoda
Feeding strategies: Arthropoda
Ecological Interpretations:

Habelia? brevicauda is assumed to have walked on trunk limbs, using its head appendages to manipulate food items. If gnathobases were present, they may have served to masticate food. The frontal antennae were presumably sensory. Considerable flexure of the head may have been possible, which may have allowed Habelia to use its cephalon to dig into the sediment in search of food. It walked along the sea floor while digging and scavenging food items.

References:

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

ELLIOTT, D. K. AND D. L. MARTIN. 1987. A new trace fossil from the Cambrian Bright Angel Shale, Grand Canyon, Arizona. Journal of Paleontology, 61: 641-648.

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.

SIMONETTA, A. M. 1964. Osservazioni sugli artropodi non trilobiti della ‘Burgess Shale’ (Cambriano medio). III conributo. Monitore Zoologico Italiano, 72: 215-231.

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

WHITTINGTON, H. B. 1981. Rare arthropods from the Burgess Shale, Middle Cambrian, British Columbia. Philosophical Transactions of the Royal Society of London Series B-Biological Sciences, 292: 329-357.

Other Links:

None

Habelia optata

Reconstruction of Habelia optata.

© Marianne Collins

Taxonomy:

Kingdom: Arthropoda
Phylum: Arthropoda
Higher Taxonomic assignment: Unranked clade (stem group arthropods)
Species name: Habelia optata
Remarks:

Habelia optata is an arthropod, but its exact relationships remain poorly understood. It has been aligned in some studies to the arachnomorphs (a group including chelicerates and trilobites), and has either been allied with lamellipedians such as Naraoia and the trilobites (Briggs and Fortey, 1989), or placed within Megacheira as closely related to Leanchoilia (Wills et al., 1998).

Described by: Walcott
Description date: 1912
Etymology:

Habelia – from Mount Habel (3,161 m), today known as Mount Des Poilus, at the head of Yoho Valley. Named in 1900 by Norman Collie in honour of Jean Habel, a German mountaineer. The name Mount Habel is now applied to a peak north of Mount Des Poilus.

optata – unspecified; may derive from the Latin optatus, “wish or desire.”

Type Specimens: Holotype –USNM57693 in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
Other species:

Burgess Shale and vicinity: Habelia? brevicauda from Walcott Quarry and Raymond Quarry, Fossil Ridge.

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:

Habelia optata was first described by Walcott in 1912, and a possible second species Habelia? brevicauda was added to the genus by Simonetta in 1964. Habelia was later restudied by Whittington (1981). Habelia has been included in some phylogenetic analyses of arthropod relationships (Briggs and Fortey, 1989; Wills et al., 1998) and unusual zig-zag fossil tracks from the Middle Cambrian of the Grand Canyon have been ascribed to an arthropod similar to Habelia (Elliott and Martin, 1987).

Description:

Morphology:

Habelia optata is unusual in that its entire body is covered in tubercles (small, rounded nodules) that are particularly dense on the head shield and the axis of the body trunk. Its body consists of a convex head shield without eyes, and twelve body tergites with a long, jointed posterior spine projecting from the twelfth segment. The first three tergites have a thick median spine that bore tubercles. The head has a pair of multi-segmented setose antennae at the front, and two pairs of possibly biramous appendages with segmented walking limbs and dark sheets that may be filamentous branches.

The twelve body segments have a thick, blunt median spine on the dorsal surface. The first six body segments have appendages that are segmented and branch into two (biramous), including long stout segmented gnathobasic walking limbs (i.e., with a robust and spiny basal podomere or segment used for crushing food items) and a lobed outer branch with lamellae (small elongated structures) along the margin. The lobes are also present on the posterior segments, but no walking branches are associated with them. The tail is a long spine with a single joint midway along its length.

Abundance:

Extremely rare

Maximum Size:
41 mm

Ecology:

Life habits: Arthropoda
Feeding strategies: Arthropoda
Ecological Interpretations:

Habelia optata probably used its six trunk limbs for walking, reserving the head appendages for manipulating food items. It is likely that the frontal antennae were used to sense the environment since there are no obvious eyes. The size and shape of the posterior margin of the head suggests that there was considerable flexure possible between the head and the body, indicating that Habelia may have dug in the sediment for food items. It lived on the muddy seafloor and was heavily protected against predators by its thick body armor and pointed posterior spine, the latter of which would make it difficult for predators to attack from behind.

References:

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

ELLIOTT, D. K. AND D. L. MARTIN. 1987. A new trace fossil from the Cambrian Bright Angel Shale, Grand Canyon, Arizona. Journal of Paleontology, 61: 641-648.

