Abstract

Specimens of Cardiograptus crawfordi Harris from the middle Table Head Formation on Port-au-Port Peninsula display a partially monopleural arrangement of the two thecal series. This feature and the rhabdosome size and shape make C. crawfordi so different from the genotype of Cardiograptus that it can no longer be retained in that genus. The Port-au-Port specimens are identical to isolated specimens from the middle Table Head Formation at Daniel's Harbour previously identified as Skiagraptus sp., especially with regard to the partially monopleural construction. However, Australian specimens of the genotype of Skiagraptus probably have a dipleural arrangement. Thus, the Newfoundland specimens cannot be assigned to that genus. The proximal-end development of C. crawfordi is very different from that of Apoglossograptus and Kalpinograptus, the other graptolites with partially monopleural arrangements. Therefore, a new genus, here named Bergstroemograptus, is defined for it. Bergstroemograptus represents an independent line of graptolite evolution in which a partially monopleural rhabdosome is attained.

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