Ordovician graptolite evolutionary radiation: a review CHEN XU * , ZHANG YUAN-DONG and FAN JUN-XUAN State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, P.R. China Based on the global graptolite genera and higher rank taxa, we propose three radiation stages through the Ordovician. The isograptid type of development is present within anisograptids predominating in the Tremadocian. Thus, the evolutionary radiation of the Anisograptid fauna from Tremadocian is proposed as the beginning of the Ordovician graptolite radiation. The second graptolite radiation event is the radiation of the Dichograptid fauna, which began from the T. fruticosus Biozone. The third radiation event, the radiation of Diplograptid fauna began immediately after that of the dichograptids. This radiation includes the peak in total diversity of all the Ordovician graptoloids in the Nemagraptus gracilis Biozone. The radiation extended through the Sandbian and Katian and then was interrupted by a major extinction during the early Hirnantian. Thus, the Ordovician graptolite radiation events coincide with those of the three graptolite faunas proposed by Bulman. The distribution and expansion of the Ordovician graptolites in South China may exemplify the graptolite origination pattern, which begins from the slope belt and expanded into both the shelf and oceanic zones. Copyright # 2006 John Wiley & Sons, Ltd. Received 13 June 2005; revised version received 6 March 2006; accepted 24 March 2006 KEY WORDS graptolite evolutionary radiation; anisograptid fauna; dichograptid fauna; diplograptid fauna; Ordovician; South China 1. INTRODUCTION The Ordovician faunal radiation became an important research field for Ordovician workers since the three major faunas, the Cambrian, Palaeozoic and Modern faunas, were defined by Sepkoski (1981). It represents the replacement from the Cambrian fauna to the Palaeozoic fauna. Investigations into the Ordovician radiation began with the shelly faunas, in particular the Whiterockian shelly fauna (Hintze 1953; Cooper 1956). An abundant change in the Whiterockian fauna, with a rapid diversity increase leads to the conclusion that the Ordovician faunal radiation began during this time interval. This is in accord with a total diversity increase in many different fossil groups (Webby 2004). Thus, many authors believe that the Ordovician faunal radiation began during the Whiterockian. There is no agreement about the beginning of the Ordovician graptolite radiation. The Tremadocian graptolites are dominated by species of the Anisograptidae, which are recognized as taxa transitional between the dendroids and graptoloids but included in the Dendroidea (Bulman 1949). Mu (1974, 1987) termed them Graptodendroids. However, recent important contributions dealing with graptolite systematic palaeontology (Cooper and Fortey 1982; Fortey and Cooper 1986; Mitchell 1987) indicate the general acceptance of a modern palaeobiological GEOLOGICAL JOURNAL Geo. J. 41: 289–301 (2006) Published online 11 August 2006 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/gj.1051 *Correspondence to: Chen Xu, State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy, 39 East Beijing Road, Nanjing 210008, P.R. China. E-mail: xu1936@yahoo.com Contract/grant sponsor: Chinese Academy of Sciences; contract/grant number: KZCX3-SW-149. Contract/grant sponsor:Major Basic Research Project of the Ministry of Sciences and Technology, China; contract/grant number: G2000077700. Contract/grant sponsor: National Natural Science Foundation; contract/grant numbers: 40372007, 40402003. Copyright # 2006 John Wiley & Sons, Ltd.