The Burgess Shale

Phylas: Arthropoda

Tokummia katalepsis

Tokummia katalepsis, paratype, ROMIP 63826

Taxonomy:

Kingdom: Arthropoda
Phylum: Arthropoda
Higher Taxonomic assignment: Hymenocarines, Family Protocarididae (Miller 1889).
Species name: Tokummia katalepsis
Remarks:

Hymenocarines were early arthropods with bivalved carapaces and mandibles, forming the bulk of the first mandibulates (represented today by myriapods, crustaceans and insects) (Aria & Caron 2017; Vannier et al. 2018). Tokummia was a close relative of Branchiocaris, both grouped within the eponymous family Protocarididae Miller, 1889—one of the oldest formal taxa from the Burgess Shale. The relationship of Protocarididae within hymenocarines, as well as the relative placement of hymenocarines within early mandibulates is still under investigation (Aria 2022; Izquierdo-López & Caron 2022).

Described by: Aria and Caron
Description date: 2017
Etymology:

Tokummia — from Tokumm Creek, a river of the Kootenay area, in British Columbia, running through Marble Canyon, near the outcrop where the fossil was first found.

katalapsis — from the Greek, meaning “seizing, grasping,” by reference to the well-developed pincers of the animal.

Type Specimens: Holotype ROMIP 63823; paratypes ROMIP 63014, 63081, 63824–63827, 63736 (7 specimens), in the Royal Ontario Museum, Toronto, Canada.
Other species:

Burgess Shale and vicinity: none.
Other deposits: none.

Age & Localities:

Age:
Middle Cambrian, Wuliuan Stage, upper part of the Burgess Shale Formation (around 507 million years old).
Principal localities:

The Marble Canyon and Tokumm Creek areas of the Burgess Shale, British Columbia.

History of Research:

Brief history of research:

Tokummia was discovered during the original excavation of the Marble Canyon locality in 2012, along Yawunik and other taxa characteristic of this area. Additional specimens were later discovered during quarrying operations and along Tokumm Creek. Tokummia’s description was published in 2017: Tokummia’s size and quality of preservation helped identify mandibles and other diagnostic traits of mandibulates. Mandibles were also identified in Branchiocaris in the same study. This study partially rehabilitated original interpretations by Derek Briggs recognizing mandibulate affinities of Cambrian bivalved arthropods (hymenocarines) (Briggs 1992) but were not without their issues, notably that of the presence of an intercalary segment (e.g. Edgecombe 2017). However, research on hymenocarines has since been supportive of the mandibulate affinity of these arthropods (Vannier et al. 2018; Izquierdo-López & Caron 2022). Tokummia therefore remains central to our modern understanding of early arthropod evolution as a whole (Aria 2022).

Description:

Morphology:

Like other protocaridids, Tokummia’s long, tubular, multisegmented body is largely enclosed in a broad bivalved carapace with ample, lobate corners. Small processes are present medially at the front and rear of both valves. Eyes are very reduced or absent. The very front of the animal bears a bilobed organ covered by triangular sclerite. A pair of short, stout, multisegmented antennules are the most anterior appendages. The next pair of appendages are large, round mandibles, followed by modified appendages identified as maxillules and maxillae. The first pair of thoracic limbs are very large pincers projecting at the front of the animal, and therefore called maxillipeds. Trunk limbs are composed of well-developed walking legs ending in strong claws, and of lobate flaps that get much larger starting with trunk limb pair 9. There is a total of about 50 limb pairs in the trunk, one for each segment, which gradually decrease in size towards the back. Some tergites are fused at the back of the animal, forming a plate, and the tailpiece is a pair of caudal rami, typical of mandibulates.

Abundance:

The original description was based on 21 specimens (Aria & Caron 2017), but this count has so far doubled (Nanglu et al. 2020). Tokummia is a signature taxon of both the Marble Canyon quarry and the Tokumm sites.

Maximum Size:
About 15 cm.

Ecology:

Life habits: Arthropoda
Feeding strategies: Arthropoda
Ecological Interpretations:

The combination of large pincers and strong walking appendages in Tokummia suggests it was a nektobenthic predator. However, as in Branchiocaris and Protocaris, the absence of distinct eyes in the fossils, implying they were either very reduced or absent, indicates that the predatory lifestyle of Tokummia and other Protocarididae had its own specificity. Protocaridids either relied more heavily on their other sensory organs or were perhaps more passive predators.

References:

  • ARIA, C. 2022. The origin and early evolution of arthropods. Biological Reviews, 97, 1786–1809.
  • ARIA, C. and CARON, J. B. 2017. Burgess Shale fossils illustrate the origin of the mandibulate body plan. Nature, 545, 89–92.
  • BRIGGS, D. E. G. 1992. Phylogenetic significance of the Burgess Shale crustacean Canadaspis. Acta Zoologica, 73, 293–300.
  • EDGECOMBE, G. D. 2017. Palaeontology: The cause of jaws and claws. Current Biology, 27, R796–R815.
  • IZQUIERDO-LÓPEZ, A. and CARON, J.-B. 2022. The problematic Cambrian arthropod Tuzoia and the origin of mandibulates revisited. Royal Society Open Science, 9.
  • MILLER, S. A. 1889. North American geology and palaeontology for the use of amateurs, students and scientists. Western Methodist Book Concern, Cincinnati.
  • NANGLU, K., CARON, J.-B. and GAINES, R. R. 2020. The Burgess Shale paleocommunity with new insights from Marble Canyon, British Columbia. Paleobiology, 46, 58–81.
  • VANNIER, J., ARIA, C., TAYLOR, R. S. and CARON, J. B. 2018. Waptia fieldensis Walcott, a mandibulate arthropod from the middle Cambrian Burgess Shale. Royal Society Open Science, 5:172206.
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Titanokorys gainesi

Titanokorys gainesi, holotype ROMIP 65168

Taxonomy:

Kingdom: Arthropoda
Phylum: Arthropoda
Higher Taxonomic assignment: Order Radiodonta, Family Hurdiidae
Species name: Titanokorys gainesi
Remarks:

With its single pair of jointed frontal appendages, lateral swimming flaps, and circular mouth structure, Titanokorys possesses all the hallmarks of Radiodonta, part of the stem group to the true arthropods which also includes the iconic Anomalocaris (Collins 1996). The frontal appendages with comb or rake-like inner spines are characteristic of the radiodont family Hurdiidae. Phylogenetic analysis has found it to be closely related to Cambroraster from the Burgess Shale and Zenghecaris from the Chengjiang deposit, which share similarities in carapace shape and a large number of finely-spaced spines on the appendages (Caron and Moysiuk 2021).

Described by: Caron and Moysiuk
Description date: 2021
Etymology:

Titanokorys – from Titans, a group of powerful Greek deities of great sizes, in reference to the large size of the central carapace and from the Greek word Korys meaning helmet.

gainesi – after Robert R. Gaines, Professor of Geology at Pomona College, who was instrumental in the co-discovery of the Marble Canyon fossil deposit in 2012.

Type Specimens: Holotype ROMIP 65415; Paratypes ROMIP 65168, 65741, 65748, and 65749, at the Royal Ontario Museum.
Other species:

Burgess Shale and vicinity: None
Other deposits: None

Age & Localities:

Age:
Middle Cambrian, Wuliuan Stage, upper part of the ‘thick’ Stephen Formation (Burgess Shale) (around 507 million years old).
Principal localities:

Marble Canyon and Mount Whymper / Tokumm Creek, Kootenay National Park, British Columbia.

