Ordovician graptolite evolutionary radiation: a review

• Published in: Geological journal (Chichester, England) Vol. 41; no. 3-4; pp. 289 - 301
• Main Authors: Xu, Chen, Yuan-Dong, Zhang, Jun-Xuan, Fan
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.09.2006
• Subjects: anisograptid fauna; dichograptid fauna; diplograptid fauna; graptolite evolutionary radiation; Ordovician; South China
• ISSN: 0072-1050; 1099-1034
• DOI: 10.1002/gj.1051

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.