Creatures: Swimmers



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Pakucaris apatis

Artistic reconstruction of Pakucaris apatis. Danielle Dufault © ROM

Taxonomy:

Kingdom: Swimmers
Phylum: Swimmers
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: Swimmers
Feeding strategies: Swimmers
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.
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Fibulacaris nereidis

Artistic reconstruction of Fibulacaris nereidis. Danielle Dufault © ROM

Taxonomy:

Kingdom: Swimmers
Phylum: Swimmers
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: Swimmers
Feeding strategies: Swimmers
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.
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Pikaia gracilens

3D animation of Pikaia gracilens.

ANIMATION BY PHLESCH BUBBLE © ROYAL ONTARIO MUSEUM

Taxonomy:

Kingdom: Swimmers
Phylum: Swimmers
Higher Taxonomic assignment: Unranked clade (stem group chordates)
Species name: Pikaia gracilens
Remarks:

Pikaia is considered to represent a primitive chordate (Conway Morris, 1979; Conway Morris et al., 1982) possibly close to craniates (Janvier, 1998); a stem-chordate (Smith et al., 2001); or a cephalochordate (Shu et al., 1999). Its exact position within the chordates is still uncertain and this animal awaits a full redescription.

Described by: Walcott
Description date: 1911
Etymology:

Pikaia – from the pika, a small alpine mammal and cousin of the rabbits. Pikas live in the Rocky Mountains, including near the Burgess Shale.

gracilens – from the Latin gracilens, “thin, simple,” in reference to the shape of the body.

Type Specimens: Syntypes –USNM57628b, 57629 in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
Other species:

Burgess Shale and vicinity: none.

Other deposits: none.

Age & Localities:

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

The Walcott Quarry on Fossil Ridge.

History of Research:

Brief history of research:

Pikaia was first described by Walcott based on a couple of specimens in a 1911 monograph dealing with various Burgess Shale worms. Two additional specimens were figured in a posthumous publication (Walcott, 1931). Walcott placed Pikaia in a now defunct group called the Gephyrea with other vermiform fossils such as Banffia, Ottoia and Oesia. Pikaia was later considered to be a primitive chordate (Conway Morris, 1979; Conway Morris et al., 1982), an interpretation which has since been followed to some degree in most discussions about early chordate evolution (e.g., Janvier, 1998). Pikaia played a major part in Gould’s interpretations of the Burgess Shale fossils in Wonderful Life (Gould, 1989; see also Briggs and Fortey, 2005). A full redescription of this animal is currently under way (Conway Morris and Caron, in prep.).

Description:

Morphology:

Pikaia resembles Metaspriggina in outline, another chordate animal from the Burgess Shale, with an elongate body and a small anterior region bearing the head. The body is laterally flattened and there is evidence of a ventral fin towards the posterior. Numerous V-shaped or ziz-zag segments interpreted as myomeres or muscle bands are visible in all specimens. A narrow dorsal structure which runs down the length of the organism might represent a notochord, but this interpretation remains to be confirmed. The head bears two equal lobes and a pair of short and slender tentacle-like structures. There is no evidence of eyes. Just behind the head, on the ventral side of the body, there is a series of up to twelve pairs of small, short, pointed structures on either side of the midline. These are thought to be related to gill openings. The gut is narrow and the anus is terminal.

Abundance:

Pikaia is relatively rare, known from more than 60 specimens, all from the Walcott Quarry where it represents 0.03% of the specimens counted in the community (Caron and Jackson, 2008).

Maximum Size:
55 mm

Ecology:

Life habits: Swimmers
Feeding strategies: Swimmers
Ecological Interpretations:

The eel-like morphology and musculature of the animal suggest that it was likely free-swimming, although it probably spent time on the sea floor. The tentacles may have had a sensory function, and the presence of mud in its gut suggests that Pikaia was potentially a deposit feeder.

References:

BRIGGS, D. E. G. AND R. A. FORTEY. 2005. Wonderful strife: Systematics, stem groups, and the phylogenetic signal of the Cambrian radiation. Paleobiology, 31(SUPPL.2 ): 94-112.

CONWAY MORRIS, S. 1979. The Burgess Shale (Middle Cambrian) fauna. Annual Review of Ecology and Systematics, 10(1): 327-349.

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

CONWAY MORRIS, S. H. B. WHITTINGTON, D. E. G. BRIGGS, C. P. HUGHES AND D. L. BRUTON. 1982. Atlas of the Burgess Shale. Palaeontological Association, 31 p. + 23 pl.

GOULD, S. J. 1989. Wonderful Life. The Burgess Shale and the Nature of History. Norton, New York, 347 p.

JANVIER, P. 1998. Les vertébrés avant le Silurien. GeoBios, 30: 931-950.

SHU, D.-G,. H. L. LUO, S. CONWAY MORRIS, X. L. ZHANG, S. X. HU, L. CHEN, J. HAN, M. ZHU, Y. LI AND L. Z. CHEN. 1999. Lower Cambrian vertebrates from south China. Nature, 402(4 November 1999): 42-46.

SMITH, M. P., I. J. SANSOM AND K. D. COCHRANE. 2001. The Cambrian origin of vertebrates, p. 67-84. In P. E. Ahlberg (ed.), Major Events in Early Vertebrate Evolution: Palaeontology, Phylogeny, Genetics and Development. Taylor and Francis, London.