History of Research:

Brief history of research:

Several specimens of Titanokorys were discovered at the Marble Canyon and North Tokumm sites in Kootenay National Park in 2014 and 2018. Because of their distinctive shape, large size, and resemblance to the smaller Cambroraster (nicknamed “spaceship”), the head carapaces were nicknamed the “mothership.” The genus and species were formally described in 2021 (Caron and Moysiuk 2021).

Description:

Morphology:

The defining feature of Titanokorys gainesi is its large dorsal carapace. This is roughly elliptical in overall shape. Frontally this carapace has a small spine flanked by a pair of blunt lobes. The rear sides of the carapace are developed into short, wing-like projections. Each “wing” has a small spine along its inner margin. The rear central part of the carapace extends into a bilobate projection. Between the lateral “wings” and bilobate projection are notches that presumably accommodated the eyes. On the underside, the head is protected by two additional plates, shaped like elongate paddles and joined together at the front by their narrow ends, each of which bears a stout, downward-directed spine. All three plates are covered in longitudinal rows of small bumps. A circular, tooth-lined jaw and a pair of jointed frontal appendages with five long, curving, rake-like inner spines are located on the underside, near the front of the head. The body bears rows of stacked gill blades.

Abundance:

Titanokorys is rare in Kootenay National Park, being known from just twelve specimens. Only disarticulated frontal appendages, mouthparts, carapace elements, and gills are known.

Maximum Size:
About 500 mm.

Ecology:

Life habits: Arthropoda
Feeding strategies: Arthropoda
Ecological Interpretations:

Like other hurdiids, Titanokorys shows adaptations to sweep feeding. Specifically, the rake-like inner spines on its stout frontal appendages form a rigid basket-like apparatus of spines surrounding the mouth, which could have functioned to disturb the sediment, sift out burrowing organisms, and move them into the mouth for further processing. Compared to related hurdiids like Hurdia and Stanleycaris, the particularly finely-spaced, strong, hooked secondary spines on the inner spines could have enabled capture of minute benthic organisms, although larger prey may also have been consumed. As the largest animal known from the Marble Canyon and Tokumm communities, Titanokorys would have been at the top of the food chain. Titanokorys shared the environment with the slightly smaller Cambroraster, which probably employed a similar mode of feeding, although body size differences may have entailed distinct prey size niches (Moysiuk and Caron 2019; Caron and Moysiuk 2021). Respiration would have been accomplished primarily through the rows of gill blades on the body (Daley et al. 2013).

References:

  • CARON, J.-B. and MOYSIUK, J. 2021. A giant nektobenthic radiodont from the Burgess Shale and the significance of hurdiid carapace diversity. Royal Society Open Science, 8: 210664.
  • 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.
  • DALEY, A. C., BUDD, G. E. and CARON, J.-B. 2013. Morphology and systematics of the anomalocaridid arthropod Hurdia from the Middle Cambrian of British Columbia and Utah. Journal of Systematic Palaeontology, 11: 743–787.
  • MOYSIUK, J. and CARON, J.-B. 2019. A new hurdiid radiodont from the Burgess Shale evinces the exploitation of Cambrian infaunal food sources. Proceedings of the Royal Society B, 286: 20191079.
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Surusicaris elegans

Surusicaris elegans, holotype ROMIP 62976. Specimen dry – direct light (left column), dry – polarized light (right column).

Taxonomy:

Kingdom: Arthropoda
Phylum: Arthropoda
Higher Taxonomic assignment: Family Isoxyidae?
Species name: Surusicaris elegans
Remarks:

Surusicaris is a close relative of Isoxys, as indicated by the type of carapace, eyes, and frontal pair of raptorial appendages (Aria & Caron, 2015). The presence of spines on the dorsal side of the frontal appendage is a character shared with radiodontans, such as Anomalocaris. Current evidence draws out a consensus among authors placing isoxyids as sister taxa to true arthropods (Edgecombe, 2020; Aria, 2022), although it is not clear whether Surusicaris and Isoxys are part of a single separate lineage (that is, form a monophyletic group).

Described by: Aria and Caron
Description date: 2015
Etymology:

Surusicaris – After Surus, “the Syrian,” which would have been the last elephant of Hannibal, with broad shields covering its sides and missing a tusk.

elegans – Referring to the delicate, laced appearance of the limbs.

Type Specimens: Holotype ROMIP 62977, at the Royal Ontario Museum, Toronto, Canada
Other species:

Burgess Shale and vicinity: None
Other deposits: None

Age & Localities:

Age:
Middle Cambrian, Wuliuan stage, upper part of the Burgess Shale Formation (around 507 million years old).
Principal localities:

Marble Canyon, Kootenay National Park, British Columbia.

History of Research:

Brief history of research:

Along with Yawunik kootenayi (Aria, Caron & Gaines, 2015), Surusicaris elegans (Aria & Caron, 2015) is one of the first two new arthropods described from the Marble Canyon locality of the Burgess Shale. The original study was based on a single specimen from the original 2012 expedition. No other specimen has been confirmed so far, in the Burgess Shale or elsewhere. Surusicaris has remained a critical taxon in understanding the place of isoxyids in the transition to a euarthropod body plan (Fu et al., 2022; Aria, 2022).

Description:

Morphology:

Surusicaris elegans is about 15mm long and enclosed in a broad carapace made of two semi-circular valves, without spines. Only the posterior extremity of the body and tailpiece remain uncovered. The animal has a well-defined head composed of, at the front, a pair of large spherical eyes and a segmented predatory appendage, and, at the back of the head, under the carapace, three pairs of short limbs with a lobopod aspect. The frontal appendages show a complex ornament of spines on both the ventral and dorsal margins. The trunk limbs are clearly bipartite, forming two separate but similar branches. As for Isoxys, external segmentation of the trunk is not clearly visible. Inside the body, a bold, black trace runs alongside the gut and branches out inside one limb branch, showing similarities to hemolymphatic (“blood”) channels (Aria & Caron, 2015).

Abundance:

A single specimen from the Marble Canyon quarry.

Maximum Size:
About 15 mm.

Ecology:

Life habits: Arthropoda
Feeding strategies: Arthropoda
Ecological Interpretations:

The large lateral eyes and clawed frontal appendages suggest Surusicaris was an active predator, like its close relative Isoxys (Legg & Vannier, 2013). Trunk limbs lack strong functional modifications, but their lobate aspect in addition to their position underneath the carapace indicates that Surusicaris was mostly a swimmer (Aria & Caron, 2015). Although some authors implied a pelagic lifestyle (Vannier & Chen, 2000), isoxyids are commonly found among benthic/nektobenthic assemblages (Caron & Jackson, 2008) and possess general morphological characteristics of other nektobenthic Cambrian arthropods.

