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Monograptus spiralis and its phylogenetic relationship to early cyrtograptids

Published online by Cambridge University Press:  19 May 2016

A. C. Lenz  and
M. J. Melchin
A. C. Lenz
Affiliation:
Department of Geology, University of Western Ontario, London N6A 5B7, Canada
M. J. Melchin
Affiliation:
Department of Earth Sciences, University of Waterloo, Waterloo N2L 3GI, Canada
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Abstract

Isolated, uncompressed specimens of Monograptus spiralis show that the thecae become increasingly asymmetric and twisted distally and that the lateral margins of the apertures possess lobate veins and extend laterally as spatulate rostral processes. These too become increasingly asymmetric distally.

Three species of Cyrtograptus, obtained uncompressed from the same and overlying strata, are compared with M. spiralis. They show little similarity in the details of proximal or distal thecal form. Cyrtograptus sakmaricus possesses more stout, overlapping proximal thecae, while those of C. cf. C. laqueus are slender and elongate. In both species, the thecae are moderately asymmetrical, become simpler and less strongly hooked distally, and have simple lateral margins. The third species, Cyrtograptus sp., possesses proximal thecae very like those of C. sakmaricus, but its distal thecae, while strongly twisted, are very much simpler than the type found in M. spiralis.

Despite superficial rhabdosomal similarities in flattened material, the thecal details clearly indicate that M. spiralis is very unlikely to be ancestral to any known species of Cyrtograptus owing to its unique and highly specialized thecal form. Comparison among species of Cyrtograptus suggests, however, that this genus might be polyphyletic, with its ancestors being other members of the “Spirograptus” group.

Type
Research Article
Information
Journal of Paleontology , Volume 63 , Issue 3 , May 1989 , pp. 341 - 348
Copyright
Copyright © The Paleontological Society 

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References

Bjerreskov, M. 1975. Llandoverian and Wenlockian graptolites from Bornholm. Fossils and Strata, 8, 94 p.Google Scholar
Boucek, B. 1933. Monographic der obersilurischen Graptolitien aus der Familie Cyrtograptidae. Prace geologicko–paleontologického ustavu Karlovy university v Praze zar. 1933, c. 1, 84 p.Google Scholar
Geinitz, H. B. 1842. Über Graptolithen. Neues Jahrbuch für Mineralogie, Geografie, Geologie und Petrefak. -Kunde, Stuttgart, p. 697–701.Google Scholar
Jackson, D. E., and Etherington, J. E. 1969. New Silurian cyrtograptid graptolites from northwestern Canada and northern Greenland. Journal of Paleontology, 43:1114–1121.Google Scholar
Koren', T. N. 1968. Novye rannesiluriiskie graptolity yuzhnogo Urala. Paleontologicheskie Zhurnal, 4:101–103.Google Scholar
Lenz, A. C. 1974. A membrane-bearing Cyrtograptus, and an interpretation of the hydrodynamics of cyrtograptids, p. 205–214. In Rickards, R. B., Jackson, D. E. and Hughes, C. P. (eds.), Graptolite studies in honour of O. M. B. Bulman. Special Papers in Palaeontology No. 13.Google Scholar
Rickards, R. B., Jackson, D. E. and Hughes, C. P. (eds.), 1978. Llandoverian and Wenlockian Cyrtograptus, and some other Wenlockian graptolites from northern and arctic Canada. Geobios, 11:623–653.Google Scholar
Rickards, R. B., Jackson, D. E. and Hughes, C. P. (eds.), 1982. Llandoverian graptolites of the northern Canadian Cordillera: Petalograptus, Cephalograptus, Rhaphidograptus, Dimorphograptus, Retiolotidae, and Monograptidae. Life Sciences Contributions, Royal Ontario Museum, No. 130, 154 p.Google Scholar
Melchin, M. J. 1987. Late Ordovician and Early Silurian graptolites, Cape Phillips Formation, Canadian Arctic Archipelago. Unpubl. Ph.D. thesis, University of Western Ontario, London, 780 p.Google Scholar
Melchin, M. J., and Lenz, A. C. 1986. Uncompressed specimens of Monograptus turriculatus (Barrande, 1850) from Cornwallis Island, Arctic Canada. Canadian Journal of Earth Sciences, 23:579–582.Google Scholar
Pribyl, A. 1944. The Middle-European monograptids of the genus Spirograptus Gürich. Académie Tchèque de Science, Bulletin Internationale, 54:1–47.Google Scholar
Rickards, R. B., Hutt, J. E., and Berry, W. B. N. 1977. Evolution of Silurian and Devonian graptoloids. Bulletin of the British Museum (Natural History), Geology, 28, 120 p.Google Scholar
Sudbury, M. 1958. Triangulate monograptids from the Monograptus gregarius Zone (Lower Llandovery) of the Rheidol Gorge (Cardiganshire). Philosophical Transactions of the Royal Society of London (B), 241:485–549.Google Scholar
Thorsteinsson, R. 1955. The mode of cladial generation in Cyrtograptus. Geological Magazine, 92:37–49.CrossRefGoogle Scholar
Urbanek, A. 1966. On the morphology and evolution of the Cucullograptinae (Monograptidae, Graptolithina). Acta Palaeontologica Polonica, 11:291–544.Google Scholar