Trilobites of the Wheeler Shale,
Utah
Locality: House Range & Drum
Mountains, Western Utah, USA
Stratigraphy: Wheeler Shale Formation
Age: Cambrian - ca 505 mya
The U-Dig
Quarry, west of Delta, Utah.
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Location of Utah today
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Locality of Utah during the Early Cambrian
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Western Utah is one of the best-known Cambrian
fossil localities in the world. The Wheeler Shale and Marjum Formation, strata
of Middle Cambrian age, exhibit various exposures throughout the House Range
and nearby mountain ranges west of the town of Delta, Utah. The Wheeler
Shale is named for a major feature in the House Range, the Wheeler Amphitheater.
The Wheeler Shale contains interbeds of shaley limestone, mudstone, and
thin platy limestone. Much of the Wheeler Shale is not particularly fossiliferous,
but certain layers contain abundant trilobites and other shelly fossils.
The Wheeler Shale also is known for a diverse biota of soft-bodied fossils,
including many of the same taxa found in the Burgess Shale.
In the Cambrian, the continent of Laurentia (now the majority of North
America), was equatorial, and oriented about ninety degrees from its current
position. Close to the shorelines of Laurentia, limestone was deposited
as shallow-ater reefs. Beyond the limestone belt, fine sediments built in
deeper offshore contours, sometimes rapidly via undersea landslides off
the reef platform. These offshore deposits along the paleoequator include
much of the Wheeler Shale, the Burgess Shale of western Canada, and other
sites from California through Utah to the Northwest territories of Canada.
All of these sites yield remarkably preserved Cambrian fossils.
The most famous Wheeler Shale fossil is the trilobite Elrathia kingi;
so common at some sites that specimens are commercially quarried and are
made into novelty accessories, as well as sold to collectors and institutions
all over the world. However, Elrathia is just one of about fifteen
trilobite genera of the Wheeler Shale. Bathyuriscus fimbriatus is
also relatively common at certain sites. Even more abundant are several species
of agnostid trilobites, such a Peronopsis interstricta. These
are typically less than a centimeter in length. Here are eight representative
species of the Wheeler Shale:
It is notable that the trilobite fauna of the Wheeler Shale, being a Middle
Cambrian locality, is dominated by Ptychopariida, Corynexochida, and Agnostida.
In addition to trilobites, there were other species of arachnomorph (trilobite-like clade) arthropods
such as Naraoia. These trilobite-like
arthropods demonstrate that the group from which trilobites
arose was itself successful and diverse, though being uncalcified,
are only preserved under exceptional conditions, such as at exceptional
lagerstätten such as the Burgess Shale and
Chengjiang. Because the Burgess Shale was the
first lagerstätte with such exceptional preservation, other sites with
similar preservation are referred to as "Burgess Shale type" lagerstätten.
This level of preservation occurs only infrequently in the Wheeler Shale.
TRILOBITA OF THE WHEELER FORMATION, UTAH
courtesy of the
Western Trilobites
Association
Taxa held in common in
red
HOUSE RANGE
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DRUM MOUNTAINS
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Order Ptychopariida
Altiocculus
harrisi
Alokistocare
sp.
Asaphiscus wheeleri
Bathyocos
housensis
Bolaspidella
housensis
Bolaspidella
wellsvillensis
Brachyaspidion
microps
Brachyaspidion
sulcatum
Elrathia kingi
Elrathina(=Ptychoparella)
wheeleri
Jenkinsonia varga
Modocia
brevispina
Modocia
laevinucha
Modocia
typicalis
Ptychoparella
wheeleri
Order
Agnostida
Baltagnostus
eurypyx
Hypagnostus
parvifrons
Peronopsis amplaxis
Peronopsis bidens
Peronopsis fallax
Peronopsis gaspensis
Peronopsis intermedius
Peronopsis interstrictus
Peronopsis montis
Peronopsis segmenta
Ptychagnostus atavus
Ptychagnostus gibbus
Ptychagnostus
germanus
Ptychagnostus
occultatus
Ptychagnostus
seminula
Order Corynexochida
Bathyuriscus
fimbriatus
Olenoides expansus
Olenoides nevadensis
Zacanthoides sp.
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Order
Ptychopariida
Altiocculus
sp.
Asaphiscus wheeleri
Bathyuriscus
sp.
Bolaspidella
drumensis
Bolaspidella
sp.
Elrathia kingi
Elrathia
sp.
Ptychoparella
sp.
Spencella
sp.
Order
Agnostida
Peronopsis
amplaxis
Peronopsis
fallax
Peronopsis
gaspensis
Peronopsis interstricta
Peronopsis montis
Peronopsis segmenta
Ptychagnostus atavus
Ptychagnostus gibbus
Ptychagnostus
intermedius
Ptychagnostus seminula
Order Corynexochida
Olenoides expansus
Olenoides
serratus
Tonkinella
breviceps
Zacanthoides
divergens
Zacanthoides
sp.
Order
Asaphida
Glyphaspis
concavus
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Gunther, L. F., Gunther, V. G., and
Gunther, G., 1994, Some Middle Cambrian fossils of Utah, in Special issue
on Utah: Utah Geological Survey Public Information Series 26, p.
59-62.
Robison, Richard Ashby; 1962. Late Middle Cambrian Faunas
from the Wheeler and Marjum Formations of Western Utah. PhD
Thesis, University of Texas at Austin
Robison, Richard Ashby;
1971. Additional Middle Cambrian Trilobites
From the Wheeler Shale of Utah. Journal of Paleontology
45(5):796-804
Sundberg, Frederick A.;
1994. Corynexochida and Ptychopariida
(Trilobita,Arthropoda) of the Ehmaniella Biozone (Middle Cambrian), Utah
and Nevada. Natural History Museum of Los Angeles County - Contributions in Science, No.446
Utah's Cambrian Life: Evolution and Biogeography of Burgess Shale Type Fossils
Western Trilobites Association
