Phylogeny and biogeography of Cambrian-early Ordovician brachiopods, especially relating to North Gondwanan terranes

Introduction

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Exposures with the Middle Cambrian and Lower Ordovician olistoliths in the area about 3-6km south-east of the Ulugtau Mountains. These olistoliths contain moderately diverse brachiopod fauna which is currently under study.

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These unusual brachiopods with a large shell perforation anterior to the ventral umbo belong to the Class Chileata, a short lived group of primitive brachiopods placed in the base of whale rhynchonelliformean stocks according to the recent phylogenetic models (Williams et al.1996). Genus Chile firstly discovered in the olistoliths of Lower Cambrian Limestone in southern Kyrgyzstan otherwise is known only from southern Israel.

This project concentrates on the diverse, but poorly known, Cambrian and early Ordovician brachiopod faunas from Central Asia and the Near and Middle East The results will potentially be of importance for understanding more fully the palaeogeographical positions of the early Palaeozoic terranes included in the Kazakhstan and Central Asia tectonic collage during the early Palaeozoic. At this time, these microcontinents and volcanic island arc systems were located on migration routes linking the benthic faunas of Gondwana, North and South China and Baltica, and represented a locus of origin and subsequent dispersion of some biogeographically important brachiopod groups, e.g. trimerellides, atrypidines, athyridides and pentameroideans.

An integral part of the project is to involve sharing the expertise of British palaeontologists who contributed to the revised brachiopod volumes of The Treatise on Invertebrate Paleontology with scientists from central Asian nations and Iran. This cooperation is important for the latter's scientific development, and will provide them with opportunities for ready access to the extensive scientific information, palaeontological collections, research facilities and libraries held in the British institutions.

A review of the Cambrian rhynchonelliformean brachiopod biogeography reveal a great importance of peri-Gondwanan sets for understanding of the early evolution of the advanced early Palaeozoic rhynchonelliformean orders e.g. protorthides, orthides and pentamerides. For instance, all known occurrences of the Cambrian protorthides are coonfined to mainland Gondwana (North Africa, Middle East, Avalonia and Australia), or some peri-Gondwanan island arcs (south Tien-Shan). Diversity of the Mid Cambrian rhynchonelliformean brachiopod assemblages of Gondwana is much higher than that ones of Laurentia, Siberia, whereas they are almost missing in Baltica. It is highly probable that new brachiopod faunas introduced at the beginning of the Ordovician in Baltica, Sibiria and Laurentia, as well as new benthic assemblages dominated by suspension feeders originally evolved in peri-Gondwana sets (Bassett et al.2002, Popov et al.2009). However, an extremely poor knowledge of the late Cambrian brachiopod faunas from the regions, which constitute early Palaeozoic Gondwana, makes difficult to trace Gondwanan connections of these newly appeared faunas. A study of the Cambrian to early Ordovician brachiopod faunas from the Middle East, which is now in a good progress, helps to fill this gap.

References

Bassett, M. G., Popov, L. E. and Holmer, L. E. 2002. Brachiopods: Cambrian – Tremadoc precursors to Ordovician radiation events, 13-23. In Crame, J. A. and Owen, A. W. (eds) Palaeobiogeography and biodiversity change: a comparison of the Ordovician and Mesozoic-Cenozoic radiations. Geological Society, London, Special Publications , 194, 206 pp.

Popov, L.E., Ghobadi Pour, M., Bassett, M.G. & Kebria-Ee, M. 2009. Billingsellide and orthide brachiopods: New insights into earliest Ordovician evolution and biogeography from northern Iran. Palaeontology, 52, 35-52.

Williams, A., Carlson, S. J., Brunton, C. H. C., Holmer, L. E., and Popov, L. E. 1996. A supra-ordinal classification of the Brachiopoda. Philosophical Transactions of the Royal Society: Biological Sciences . 35, 1171-1193.