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

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

Other Links:

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



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Liangshanella burgessensis

3D animation of Liangshanella burgessensis.

ANIMATION BY PHLESCH BUBBLE © ROYAL ONTARIO MUSEUM

Taxonomy:

Kingdom: Swimmers
Phylum: Swimmers
Higher Taxonomic assignment: Hymenocarines?, Order Bradoriida (Raymond 1935).
Species name: Liangshanella burgessensis
Remarks:

Liangshanella is a bradoriid belonging to the family Svealutidae (Siveter & Williams 1997). The bradoriids were traditionally compared to other bivalved arthropods within or close to crustaceans, such as Recent ostracods (e.g. Sylvester-Bradley, 1961) and Cambrian phosphatocopids (e.g. Maas et al. (2003)). More recently, authors have argued bradoriids to represent more basal members of the arthropod stem group (e.g. Hou et al. (1996); Shu et al. (1999); Hou et al. (2010)). A recent reexamination of appendage morphology in the bradoriid Kunmingella supports a placement of these arthropods outside of crown groups (Zhai et al. 2019), but their exact phylogenetic placement remains unclear.

Described by: Siveter and Williams
Description date: 1997
Etymology:

Liangshanella – from Liangshan, a region in South Shaanxi, China.

burgessensis – from the Burgess Shale. The name is derived from Mount Burgess (2,599 m), a mountain peak in Yoho National Park. Mount Burgess was named in 1886 by Otto Klotz, the Dominion topographical surveyor, after Alexander Burgess, a former Deputy Minister of the Department of the Interior.

Type Specimens: Holotype –USNM272083 in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
Other species:

Burgess Shale and vicinity: none.

Other deposits: L. circumbolina from the Flinders Ranges in South Australia; L. liangshanensis, L. rotundata, L. orbicularis, L. yunnanensis and L. baensis from southern China; L. lubrica from the Tongying Formation in Hubei, China; L. sayutinae from the Trans-Baikal area in the Russian Far-East and Greenland; L. birkenmajeri from Antarctica. See references in Siveter and Williams (1997).

Age & Localities:

Age:
Middle Cambrian, Wuliuan stage, Burgess Shale Formation (approximately 505 million years ago).
Principal localities:

The Walcott and Raymond Quarries on Fossil Ridge.

History of Research:

Brief history of research:

Liangshanella liangshanensis is the type species of this genus and was first described by Huo (1956) from Lower Cambrian rocks of south China. urther species have since been described in China (Zhang, 1974; Li, 1975; Qian and Zhang, 1983; Zhang, 2007), Russia and Greenland (Melnikova, 1988), Australia (Topper et al., in press) and Antarctica (Wrona, 2009). Liangshanella burgessensis from the Burgess Shale was described by Siveter and Williams (1997), and the genus has been included in studies on the biogeography, evolution and affinity of the bradoriids (e.g. Shu and Chen, 1994; Williams et al., 2007). The most recent insight on the morphoanatomy of these arthropods comes from computed tomographic imagery of Kunmingella species from the Chengjiang biota (Zhai et al. 2019), which confirms both the presence of biramous enditic appendages and the lack of clear crown-group synapomorphies.

Description:

Morphology:

Like all bradoriids, Liangshanella burgessensis has a small bivalved carapace with a straight dorsal hinge held together by a band of cuticle. The carapaces range in length from 0.66 mm – 4.25 mm and were soft and unmineralized. The bivalved carapace of L. burgessensis is sub-circular, with the anterior end being slightly narrower than the posterior end. There is a marginal ridge along the lateral surface of the valves. A centrally situated, sub-circular muscle scar composed of numerous small pits can be seen inside the valve. Based on appendicular evidence from other bradoriid taxa, L. burgessensis would have possessed short, spinose antennules, very reduced eyes—if at all present—, and biramous post-frontal appendages characterized by the presence of well-developed “fingers” on the inner side, called endites.

Abundance:

Liangshanella burgessensis is known from thousands of specimens and is the most common taxon in the Walcott Quarry (11.8% of the community, Caron and Jackson, 2008).

Maximum Size:
10 mm

Ecology:

Life habits: Swimmers
Feeding strategies: Swimmers
Ecological Interpretations:

Williams et al. (2007) considered bradoriids to be most likely epibenthic dwellers feeding on organic detritus or small non-biomineralized prey items; an ecology comparable to that of ostracods. These authors also pointed out that the large disparity of carapace shapes probably reflected a variety of different sub-niches and lifestyles. Their size and abundance would have made them in turn a common food source for larger animals, as indicated by coprolite composition (Vannier & Chen 2005).

