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Aysheaia pedunculata

A very primitive arthropod-like animal with spiked legs

Reconstruction of Aysheaia pedunculata.

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Reconstruction of Aysheaia pedunculata.

© Marianne Collins

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Taxonomy

Kingdom:

Animalia

Phylum:

Onychophora (Lobopodia)

Class:

Xenusia (Order: Scleronychophora, stem group onychophorans)

Affinity:

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).

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Age

Period:

Middle Cambrian, Bathyuriscus-Elrathina Zone (approximately 505 million years ago).

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Localities

Principal localities:

The Walcott Quarry on Fossil Ridge.

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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).

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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

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Ecology

Life habits:

Epibenthic

Feeding strategies:

Carnivorous

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.

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References

Bibliography:

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.

Other links:

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

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