SIMONETTA, A. M. 1964. Osservazioni sugli artropodi non trilobiti della ‘Burgess Shale’ (Cambriano medio). III conributo. Monitore Zoologico Italiano, 72: 215-231.

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

WHITTINGTON, H. B. 1981. Rare arthropods from the Burgess Shale, Middle Cambrian, British Columbia. Philosophical Transactions of the Royal Society of London Series B-Biological Sciences, 292: 329-357.

Other Links:

None

Emeraldella brocki

Reconstruction of Emeraldella brocki.

© Marianne Collins

Taxonomy:

Kingdom: Arthropoda
Phylum: Arthropoda
Higher Taxonomic assignment: Unranked clade (stem group arthropods)
Species name: Emeraldella brocki
Remarks:

Emeraldella is of uncertain phylogenetic affinity due to the paucity of specimens. It was previously placed in the arachnomorphs, as closely allied either with the chelicerates (Wills et al. 1998; Cotton and Braddy, 2004; Hendricks and Lieberman, 2008) or the trilobites and lamellipedians (Hou and Bergström, 1997; Edgecombe and Ramsköld, 1999; Scholtz and Edgecombe, 2006), but it has also been considered as a stem-lineage euarthropod (Budd, 2002).

Described by: Walcott
Description date: 1912
Etymology:

Emeraldella – from Emerald Lake, Peak, Pass, River and Glacier north of Burgess Pass, British Columbia, Canada. Emerald Lake was named by guide Tom Wilson in 1882 for the remarkable deep green colour of the water.

brocki – for Reginald Walter Brock, Director of the Geological Survey of Canada from 1907 to 1914.

Type Specimens: Lectotype –USNM57702 in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
Other species:

Burgess Shale and vicinity: none.

Other deposits: Emeraldella sp? from the Marjum Formation, House Range, Utah, USA.

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:

Emeraldella brocki was first described by Walcott (1912). Bruton and Whittington (1983) restudied the material in detail, clarifying many aspects of the animal’s morphology. One possible specimen of Emeraldella has also been described from the Marjum Formation in Utah (Briggs and Robison, 1984). Further work examining the phylogenetic placement of Emeraldella and the arachnomorphs has been conducted by Hou and Bergström (1997), Wills et al.(1998), Edgecombe and Ramsköld (1999), Budd (2002), Cotton and Braddy (2004), Scholtz and Edgecombe (2006) and Hendricks and Lieberman (2008).

Description:

Morphology:

The body consists of a semicircular head shield, segmented trunk and elongated posterior spine, with total body length (excluding spine and antennae) ranging between 1.1 cm and 6.5 cm. With antennae and spine the entire animal would have reached up to 15 cm in length. The body is convex in cross-section and tapers along the posterior half of the trunk. The head shield is smooth, with no evidence of eyes. A pair of long, flexible antennae consisting of over 110 short segments with bristled junctions is attached to the ventral surface at the front of the head. The mouth is ventral and faces backwards. Behind the antennae are five pairs of biramous limbs with a segmented inner branch and a lobed outer branch. The inner branch has six podomeres, including the gnathobase (a robust and spiny basal podomere or segment used for crushing food items), four adjacent podomeres that also bear spines, and a slender terminal podomere armed with three sharp claws. The outer branch of the biramous limb is broad and has three main lobes with filaments and blades.

The trunk of Emeraldella has eleven broad segments with curved, smooth margins. Each segment has a pair of biramous limbs similar to the ones of the head. Behind the trunk segments are two cylindrical body tergites and a long, tapering posterior spine. A dark band running the length of the trunk and into the base of the posterior spine may be the alimentary canal. In the head region, the alimentary canal is U-shaped as it leads forward and upwards from the backward-facing mouth.

Abundance:

Emeraldella brocki is very rare in the Walcott Quarry (less than 0.01% of the community, Caron and Jackson, 2008).

Maximum Size:
202 mm

Ecology:

Life habits: Arthropoda
Feeding strategies: Arthropoda
Ecological Interpretations:

The inner branches of the biramous limbs were likely used for walking on the sea floor, especially the middle eight or nine limbs, which were longer than the posterior limbs. Spines on the inner margin of the walking limbs could have been used to grasp soft prey items, and the terminal claws would push food towards the ventral gnathobases. These strong spiny plates would then shred the food and pass it along the underside of the body towards the mouth. The antennae were used to explore the environment and search for live prey or carcasses, perhaps by ploughing through the soft sediment. While the head was tilted down in the search for food, the posterior segments of the body and the posterior spine may have flexed upwards for balance. The outer limb lobes likely served as gills for respiration. The animal might have been capable of short bursts of swimming, using its broad outer limb branches to propel itself through the water using a wave-like motion.