References:

  • Aria, C. (2022) The origin and early evolution of arthropods. Biological Reviews 97, 1786–1809.
  • Aria, C. & Caron, J.-B. (2015) Cephalic and limb anatomy of a new isoxyid from the Burgess Shale and the role of ‘stem bivalved arthropods’ in the disparity of the frontalmost appendage. PLoS ONE 10, e0124979.
  • Aria, C., Caron, J.-B. & Gaines, R. (2015) A large new leanchoiliid from the Burgess Shale and the influence of inapplicable states on stem arthropod phylogeny. Palaeontology 58, 629–660.
  • Caron, J.B. & Jackson, D.A. (2008) Paleoecology of the Greater Phyllopod Bed community, Burgess Shale. Palaeogeography, Palaeoclimatology, Palaeoecology 258, 222–256.
  • Edgecombe, G.D. (2020) Arthropod origins: Integrating paleontological and molecular evidence. Annual Review of Ecology, Evolution, and Systematics 51, 1–25.
  • Fu, D., Legg, D.A., Daley, A.C., Budd, G.E., Wu, Y. & Zhang, X. (2022) The evolution of biramous appendages revealed by a carapace-bearing Cambrian arthropod. Philosophical Transactions of the Royal Society B: Biological Sciences 377, 20210034.
  • Legg, D.A. & Vannier, J. (2013) The affinities of the cosmopolitan arthropod Isoxys and its implications for the origin of arthropods. Lethaia 46, 540–550.
  • Vannier, J. & Chen, J.Y. (2000) The Early Cambrian colonization of pelagic niches exemplified by Isoxys (Arthropoda). Lethaia 33, 295–311.
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Peronopsis columbiensis

Peronopsis columbiensis, cephalon showing appendages ROMIP 64993

Taxonomy:

Kingdom: Arthropoda
Phylum: Arthropoda
Higher Taxonomic assignment: Artiopoda, Order: Agnostida
Species name: Peronopsis columbiensis
Remarks:

Owing to their distinctive appearance, agnostids have been classified either as trilobites, related to Eodiscina, or as stem group “crustaceans” (Müller and Walossek 1987; Cotton and Fortey 2005; Haug et al. 2009). The most recent phylogenetic analysis finds that agnostids form a grouping with trilobites, supported by shared features of the dorsal exoskeleton, such as mineralization, the expression of segmental boundaries, and the form of the thoracic joints (Moysiuk and Caron 2019). More taxonomically inclusive analyses will be needed to determine whether they belong inside or outside the group of true trilobites.

Described by: Rasetti
Description date: 1951
Etymology:

Peronopsis – From the Greek perone, “pin, brooch ” and opsis, “looking like.”

columbiensis – No etymology provided, but presumably in reference to the occurrence of the species in British Columbia, Canada.

Type Specimens: Holotype – USNM 116267; paratypes – USNM 116268-9; in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
Other species:

Burgess Shale and vicinity: P. montis

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

Age & Localities:

Age:
Middle Cambrian, Wuliuan stage, Burgess Shale Formation (around 507 million years old).
Principal localities:

Mount Stephen, Mount Odaray, Marble Canyon.

History of Research:

Brief history of research:

Burgess Shale material was originally named Peronopsis columbiensis by Rasetti (1951). Naimark (2012) proposed to reassign the species to the genus Quadragnostus based on published images, but we maintain it here under Peronopsis pending taxonomic restudy of Burgess Shale specimens. Moysiuk and Caron (2019) recently described the appendages, digestive tract, and other soft tissues from exceptionally preserved specimens.

Description:

Morphology:

Adult dorsal exoskeletons reach about 20 mm in length. The semicircular cephalon has a narrow marginal rim around the front and sides and rounded genal angles. There are no dorsal eyes and no facial sutures. The narrow glabella comes to an ogival point, with no anterior median furrow; a transverse furrow crosses the glabella near its anterior. A pair of short genal spines are present. 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 and a pair of short, backwards-directed marginal spines posterolaterally. 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 is separated by a gap from the pygidial rim posteriorly, without a median furrow. A saddle-shaped hypostome is present ventrally, unfused to the headshield. Unmineralized anatomy: The head probably bears six pairs of appendages, including one pair of elongate sensory antennules, two pairs of appendages with oar-like outer branches, and probably three pairs of stout walking limbs with a row of club-like projections. Additional walking limbs were present beneath the thorax (2) and pygidium (probably 4). The digestive tract curves dorsally from the mouth before emitting two pairs of branching gut glands, the first of which is the largest and occupies much of the space below the headshield. Behind this, the cylindrical midgut extends back to the pygidium. The hindgut begins roughly below the pygidial tubercle, and narrows considerably before reaching the anus below the tip of the pygidial axis.

Abundance:

Specimens likely assignable to this species are very common at Tokumm Creek and in the upper levels of the Marble Canyon quarry, where it is the most abundant artiopodan (Nanglu et al. 2020). Peronopsis columbiensis also occurs in notable numbers at Mount Odaray, Mount Stephen, and a few smaller localities (Rasetti 1951).

Maximum Size:
About 20 mm.

Ecology:

Life habits: Arthropoda
Feeding strategies: Arthropoda
Ecological Interpretations:

The mode of life of agnostids has been extensively debated (Fortey and Owens 1999). With the oar-like appendages capable of protruding while the animal was partially enrolled, agnostids certainly appear well-adapted for swimming (Müller and Walossek 1987). Together with their occurrence in mass mortality beds with wide geographic range, this evidence has been proposed to support a pelagic lifestyle (Fortey 1985). However, most specimens at the Burgess Shale are found in unrolled position, suggesting they did not live permanently enrolled. Further, Peronopsis is sometimes found in groups, associated with the remains of other Burgess Shale organisms, where it was potentially feeding on carrion or bacterial films, providing evidence for a benthic habitat. The huge, branching gut glands in the head likely acted as a food storage organ, possibly enabling a feast-and-famine lifestyle. The club-like outgrowths on the walking legs may have functioned in respiration (Moysiuk and Caron 2019).

References:

  • COTTON, T. J. and FORTEY, R. A. 2005. Comparative morphology and relationships of the Agnostida. In KOENEMANN, S. and JENNER, R. (eds.) Crustacea and Arthropod Relationships, CRC Press, 95–136 pp.
  • FORTEY, R. A. 1985. Pelagic trilobites as an example of deducing the life habits of extinct arthropods. Earth and Environmental Science Transactions of The Royal Society of Edinburgh, 76: 219–230.
  • FORTEY, R. A. and OWENS, R. M. 1999. Feeding habits in trilobites. Palaeontology, 42: 429–465.
  • HAUG, J. T., MAAS, A. and WALOSZEK, D. 2009. †Henningsmoenicaris scutula, †Sandtorpia vestrogothiensis gen. et sp. nov. and heterochronic events in early crustacean evolution. Earth and Environmental Science Transactions of the Royal Society of Edinburgh, 100: 311–350.
  • MOYSIUK, J. and CARON, J.-B. 2019. Burgess Shale fossils shed light on the agnostid problem. Proceedings of the Royal Society B: Biological Sciences, 286: 20182314.
  • MÜLLER, K. J. and WALOSSEK, D. 1987. Morphology, ontogeny, and life habit of Agnostus pisiformis from the Upper Cambrian of Sweden. Fossils and Strata, 19: 1–124.
  • NAIMARK, E. B. 2012. Hundred species of the genus Peronopsis Hawle et Corda, 1847. Paleontological Journal, 46: 945–1057.
  • NANGLU, K., CARON, J.-B. and GAINES, R. R. 2020. The Burgess Shale paleocommunity with new insights from Marble Canyon, British Columbia. Paleobiology, 46: 58–81.
  • RASETTI, F. 1951. Middle Cambrian stratigraphy and faunas of the Canadian Rocky Mountains. Smithsonian Miscellaneous Collections, 116: 1–277.
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Pakucaris apatis

Pakucaris apatis, holotype ROMIP 65739

Taxonomy:

Kingdom: Arthropoda
Phylum: Arthropoda
Higher Taxonomic assignment: Hymenocarines, Family: Odaraiidae
Species name: Pakucaris apatis
Remarks:

Hymenocarines were early arthropods with bivalved carapaces and mandibles, forming the bulk of the first mandibulates (represented today by myriapods, crustaceans and insects) (Aria and Caron 2017; Vannier et al. 2018). In many hymenocarines, including Pakucaris, determining the exact number and types of appendages in their head remains difficult, which hinders a detailed understanding of the evolutionary relationships inside this group. Pakucaris most probably belongs to the family Odaraiidae, a group of hymenocarines with highly multisegmented bodies, reduced or absent antennae and highly multisegmented legs.

