Mackenzia costalis

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A Burgess Shale sea anemone-like animal

3D animation of Mackenzia costalis.

ANIMATION BY PHLESCH BUBBLE © ROYAL ONTARIO MUSEUM

Mackenzia costalis (ROM 56975) – Part and counterpart. Complete specimen attached to a brachiopod shell (probably Diraphora bellicostata), bottom of images. Specimen height = 133 mm. Specimen dry – polarized light (far left and far right), wet – direct light (middle left and middle right). Walcott Quarry.

Mackenzia costalis (ROM 61115). The largest specimen known. Note the base is attached to isolated shells of the hyolith Haplophrentis carinatus(close ups to the right). Specimen height = 200 mm. Specimen dry – direct light (far left), dry – polarized light (middle left), wet – polarized light (middle right, top right), wet – direct light (bottom right). Walcott Quarry.

Mackenzia costalis (USNM 57556) – Lectotype. Left, plate 13 of Walcott (1911), showing a retouched image of the original specimen described as a holothurian (figure 3 – figure 2 is another specimen). Right, images of the lectotype. Specimen height = 125 mm. Specimen dry – direct light (left), wet – polarized light (right). Walcott Quarry.

Taxonomy:

Kingdom: Animalia

Phylum: Cnidaria

Higher Taxonomic assignment: Anthozoa? (Order: Actiniaria(?), stem group cnidarians)

Species name: Mackenzia costalis

Remarks:

Mackenzia is thought to be a cnidarian (a group which includes modern coral and jellyfish) and appears most similar to modern sea anemones (Conway Morris, 1993).

Described by: Walcott

Description date: 1911

Etymology:

Mackenzia – from Mount Mackenzie (2,461 m) near Revelstoke, southwest of the Burgess Shale. Mount Mackenzie was named in honor of Alexander Mackenzie (1822-1892), Canada’s 2nd Prime Minister.

costalis – from the Latin costalis, “pertaining to ribs.” The name refers to the lineations along the length of the animal.

Type Specimens: Lectotype –USNM57556 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 and Raymond Quarries on Fossil Ridge. The Tulip Beds (S7) on Mount Stephen.

History of Research:

Brief history of research:

Mackenzia was first described as a holothurian, a group of echinoderms commonly known as the sea-cucumbers (Walcott, 1911). Additional fossils collected by the Geological Survey of Canada and restudy of Walcott’s collection led Conway Morris (1989, 1993) to reinterpret this animal as a cnidarian.

Description:

Morphology:

Mackenzia is a large saclike animal, up to 16 cm in height, which was anchored to hard substrates with a disc or holdfast via a short stalk; it probably stood upright. The surface of the body is folded longitudinally into 8-10 ridges. There is a large gut cavity and some evidence of internal partitioning, but little else is known of the anatomy. Tentacles are absent; the mouth was probably at the end opposite the stalk.

Abundance:

Mackenzia is very rare and represents only 0.03% of the Walcott Quarry community (Caron and Jackson, 2008).

Maximum Size:

200 mm

Ecology:

Life habits: Epibenthic, Sessile

Feeding strategies: Suspension feeder, Carnivorous

Ecological Interpretations:

Mackenzia probably lived on the seabed and may have attached to animal remains such as brachiopod shells for stability. Its mode of feeding is uncertain.

References:

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. 1989. Burgess Shale faunas and the Cambrian explosion. Science, 246: 339-346.

CONWAY MORRIS, S. 1993. Ediacaran-like fossils in Cambrian Burgess Shale-type faunas of North America. Palaeontology, 36(3): 593-635.

WALCOTT, C. D. 1911. Middle Cambrian holothurians and medusae. Cambrian Geology and Paleontology II. Smithsonian Miscellaneous Collections, 57(3): 41-68.