References:

  • CARON, J. B. and JACKSON, D. A. 2008. Paleoecology of the Greater Phyllopod Bed community, Burgess Shale. Palaeogeography, Palaeoclimatology, Palaeoecology, 258, 222–256.
  • HOU, X., WILLIAMS, M., SIVETER, D. J., SIVETER, D. J., ALDRIDGE, R. J. and SANSOM, R. S. 2010. Soft-part anatomy of the Early Cambrian bivalved arthropods Kunyangella and Kunmingella : significance for the phylogenetic relationships of Bradoriida. Proceedings of the Royal Society B: Biological Sciences, 277, 1835–1841.
  • HOU, X., SIVETER, D. J., WILLIAMS, M., WALOSSEK, D., BERGSTRÖM, J., SMITH, M. P. and THOMAS, A. T. 1996. Appendages of the arthropod Kunmingella from the Early Cambrian of China; its bearing on the systematic position of the Bradoriida and the fossil record of the Ostracoda. Palaeontology Newsletter, 32.
  • HUO, S. 1956. Brief notes on lower Cambrian Archaeostraca from Shensi and Yunnan. Acta Palaeontologica Sinica, 4, 1131–1145.
  • LI, Y. 1975. On the Cambrian ostracods with new material from Sichuan, Yunnan and Shaanxi, China. Professional Papers on Stratigraphy & Palaeontology, 2, 37–72.
  • MAAS, A., WALOSZEK, D. and MÜLLER, K. J. 2003. Morphology, ontogeny and phylogeny of the Phosphatocopina (Crustacea) from the Upper Cambrian ‘Orsten’ of Sweden. Fossil and Strata. Vol. 49. Taylor & Francis, Oslo.
  • MELNIKOVA, L. M. 1988. Nekotoryye bradoriidy (Crustacea) iz botomskogo yarusa vostochnogo Zabaykal’ya. Paleontologicheskiy Zhurnal, 1, 114–117.
  • MILLER, S. A. 1889. North American geology and palaeontology for the use of amateurs, students and scientists. Western Methodist Book Concern, Cincinnati.
  • QIAN, Y. and ZHANG, S. 1983. Small shelly fossils from the Xihaoping Member of the Tongying Formation in Fangxian County of Hubei Province and their stratigraphical significance. Acta Palaeontologica Sinica, 22, 82–94.
  • SHU, D. and CHEN, L. 1994. Cambrian palaeobiogeography of Bradoriida. Journal of Southeast Asian Earth Sciences, 9, 289–299.
  • SHU, D. G., VANNIER, J., LUO, H. L., CHEN, L., ZHANG, X. L. and HU, S. X. 1999. Anatomy and lifestyle of Kunmingella (Arthropoda, Bradoriida) from the Chengjiang fossil Lagerstätte (lower Cambrian; Southwest China). Lethaia, 32, 279–298.
  • SIVETER, D. J. and WILLIAMS, M. 1997. Cambrian bradoriid and phosphatocopid arthropods of North America. Special Papers in Palaeontology, 57, 67.
  • TOPPER, T. P., SKOVSTED, C. E., BROCK, G. A. and PATERSON, J. R. 2007. New bradoriids from the lower Cambrian Mernmerna Formation, South Australia: systematics, biostratigraphy and biogeography. Memoirs of the Association of Australasian Palaeontologists, 33, 67–100.
  • VANNIER, J. and CHEN, J. 2005. Early Cambrian food chain: New evidence from fossil aggregates in the Maotianshan Shale biota, SW China. PALAIOS, 20, 3–26.
  • WILLIAMS, M., SIVETER, D. J., POPOV, L. E. and VANNIER, J. M. C. 2007. Biogeography and affinities of the bradoriid arthropods: Cosmopolitan microbenthos of the Cambrian seas. Palaeogeography, Palaeoclimatology, Palaeoecology, 248, 202–232.
  • WRONA, R. 2009. Early Cambrian bradoriide and phosphatocopide arthropods from King George Island, West Antarctica: Biogeographic implications. Polish Polar Research, 30, 347–377.
  • ZHAI, D., WILLIAMS, M., SIVETER, D. J., HARVEY, T. H. P., SANSOM, R. S., GABBOTT, S. E., SIVETER, D. J., MA, X., ZHOU, R., LIU, Y. and HOU, X. 2019. Variation in appendages in early Cambrian bradoriids reveals a wide range of body plans in stem-euarthropods. Communications Biology, 2, 329.
  • ZHANG, W. 1974. Bradoriida. In Handbook of Stratigraphy and Palaeontology of Southwest China, Science Press, Beijing, 107–111 pp.
  • ZHANG, X.-G. 2007. Phosphatized Bradoriids (Arthropoda) from the Cambrian of China. Palaeontographica Abteilung A, 281, 93–173.
Other Links:

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Opabinia regalis

3D animation of Opabinia regalis.

ANIMATION BY PHLESCH BUBBLE © ROYAL ONTARIO MUSEUM

Taxonomy:

Kingdom: Swimmers
Phylum: Swimmers
Higher Taxonomic assignment: ‘Dinocarida’, Family Opabiniidae
Species name: Opabinia regalis
Remarks:

Opabinia’s bizarre morphology has made its affinity challenging to resolve. Although it was initially considered a crustacean by Walcott (1912), later researchers beginning with Whittington (1975) suggested a more distant relationship with arthropods. Collins (1996) proposed the name Dinocarida for a group including radiodontans (Anomalocaris and its relatives) and Opabinia, though this has not been generally supported. The flexible frontal “nozzle” and possible lobopodous appendages suggest a connection with lobopodians, implying that Opabinia might have diverged before the evolutionary split between radiodontans and true arthropods. On the other hand, Opabinia has a backward facing mouth and five eyes, which could suggest a position closer to the some of the earliest true arthropods which share these features. Both placements have been found in recent analyses (Lerosey-Aubril and Pates 2018; Aria et al. 2020; Zeng et al. 2020; Pates et al. 2021; Moysiuk and Caron 2022). Several less well-preserved fossils have been proposed to share close affinities with Opabinia, including Utaurora comosa (Pates et al. 2021) and Myoscolex ateles (Briggs and Nedin 1997).

