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Graptolite Net | Graptolites and Graptoliters | Evolution of Graptolites | Rhabdopleuroidea | Cephalodiscoidea | Crustoidea |
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A new classification of ancorate diplograptids A. Kozlowska-Dawidziuk, A.C. Lenz & D.E.B. Bates Proceedings of the 7th International Graptolite Conference, Ed. by G.Ortega & G.F.Acenolaza 2003, 49-53 |
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Abstract of the paper: "The development mode and proximal structures are commonly accepted as the best for classification of higher taxa within Graptoloidea. The retiolitids and petalolithids are unique in possesing a virgellar ancora and /or distal ancora development. The ancora structures are considered homologous, and they are regarded as synapomorphic features on which the new superfamily Retiolitoidea has been founded. The ancora structures are considered homologous, and they are here regarded as synapomorphic features on which the new superfamily Retiolitoidea has been founded. The ancora is defined by Bulman (1970) as "anchor-shaped initial growth stage of retiolitids, apparently formed of virgella with two distal bifurcations" emphases are ours). Now we know that the true ancora is developed in diplograptid Pattern I forms (Melchin, 1998) and retiolitids Pattern R. The first true ancora, beginning with a bifurcation, was developed in petalolithids representing Pattern I forms. Some evolution of the ancorae from small and simple to more complex is observed, although there has been no detailed study of the petalolithid group focusing on the astogenetic and historic development of ancorae. In Petalolithus and Pseudorthograptus there is sometimes considerable distal growth beyond the ancora umbrella to the point of partial envelopment of the post-sicular region of the rhabdosome (e.g., Koren' and Rickards, 1996; see Figure 1 A, B). The most studied ancorate petalolithid Hercograptus Melchin, 1999 possesses an ancora umbrella connected to the thecae (Figure 1C). The next and the most advanced stage of the ancora development occurs in the Retiolitidae in the form of an ancora sleeve (Fig. 1 D, E). In this case the ancora sleeve is deeply integrated with thecal skeleton, which in addition, is built mostly by lists similar to those of the ancora. These two features: ancora sleeve and thecal wall and thecal framework are critical and unique for the retiolitids. The ancora sleeve may form walls, outside the thecal skeleton, making an additional internal environment. The retiolitid ancora sleeve wall may possess orifices and some additional structures as large stomas or long spines on the obverse and reverse sides of rhabdosomes (Bates and Kirk, 1997; Kozlowska-Dawidziuk, 2001; Lenz and Kozlowska-Dawidziuk, 2001)." |
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Order Graptoloidea Lapworth, 1875 Suborder Virgellina Fortey and Cooper, 1986 Superfamily Retiolitoidea Kozlowska, Lenz & Bates, 2003 Family Petalolithidae Bulman, 1955 Family Retiolitidae Lapworth, 1873 Subfamily Pseudoretiolitinae Kozlowska-Dawidziuk, Lenz & Bates, 2003 Subfamily Rotaretiolitinae Kozlowska-Dawidziuk, Lenz & Bates, 2003 Subfamily Retiolitinae Lapworth, 1973 Subfamily Paraplectograptinae Kozlowska-Dawidziuk, Lenz & Bates, 2003 Subfamily Sokolovograptinae Kozlowska-Dawidziuk, Lenz & Bates, 2003 Subfamily Gothograptinae Obut & Zaslavskaya, 1983 Subfamily Cometograptinae Kozlowska-Dawidziuk, Lenz & Bates, 2003 Subfamily Neogothograptinae Kozlowska-Dawidziuk, Lenz & Bates, 2003 Subfamily Spinograptinae Kozlowska-Dawidziuk, Lenz & Bates, 2003 Subfamily Plectograptinae Boucek & Munch, 1952 |
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________________________________________________________________________________ GRAPTOLITE NET edited by Piotr Mierzejewski, the Count of Calmont and Countess Maja Anna Korwin-Kossakowska Since 2002 |
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