References:

BRIGGS, D. E. G. AND R. A. ROBISON. 1984. Exceptionally preserved non-trilobite arthropods and Anomalocaris from the Middle Cambrian of Utah. The University of Kansas Paleontological Contributions, 111: 1-24.

BRUTON, D. L. AND H. B. WHITTINGTON. 1983. Emeraldella and Leanchoilia, two arthropods from the Burgess Shale, Middle Cambrian, British Columbia. Philosophical Transactions of the Royal Society of London B, 300: 553-582.

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

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

COTTON, T.J. AND S. J. BRADDY. 2004. The phylogeny of arachnomorph arthropods and the origin of the Chelicerata. Transactions of the Royal Society of Edinburgh-Earth Sciences, 94: 169-193.

EDGECOMBE, G. D. AND L. RAMSKÖLD. 1999. Relationships of Cambrian Arachnata and the systematic position of Trilobita. Journal of Paleontology, 73: 263-287.

HENDRICKS , J. R. AND B. S. LIEBERMAN. 2008. Phylogenetic insights into the Cambrian radiation of arachnomorph arthropods. Journal of Paleontology, 82: 585-594.

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

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

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

Other Links:

None

Elrathina cordillerae

Elrathina cordillerae (ROM 53273). Complete individual; a presumed carcass with free cheeks in place (coated with ammonium chloride sublimate to show details). Specimen length = 24 mm. Specimen dry – direct light. Mount Stephen Trilobite Beds on Mount Stephen.

© Royal Ontario Museum. Photo: Jean-Bernard Caron

Taxonomy:

Kingdom: Arthropoda
Phylum: Arthropoda
Higher Taxonomic assignment: Trilobita (Order: Ptychopariida)
Species name: Elrathina cordillerae
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:

Elrathina – unspecified.

cordillerae – in reference to the Western Cordillera (Canadian Rocky Mountain ranges), derived from the Spanish cordilla, the diminutive of cuerda, meaning “cord.”

Type Specimens: Type status under review – UMMP 4883 (6 specimens), University of Michigan Museum of Paleontology, Ann Arbor, Michigan, USA.
Other species:

Burgess Shale and vicinity: Elrathina parallela, E. brevifrons, E. spinifera, and E. marginalis have been described from similar stratigraphic horizons at nearby sites on Mount Field, Mount Stephen, and Mount Odaray.

Other deposits: Other species of Elrathina have been reported from the Cambrian of North America and Greenland.

Age & Localities:

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

The Walcott Quarry on Fossil Ridge. The Trilobite Beds and additional localities on Mount Stephen.

History of Research:

Brief history of research:

E. cordillerae was originally described under the genus name Conocephalites in Rominger’s 1887 publication on trilobites from Mount Stephen. In 1888 Walcott reallocated the species to Ptychoparia where it remained until Charles Resser, Walcott’s former assistant at the United States National Museum, established the new replacement genus Elrathina (Resser, 1937). Other workers have subsequently suggested that Elrathina is indistinguishable from Ptychoparella (see Blaker and Peel, 1997).

Species of Elrathina, along with those of the corynexochid Bathyuriscus, were found to be very abundant in a narrow interval of Middle Cambrian rocks throughout western North America, forming the basis of the Bathyuriscus-Elrathina Zone erected by Charles Deiss (1940).

Description:

Morphology:

Hard parts: adult dorsal exoskeletons average about 2 cm long. The semicircular cephalon is about one-third the length of the entire dorsal shield, bordered by a well-defined narrow rim, and with rounded genal angles. Weak transverse eye ridges extend to the small eyes, which are located just forward of cephalic mid-length. The slightly anteriorly narrowing glabella is rounded in front and exhibits three pairs of shallow lateral furrows; the pre-glabellar field is about the same width as the narrow anterior rim. The long, tapering thorax with a narrow axial lobe contains between 17 and 19 straight-sided segments, flexed gently downwards a short distance from the rounded tips. The tiny elliptical pygidium usually features two segments.

Unmineralized anatomy: rare specimens from the Walcott Quarry on Fossil Ridge retain tantalizing evidence of soft parts, including a pair of slender uniramous antennae, followed by very delicate looking biramous limbs beneath the cephalon, thorax and pygidium. These and other individuals of E. cordillerae are occasionally associated with a dark stain adjacent to the exoskeleton, presumably representing fluidized decay products.