Described by: Walcott
Description date: 1912
Etymology:

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

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

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

Burgess Shale and vicinity: none.

Other deposits: none.

Age & Localities:

Age:
Middle Cambrian, Wuliuan stage, Burgess Shale Formation (approximately 505 million years ago).
Principal localities:

The Walcott and Raymond Quarries on Fossil Ridge.

History of Research:

Brief history of research:

Opabinia regalis was first described by Walcott (1912) as an anostracan crustacean. Owing to its unique morphology with a bizarre frontal “nozzle,” Opabinia became a flagship fossil for the Burgess Shale, leading to much speculation on its affinity and lifestyle. One famous early reconstruction even shows the animal swimming upside down like a living anostracan (Hutchinson 1930). It wasn’t until the detailed redescription by Whittington (1975) that Opabinia was revealed to be one of the most enigmatic of all fossils. It was so unusual, in fact, that when Whittington showed an early version of his reconstruction in a meeting of palaeontologists in 1972, the whole room burst out laughing! Owing to its unique morphology with a bizarre frontal “nozzle,” Opabinia became a flagship fossil for the Burgess Shale, leading to much speculation on its affinity and lifestyle. Later work by Bergström (1986) identified similarities between Opabinia and the recently discovered whole-body specimens of Anomalocaris (Whittington and Briggs 1985), and updated the morphology of the gills and frontal proboscis. Budd (1996) was the first to place Opabinia in the stem lineage of the true arthropods, and also suggested the animal had lobopodous limbs in addition to lateral swimming flaps, although this idea was contested by Zhang and Briggs (2007). The issue of whether Opabinia had lobopodous limbs remains controversial. Budd and Daley (2012) figured additional material and provided further arguments in support of this hypothesis. However, other authors have noted similar features in other Burgess Shale arthropods and in decay experiments which appear to represent decayed remains of internal tissues or body cavities extending into the appendages rather than distinct appendages in themselves (Aria and Caron 2015; Butler et al. 2015; Mayers et al. 2018; Moysiuk and Caron 2022). While the morphology of Opabinia remains unique, several recent discoveries have shown that some of its unusual traits are shared by other Cambrian arthropods. Anomalocaris canadensis from the Burgess Shale possessed a similar tail fan (Collins 1996). Several radiodontans, including Stanleycaris and Peytoia appear to share the presence of a large median eye with Opabinia (Moysiuk and Caron 2022). Another animal, Kylinxia zhangi from the Chengjiang deposit, has an even more similar cluster of five large eyes, while also possessing traits of true arthropods like biramous limbs and a headshield (Zeng et al. 2020).

Description:

Morphology:

Opabinia has five eyes, a frontal “nozzle,” or proboscis, a body with segmentally repeated lateral lobes and gills, and a prominent tail fan. The whole body length ranges between 4.3 and 7.0 cm (excluding proboscis). The head has a rounded anterior margin, with a cluster of four bulbous eyes on short stalks and a large fifth eye positioned centrally on the dorsal surface of the head. The annulated frontal proboscis is four times longer than the head. It is highly flexible, and has a fused pair of appendages at the distal end, consisting of two opposing claws with five or six spines each. The mouth was ventral and faced to the rear. The trunk was divided into 15 segments, each bearing a pair of lateral lobes in association with gill structures consisting of bands of lanceolate blades. There is some controversy as to the exact location of the gills (dorsal, ventral or posterior) relative to the lobes. The tail fan consists of three pairs of upward-directed flaps. The trunk ends in a pair of tiny, rigid spines. The gut begins with a U-shaped bend near the rearward opening ventral mouth end extends to the body termination. Paired, segmentally arranged digestive glands flank the gut. There are also controversial triangular features in the central region of the body, connected to a dark stain surrounding the gut, which have alternatively been interpreted as lobopod-like walking limbs (Budd 1996; Budd and Daley 2012), or extensions of the gut or haemolymph cavities into the flaps (Whittington 1975; Zhang and Briggs 2007; Aria and Caron 2015; Moysiuk and Caron 2022).

Abundance:

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

Maximum Size:
101 mm

Ecology:

Life habits: Swimmers
Feeding strategies: Swimmers
Ecological Interpretations:

Opabinia was a swimmer. As for Anomalocaris (Usami 2006; Sheppard et al. 2018), undulatory waves along its lateral flaps could have propelled it forward, while it used its tail fan to steer. Opabinia probably used the claws at the tip of its flexible nozzle to grasp food items and carry them towards its ventral mouth. The spinous morphology of the claws, the large eyes, and the paired digestive glands suggest that Opabinia was an active predator (Whittington 1975; Vannier et al. 2014).