Described by: Izquierdo-López & Caron
Description date: 2021
Etymology:

Pakucaris – from the Japanese onomatopoeia paku, suggestive of ‘eating’, related to the video game character Pac-Man, due to the naked eye resemblance of the carapace and shield of Pakucaris to the shape of the character. Latin caris, meaning “crab” or “shrimp”, and

apatis – from the goddess of deception in Greek mythology Apate, in reference to the resemblance of Pakucaris to a trilobite.

Type Specimens: Holotype ROMIP65739
Other species:

Burgess Shale and vicinity: None
Other deposits: None

Age & Localities:

Age:
Middle Cambrian, Wuliuan Stage, upper part of the Burgess Shale Formation (around 507 million years old)
Principal localities:

Marble Canyon, Tokumm Creek

History of Research:

Brief history of research:

The holotype of Pakucaris apatis was first discovered during the 2012 expedition to the Marble Canyon site of the Burgess Shale. A few other specimens were discovered during the following 2014 and 2016 expeditions and classified as “New arthropod E” (Nanglu et al. 2020). The 2018 expedition at the Tokumm Creek site uncovered one additional specimen. The first description of Pakucaris apatis was published in 2021 in the journal Papers in Paleontology (Izquierdo-López and Caron, 2021). Several other authors have noted the similarity between the shield of Pakucaris and pygidia (O’Flynn et al. 2022). A pygidium is a structure in which the most posterior segments of an arthropod become fused, usually into a shield. The pygidium is typically found in trilobites, but also across many other groups in the Cambrian, suggesting that this structure appeared multiple times independently.

Description:

Morphology:

Pakucaris has two morphotypes: a small one (around 1 cm) with its body subdivided into 30-35 segments, and a larger one (around 2.5 cm), with its body subdivided into 70-80 segments. The carapace of Pakucaris covers up to two-thirds of the total body length. It has a dome-like shape with a small dorsal crest that runs across its entire length. The carapace bends towards the front, extending into a small process (rostrum). Similarly, the lateral sides of the carapace also extend frontally into small lateral processes. The head has one pair of pedunculate eyes, one pair of thin small appendages, and at least one pair of larger segmented antennae. The small thin appendages are not segmented and represent a sensorial organ known as frontal filaments. The first antennae (also termed antennules) have 7 to 8 segments, with each segment bearing a small spine. Each segment of the body bears one pair of limbs, each subdivided into two branches (biramous): a walking leg (endopod) and a paddle-like flap (exopod). The endopod is thin and is subdivided into at least 20-21 segments. The exopod has an ovoid, flattened shape and is as long as half the endopod. The posterior section of the body has a shield-like structure. This shield is formed by the fusion and lateral extensions of the segments. The shield bears around 10 big spines on each of its lateral sides, as well as a series of smaller spines on its posterior side.

Abundance:

Pakucaris is rare, only known from eight specimens from the Marble Canyon and Tokumm Creek sites. The bigger morphotype is only known from one specimen.

Maximum Size:
About 2.5 cm

Ecology:

Life habits: Arthropoda
Feeding strategies: Arthropoda
Ecological Interpretations:

Pakucaris was probably a nektobenthic animal living close to the benthos (Izquierdo-López and Caron 2021). It may have used its antennae with spines to scrape rocks or other objects and may have also used its paddle-like exopods to create currents and capture organic particles, aided by its antennae and other head appendages. The tail shield (or pygidium) of Pakucaris was most probably a structure to protect against predators. The two morphotypes of Pakucaris may represent different growth stages of males and females, but the number of specimens available to date is too limited to reach a conclusion.

References:

  • ARIA, C. and CARON, J. B. 2017. Burgess Shale fossils illustrate the origin of the mandibulate body plan. Nature, 545: 89–92.
  • IZQUIERDO-LÓPEZ, A. and CARON, J. B. 2021. A Burgess Shale mandibulate arthropod with a pygidium: a case of convergent evolution. Papers in Palaeontology, 7: 1877–1894.
  • NANGLU, K., CARON, J. and GAINES, R. 2020. The Burgess Shale paleocommunity with new insights from Marble Canyon, British Columbia. Paleobiology, 46(1): 58–81.
  • O’FLYNN, R. J., WILLIAMS, M., YU, M., HARVEY, T. and LIU, Y. 2022. A new euarthropod with large frontal appendages from the early Cambrian Chengjiang biota. Palaeontologia Electronica, 25(1):a6: 1–21.
  • VANNIER, J., ARIA, C., TAYLOR, R. S. and CARON, J. B. 2018. Waptia fieldensis Walcott, a mandibulate arthropod from the middle Cambrian Burgess Shale. Royal Society Open Science, 5:172206.
Other Links:

Nereocaris exilis

Nereocaris briggsi, holotype ROMIP 62153

Taxonomy:

Kingdom: Arthropoda
Phylum: Arthropoda
Higher Taxonomic assignment: Hymenocarines, Family: Odaraiidae
Species name: Nereocaris exilis
Remarks:

Hymenocarines were early arthropods with bivalved carapaces and mandibles, forming the bulk of the first mandibulates (represented today by myriapods, crustaceans and insects) (Aria and Caron 2017; Vannier et al. 2018). In many hymenocarines, including Nereocaris, determining the exact number and types of appendages in their head remains difficult, which hinders a detailed understanding of the evolutionary relationships inside this group. Nereocaris most probably belongs to the family Odaraiidae, a group of hymenocarines with highly multisegmented bodies, reduced or absent antennae and highly multisegmented legs.

Described by: Legg, D. A., Sutton, M. D., Edgecombe, G. D., Caron, J-B.
Description date: 2012
Etymology:

Nereocaris – After “Nereus”, the Greek titan with a fish-like tail and the Latin caris, meaning “crab” or “shrimp”, and

exilis – from the Latin exilis, meaning “slender”.

Type Specimens: dsfsdfdsfdsfdasf
Other species:

Holotype ROMIP61831

Age & Localities:

Age:
Middle Cambrian, Wuliuan Stage, Burgess Shale Formation (around 507 million years old)
Principal localities:

Tulip Beds (S7) (N. exilis) and the Collins Quarry (N. briggsi).

History of Research:

Brief history of research:

The first description of Nereocaris exilis was published in 2012 based on specimens from the Tulip Beds site in Mount Stephen (Yoho National Park). Two years later, Nereocaris briggsi was described based on specimens from the Collins Quarry in Mount Stephen (Legg and Caron 2014). Nereocaris was originally described with a median eye protruding from a single eye peduncle located between the lateral eyes (Legg et al. 2012; Legg and Caron 2014). This structure was later reinterpreted as one of a pair of frontal filaments; short unsegmented limb-like structures with a sensorial function (Izquierdo-López and Caron 2022). Similarly, the tail fan of Nereocaris exilis was initially interpreted as having six pairs of lateral caudal rami (termed telson processes in the original study) and one medial telson process. This structure was later reinterpreted as two pairs of three-partite caudal rami borne by the terminal segment (“te” in Izquierdo-López and Caron, 2022), and was also reconstructed as such for N. briggsi (Izquierdo-López and Caron 2022). The discovery of Nereocaris and the phylogenetic analyses adjunct to the publication have been key to the interpretation of hymenocarines as earliest euarthropods (Legg et al. 2013; Fu et al. 2022) (or ‘upper stem-euarthropods’ based on Ortega-Hernández 2014). The discovery of mandibles in several hymenocarines (Aria and Caron 2017; Vannier et al. 2018; Zhai et al. 2019) has prompted the reinterpretation of this group as mandibulates, although the mandibulates affinities of Nereocaris and other odaraiids remain unclear pending clearer resolution of their head appendages.

