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Micromitra burgessensis

A brachiopod with long, slender spines extending from the shell margin

3D animation of brachiopods.

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3D animation of Micromitra burgessensis and other brachiopods (Acrothyra gregaria, Diraphora bellicostata, Nisusia burgessensis, and Paterina zenobia).

Animation by Phlesch Bubble © Royal Ontario Museum

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Taxonomy

Kingdom:

Animalia

Phylum:

Brachiopoda

Class:

Paterinata (Order: Paterinida)

Affinity:

Micromitra belongs within the Family Paterinidae.

Species name:

Micromitra burgessensis

Described by:

Walcott

Description date:

1908

Etymology:

Micromitra – from the Greek mikros, “small,” and mitra, “turban.”

burgessensis – 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 –USNM69646 in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.

Other species:

Burgess Shale and vicinity: none to date. The Burgess Shale brachiopods, in particular from the Trilobite Beds on Mount Stephen, need to be re-examined (see also Brief history of research).

Other deposits: Numerous species, all from the Cambrian, are known worldwide.

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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 and Raymond Quarries on Fossil Ridge. Additional localities are known on Mount Field, Mount Stephen, and near Stanley Glacier.

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History of Research

Brief history of research:

Originally identified as Micromitra (Iphidella) pannula by Walcott (1908) from the Trilobite Beds on Mount Stephen (see also Walcott, 1912), it was redescribed as a new species by Resser (1938). Resser's description fails to distinguish Micromitra burgessensis from any other species of the genus, it was based upon only a single valve, and it was not illustrated. The validity of this species is questionable and needs reassessment.

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Description

Morphology:

This species is the most ornamented of the Burgess Shale brachiopods. The shell was originally mineralized. It has pronounced growth lines and fine raised lines which cut obliquely across the shell. The intersection between the different lines creates small diamonds on the surface of the shell. The valves are subcircular with the hinge nearly straight. Perhaps the most striking of the preserved features of this animal are long and slender bristles (setae) which extend far beyond the margins of the shell. These would have been attached to the edge of the mantle along both the dorsal and ventral valves.

Abundance:

Micromitra burgessensis is relatively common in the Walcott Quarry but overall represents a small fraction of the fauna (<0.3%) (Caron and Jackson, 2008). This species is also present in the Raymond Quarry on Fossil Ridge.

Maximum size:

10 mm

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Ecology

Life habits:

Epibenthic, sessile

Feeding strategies:

Suspension feeder

Ecological Interpretations:

Many specimens of Micromitra burgessensis are preserved attached to spicules of the sponge Pirania, suggesting that this species was epibenthic, supported above the sediment-water interface. In this way the brachiopod would have been relatively protected from flocculent mud travelling along the sediment-water interface, which could have been detrimental to its filter-feeding apparatus (located between the shells) called a lophophore - The bristles might have also helped reduce mud particles.

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References

Bibliography:

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

RESSER, C. E. 1938. Fourth contribution to nomenclature of Cambrian Fossils. Smithsonian Miscellaneous Collections, 97: 1-43.

WALCOTT, C. 1908. Mount Stephen rocks and fossils. Canadian Alpine Journal, 1: 232-248.

WALCOTT, C. D. 1912. Cambrian Brachiopoda. United States Geological Survey, Monograph, 51: part I, 812 p; part II, 363 p.

Other links:

None

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