| Cambrian | ||
| Paleozoic Era | Sirius Passet Lagerstätte |
| Timescale |
The Sirius Passet fauna (named after the Sirius sledge patrol that operates in North Greenland) derives from the Buen Formation, exposed on the eastern shore of J.P. Koch Fjord in the far north of Greenland (fig. 1).
It was discovered in 1984 by A. Higgins of the Geological Survey of Greenland. A preliminary account was published by Conway Morris et al. (1987), but since then, three expeditions led by J. S. Peel and Simon Conway Morris have returned to the site, in 1989, 1991 and 1994, and a field collection of perhaps 10,000 fossil specimens has been amassed.
The fauna is inevitably compared to that of the Burgess Shale, although it is probably ten to fifteen million years older – 518 vs. 505 Ma (Martin et. al. 2000) – and more closely contemporaneous with that from Chengjiang.
The Sirius Passet soft-body fossils are found in rocks of the Lower Cambrian Buen Formation, in mud shales, representing a rather deeper water facies than the Burgess Shale, formed on the outer continental shelf, off-shore from a carbonate escarpment. "Large chunks from the edge of the carbonate platform occasionally fell or slid into the adjacent basin, where the Sirius Passet fauna lived" (Conway Morris 1998, p. 117).
 Fig. 1: Locality map showing approximate location of the Sirius Passet location on the eastern side of J.P. Koch Fjord. |
Discussion of early metazoan evolution has for many years been dominated by fossil evidence from the Middle Cambrian Burgess Shale and, in particular, by its famous problematic arthropods – Anomalocaris, Leancoila, Opabinia, and so on." (Budd 1997, p.125). The Sirius Passet fossils are approximately ten to fifteen Ma older than those of the Burgess Shale, presenting us with an even earlier window upon metazoan evolution; a glimpse of forms which, if anything, are even more challenging to interpret.
As in the Burgess Shale and Chengjiang assemblages, arthropods are the most abundant component of the Sirius Passet fauna although there is only one or two species of trilobite whereas there are more at Chengjiang and twelve or so in the Burgess Shale. In fact there are generally few taxa having shelly skeletons; the trilobites, "rare hyoliths, a number of sponges with prominent spicules, a few small brachiopods, and no echinoderms or molluscs" (Conway Morris 1998, pp. 120-121). Of the arthropods lacking calcified exoskeletons, some are somewhat – but not markedly – similar to Burgess Shale species. Many are large, reaching 50 cm or more in length. In addition there are a number of polychaete annelids and large priapulids (ibid.)
In general, preservation of the Sirius Passet fossils is not spectacular.
A few of the Sirius Passet taxa are described below.
Family Halkieriidae
Halkieria evangelista
Family Unspecified
Kerygmachela kierkegaardi Budd 1998
Family Unspecified
Pambdelurion whittingtoni Budd 1997
Another Anomalocaridid-like taxon, but with annulated and flexible spinose frontal appendages. No eyes are known. The 'Peytoia' mouthpart is poorly sclerotised. The trunk bears lobopodous paired limbs, probably unconnected to the lateral flaps. The tail is poorly known but apparently consisting of a sub-circular flap.
Genus Buenellus Blaker 1988
Glabella slightly tapered forward; ocular lobe small, posterior tip about opposite S1 or anterior part of L1; width (tr.) of interocular area equal to or greater than that of extraocular area. Thorax with 17 or 18 segments, maintaining width or widening slightly backward to 8th segment, then tapering posteriorly; posterior segment may be fused with anterior part of simple pygidium; pleural spines short (exsag.); inner pleural regions only slightly wider (tr.) than axis.
The species found in the Sirius Passet assemblage is Buenellus higginsi Blaker 1988.
Kleptothule rasmusseni Budd 1995
Author(s): Budd, G. E.
Year: 1995
Title: Kleptothule rasmusseni gen. et sp. nov.: an ?olenellid-like trilobite from the Sirius Passet fauna (Buen Formation, Lower Cambrian, North
Greenland)
Pauloterminus spinodorsalis (nomen nudum)
"In 1912, Charles D. Walcott erected the Family Waptiidae to accommodate Waptia fieldensis, a still poorly understood bivalved arthropod from the Middle Cambrian Burgess Shale of British Columbia, Canada. Several other bivalved arthropods seemingly similar to Waptia have since been discovered, such as the Lower Cambrian taxa Pauloterminus spinodorsalis (nomen nudum) from the Sirius Passet fauna of North Greenland and Chuandianella ovata from the Chengjiang fauna of southwest China.
"Despite their overall waptiid-like appearance, however, each of these animals possesses features which suggest their apparent similarity to Waptia fieldensis may be superficial. Variability in segment number, limb number and limb type between these taxa, for example, suggests these animals may not in fact be closely related.
"Other non-waptiid Cambrian arthropods also possess bivalved carapaces, including the Burgess Shale taxa Canadaspis perfecta and Plenocaris plena. This indicates two alternative evolutionary scenarios. First, the relatively common occurrence of bivalved carapaces may indicate a stem-group clade of bivalved arthropods in the Cambrian, united (at least) by their possession of this specialized carapace. A second, perhaps more likely, possibility is the occurrence of evolutionary convergence, resulting in the presence of a bivalved carapace in multiple unrelated Cambrian arthropod taxa." (Taylor 1999)
Budd, G.E. (1997): Stem Group Arthropods from the Lower Cambrian Sirius Passet Fauna of North Greenland. In Fortey, R.A.; Thomas R.H. (eds.): Arthropod Relationships. Systematics Association Special Volume Series 55.
Budd, Graham E. (1999): The morphology and phylogenetic significance of Kerygmachela kierkegaardi Budd (Buen Formation, Lower Cambrian, N Greenland). Transactions of the Royal Society of Edinburgh: Earth Sciences, 89, 249-290.
Butterfield, N.J. (1999): Interpreting Axial Structures in Burgess Shale-Type Fossils. Palaeontological Association 44th Annual Meeting, University of Edinburgh, 17-20 December 1999 (Oral Presentation)
Conway Morris, Simon (1998): The Crucible of Creation. Oxford.
Conway Morris, Simon; Peel, J.S.; Higgins, A.K.; Soper, N.J.; Davis, N.C. (1987): A Burgess Shale-Like Fauna From the Lower Cambrian of North Greenland. Nature, 345: 802-805.
Martin, M.W.; Grazhdankin, D.V.; Bowring, S.A.; Evans, D.A.D.; Fedonkin, M.A.; Kirschvink, J.L. (2000): Age of Neoproterozoic Bilaterian Body and Trace Fossils, White Sea, Russia: Implications for Metazoan Evolution. Science v.288: 841-845.
Taylor, Rod S. (1999): 'Waptiid' Arthropods and the Significance of Bivalved Carapaces in the Lower Cambrian. Palaeontological Association 44th Annual Meeting, University of Edinburgh, 17-20 December 1999 (Oral Presentation)