Description:

Morphology:

The carapace of Nereocaris has a dome-like shape, compressed laterally, which becomes progressively wider towards the back of the animal. The top of the carapace bears a dorsal crest (keel) that runs across its entire length and extends posteriorly into a small process. The carapace is truncated anteriorly, and each valve extends towards the ventral side, terminating into an anterior hook. The carapace valves extend beyond the length of the legs, and in N. briggsi extend across the ventral side, similar to Odaraia alata. The head bears one pair of short pedunculate eyes and one pair of thin and small, unsegmented appendages (frontal filaments). Antennulae appear to be absent, and further cephalic specializations are unknown from the material available. The body of Nereocaris is highly multisegmented, reaching more than 90 segments in N. exilis. The trunk is subdivided into a thoracic region with limbs and a long limbless abdomen. Limbs are short, subdivided into two branches (biramous): a walking leg (endopod) and a seemingly paddle-like flap (exopod). Based on N. briggsi, the walking legs are probably subdivided into 14 or similar segments (podomeres). The exact morphology and size of the exopods is not well-preserved, but darker areas close to the legs’ base could indicate their approximate shape and length. The terminal segment is distinctly larger than the preceding segments and extends into a blunt process towards the posterior side of the animal (the “mtp” in Legg & Caron, 2014). This last segment bears one pair of caudal rami, each being partly subdivided into three smaller segments (tripartite). Each segment bears one spine on its outer edge.

Abundance:

Nereocaris exilis is rare, only known from three specimens from the same locality. Nereocaris briggsi is highly abundant in its locality, with over 190 specimens known.

Maximum Size:
About 14.2 cm (N. exilis)

Ecology:

Life habits: Arthropoda
Feeding strategies: Arthropoda
Ecological Interpretations:

The limbs of Nereocaris exilis do not extend beyond the carapace ventral margin, indicating that they were not used for crawling. By contrast, the limbs of Nereocaris briggsi protrude from the carapace, but these were considered ill-suited to walk on the benthos (Legg and Caron 2014). For this reason, Nereocaris was reconstructed as a nektonic species, using its long abdomen as a means of propulsion (Legg et al. 2012; Perrier et al. 2015). N. exilis could have been a suspension-feeder, based on the lack of any raptorial or similar predatory limbs, but this possibility was questioned based on the lack of endites or setae on the limbs (Legg et al. 2012), which are widely used by extant filter-feeding crustaceans (Riisgård and Larsen 2010). A straight gut in N. briggsi, a simple tube filled with sediment may support the presence of a suspension or deposit feeding lifestyle, in which the animal would have consumed mud containing organic material (Legg and Caron 2014). It was also hypothesized that multiple odaraiids (Izquierdo-López and Caron 2022), most prominently Fibulacaris (Izquierdo-López and Caron 2019), could have swum upside-down, thus facilitating the capture of particles by the carapace. Whether Nereocaris could have adopted such behaviour remains uncertain.

References:

  • ARIA, C. and CARON, J. B. 2017. Burgess Shale fossils illustrate the origin of the mandibulate body plan. Nature, 545: 89–92.
  • FU, D., LEGG, D. A., DALEY, A. C., BUDD, G. E., WU, Y. and ZHANG, X. 2022. The evolution of biramous appendages revealed by a carapace-bearing Cambrian arthropod. Philosophical Transactions of the Royal Society of London B, 377.
  • IZQUIERDO-LÓPEZ, A. and CARON, J. B. 2019. A possible case of inverted lifestyle in a new bivalved arthropod from the Burgess Shale. Royal Society Open Science, 6: 191350.
  • IZQUIERDO-LÓPEZ, A. and CARON, J.-B. 2022. Extreme multisegmentation in a giant bivalved arthropod from the Cambrian Burgess Shale. IScience, 25, 104675.
  • LEGG, D., SUTTON, M. D. and EDGECOMBE, G. D. 2013. Arthropod fossil data increase congruence of morphological and molecular phylogenies. Nature Communications, 4: 1–7.
  • LEGG, D. A. and CARON, J. B. 2014. New Middle Cambrian bivalved arthropods from the Burgess Shale (British Columbia, Canada). Palaeontology, 57: 691–711.
  • LEGG, D. A., SUTTON, M. D., EDGECOMBE, G. D. and CARON, J. B. 2012. Cambrian bivalved arthropod reveals origin of arthrodization. Proceedings of the Royal Society B: Biological Sciences, 279: 4699–4704.
  • ORTEGA-HERNÁNDEZ, J. 2014. Making sense of ‘lower’ and ‘upper’ stem-group Euarthropoda, with comments on the strict use of the name Arthropoda von Siebold, 1848. Biological Reviews, 91: 255–273.
  • PERRIER, V., WILLIAMS, M. and SIVETER, D. J. 2015. The fossil record and palaeoenvironmental significance of marine arthropod zooplankton. Earth-Science Reviews, 146: 146–162.
  • RIISGÅRD, H. U. and LARSEN, P. S. 2010. Particle capture mechanisms in suspension-feeding invertebrates. Marine Ecology Progress Series, 418: 255–293.
  • VANNIER, J., ARIA, C., TAYLOR, R. S. and CARON, J. B. 2018. Waptia fieldensis Walcott, a mandibulate arthropod from the middle Cambrian Burgess Shale. Royal Society Open Science, 5:172206.
  • ZHAI, D., ORTEGA-HERNÁNDEZ, J., WOLFE, J. M., HOU, X.-G., CAO, C. and LIU, Y. 2019. Three-dimensionally preserved appendages in an early Cambrian stem-group pancrustacean. Current Biology, 29: 171–177.
Other Links:

Misszhouia canadensis

Misszhouia canadensis, two specimens, ROMIP 65408

Taxonomy:

Kingdom: Arthropoda
Phylum: Arthropoda
Higher Taxonomic assignment: Subphylum Artiopoda (Hou & Bergström 1997), Class Nektaspida (Raymond 1920), Family Naraoiidae (Walcott 1912).
Species name: Misszhouia canadensis
Remarks:

Artiopoda is the clade including trilobites and their non-biomineralized relatives. The placement of Artiopoda relative to other arthropod groups, and particularly extant lineages, has been the subject of a long and ongoing debate (e.g. Aria et al. 2015; Paterson 2020). Misszhouia is the closest relative of Naraoia, together forming the family Naraoiidae, typified notably by having both cephalon and trunk forming smooth, articulating shields. Naraoiidae could be derived taxa among artiopodans (Mayers et al. 2019), but the internal relationships of Artiopoda have been difficult to resolve and continue to remain at odds between phylogenetic studies (e.g. Lerosey-Aubril et al. 2017; Moysiuk & Caron 2019).

Described by: Mayers, Aria and Caron
Description date: 2018
Etymology:

Misszhouia — in honour of Miss Guiqing Zhou, fossil preparator and technical assistant to Prof. Junyuan Chen from the Nanjing Institute of Geology and Palaeontology, Academia Sinica, China.

canadensis — from being discovered in Canada.

Type Specimens: dsfsdfdsfdsfdasf
Other species:

Holotype ROMIP 64408; paratypes ROMIP 64411, 64438, 64450, 64451, 64509, 64510, 64511, in the Royal Ontario Museum, Toronto, Canada.

