Chapter 17 Biogeographical distribution patterns in Early Palaeozoic Rostroconchia (Mollusca)

Abstract

The geographical distribution of rostroconch taxa of the orders Ribeirioida and Conocardiida, mostly across the equatorial continents and oceans, is compiled for six presumed diversity acmes in the early Early Ordovician (c.485 Ma), the late Early–early Middle Ordovician (c.475 Ma), the Late Ordovician (c.455 Ma), the Early Silurian (c.435 Ma), the late Early–early Late Silurian (c.425 Ma) and the early Early Devonian (c.415 Ma), based on our present, uneven knowledge. Rostroconchs show distribution patterns which enable a provisional separation of biogeographical provinces at least from the Silurian onward, comparable with Late Palaeozoic rostroconch distributional patterns. The distributions of tabulate corals, trilobites and bivalves appear roughly comparable, but not the nektic and planktic groups. A restriction to low latitudes (‘tropical’ realms) is clear for members ofRibeiriaandEopteriain the Early Ordovician, similar to proven patterns for hippocardiid rostroconchs from the Late Silurian onward until the Middle Permian. Preliminary rostroconch provinces or subprovinces, respectively, are currently discernable in the Silurian and Devonian for northwestern Laurentia, south-central Laurentia/Baltica and the north-central margin of Gondwana (i.e. Perunica, Bohemia). Rostroconch distributional data for SE Asia, China, Kazakhstan, Siberia and Australia are sparse and require further studies.

Late Ordovician rostroconchs (Mollusca) from fluvial erratics in northwestern Europe

“…The distribution of the ischyriniid ribeirioids Ischyrinia and Buekeria as well as the conocardiid Bitrigonocardia shows a much more consistent pattern and similar to that shown by Amler & Rogalla (2013). The major new addition is the clear dominance of the ischyriniid branch in Baltica during the Sandbian and Katian with Ischyrinia finding its way to Laurentia in the late Katian and Hirnantian (Tab.…”

“…The samples represent both ribeirioid and conocardiid rostroconchs of which most have a known previous evolutionary history. As pointed out by Amler & Rogalla (2013) the Tremadocian occurrences of Tolmachovia are restricted to low latitude areas of Australia and Argentina. They included here T. crassa Thoral, 1935 from France as a high latitude exception to this pattern.…”

“…Additionally, the provenance of the glacially derived material is more to the west, deriving from the Central Scandinavian Confacies Belt. Amler & Rogalla (2013) made an extensive review of the biogeographical distribution of Early Palaeozoic rostroconchs, and the material presented here adds some new information. The material described herein derives most likely from the North Estonia Confacies Belt, representing deposits in shallow water shelf areas in a low latitude position during the Sandbian and Katian.…”

“…2) as well as a number of other Ordovician species in open nomenclature, mainly from the Darriwilian of Iberia (Gutiérrez-Marco 1997, Sá 2008 but also from the Darriwilian of Argentina (Sánchez 1998). The oldest taxa are known from Australia, Argentina and France and show a general early distribution in low latitude areas and a subsequent spread into high latitude areas during the Lower Ordovician (Amler & Rogalla 2013). Australia belongs to the low latitude province and Argentina and France the high latitude province following Harper et al (2013).…”

“…The characteristic protruding posterior tube with a terminal opening is called the rostrum which in part gave the name to the group (Pojeta et al 1972). Currently three orders are recognized (but see Engeser & Riedel 1996), the Ribeirioida found through the early Cambrian to the early Silurian, the Conocardiida occurred from the Middle Ordovician to the late Permian and the Permian Anetshelloida (Pojeta & Runnegar 1976, Pojeta 1987, Hoare & Plas 2003, Mazaev 2012, Amler & Rogalla 2013). …”