Quantitative taxonomy and biostratigraphy of Middle Cambrian trilobites from Montana and Wyoming

Schwimmer, David R.

doi:10.1007/bf02080490

Cited by 17 publications

(11 citation statements)

References 12 publications

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“…Specimens of U . curio from the Gordon Shale (Schwimmer, 1973) agree well with the material from the Emigrant Formation. Additional specimens from the Spence Shale, Ute Limestone, illustrated by Campbell (1974), match well with the type material from the same member.…”

Section: Systematic Paleontologysupporting

confidence: 59%

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Trilobite biostratigraphy of the Cambrian 5 and Drumian stages, Series 3 (Laurentian Delamaran, Topazan, and Marjuman stages, Lincolnian Series) of the lower Emigrant Formation at Clayton Ridge, Esmeralda County, Nevada

Sundberg¹

2018

J. Paleontol.

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The Emigrant Formation at Clayton Ridge, Nevada, consists of 420 m of variably interbedded shale, siltstone, and limestone representing an outer shelf environment. It ranges in age from the youngest portion of the Dyeran Stage (Laurentian Waucoban Series; Cambrian Stage 4, Series 2) to Skullrockian Stage (Ibexian Series; Tremadocian Stage, Lower Ordovician). Consequently, it is condensed compared to other localities. For example, the age-equivalent succession in the House Range and the Wendover Range of Utah and Nevada, respectively, is seven times thicker.The 100 m thick lower limestone and siltstone member of the Emigrant Formation at Clayton Ridge ranges in age from the Bolbolenellus euryparia/Nephrolenellus multinodus Zone (Laurentian Dyeran Stage) to the Cedaria brevifrons Zone (Laurentian Marjuman Stage; Drumian Stage; this study). The 40 trilobites described herein from two closely spaced sections of the lower member belong to the Glossopleura walcotti/Ptychagnostus praecurrens Zone (Laurentian Delamaran Stage; Stage 5), Ehmaniella Zone (Laurentian Topazan Stage; Stage 5), and Cedaria selwyni to C. brevifrons zones (Laurentian Marjuman Stage; Drumian Stage) zones. The lower Emigrant Formation is <10% as thick as age-equivalent age strata elsewhere in Nevada, California, and Utah. This condensed nature of the lower Emigrant Formation began with the flooding event at the beginning of the Oryctocephalus indicus biochron and the subsequent build-ups of the thick carbonate platforms to the south and northeast.New species are Pagetia aspinosa, P. claytonensis, and Syspacephalus mccollumorum.

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Section: Systematic Paleontologysupporting

confidence: 59%

“…Lakeview Limestone ( Glossopleura Zone), Pend Oreille Lake, Idaho (Resser, 1938a). Gordon Shale ( Glossopleura Zone), Libby, Lincoln County, Montana (Schwimmer, 1973). Emigrant Formation ( Ehmaniella Zone), Split Mountain, Nevada.…”

Section: Systematic Paleontologymentioning

confidence: 99%

Trilobite biostratigraphy of the Cambrian 5 and Drumian stages, Series 3 (Laurentian Delamaran, Topazan, and Marjuman stages, Lincolnian Series) of the lower Emigrant Formation at Clayton Ridge, Esmeralda County, Nevada

Sundberg¹

2018

J. Paleontol.

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“…Compaction distorts shape and increases shape variation (Webster and Hughes, 1999) and fractures can sometimes be misinterpreted as biological structures (see discussion in Bright, 1959, p. 85). Features of potential phylogenetic significance such as furrow depth, relief of ocular ridges, and ornament can differ between internal and external surfaces of sclerites (Lochman, 1947;Rasetti, 1955;Palmer, 1958;Schwimmer, 1975;Blaker and Peel, 1997). The extent to which a sample is time-averaged can also affect variation within that sample (Hunt, 2004a, b).…”

Section: Previous Workmentioning

confidence: 99%

The structure of cranidial shape variation in three early ptychoparioid trilobite species from the Dyeran-Delamaran (traditional “Lower-Middle” Cambrian) boundary interval of Nevada, U.S.A.

Webster

2011

J. Paleontol.

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The structure of cranidial shape variation in the early ptychoparioid trilobites Crassifimbra walcotti, Crassifimbra? metalaspis (new combination), and Eokochaspis nodosa is explored using landmark-based geometric morphometric techniques, and is found to be generally similar among the species. Allometry is the strongest single source of cranidial shape variation within each species. The species share several trends in their respective patterns of ontogenetic shape change, but differ in the relative magnitude of these shared trends. Species-specific trends are also present. Each species follows a unique trajectory of ontogenetic shape change. The species exhibit subtle but significant differences in mean cranidial shape even at small size (sagittal length 1.75 mm); the magnitude of interspecific differences becomes larger at larger size (sagittal length 4.2 mm).For conspecific cranidia of a given size, the major pattern of covariance among anatomical parts is essentially identical to the pattern of covariance among those parts during ontogeny. Developmentally determined covariance patterns among cranidial regions might be responsible for ontogenetic shape change and a portion of non-allometric shape intraspecific variation. Interspecific differences in cranidial shape resulted from complex local modifications to growth pattern and cannot be attributed to simple ontogenetic scaling.The new collections permit the first description of non-cranidial sclerites of C. walcotti. A cephalic median organ is documented on C. walcotti, representing the oldest known occurrence of this structure in trilobites.

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“…Ordovician taxa occupy morphospace more discontinuously than Cambrian taxa, resulting in discrete Ordovician higher taxa characterized by stable synapomorphies, which have long been been recognized by trilobite systematists. Cambrian taxa occupy morphospace in a more continuous fashion which explains the difficulty of imposing trilobite higher level systematics on Cambrian trilobites, which has been called the ptychoparioid problem (Lochman, 1947;Rasetti, 1955;Schwimmer, 1975;Blaker, 1986;Fortey, 1990;Babcock, in press). It has recently been recognized that the Order Ptychoparida is based on symple-siomorphies and hence is an artificial group (Fortey and Chatterton, 1988;Fortey, 1990).…”

Section: Variation Controlsmentioning

confidence: 99%

Ontogeny, Intraspecific Variation, and Systematics of the Late Cambrian Trilobite Dikelocephalus

Hughes¹

1994

Smithsonian Contributions to Paleobiology

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Quantitative taxonomy and biostratigraphy of Middle Cambrian trilobites from Montana and Wyoming

Cited by 17 publications

References 12 publications

Trilobite biostratigraphy of the Cambrian 5 and Drumian stages, Series 3 (Laurentian Delamaran, Topazan, and Marjuman stages, Lincolnian Series) of the lower Emigrant Formation at Clayton Ridge, Esmeralda County, Nevada

Trilobite biostratigraphy of the Cambrian 5 and Drumian stages, Series 3 (Laurentian Delamaran, Topazan, and Marjuman stages, Lincolnian Series) of the lower Emigrant Formation at Clayton Ridge, Esmeralda County, Nevada

The structure of cranidial shape variation in three early ptychoparioid trilobite species from the Dyeran-Delamaran (traditional “Lower-Middle” Cambrian) boundary interval of Nevada, U.S.A.

Ontogeny, Intraspecific Variation, and Systematics of the Late Cambrian Trilobite Dikelocephalus

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