Age & Localities:

Age:
Middle Cambrian, Wuliuan Stage, upper part of the Burgess Shale Formation (around 507 million years old)
Principal localities:

The Marble Canyon and Tokumm Creek areas of the Burgess Shale, British Columbia.

History of Research:

Brief history of research:

Chen and colleagues created the genus Misszhouia mostly based on the distinction that these individuals of “Naraoia” longicaudata did not possess gut ramifications inside the head, compared to Naraoia species from the Chengjiang biota and Burgess Shale. The morphoanatomy and taxonomy of Naraoiidae from China were later thoroughly revised by Zhang and colleagues (2007). Misszhouia canadensis was one of the first taxa found on talus when the Marble Canyon outcrop was discovered in 2012 (Caron et al. 2014). Although these fossils do possess extensive digestive ramifications in the head, morphometric analyses of body shape showed that specimens from both Canada and China formed a genus distinct from Naraoia (Mayers et al. 2019). Morphometric data also allowed for the identification of putative sexual morphs (Zhang et al. 2007; Mayers et al. 2019).

Description:

Morphology:

As an artiopodan, Misszhouia possesses a flattened body divided into a circular cephalon and a trunk, a pair of sensory antennules, and robust walking limbs with masticatory gnathobases, oriented parallel to the ventral surface of the body. Both cephalon and trunk form single smooth shields articulating to one another. In the cephalon, the gut ramifies into extensive diverticula; it is completed by lateral extensions called caeca in the trunk. In addition to the frontal antennules, the head bears another three pairs of limbs. The trunk represents 65% of total body length, with at least 30 limb pairs. The appendages are likely similar to M. longicaudata, with an inner walking branch and an outer, rod-shaped respiratory branch bearing packed lamellae.

Abundance:

Misszhouia is relatively rare at the Marble Canyon Quarry proper, but can be common along Tokumm Creek sites (Mayers et al. 2019).

Maximum Size:
About 8 cm.

Ecology:

Life habits: Arthropoda
Feeding strategies: Arthropoda
Ecological Interpretations:

Misszhouia was construed to be a predator or scavenger based on the presence of long antennules and well-developed gnathobases (masticatory surfaces at the base of the limbs) (Chen et al. 1997). The absence of digestive ramifications in the head of the Burgess Shale species, compared to the one from Chengjiang, suggests either different diets or different frequencies of feeding (Mayers et al. 2019).

References:

  • ARIA, C., CARON, J.-B. and GAINES, R. 2015. A large new leanchoiliid from the Burgess Shale and the influence of inapplicable states on stem arthropod phylogeny. Palaeontology, 58, 629–660.
  • CARON, J.-B., GAINES, R. R., ARIA, C., MANGANO, M. G. and STRENG, M. 2014. A new phyllopod bed-like assemblage from the Burgess Shale of the Canadian Rockies. Nature Communications, 5.
  • CHEN, J. Y., EDGECOMBE, G. D. and RAMSKÖLD, L. 1997. Morphological and ecological disparity in naraoiids (Arthropoda) from the Early Cambrian Chengjiang fauna, China. Records of the Austalian Museum, 49, 1–24.
  • HOU, X. G. and BERGSTRÖM, J. 1997. Arthropods of the Lower Cambrian Chengjiang fauna, southwest China. Fossils and Strata, 45, 1–116.
  • LEROSEY-AUBRIL, R., ZHU, X. and ORTEGA-HERNÁNDEZ, J. 2017. The Vicissicaudata revisited – insights from a new aglaspidid arthropod with caudal appendages from the Furongian of China. Scientific Reports, 7, Article number: 11117.
  • MAYERS, B., ARIA, C. and CARON, J. B. 2019. Three new naraoiid species from the Burgess Shale, with a morphometric and phylogenetic reinvestigation of Naraoiidae. Palaeontology, 62, 19–50.
  • MOYSIUK, J. and CARON, J. B. 2019. Burgess Shale fossils shed light on the agnostid problem. Proc Biol Sci, 286, 20182314.
  • PATERSON, J. R. 2020. The trouble with trilobites: classification, phylogeny and the cryptogenesis problem. Geological Magazine, 157, 35–46.
  • RAYMOND, P. E. 1920. The appendages, anatomy and relationships of trilobites. Memoirs of the Connecticut Academy of Arts and Sciences, 7, 1–169.
  • WALCOTT, C. 1912. Cambrian Geology and Paleontology II. Middle Cambrian Branchiopoda, Malacostraca, Trilobita and Merostomata. Smithsonian Miscellaneous Collections, 57(6), 145–228.
  • ZHANG, X. L., SHU, D. G. and ERWIN, D. H. 2007. Cambrian naraoiids (Arthropoda): morphology, ontogeny, systematics, and evolutionary relationships. Journal of Paleontology, 81, 1–52.
Other Links:

Loricicaris spinocaudatus

Loricicaris spinocaudatus, paratype, ROMIP 43188

Taxonomy:

Kingdom: Arthropoda
Phylum: Arthropoda
Higher Taxonomic assignment: Hymenocarines, Family Protocarididae (Miller 1889).
Species name: Loricicaris spinocaudatus
Remarks:

Hymenocarines were early arthropods with bivalved carapaces and mandibles, forming the bulk of the first mandibulates (represented today by myriapods, crustaceans and insects) (Aria & Caron 2017; Vannier et al. 2018). Loricicaris was a close relative of Branchiocaris, both grouped within the eponymous family Protocarididae Miller, 1889—one of the oldest formal taxa from the Burgess Shale. The relationship of Protocarididae within hymenocarines, as well as the relative placement of hymenocarines within early mandibulates is still under investigation (Aria 2022; Izquierdo-López & Caron 2022).

Described by: Legg and Caron
Description date: 2014
Etymology:

Loricicaris — from the Latin “lorica,” meaning armoured or armour plating, referring to the armoured (spinose) appearance of the trunk, and “caris” meaning shrimp.

spinocaudatus — from the Latin “spinosus” and “cauda,” meaning spiny and tail respectively, in reference to the spinose trunk and tailpiece of this species.

Type Specimens: Holotype ROMIP 62143 and paratype ROMIP 43188, in the Royal Ontario Museum, Toronto, Canada.
Other species:

Burgess Shale and vicinity: none.
Other deposits: none.

Age & Localities:

Age:
Middle Cambrian, Wuliuan Stage, upper part of the Burgess Shale Formation (around 507 million years old)
Principal localities:

The Collins Quarry on Mount Stephen.

History of Research:

Brief history of research:

Following the discovery and initial excavation of the Collins Quarry on Mount Stephen (initially referred as “locality 9”, (Collins et al. 1983)), the small protocaridid material from the Collins Quarry had been referred to as possible juvenile specimens of Branchiocaris (Briggs & Robison 1984). The material was formally described much later as a new genus and species by Legg and Caron (2014), alongside Nereocaris briggsi, and interpreted in the light of a very basal placement of bivalved arthropods in the evolution of the group—a view that has since given way to the mandibulate classification of these taxa (Aria 2022).

Description:

Morphology:

Loricicaris has a stout, tubular, multisegmented body largely enclosed in a broad bivalved carapace with ample, lobate corners, like other protocaridids. Eyes are very reduced or absent. The very front of the animal bears a rounded sclerite. A pair of short, stout, multisegmented antennules are the most anterior appendages. The rest of the head is poorly known, but clawed appendages are present in proximity to the antennules. The trunk limbs bear round exopods; endopods are reduced or absent. The tailpiece is a pair of caudal rami bearing setae.