Abundance:

Relatively common on Fossil Ridge and locally very abundant in the Walcott Quarry, where it represents about 25% of all trilobites collected (Caron and Jackson, 2008).

Maximum Size:
28 mm

Ecology:

Life habits: Arthropoda
Feeding strategies: Arthropoda
Ecological Interpretations:

Like similar-looking ptychoparioid trilobites, E. cordillerae may be interpreted as a fully mobile, epibenthic deposit (particle) feeder adapted to very low oxygen levels.

References:

BLAKER, M. R. AND J. S. PEEL. 1997. Lower Cambrian trilobites from North Greenland. Meddeleser om Grønland, Geoscience, 35, 145 p.

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

DEISS, C. 1940. Lower and Middle Cambrian stratigraphy of southwestern Alberta and southeastern British Columbia. Bulletin of the Geological Society of America, 51: 731-794.

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.

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. 1989. Trilobites with appendages from the Middle Cambrian Stephen Formation of British Columbia. 28th International Geological Congress, Washington, D.C. July 9-19, 1989. Abstracts: 2-729.

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. 1918. Cambrian Geology and Paleontology IV. Appendages of trilobites. Smithsonian Miscellaneous Collections, 67(4): 115-216.

WALCOTT, C. D. 1924. Cambrian and Lower Ozarkian trilobites. Smithsonian Miscellaneous Collections, 75(2): 53-60.

Other Links:

Elrathia permulta

Elrathia permulta (ROM 60762). Complete individual; a presumed carcass with free cheeks in place. Specimen length = 27 mm. Specimen dry – direct light (left) and coated with ammonium chloride sublimate to show details (right). Walcott Quarry.

© Royal Ontario Museum. Photo: Jean-Bernard Caron

Taxonomy:

Kingdom: Arthropoda
Phylum: Arthropoda
Higher Taxonomic assignment: Trilobita (Order: Ptychopariida)
Species name: Elrathia permulta
Remarks:

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

Described by: Walcott
Description date: 1918
Etymology:

Elrathia – unspecified.

permulta – from the Latin per, “very much”, and multus, “many”.

Type Specimens: Holotype –USNM65517 in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
Other species:

Burgess Shale and vicinity: none.

Other deposits: other species occur, sometimes abundantly, elsewhere in the Cambrian of North America and Greenland.

Age & Localities:

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

The Walcott Quarry on Fossil Ridge. Elrathia sp. has been reported from localities on Mount Stephen.

History of Research:

Brief history of research:

The concept of Elrathia permulta is quite confused. Walcott named the species Ptychoparia permulta in 1918 and illustrated two specimens, one clearly designated as the type. Resser (1937) noted that the illustrated specimens were quite different, moved both to Walcott’s 1924 genus Elrathia, and proposed the name Elrathia dubia for the second species. Unfortunately, he based this on the original type of permulta; Rasetti (1951) declared dubia invalid, returned the type specimen to Elrathia permulta, and designated the other of Walcott’s specimens as a paratype of Ehmaniella burgessensis. The holotype of permulta, however, lacks many of the diagnostic characters of Elrathia, and Robison (1964) suggested it represents a new genus.

Description:

Morphology:

Hard parts: the adult dorsal exoskeleton is up to 25 mm long, with a large semicircular cephalon occupying about one-third the total length. The cephalon is bordered by a rounded rim and broad inner furrow; genal angles are produced into sharp triangular spines extending back to the fourth thoracic segment. There is a relatively long field between the narrow, tapered, and anteriorly rounded glabella and the frontal rim. Eyes are small and transverse eye ridges are very weak. Three pairs of shallow lateral furrows mark the glabella. The thorax comprises 14 segments, and tapers back more rapidly over the posterior half to a small rounded pygidium. The surface of the exoskeleton is variably granulate.

Unmineralized anatomy: not known.

Abundance:

Rare in the Walcott Quarry on Fossil Ridge, and elsewhere.

Maximum Size:
25 mm

Ecology:

Life habits: Arthropoda
Feeding strategies: Arthropoda
Ecological Interpretations:

E. permulta may, like similar small ptychoparioid trilobites, be interpreted as a mobile, epibenthic deposit (particle) feeder adapted to low oxygen levels.

References:

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.

ROBISON, R. A. 1964. Late Middle Cambrian faunas from western Utah. Journal of Paleontology, 38:510-566.

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. 1918. Cambrian Geology and Paleontology IV. Appendages of trilobites. Smithsonian Miscellaneous Collections, 67(4): 115-216.

WALCOTT, C. D. 1924. Cambrian and Lower Ozarkian trilobites. Smithsonian Miscellaneous Collections, 75(2): 53-60.

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