Cambrian Hyolitha and problematica from West Laurentian North America: taxonomy and palaeobiogeography

Abstract

Fifteen species of hyoliths and problematic fossils from the present-day western margin of the Laurentian palaeocontinent (Cordilleran North America) are described and/or reassigned. Early Cambrian strata of this region are home to the orthothecid hyolith Guduguwan buelna (Lochman) and the hyolithids Nevadotheca whitei (Resser), Grantitheca? montis (Howell) and Hyolithes sp. B. Diversity of hyoliths increases in the middle Cambrian, featuring an un-named species of the orthothecid Decoritheca Sysoev, three un-named hyolithid species possibly representing Hyolithes Eichwald and one individual referred to as Hyolith sp. that bears resemblance to the Siberian Linevitus fossularis Val’kov. Haydenoconus prolixus (Resser) is documented from southeastern Idaho, and Doescherina clarki Malinky occurs in west-central Montana as pavements of conchs and opercula on bedding surfaces, with such large numbers of specimens affording an opportunity to further assess the range of morphologic variability within a single hyolith species. The upper Cambrian contains the hyolithids Haydenoconus gallatinesis (Resser), one un-named species each of Crestjahitus Sysoev and possibly Hyolithes Eichwald. An un-named species of the orthothecid Contitheca Sysoev occurs within this interval, as do the unusual problematic forms of uncertain affinity, Attenuella attenuata (Walcott 1890) and Kygmaeoceras corrugatus (Walcott 1890). The occurrence of Guduguwan recorded herein suggests a faunal connection between North America and Australia, and Contitheca, Decoritheca and the possible Hyolithes with Baltica and central Europe. Crestjahitus, Hyolith sp. and Kygmaeoceras demonstrate faunal affinity with Siberia. Whereas Doescherina and Grantitheca are endemic to North America, the families they represent also occur in Siberia. Attenuella is currently known from North America only at this time. The stratigraphic range of Contitheca is extended from middle to upper Cambrian; Crestjahitus from lower to upper Cambrian, and if the species of Hyolithes are authentic representatives of that genus, the range of the genus now definitively extends into the lower Cambrian.

本文描述了劳伦斯古陆（北美科迪勒拉）现今西缘的15个软舌螺种和有争议化石并进行了重新分类。这一地区的早寒武世地层富含直管螺类软舌螺Guduguwan buelna (Lochman) 和软舌螺类Nevadotheca whitei (Resser)、Grantitheca? montis (Howell) 及 Hyolithes sp. B. 。中寒武世期间，软舌螺的分异度增加，其特点是直管螺 Decoritheca Sysoev的一个未命名种、三个软舌螺类未命名种（可能代表Hyolithes Eichwald）和一个被称为Hyolith sp.的种（与西伯利亚Linevitus fossularis Val'kov 相似）。 在爱达荷州东南部记录有Haydenoconus prolixus （Resser）；Doescherina clarki Malinky 出现在Montana中西部，以铺满层面的海螺和鳃盖的形式出现。如此大量的标本为进一步评估单个软舌螺种内的形态变异范围提供了机会。上寒武统含有直管螺 Haydenoconus gallatinesis（Resser）以及Crestjahitus Sysoev 和Hyolithes Eichwald 各自的一个未命名种。直管螺类Contitheca Sysoev的一个未命名种出现于此时段内，亲缘关系不明的不寻常的有争议分子Attenuella attenuata（Walcott1890）和Kygmaeoceras corrugatus（Walcott1890）也是如此。 Guduguwan的出现表明北美和澳大利亚的动物群相关性； Contitheca、Decoritheca以及也许Hyolithes的出现表明波罗的海和中欧之间的动物群相关性。 Crestjahitus、Hyolith sp.和Kygmaeoceras展示与西伯利亚区系的动物群亲缘关系。虽然Doescherina和Grantitheca是北美地方性分子，他们所代表的科也出现于西伯利亚。 Attenuella目前只出现于北美。 Contitheca的地层范围从中寒武统扩大到上寒武统; Crestjahitus由下到上寒武统；如果Hyolithes的种真正代表了这个属，它的地层范围现在明确无误地延伸到下寒武统。

Key words:

• Cambrian
• Hyolitha
• palaeobiogeography
• Guduguwan
• Haydenoconus
• Attenuella
• Kygmaeoceras.

Acknowledgements

I thank the Smithsonian Institution for support of this project in the form of a Postdoctoral Fellowship. I am grateful to the late R.E. Grant, National Museum of Natural History, the late E.L. Yochelson, US Geological Survey, and the late C. Lochman-Balk, New Mexico Institute of Mining and Technology for consultations during the preparation of this manuscript. J. Peel, Department of Earth Sciences (Palaeobiology), Uppsala University, and O. Fatka, Institute of Geology and Palaeontology, Charles University, Prague, kindly provided many useful comments on this manuscript for the journal. J. Thompson, M. Florence, J. Wingerath, D. Levin and W. Brindle were most welcoming and helpful in many ways during my visits to the USNM to examine specimens. S. McLoughlin is greatly acknowledged for his efforts in making technical corrections to the manuscript. D. Peter kindly proof-read the manuscript and assisted with final preparation and submission.