Sarotrocercus oblita
Reconstruction of Sarotrocercus oblita.
© MARIANNE COLLINS
Taxonomy:
The phylogenetic affinity of Sarotrocercus is uncertain because its morphology is too poorly known to make a definitive designation. Fryer (1998) suggested it was the most primitive of all arthropods, and it was placed within the Arachnomorpha by Cotton and Braddy (2004). Sarotrocercus has also been aligned with Megacheiran taxa such as Yohoia (e.g. Briggs and Fortey, 1989) and Leanchoilia (e.g., Wills et al. 1995; 1998).
Sarotrocercus – from the Greek sarotes, “sweeper”, and kerkops, “a long tailed-monkey”, in reference to the feathery aspect of the tail.
oblita – from the Latin oblitus, “forgotten”, perhaps in reference to the fact that the few specimens of this species were described as part of another species.
Burgess Shale and vicinity: none.
Other deposits: none.
Age & Localities:
The Walcott Quarry on Fossil Ridge.
History of Research:
The genus Sarotrocercus was erected by Harry Whittington in 1981 based on seven specimens originally included within Molaria spinifera (Simonetta and Delle Cave, 1975). No further research has been performed on the fossil material since then, although Sarotrocercus has been included in many studies of arthropod relationships (e.g. Briggs and Fortey, 1989; Wills et al., 1995; Fryer, 1998).
Description:
Sarotrocercus has an oval body consisting of a head shield and nine overlapping trunk segments; a cylindrical posterior segment carries a relatively short, narrow spine ending in a fan-shape cluster of small spikes. The whole animal was about 1.5 cm long. Although the head shield was not very strongly developed, it did bear a pair of large, stalked eyes that poked out from beneath the margin, and a pair of jointed appendages. Each of the nine body segments bore a pair of lobate appendages, with comb-like fringes which might have functioned as gills.
S. oblita is rare in the Burgess Shale. It was originally described on the basis of 7 specimens (Whittington, 1981), and 28 further specimens have been recovered from the Walcott Quarry representing less than 0.1% of the community (Caron and Jackson, 2008).
Ecology:
The absence of walking limbs combined with an inferred flexibility of the body imply that the organism swam, probably in an inverted position, using its paddle-like appendages and long tail. Its rarity in the Burgess Shale suggests that it may have spent much time in the water column, thus avoiding submarine landslides that trapped animals living on the sea floor. The absence of sediment in its gut suggest that Sarotrocercus was a filter feeder (Briggs and Whittington, 1985; Whittington, 1981).
References:
BRIGGS, D. E. G. AND R. A. FORTEY, 1989. The Early radiation and relationships of the major arthropod groups. Science, 246: 241-243.
BRIGGS, D. E. G. AND H. B. WHITTINGTON, 1985. Modes of life of arthropods from the Burgess Shale, British Columbia. Transactions of the Royal Society of Edinburgh. Earth Sciences, 76(2-3): 149-160.
CARON, J.-B. AND D. A. JACKSON, 2008. Paleoecology of the Greater Phyllopod Bed community, Burgess Shale. Palaeogeography, Palaeoclimatology, Palaeoecology, 258: 222-256.
COTTON, T. J. AND S. J. BRADDY, 2004. The phylogeny of arachnomorph arthropods and the origin of the Chelicerata. Transactions of the Royal Society of Edinburgh, 94(03): 169-193.
FRYER, G. 1998. A defence of arthropod polyphyly, p. 23. In R. A. Fortey and R. H. Thomas (eds.), Arthropod relationships. Springer, London.
SIMONETTA, A. M. AND L. DELLE CAVE, 1975. The Cambrian non-trilobite arthropods from the Burgess shale of British Columbia: A study of their comparative morphology, taxonomy and evolutionary significance. Palaeontographia Italica, 69: 1-37.
WHITTINGTON, H. B. 1981. Rare arthropods from the Burgess Shale, Middle Cambrian, British Columbia. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences, 292(1060): 329-357.
WILLS, M. A., D. E. G. BRIGGS, R. A. FORTEY AND M. WILKINSON, 1995. The significance of fossils in understanding arthropod evolution. Verhandlungen den deutschen zoologischen Gesellschaft, 88: 203-216.
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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