References:

  • ARIA, C. and 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., ZHAO, F., ZENG, H., GUO, J. and ZHU, M. 2020. Fossils from South China redefine the ancestral euarthropod body plan. BMC Evolutionary Biology, 20: 1–17.
  • BERGSTRÖM, J. 1986. Opabinia Anomalocaris, unique Cambrian ‘arthropods’. Lethaia, 19: 241–246.
  • BRIGGS, D. E. G. and NEDIN, C. 1997. The taphonomy and affinities of the problematic fossil Myoscolex from the Lower Cambrian Emu Bay Shale of South Australia. Journal of Paleontology, 71: 22–32.
  • BUDD, G. E. 1996. The morphology of Opabinia regalis and the reconstruction of the arthropod stem-group. Lethaia, 29: 1–14.
  • BUDD, G. E. and DALEY, A. C. 2012. The lobes and lobopods of Opabinia regalis from the middle Cambrian Burgess Shale. Lethaia, 45: 83–95.
  • BUTLER, A. D., CUNNINGHAM, J. A., BUDD, G. E. and DONOGHUE, P. C. J. 2015. Experimental taphonomy of Artemia reveals the role of endogenous microbes in mediating decay and fossilization. Proceedings of the Royal Society B: Biological Sciences, 282: 20150476.
  • CARON, J.-B. and JACKSON, D. A. 2008. Paleoecology of the Greater Phyllopod Bed community, Burgess Shale. Palaeogeography, Palaeoclimatology, Palaeoecology, 258: 222–256.
  • 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.
  • HUTCHINSON, G. E. 1930. Restudy of some Burgess Shale fossils. Proceedings of the United States National Museum, 78: 1–11.
  • LEROSEY-AUBRIL, R. and PATES, S. 2018. New suspension-feeding radiodont suggests evolution of microplanktivory in Cambrian macronekton. Nature Communications, 9: 3774.
  • MAYERS, B., ARIA, C. and CARON, J.-B. 2018. Three new naraoiid species from the Burgess Shale, with a morphometric and phylogenetic reinvestigation of Naraoiidae. Palaeontology, 62: 1–32.
  • MOYSIUK, J. and CARON, J.-B. 2022. A three-eyed radiodont with fossilized neuroanatomy informs the origin of the arthropod head and segmentation. Current Biology, 32: 3302–3316.
  • PATES, S., WOLFE, J. M., LEROSEY-AUBRIL, R., DALEY, A. C. and ORTEGA-HERNÁNDEZ, J. 2021. New opabiniid diversifies the weirdest wonders of the euarthropod stem group. Proceedings of the Royal Society B, 289: 20212093.
  • SHEPPARD, K. A., RIVAL, D. E. and CARON, J. B. 2018. On the Hydrodynamics of Anomalocaris Tail Fins. Integrative and comparative biology,.
  • 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.
  • VANNIER, J., LIU, J., LEROSEY-AUBRIL, R., VINTHER, J. and DALEY, A. C. 2014. Sophisticated digestive systems in early arthropods. Nature Communications, 5: 3641.
  • WALCOTT, C. D. 1912. Middle Cambrian Branchiopoda, Malacostraca, Trilobita and Merostomata. Smithsonian Miscellaneous Collections, 57: 145–228.
  • WHITTINGTON, H. B. 1975. The enigmatic animal Opabinia regalis, middle Cambrian, Burgess Shale, British Columbia. Philosophical Transactions of the Royal Society B: Biological Sciences, 271: 1–43.
  • WHITTINGTON, H. B. and BRIGGS, D. E. G. 1985. The largest Cambrian animal, Anomalocaris, Burgess Shale, British Columbia. Philosophical Transactions of the Royal Society B: Biological Sciences, 309: 569–609.
  • ZENG, H., ZHAO, F., NIU, K., ZHU, M. and HUANG, D. 2020. An early Cambrian euarthropod with radiodont-like raptorial appendages. Nature, 588: 101–105.
  • ZHANG, X. and BRIGGS, D. E. G. 2007. The nature and significance of the appendages of Opabinia from the Middle Cambrian Burgess Shale. Lethaia, 40: 161–17.
Other Links:

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



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Odaraia alata

3D animation of Odaraia alata.

ANIMATION BY PHLESCH BUBBLE © ROYAL ONTARIO MUSEUM

Taxonomy:

Kingdom: Swimmers
Phylum: Swimmers
Higher Taxonomic assignment: Hymenocarines, Family Odaraiidae
Species name: Odaraia alata
Remarks:

Odaraia was originally considered a crustacean (Walcott 1912; Briggs 1981; Briggs and Fortey 1989; Hou and Bergstrom 1997; Wills et al. 1998), following previous interpretations on the affinities of other bivalved arthropods (hymenocarines), like Branchiocaris (Briggs 1976) or Canadaspis (Briggs 1978). In the early 2000s, the affinities of Odaraia were re-evaluated and placed in the stem lineage of arthropods (Budd 2002, 2008). Following the discovery of mandibles in several hymenocarines and the re-interpretation of this group as early mandibulate arthropods (which include myriapods, crustaceans and insects), Odaraia was moved to the stem of mandibulates (Aria and Caron 2017; Vannier et al. 2018), and was perhaps even more closely related to myriapods (Aria et al. 2021). Odaraia gives its name to the family Odaraiidae, a group of hymenocarines with highly multisegmented bodies, reduced or absent antennulae and highly multisegmented legs, which includes other Burgess Shale taxa such as Nereocaris or Fibulacaris.

Described by: Walcott
Description date: 1912
Etymology:

Odaraia – from Odaray Mountain (3,159 m) in Yoho Park, which was named by J. J. McArthur in 1887 from the Stoney First Nation Nakoda expression for “many waterfalls.”

alata – from the Latin ala, “wing,” referring to the wing-like fins of the tail.

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

Burgess Shale and vicinity: none.

Other deposits: none.

Age & Localities:

Age:
Cambrien moyen, étage Wuliuen, formation des schistes de Burgess (environ 505 millions d’années).
Principal localities:

The Walcott and Raymond Quarries on Fossil Ridge.