Abundance:

24 specimens (Legg & Caron 2014).

Maximum Size:
About 3 cm.

Ecology:

Life habits: Arthropoda
Feeding strategies: Arthropoda
Ecological Interpretations:

Loricicaris was considered by its authors to be a nektobenthic deposit feeder, based on the possession of a swimmer body and three-dimensional preservation of the gut (Legg & Caron 2014). Loricicaris could be a predator or particle feeder like other hymenocarines.

References:

  • ARIA, C. 2022. The origin and early evolution of arthropods. Biological Reviews, 97, 1786–1809.
  • ARIA, C. and CARON, J. B. 2017. Burgess Shale fossils illustrate the origin of the mandibulate body plan. Nature, 545, 89–92.
  • BRIGGS, D. E. G. and ROBISON, R. A. 1984. Exceptionally preserved nontrilobite arthropods and Anomalocaris from the Middle Cambrian of Utah. The University of Kansas Paleontological Contributions, 111, 1–23.
  • COLLINS, D., BRIGGS, D. E. G. and CONWAY MORRIS, S. 1983. New Burgess Shale fossil sites reveal Middle Cambrian faunal complex. Science, 222, 163–167.
  • IZQUIERDO-LÓPEZ, A. and CARON, J.-B. 2022. The problematic Cambrian arthropod Tuzoia and the origin of mandibulates revisited. Royal Society Open Science, 9.
  • LEGG, D. and CARON, J. B. 2014. New Middle Cambrian bivalved arthropods from the Burgess Shale (British Columbia, Canada). Journal of Paleontology, 57, 691–711.
  • MILLER, S. A. 1889. North American geology and palaeontology for the use of amateurs, students and scientists. Western Methodist Book Concern, Cincinnati.
  • VANNIER, J., ARIA, C., TAYLOR, R. S. and CARON, J. B. 2018. Waptia fieldensis Walcott, a mandibulate arthropod from the middle Cambrian Burgess Shale. Royal Society Open Science, 5:172206.
Other Links:

Fibulacaris nereidis

Fibulacaris nereidis, carapace ROMIP 64511

Taxonomy:

Kingdom: Arthropoda
Phylum: Arthropoda
Higher Taxonomic assignment: Hymenocarines, Family: Odaraiidae
Species name: Fibulacaris nereidis
Remarks:

Hymenocarines were early arthropods with bivalved carapaces and mandibles, forming the bulk of the first mandibulates (represented today by myriapods, crustaceans and insects) (Aria and Caron 2017; Vannier et al. 2018). In many hymenocarines, including Fibulacaris, determining the exact number and types of appendages on their head remains difficult, which hinders a detailed understanding of the evolutionary history of this group. Fibulacaris most probably belongs to the family Odaraiidae, a group of hymenocarines with highly multisegmented bodies, reduced or absent antennae and highly multisegmented legs.

Described by: Izquierdo-López & Caron
Description date: 2019
Etymology:

Fibulacaris – from a “fibula”, a type of brooch, the latin caris, meaning “crab” or “shrimp”

nereidis – from the Greek mythological creatures known as Nereids, the daughters of Nereus, given the similarities of Fibulacaris to the Burgess Shale odaraiid Nereocaris (Legg et al. 2012).

Type Specimens: Holotype ROMIP65380
Other species:

Burgess Shale and vicinity: None
Other deposits: None

Age & Localities:

Age:
Middle Cambrian (Wuliuan Stage), upper part of the Burgess Shale Formation (around 507 million years old)
Principal localities:

Marble Canyon, Tokumm Creek.

History of Research:

Brief history of research:

Several specimens of Fibulacaris nereidis were discovered at the Marble Canyon site in 2014 and nicknamed “epsilon-arthropod” based on the characteristic shape of its carapace. The majority of specimens were discovered at Mount Whymper and Tokumm Creek sites during the expeditions of 2016 and 2018, sometimes referred as “safety-pin”. Its genus and species were later described in 2019 (Izquierdo-López and Caron 2019).

Description:

Morphology:

Fibulacaris is generally small, with most specimens measuring around 1 cm. It has a distinct bivalved carapace enclosing its body laterally, covering up to two-thirds of its entire length. The dorsal side of the carapace is dome-shaped with a small crest that runs across the entire length, and a small spinose process on its posterior side. The frontal side of the carapace bends ventrally into a highly elongated spine, almost as long as the carapace itself. The ventral margins of the carapace are thicker, and end with a small process posteriorly on both sides. One pair of pedunculate eyes protrudes from the notches formed between the carapace and the spine. Other details about its head remain unknown, but antennae are either absent or highly reduced. The anterior side of the body is bent posteriorly, so that the eyes are facing backward. The body is multisegmented, subdivided into 30 segments, with each segment bearing limbs subdivided into two branches (biramous). Its tail has two small appendages shaped like a paddle (caudal rami).

Abundance:

Fibulacaris is rare at the Marble Canyon site, but very abundant (with more than 100 specimens) along Tokumm Creek.

Maximum Size:
About 2 cm.

Ecology:

Life habits: Arthropoda
Feeding strategies: Arthropoda
Ecological Interpretations:

Fibulacaris was likely a nektobenthic suspension feeder (Izquierdo-López and Caron 2019). Its gut is sometimes preserved as a three-dimensional structure, a type of preservation that has been associated with deposit feeders (Legg and Caron 2014). However, Fibulacaris’ carapace extends through its ventral side, indicating that this arthropod was not able to walk on surfaces and obtain organic material from the sediment, like a deposit feeder. Extant branchiopod crustaceans, such as many water fleas (Cladocera), have carapaces similar to that of Fibulacaris. Using their limbs, they generate small water currents carrying organic particles that pass through their limbs and carapace. Fibulacaris, could have used a similar suspension-feeding strategy. Given that the dorsal side of Fibulacaris was covered by its carapace, and that its eyes were facing towards the back of its body, it has been suggested that it was swimming upside down (Izquierdo-López and Caron 2019), as fairy shrimps do (Anostraca) (Fryer 2006). This way, Fibulacaris would have had capture organic particles falling from the water column, while being protected from predators from its back thanks to the carapace, from its ventral and posterior side thanks to the spine.

References:

  • ARIA, C. and CARON, J. B. 2017. Burgess Shale fossils illustrate the origin of the mandibulate body plan. Nature, 545: 89–92.
  • FRYER, G. 1968. Evolution and adaptive radiation in the Chydoridae (Crustacea: Cladocera): a study in comparative functional morphology and ecology. Philosophical Transactions of the Royal Society of London. B, Biological Sciences, 254: 221–382.
  • FRYER, G. 2006. The brine shrimp’s tale: a topsy turvy evolutionary fable. Biological Journal of the Linnean Society, 88(3): 377–382.
  • IZQUIERDO-LÓPEZ, A. and CARON, J. B. 2019. A possible case of inverted lifestyle in a new bivalved arthropod from the Burgess Shale. Royal Society Open Science, 6: 191350.
  • IZQUIERDO-LÓPEZ, A. and CARON, J. B. 2021. A Burgess Shale mandibulate arthropod with a pygidium: a case of convergent evolution. Papers in Palaeontology, 7: 1877–1894.
  • LEGG, D. A. and CARON, J. B. 2014. New Middle Cambrian bivalved arthropods from the Burgess Shale (British Columbia, Canada). Palaeontology, 57: 691–711.
  • LEGG, D. A., SUTTON, M. D., EDGECOMBE, G. D. and CARON, J. B. 2012. Cambrian bivalved arthropod reveals origin of arthrodization. Proceedings of the Royal Society B: Biological Sciences, 279: 4699–4704.
  • PARI, G., BRIGGS, D. E. G. and GAINES, R. R. 2022. The soft-bodied biota of the Cambrian Series 2 Parker Quarry Lagerstätte of northwestern Vermont, USA. Journal of Paleontology, 1–21.
  • VANNIER, J., ARIA, C., TAYLOR, R. S. and CARON, J. B. 2018. Waptia fieldensis Walcott, a mandibulate arthropod from the middle Cambrian Burgess Shale. Royal Society Open Science, 5:172206.
Other Links:

