Cyrtograptus sakmaricus Koren' from Langao, Shaanxi Province, China

Abstract

Specimens of Cyrtograptus sakmaricus found in the Qiaoxi section, Langao County, Shaanxi Province, China, preserve different developmental stages of the species ranging from sicula through immature single whorl primary stipe to mature rhabdosomes with a number of cladia. Langao specimens of C. sakmaricus are characterized by having about two whorls before the origin of the first cladium and very small diameter of the first whorl. Cladia spaced at the rate of three, occasionally four, thecae; stipe width increasing rapidly from 0.5 mm to a maximum of 2 mm, exclusive of the, up to, 1 mm long apertural spines. Two thecae repeat distance stable 2 mm throughout the length of the primary stipe.

Keywords::

• Silurian
• Cyrtograptus sakmaricus
• ontogeny
• Telychian
• Langao

Acknowledgments

This paper is a contribution to the Science and Technology Department of Foreign Affairs, China Geological Survey Project 1212011120144 and 1212011120142 and the IGCP Project 591 – The Early to Middle Paleozoic Revolution.