Marrella
| Marrella Temporal range:
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|---|---|
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| Fossil Marrella | |
Scientific classification 
| |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | †Marrellomorpha |
| Order: | †Marrellida |
| Family: | †Marrellidae |
| Genus: | †Marrella Walcott, 1912 |
| Species: | †M. splendens
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| Binomial name | |
| †Marrella splendens Walcott, 1912
| |
Marrella is an extinct genus of marrellomorph arthropod known from the middle Cambrian Burgess Shale of British Columbia. It is the most common animal represented in the Burgess Shale, with tens of thousands of specimens collected. Much rarer remains are also known from deposits in China.
History[edit]
Marrella was the first fossil collected by Charles Doolittle Walcott from the Burgess Shale, in 1909.[1] Walcott described Marrella informally as a "lace crab" and described it more formally as an odd trilobite. It was later reassigned to the now defunct class Trilobitoidea in the Treatise on Invertebrate Paleontology. In 1971, Whittington undertook a thorough redescription of the animal and, on the basis of its legs, gills and head appendages, concluded that it was neither a trilobite, nor a chelicerate, nor a crustacean.[2]
Marrella is one of several unique arthropod-like organisms found in the Burgess Shale. Other examples are Opabinia and Yohoia. The unusual and varied characteristics of these creatures were startling at the time of discovery. The fossils, when described, helped to demonstrate that the soft-bodied Burgess fauna was more complex and diverse than had previously been anticipated.[3]
Morphology[edit]
Marrella itself is a small animal, ranging from 2.4 mm to 24.5 mm in length. The head shield has two pairs of long posteriorly directed spikes. On the underside of the head there is a pair of long and sweeping antennae, along with a pair of short and stout swimming appendages. Marrella has a body composed of 24–26 body segments (tagma), each with a pair of branched (biramous) appendages. The lower branch of each appendage is a leg for walking, while the upper branch is a long, feathery gill. There is a tiny, button-like telson at the end of the thorax.[4] The identification of a diffraction grating pattern on well-preserved Marrella specimens proves that it would have harboured an iridescent sheen—and thus would have appeared colourful.[5] Dark stains are often present at the posterior regions of specimens, probably representing extruded waste matter[6] or hemolymph.[7]
Ecology[edit]
A – dorsal view on a rendered 3D model, based on own observations B–E – micrographs under polarized light
B – well preserved specimen USNM 83486f with the exopods in a "rusty" preservation (cf. García−Bellido and Collins 2006)
C – stereo image of specimen USNM 139665. Exopods of preceding limbs are super−imposing each other, separated by a thin layer of sediment
D – detail of specimen ROM 56766A in "rusty" preservation. Here the spines on the lateral side of the exopod ringlets are well preserved
E – one of the smallest specimens of M. splendens USNM 219817e that possesses preserved appendage remains
Marrella is likely to have been an active swimmer with its swimming appendages used in a backstroke motion, with the large spines acting as stabilizers. Food particles were likely sifted out of the water column by the posterior appendages during swimming before being passed forward by the appendages towards the mouth.[4]
Taxonomy[edit]
Marrella is placed within the Marrilida clade of the Marrellomorpha, a group of arthropods with uncertain affinities known from the Cambrian to Devonian. Within the Marrelliida, is it placed as most basal known member of the group.[9]
Occurrence[edit]
Marrella is the most abundant genus in the Burgess Shale.[10] Most Marrella specimens herald from the 'Marrella bed', a thin horizon, but it is common in most other outcrops of the shale. Over 25,000 specimens have been collected;[11]5028 specimens of Marrella are known from the Greater Phyllopod bed, where they comprise 9.56% of the community.[12]
A few dozen specimens of an indeterminate species of Marrella have been reported from the Kaili Formation of Yunnan, China, dating to the Wuliuan stage of the Cambrian. A single fragmentary specimen of an indeterminate species is also known from the Balang Formation of Yunnan, China, dating to Cambrian Stage 4. Both deposits are earlier than the Burgess Shale.[13]
References[edit]
- ^ Gould, Stephen Jay (2000). Wonderful Life: Burgess Shale and the Nature of History. Vintage. p. 108. ISBN 978-0-09-927345-5. OCLC 45316756. Also OCLC 44058853.