Cambroraster falcatus

Cambroraster falcatus, isolated H-element ROMIP 65316

Taxonomy:

Kingdom: Arthropoda
Phylum: Arthropoda
Higher Taxonomic assignment: Order Radiodonta, Family Hurdiidae
Species name: Cambroraster falcatus
Remarks:

With its single pair of jointed frontal appendages, lateral swimming flaps, and circular mouth structure, Cambroraster possesses all the hallmarks of Radiodonta, part of the stem group to the true arthropods which also includes the iconic Anomalocaris (Collins 1996). The frontal appendages with comb or rake-like inner spines are characteristic of the radiodont family Hurdiidae. Phylogenetic analysis found it to be closely related to Titanokorys from the Burgess Shale and Zenghecaris from the Chengjiang deposit, which share similarities in carapace shape and a large number of finely-spaced spines on the appendages (Caron and Moysiuk 2021).

Described by: Moysiuk and Caron
Description date: 2019
Etymology:

Cambroraster – Cambro, for Cambrian; raster, for the rake-like morphology of the inner spines on the frontal appendages.

falcatus – meaning sickle-shaped, but more specifically in reference to the dorsal carapace’s resemblance to the fictional Millennium Falcon starship in the Star Wars franchise.

Type Specimens: Holotype ROMIP 65078; Paratypes ROMIP 65079, 65081, 65083, 65084, 65092, at the Royal Ontario Museum.
Other species:

Burgess Shale and vicinity: None

Other deposits: Cambroraster sp. from the early Cambrian Chengjiang biota (Liu et al. 2020); Cambroraster cf. C. falcatus from the mid-Cambrian Mantou Formation of north China (Sun et al. 2020).

Age & Localities:

Age:
Middle Cambrian, Wuliuan stage, Burgess Shale Formation (around 507 million years old).
Principal localities:

Marble Canyon and Mount Whymper / Tokumm Creek, Kootenay National Park, British Columbia.

History of Research:

Brief history of research:

Several specimens of Cambroraster were discovered at the Marble Canyon and North Tokumm sites in Kootenay National Park in 2014. Because of their distinctive shape, the head carapaces were nicknamed the “spaceship.” Isolated frontal appendages were initially tentatively assigned to the genus Hurdia (Caron et al. 2014). The affinities of Cambroraster were not well-understood until further finds of abundant material at North Tokumm in 2018. The genus and species were formally described in 2019 (Moysiuk and Caron 2019). 3D digital modeling of an appendage of Cambroraster found it to have the lowest potential degree of appendage articulation of any of the studied radiodontans (de Vivo et al. 2021).

Description:

Morphology:

The defining feature of Cambroraster falcatus is its large, horseshoe-shaped dorsal carapace. This carapace is rounded frontally and projects along the rear sides into elongate wing-like projections lined along their margins with small spines. The rear central part of the carapace extends into a bilobate projection. Between the lateral “wings” and central projection are deep notches that accommodate the elliptical eyes, which are directed upwards. On the underside, the head is protected by two additional plates, shaped like elongate paddles and joined together at the front by their narrow ends. A circular, tooth-lined jaw and a pair of jointed frontal appendages with five long, curving, strong rake-like inner spines are located on the underside, near the front of the head. The body is stout, shorter than the dorsal carapace, and composed of 11 segments bearing rows of stacked gill blades and short lateral swimming flaps plus four short tail blades.

Abundance:

Cambroraster is abundant in Kootenay National Park, being known from over 100 specimens. It is particularly abundant around the North Tokumm locality, and may occur by the dozens on certain bedding planes, suggesting gregarious mass moulting behaviour. Rarer remains are known from Marble Canyon and single, isolated carapace fragments are known from Mount Stephen and Mount Field.

Maximum Size:
About 300 mm

Ecology:

Life habits: Arthropoda
Feeding strategies: Arthropoda
Ecological Interpretations:

Like other hurdiids, Cambroraster shows adaptations to sweep feeding. Specifically, the stout and rigid frontal appendages are ill-suited to grasping large, mobile prey (de Vivo et al. 2021). Instead, the rake-like inner spines on the appendages form a rigid, basket-like apparatus of spines surrounding the mouth. Sideways movements of the appendages could have disturbed the sediment, sifting out burrowing organisms, and transferring them to the mouth for further processing (Moysiuk and Caron 2019). Compared to related hurdiids like Hurdia and Stanleycaris, the particularly numerous and finely-spaced, strong, hooked secondary spines on the inner spines could have enabled capture of minute benthic organisms, although larger prey may also have been consumed. As one of the largest animals in the Marble Canyon and Tokumm communities, Cambroraster would have been near the top of the food chain. The broad dorsal carapace, upward facing eyes, and stubby body suggest it spent most of its time near the sea floor (Moysiuk and Caron 2019). As in other radiodontans, swimming was facilitated by undulation of the lateral flaps while respiration would have been accomplished primarily through the rows of gill blades on the body (Usami 2006; Daley et al. 2013).

References:

  • CARON, J.-B. and MOYSIUK, J. 2021. A giant nektobenthic radiodont from the Burgess Shale and the significance of hurdiid carapace diversity. Royal Society Open Science, 8: 210664.
  • CARON, J.-B., GAINES, R. R., ARIA, C., MÁNGANO, M. G. and STRENG, M. 2014. A new phyllopod bed-like assemblage from the Burgess Shale of the Canadian Rockies. Nature communications, 5: 1–6.
  • 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.
  • DALEY, A. C., BUDD, G. E. and CARON, J.-B. 2013. Morphology and systematics of the anomalocaridid arthropod Hurdia from the Middle Cambrian of British Columbia and Utah. Journal of Systematic Palaeontology, 11: 743–787.
  • LIU, Y., LEROSEY-AUBRIL, R., AUDO, D., ZHAI, D., MAI, H. and ORTEGA-HERNÁNDEZ, J. 2020. Occurrence of the eudemersal radiodont Cambroraster in the early Cambrian Chengjiang Lagerstätte and the diversity of hurdiid ecomorphotypes. Geological Magazine, 157: 1200–1206.
  • MOYSIUK, J. and CARON, J.-B. 2019. A new hurdiid radiodont from the Burgess Shale evinces the exploitation of Cambrian infaunal food sources. Proceedings of the Royal Society B, 286: 20191079.
  • SUN, Z., ZENG, H. and ZHAO, F. 2020. Occurrence of the hurdiid radiodont Cambroraster in the middle Cambrian (Wuliuan) Mantou Formation of North China. Journal of Paleontology, 94: 881–886.
  • USAMI, Y. 2006. Theoretical study on the body form and swimming pattern of Anomalocaris based on hydrodynamic simulation. Journal of Theoretical Biology, 238: 11–17.
  • DE VIVO, G., LAUTENSCHLAGER, S. and VINTHER, J. 2021. Three-dimensional modelling, disparity and ecology of the first Cambrian apex predators. Proceedings of the Royal Society B, 288.
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