The Burgess Shale

Hallucigenia sparsa

3D animation of Hallucigenia sparsa.

Animation by Phlesch Bubble © Royal Ontario Museum

Taxonomy:

Class: Xenusia (Order: Scleronychophora, stem group onychophorans)
Remarks:

Hallucigenia is regarded as a member of the “lobopodans,” a group of vermiform Cambrian organisms possessing pairs of leg-like extensions of the body. The affinities of these animals are controversial; they have been placed at the base of a clade comprised of anomalocaridids and arthropods (Budd, 1996), or in a stem-group to modern onychophorans (Ramsköld and Chen, 1998).

Species name: Hallucigenia sparsa
Described by: Walcott
Description date: 1911
Etymology:

Hallucigenia – from the Latin hallucinatio, “wandering of the mind,” after the bizarreness of the animal.

sparsa – from the Latin sparsus, “rare, or scattered,” reflecting the rarity of the specimens available in the original study.

Type Specimens: Holotype –USNM83935 in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
Other species:

Burgess Shale and vicinity: none.

Other deposits: H. fortis from the Middle Cambrian Chengjiang biota (Hou and Bergström 1995).

Age & Localities:

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

The Walcott and Raymond Quarries on Fossil Ridge. The Tulip Beds (S7) on Mount Stephen.

History of Research:

Brief history of research:

Hallucigenia was originally described as “Canadia sparsa” by Walcott (1911) in a review of various Burgess Shale “annelids.” One specimen was illustrated twenty years later (Walcott, 1931), but the first thorough study of this animal wasn’t published until Conway Morris (1977) demonstrated that it did not belong to the genus Canadia or to the annelids at all. His reconstruction showed a bizarre animal walking on spines, with dorsal tentacles interpreted as a feeding apparatus (Conway Morris, 1977). The new genus name Hallucigenia was coined in reference to this “dreamlike” appearance and also reflected the organism’s uncertain affinities. It was later shown that the supposed tentacles represented just one row of paired “legs” – the others were buried under a layer of rock and the paired spines were on the dorsal surface (Ramsköld and Hou, 1991, Ramsköld, 1992). The anteroposterior orientation was also reversed, with the former head interpreted as possible decay fluids seeping from the body (Ramsköld, 1992).

Description:

Morphology:

Hallucigenia has a worm-like body with a small head at the end of a long neck; the trunk bears seven pairs of long dorsal spines and seven pairs of slender leg-like lobes. The spacing between lobes and spines is relatively constant. The spine pairs are shifted forward so that the posterior pair of legs does not have a corresponding pair of spines above. Each leg terminates in a pair of claws and the rigid spines have inflexible basal plates. The neck area bears two or three pairs of very fine anterior “appendages” lacking terminal claws. The head is indistinct but the mouth is anterior; a straight gut ends in a posterior anus. It is possible the posterior end is in fact more bulbous than previously thought.

Abundance:

About thirty specimens were studied by Conway Morris (1977). Overall, Hallucigenia is rare, and in the Walcott Quarry it represents 0.19% of the specimens counted in the community (Caron and Jackson, 2008).

Maximum Size:
30 mm

Ecology:

Ecological Interpretations:

Hallucigenia is often found in association with the sponge Vauxia and other organic debris. This co-occurrence has led to suggestions that Hallucigenia fed on sponges, using its clawed legs to hang on, with its spines protecting it from predation. It is also possible that Hallucigenia scavenged on decaying animal remains.

References:

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

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

CONWAY MORRIS, S. 1977. A new metazoan from the Burgess Shale of British Columbia. Palaeontology, 20: 623-640.

CONWAY MORRIS, S. 1999. The crucible of creation: the Burgess Shale and the rise of animals. Oxford University Press, USA.

HOU, X. AND J. A. N. BERGTRÖM. 1995. Cambrian lobopodians – ancestors of extant onychophorans? Biological Journal of the Linnean Society, 114(1): 3-19.

RAMSKÖLD, L. 1992. The second leg row of Hallucigenia discovered. Lethaia, 25(2): 221–224.

RAMSKÖLD, L. AND X. HOU. 1991. New early Cambrian animal and onychophoran affinities of enigmatic metazoans. Nature, 351: 225-228.

RAMSKÖLD, L. AND J. Y. CHEN. 1998. Cambrian lobopodians: morphology and phylogeny, p. 107-150. In G. D. Edgecombe (ed.), Arthropod fossils and phylogeny. Volume 29. Columbia University Press, New York.

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.

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Aysheaia pedunculata

Reconstruction of Aysheaia pedunculata.

