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

摘要

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.