- ^ Whittington, H. B. (1971). "Redescription of Marrella splendens (Trilobitoidea) from the Burgess Shale, Middle Cambrian, British Columbia". Bulletin – Geological Survey of Canada. Geological Survey of Canada. 209: 1–24.
- ^ Gould, Stephen Jay (2000). Wonderful Life: Burgess Shale and the Nature of History. Vintage. p. 173. ISBN 978-0-09-927345-5. OCLC 45316756. Also OCLC 44058853.
- ^ a b García-Bellido, Diego & Collins, Desmond. (2011). 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. 10.1139/e06-012.
- ^ Parker, A. R. (1998). "Colour in Burgess Shale animals and the effect of light on evolution in the Cambrian". Proceedings of the Royal Society B: Biological Sciences. 265 (1400): 967–972. doi:10.1098/rspb.1998.0385. PMC 1689164.
- ^ Whittington, H. B. (1978). "The Lobopod Animal Aysheaia pedunculata Walcott, Middle Cambrian, Burgess Shale, British Columbia". Phil. Trans. R. Soc. Lond. B. 284 (1000): 165–197. Bibcode:1978RSPTB.284..165W. doi:10.1098/rstb.1978.0061.
- ^ PRATT, Brian R.; PUSHIE, M. Jake; PICKERING, Ingird J.; GEORGE, Graham N. SYNCHROTRON IMAGING OF BURGESS SHALE FOSSILS: EVIDENCE FOR BIOCHEMICAL COPPER (HEMOCYANIN) IN THE MIDDLE CAMBRIAN ARTHROPOD MARRELLA SPLENDENS. Archived from the original on 2016-03-09.
- ^ Haug, J. T., Castellani, C., Haug, C., Waloszek, D., Maas, A. (2012). A Marrella−like arthropod from the Cambrian of Australia: a new link between "Orsten"−type and Burgess Shale assemblages. Acta Palaeontologica Polonica 58: 629–639. doi:10.4202/app.2011.0120
- ^ Moysiuk, Joseph; Izquierdo-López, Alejandro; Kampouris, George E.; Caron, Jean-Bernard (July 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 (4): 859–874. doi:10.1017/jpa.2022.11. ISSN 0022-3360.
- ^ Bottjer, David J.; Etter, Walter; Hagadorn, James W.; Tang, Carol M. (2002). Exceptional Fossil Preservation: A unique view on the evolution of marine life. Columbia University Press. p. 70. ISBN 978-0-231-10255-1. OCLC 47650949.
- ^ García-Bellido, D. C.; Collins, D. H. (2004). "Moulting arthropod caught in the act". Nature. 429 (6987): 40. Bibcode:2004Natur.429...40G. doi:10.1038/429040a. PMID 15129272. S2CID 40015864.
- ^ Caron, Jean-Bernard; Jackson, Donald A. (October 2006). "Taphonomy of the Greater Phyllopod Bed community, Burgess Shale". PALAIOS. 21 (5): 451–65. doi:10.2110/palo.2003.P05-070R. JSTOR 20173022.
- ^ Liu, Qing (May 2013). "The First Discovery of Marrella (Arthropoda, Marrellomorpha) from the Balang Formation (Cambrian Series 2) in Hunan, China". Journal of Paleontology. 87 (3): 391–394. doi:10.1666/12-118.1. ISSN 0022-3360.
External links[edit]
- "Marrella splendens". Burgess Shale Fossil Gallery. Virtual Museum of Canada. 2011.
- "Reconstruction of Marrella from the collections of Charles Doolittle Walcott". Historical Art Gallery. National Museum of Natural History.