© Marianne Collins

Taxonomy:

Class: Xenusia (Order: Scleronychophora, stem group onychophorans)
Remarks:

Aysheaia is regarded as a member of the “lobopodans,” a group of vermiform Cambrian organisms possessing pairs of leg-like extensions of the body. The affinities of these animals are controversial; they have been placed at the base of a clade comprised of anomalocaridids and arthropods (Budd, 1996), or in a stem-group to modern onychophorans (Ramsköld and Chen, 1998).

Species name: Aysheaia pedunculata
Described by: Walcott
Description date: 1911
Etymology:

Aysheaia – after the nearby Aysha peak (since renamed Ayesha peak) in the Wapta icefield (3,065 m); original meaning unknown.

pedunculata – from the Latin pedunculus, “foot.”

Type Specimens: Holotype –USNM57655 in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
Other species:

Burgess Shale and vicinity: none

Other deposits: A.? prolata from the Middle Cambrian of Utah (Robison, 1985).

Age & Localities:

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

The Walcott Quarry on Fossil Ridge.

History of Research:

Brief history of research:

Walcott originally described Aysheaia as an annelid worm (Walcott, 1911). It was later re-described as a velvet worm (or a close relative) (Brues, 1923; Hutchinson, 1930; Walcott, 1931; Walton, 1927), although it lacked features such as jaws and slime glands. Its position remains a subject of debate, with a position in a new phylum being mooted (Tiegs and Manton, 1958). A morphological reinterpretation based on photographs (Delle Cave and Simonetta, 1975) prompted a detailed re-study of the fossil specimens (Whittington, 1978), and relationships were suggested with the water bears (tardigrades) (Bergström, 1978). Aysheaia is now grouped with close relatives in the class Xenusia (Liu et al., 2008), lobopods that fall on the arthropod stem lineage (Budd, 1996, 1998; Whittington, 1978).

Description:

Morphology:

Aysheaia is a worm-like animal, 1 to 6 cm in length and about 5 mm broad, bearing ten pairs of clawed, spiny limbs on the lower part of its body. It did not have a separate head, but a mouth occupied the very front of the body, accompanied by a pair of appendages and a circlet of bumps (papillae). The animal had a soft, flexible, non-mineralized cuticle, which had a corrugated, accordion-like form. Each stubby limb had ten corrugations, some of which bore a spiny projection. A suite of claws also adorned the end of each stub-foot. A faint line running down the axis of the organism is interpreted as its gut.

Abundance:

Aysheaia is rare in the Walcott Quarry representing less than 0.04% of the specimens counted in the community (Caron and Jackson, 2008).

Maximum Size:
60 mm

Ecology:

Ecological Interpretations:

Aysheaia is frequently associated with the remains of sponges, and an ecological association has been posited. Whether Aysheaia used its spines to adhere to sponges while feeding on them, or whether it simply hid among sponges for protection from predators, is unclear.

References:

BERGSTRÖM, J. 1978. Morphology of fossil arthropods as a guide to phylogenetic relationships, p. 1-56 In A. P. Gupta (ed.), Arthropod Phylogeny. Van Nostrand Reinhold Co. New York.

BRUES, C. T. 1923. The geographical distribution of the Onychophora. American Naturalist, 57: 210-217.

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

BUDD, G. E. 1998. Stem group arthropods from the Lower Cambrian Sirius Passet fauna of North Greenland, p. 125-138. In R. A. Fortey and R. H. Thomas (eds.), Arthropod relationships. Volume 55. Chapman & Hall, London.

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

DELLE CAVE, L. AND A. M. SIMONETTA. 1975. Notes on the morphology and taxonomic position of Aysheaia (Onycophora?) and of Skania (undetermined phylum). Monitore Zoologico Italiano, 9: 67-81.

HUTCHINSON, G. E. 1930. Restudy of some Burgess Shale fossils. Proceedings of the United States National Museum, 78(11): 59.

LIU, J., D. SHU, J. HAN, Z. ZHANG, AND X. ZHANG. 2008. Origin, diversification, and relationships of Cambrian lobopods. Gondwana Research, 14(1-2): 277-283.

ROBISON, R. A. 1985. Affinities of Aysheaia (Onychophora), with description of a new Cambrian species. Journal of Paleontology, 59(1): 226-235.

TIEGS, O. W. AND S. M. MANTON. 1958. The evolution of the Arthropoda. Biological Reviews, 33(3): 255-333.

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

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

WALTON, L. B. 1927. The polychaete ancestry of the insects. American Naturalist, 61: 226-250.

WHITTINGTON, H. B. 1978. The lobopod animal Aysheaia pedunculata Walcott, Middle Cambrian, Burgess Shale, British Columbia. Philosophical Transactions of the Royal Society of London. B, Biological Sciences, 284(1000): 165-197.

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

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