Uncompressed specimens of Monograptus turriculatus (Barrande, 1850) from Cornwallis Island, Arctic Canada

• Published in: Canadian Journal of Earth Sciences
• Main Authors: Melchin, M. J., Lenz, A. C.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1986
• Subjects: General Earth and Planetary Sciences; Arctic; Canada; Cornwallis; Cape Phillips; Cornwallis Island
• Online Access: http://dx.doi.org/10.1139/e86-057; http://www.nrcresearchpress.com/doi/pdf/10.1139/e86-057

Isolated specimens of Monograptus turriculatus (Barrande, 1850) have been recovered from calcite concretions of the turriculatus Zone (late Llandovery) from the Cape Phillips Formation, Canadian Arctic Islands. The sicula shows ventral as well as dextral lateral curvature, and the thecae show a pronounced lateral asymmetry. This asymmetry is manifest as a tear-shaped aperture, a long, laterally directed spine on the outer apertural margin, and a shorter, ventrally directed spine on the inner apertural margin. The latter spine is totally absent on the proximal thecae.Monograptus sedgwickii (Portlock, 1853) is suggested as a possible ancestor to M. turriculatus.