History of Research:

Brief history of research:

Odaraia was first described by Walcott (1912), and was re-examined briefly by Simonetta and Delle Cave (1975) A major restudy of Odaraia was published by Briggs (1981). New morphological features of the head were later incorporated, including a sclerite (Budd 2008) and nervous tissue (Ortega-Hernández 2015). A triad of organs or simple eyes at the front of the head have been associated with a sclerite known in other early arthropods (Ortega-Hernández 2015). The legs of Odaraia have been redescribed, highlighting a potential differentiation between the proximal and distal part (Aria and Caron 2017), a study which also illustrated the sternites (ventral segments) of the animal. Several closely related species to Odaraia, Jugatacaris agilis and different species of Pectocaris (Hou et al. 2004; Jin et al. 2021) have been discovered from the Lower Cambrian Chengjiang in China (Fu and Zhang 2011). The family Odaraidae was originally defined by Simonetta and Delle Cave, 1975. Since then, it has not been formally re-defined, but many other hymenocarines probably belong to this group.

Description:

Morphology:

Much of the body of Odaraia is contained within a prominent bivalved carapace in which the valves extend and meet on the ventral surface, similar to Nereocaris briggsi. The carapace forms a tube open at the front and back. The anteriormost, visible part of the head, protruding from the front of the carapace, consists of a rounded projection housing three organs or small eyes arranged triangularly, covered by a possible sclerite, and to which is attached pair of large, spherical eyes. Behind the head, the body consisted of approximately 47 narrow segments, each bearing a pair of appendages. Each limb is biramous, and has a segmented inner branch (endopod) and a paddle-like outer branch (exopod). The tail or telson has three blades or flukes, two of which extend laterally and the third of which extends vertically into a fin-like structure. The gut is typically straight with phosphatized paired midgut glands.

Abundance:

Odaraia typically makes up less than 0.5% of the community in Walcott Quarry, from which over 200 specimens have been collected (Caron and Jackson, 2008). About a dozen specimens are known from Raymond Quarry.

Maximum Size:
150 mm

Ecology:

Life habits: Swimmers
Feeding strategies: Swimmers
Ecological Interpretations:

The tubular carapace of Odaraia would have enclosed the ventral appendages, making it difficult for the animal to use its appendages for walking on the sea floor. It therefore seems to have swum through the water column by waving the outer branches of its biramous appendages, although this does not rule out interactions with other organisms on the sea floor. The large eyes and phosphatized gut glands (Butterfield 2002) suggest that Odaraia was a predator, seeking out floating or swimming organisms and sieving them out the water as the current passed through the tubular carapace. However, the lack of prehensile or sensory appendages also suggest Odaraia might have been a suspension feeder. To minimize the drag created by its dorsal hinge, it was proposed that Odaraia swam on its back, similar to horseshoe crabs, and the related hymenocarine Fibulacaris. The large telson would have been used to stabilize the animal while swimming to prevent it from rolling, and to help with steering and braking.

References:

  • 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. 1976. The arthropod Branchiocaris n. gen., middle Cambrian, Burgess Shale, British Columbia. Geological Survey of Canada, Energy, Mines and Resources Canada, 264: 1–29.
  • BRIGGS, D. E. G. 1978. The morphology, mode of life, and affinities of Canadaspis perfecta (Crustacea: Phyllocarida), middle Cambrian, Burgess Shale, British Columbia. Phylosophical Transactions of The Royal Society of London, 281: 439–487.
  • BRIGGS, D. E. G. 1981. The arthropod Odaraia alata Walcott, middle Cambrian, Burgess Shale, British Columbia. Philosophical Transactions of the Royal Society of London. B, Biological Sciences, 291: 541–582.
  • BRIGGS, D. E. G. and FORTEY, R. A. 1989. The early radiation and relationships of the major arthropod groups. Science, 246: 241–243.
  • BUDD, G. E. 2002. A palaeontological solution to the arthropod head problem. Nature, 417: 271–275.
  • BUDD, G. E. 2008. Head structure in upper stem-group euarthropods. Palaeontology, 51: 561–573.
  • BUTTERFIELD, N. J. 2002. Leanchoilia guts and the interpretation of three-dimensional structures in Burgess Shale-type fossils. Paleobiology, 28: 155–171.
  • FU, D. and ZHANG, X. 2011. A new arthropod Jugatacaris agilis n. gen. n. sp. from the early Cambrian Chengjiang Biota, South China. Journal of Paleontology, 85: 567–586.
  • HOU, X.-G. and BERGSTROM, J. 1997. Arthropods of the Lower Cambrian Chengjiang fauna, southwest China. Fossils and Strata No, 45: 1–116.
  • HOU, X.-G., BERGSTRÖM, J. and XU, G.-H. 2004. The Lower Cambrian Crustacean Pectocaris from the Chengjiang Biota , Yunnan , China. Journal of Paleontology, 78: 700–708.
  • JIN, C., MAI, H., CHEN, H., LIU, Y. U., HOU, X.-G., WEN, R. and ZHAI, D. 2021. A new species of the Cambrian bivalved euarthropod Pectocaris with axially differentiated enditic armatures. Papers in Palaeontology, 7: 1781–1792.
  • ORTEGA-HERNÁNDEZ, J. 2015. Homology of head sclerites in Burgess Shale euarthropods. Current Biology, 25: 1625–1631.
  • SIMONETTA, A. M. and DELLE CAVE, L. 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 (n.s. 3: 1–37.
  • 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:
  • WALCOTT, C. D. 1912. Cambrian geology and paleontology II: Middle Cambrian Branchiopoda, Malacostraca, Trilobita and Merostomata. Smithsonian Miscellaneous Collections, 57: 145–228.
  • WILLS, M. A., BRIGGS, D. E. G., FORTEY, R. A., WILKINSON, M. and SNEATH, P. H. A. 1998. An arthropod phylogeny based on fossil and recent taxa. In EDGECOMBE, G. D. (ed.) Arthropod Fossils and Phylogeny, Columbia University Press, New York, 33.105 pp.
Other Links:

None



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Marrella splendens

3D animation of Marrella splendens.

ANIMATION BY PHLESCH BUBBLE © ROYAL ONTARIO MUSEUM

Taxonomy:

Kingdom: Swimmers
Phylum: Swimmers
Higher Taxonomic assignment: Order Marrellida
Species name: Marrella splendens
Remarks:

Marrella has been grouped in the Order Marrellida with various Ordovician to Devonian taxa, which share two to three pairs of extremely elongate spines on the headshield, single-branched head limbs, and a body with greater than 25 ring-shaped body segments (Raymond 1920; Rak et al. 2013; Moysiuk et al. 2022). The broader placement of this group in arthropod evolution has been difficult to resolve. Marrella was historically thought to be allied with trilobites and their relatives (Raymond 1920; Whittington 1971), a result which was later supported by some phylogenetic analyses (Aria and Caron 2017). Other analyses have found affinities with the arthropod stem group (Briggs and Fortey 1989; Wills et al. 1998), or mandibulate arthropods (Legg et al. 2013; Legg 2015). The most recent studies support a placement within the broad grouping of “arachnomorph” arthropods (including trilobites and chelicerates), and possibly close to sea spiders (Vannier et al. 2018; Moysiuk et al. 2022) owing to shared loss of compound eyes and similarities in the head appendages.

Described by: Walcott
Description date: 1912
Etymology:

Genus – after Dr. John Marr, palaeontologist at Cambridge University and friend of Walcott.

species – from the Latin splendens, “beautiful, or brilliant.”

Type Specimens: Lectotype –USNM57674 in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
Other species:

Burgess Shale and vicinity: None

Other deposits: Marrella sp. from the Kaili and Balang Formations of south China (Zhao et al. 2006; Liu 2013).

Age & Localities:

Age:
Middle Cambrian, Wuliuan stage, Burgess Shale Formation (approximately 505 million years ago).
Principal localities:

The Walcott and Raymond Quarries on Fossil Ridge. Smaller collections from Mount Field, the Tulip Beds (S7) on Mount Stephen, Mount Odaray, and Mount Whymper/Tokumm Creek.

History of Research:

Brief history of research:

Marrella was one of the first fossils found by Walcott, and sketches appear in his notebook as early as August 31st, 1909. Walcott informally named them “lace crabs” at the time. The next summer, on August 9, 1910, Walcott and son Stuart found the “lace crab beds” in situ, marking the discovery of the fossil-bearing beds of the Walcott Quarry of the Burgess Shale. Walcott (1912) formally described the “lace crabs” as Marrella splendens, but a reconstruction was not attempted until Raymond (1920). Marrella was examined again by Simonetta (1962) and in a major study by Whittington (1971). New specimens collected by the Royal Ontario Museum allowed for the description of a specimen showing Marrella in the act of moulting (García-Bellido and Collins 2004), and another re-description of the taxon (García-Bellido and Collins 2006). The decay stains associated with Marrella specimens were found to contain the copper-rich mineral chalcopyrite, initially interpreted as remnants of the arthropod blood protein hemocyanin (Pushie et al. 2014), but more recent work demonstrates that this mineral in fact formed millions of years after fossilization, due to metamorphic alteration (Gaines et al. 2019).

Description:

Morphology:

Marrella is a small arthropod with a wedge-shaped head shield bearing two pairs of prominent spines that project from the sides and dorsal margin and extend back along most of the length of the body. There is also a pair of smaller posteroventral spines. The head bears a pair of long, thin antennae with as many as 30 segments, and a pair of paddle-like appendages with six segments and numerous bushy setae along the edges. Behind the head, the body consists of 26 segments that are small and subcircular, each bearing a pair of biramous appendages. The walking branch of this appendage has six segments, and the second branch is made of tapering gills with long, slim filaments that attach near the base of the legs. The last twelve appendages have conspicuous, blunt inner spines that form a net below the body. There is no developed tailpiece. The stomach is located in the head near the ventral mouth, and the intestine stretches most of the length of the body. Dark stains found around the body are suggested to be the gut contents that were squeezed out during preservation. García-Bellido and Collins (2006) also identified remains of the circulatory system, which, in light of more recent research (Aria and Caron 2015; Mayers et al. 2018), may correspond to hemocoelic cavities around the gut.

Abundance:

Marrella is one of the most common species in the Burgess Shale. Over 25,000 specimens have been collected (García-Bellido and Collins 2006), and it is the second most common arthropod species in Walcott Quarry, comprising 7.3% of the specimens counted (Caron and Jackson 2008). Marrella is commonly present in some other Burgess Shale localities, such as Marble Canyon (Nanglu et al. 2020), but conspicuously absent from others, like the Tulip Beds (O’Brien and Caron 2016). Marrella species have been reported from the Cambrian Kaili and Balang Formations in China (Zhao et al. 2006; Liu 2013), but the taxon is otherwise absent from major early Cambrian fossil assemblages of Burgess Shale type, such as the famous Chengjiang biota.

Maximum Size:
About 25 mm.

Ecology:

Life habits: Swimmers
Feeding strategies: Swimmers
Ecological Interpretations:

Marrella has been interpreted as an active swimmer that roamed above the sea floor while feeding on organic particles in the water or the sediment, and using its antennae as its main sensory apparatus. Swimming was achieved by undulating the second pair of paddle-like appendages on the head. The net of inner spines on the last twelve appendages could have been used to trap food particles located in water currents and to pass them along the underside of the animal. Food particles trapped in the net would be moved towards the mouth using the tips of the anterior limbs.

References:

  • ARIA, C. and 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. 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 FORTEY, R. A. 1989. The early radiation and relationships of the major arthropod groups. Science, 246: 241–243.
  • CARON, J.-B. and JACKSON, D. A. 2008. Paleoecology of the Greater Phyllopod Bed community, Burgess Shale. Palaeogeography, Palaeoclimatology, Palaeoecology, 258: 222–256.
  • GAINES, R. R., LOMBARDO, A. J., HOLZER, I. O. and CARON, J. B. 2019. The limits of Burgess Shale-type preservation: assessing the evidence for preservation of the blood protein hemocyanin in the Burgess Shale. PALAIOS, 34: 291–299.
  • GARCÍA-BELLIDO, D. C. and COLLINS, D. H. 2004. Moulting arthropod caught in the act. Nature, 429: 40.
  • GARCÍA-BELLIDO, D. C. and COLLINS, D. H. 2006. A new study of Marrella splendens (Arthropoda, Marrellomorpha) from the Middle Cambrian Burgess Shale, British Columbia, Canada. Canadian Journal of Earth Sciences, 43: 721–742.
  • LEGG, D. A. 2015. The morphology and affinities of Skania fragilis (Arthropoda) from the middle Cambrian Burgess Shale. Bulletin of Geosciences, 90: 509–518.
  • LEGG, D. A., SUTTON, M. D. and EDGECOMBE, G. D. 2013. Arthropod fossil data increase congruence of morphological and molecular phylogenies. Nature Communications, 4: 3485.
  • LIU, Q. 2013. The First Discovery of Marrella (Arthropoda, Marrellomorpha) from the Balang Formation (Cambrian Series 2) in Hunan, China. Journal of Paleontology, 87: 391–394.
  • MAYERS, B., ARIA, C. and CARON, J.-B. 2018. Three new naraoiid species from the Burgess Shale, with a morphometric and phylogenetic reinvestigation of Naraoiidae. Palaeontology, 62: 1–32.
  • MOYSIUK, J., IZQUIERDO-LÓPEZ, A., KAMPOURIS, G. E. and CARON, J.-B. 2022. A new marrellomorph arthropod from southern Ontario: a rare case of soft-tissue preservation on a Late Ordovician open marine shelf. Journal of Paleontology, 96: 859–874.
  • 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.
  • O’BRIEN, L. J. and CARON, J. B. 2016. Paleocommunity analysis of the Burgess Shale Tulip Beds, Mount Stephen, British Columbia: Comparison with the Walcott Quarry and implications for community variation in the Burgess Shale. Paleobiology, 42: 27–53.
  • PUSHIE, M. J., PRATT, B. R., MACDONALD, T. C., GEORGE, G. N. and PICKERING, I. J. 2014. Evidence for biogenic copper (hemocyanin) in the middle Cambrian arthropod Marrella from the Burgess Shale. PALAIOS, 29: 512–524.
  • RAK, Š., ORTEGA-HERNÁNDEZ, J. and LEGG, D. A. 2013. A revision of the late Ordovician marrellomorph arthropod Furca bohemica from Czech Republic. Acta Palaeontologica Polonica, 58: 615–628.
  • RAYMOND, P. E. 1920. The appendages, anatomy, and relationships of trilobites. Memoirs of the Connecticut Academy of Arts and Sciences, 7: 1–169.
  • SIMONETTA, A. M. 1962. Note sugli artropodi non trilobiti della Burgess Shale, Cambriano Medio della Columbia Britannica (Canada). 1. contributo: 2. genere Marrella Walcott, 1912. Monitore Zoologico Italiano, 69: 172–185.
  • 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.
  • WALCOTT, C. D. 1912. Middle Cambrian Branchiopoda, Malacostraca, Trilobita and Merostomata. Smithsonian Miscellaneous Collections, 57: 145–228.
  • WHITTINGTON, H. B. 1971. Redescription of Marrella splendens (Trilobitoidea) from the Burgess Shale, Middle Cambrian, British Columbia. Bulletin of Geological Survey of Canada, 209: 1–24.
  • WILLS, M. A., BRIGGS, D. E., FORTEY, R. A., WILKINSON, M., SNEATH, P. H. A. and EDGECOMBE, G. D. 1998. An arthropod phylogeny based on fossil and recent taxa. In EDGECOMBE, G. D. (ed.) Arthropod Fossils and Phylogeny, Columbia University Press, New York, 33–105 pp.
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Other Links:

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