''Elrathia'' is a genus of
trilobite
Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the ...
belonging to
Ptychopariacea known from the mid-
Cambrian of
Laurentia
Laurentia or the North American Craton is a large continental craton that forms the ancient geological core of North America. Many times in its past, Laurentia has been a separate continent, as it is now in the form of North America, althoug ...
(North America). ''E. kingii'' is one of the most common trilobite
fossils in the USA
locally found in extremely high concentrations within the
Wheeler Formation
The Wheeler Shale (named by Charles Walcott) is a Cambrian ( 507 Ma) fossil locality world-famous
for prolific agnostid and ''Elrathia kingii'' trilobite remains (even though many areas are barren of fossils)
and represents a Konzent ...
in the U.S. state of
Utah
Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to it ...
.
''E. kingii'' has been considered the most recognizable trilobite. Commercial quarries extract ''E. kingii'' in prolific numbers,
with just one commercial collector estimating 1.5 million specimens extracted in a 20-year career.
1950 specimens of ''Elrathia'' are known from the Greater
Phyllopod bed
The Phyllopod bed, designated by USNM locality number 35k, is the most famous fossil-bearing member of the Burgess Shale fossil ''Lagerstätte''. It was quarried by Charles Walcott from 1911–1917 (and later named Walcott Quarry), and was t ...
, where they comprise 3.7% of the community.
Etymology
Even though the generic name ''Elrathia'' was first published in the combination ''E. kingii'', a species from the
House Range,
Utah
Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to it ...
, the name, itself, is derived from Elrath, Cherokee County, Alabama.
Description
''E. kingii'' is a medium-sized trilobite with a smooth sub-ovate carapace that is tapered towards the rear.
Thorax
The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the cre ...
is usually 13 segments.
Pygidium
The pygidium (plural pygidia) is the posterior body part or shield of crustaceans and some other arthropods, such as insects and the extinct trilobites. In groups other than insects, it contains the anus and, in females, the ovipositor. It is compo ...
has four axial rings and a long terminal piece. Posterior margin of the pygidium has a long broad medial notch.
In contrast, ''E. marjum'' usually has 12 segments, 5 axial rings, lacks a notched posterior margin and possess incipient antero-lateral spines.
The British Columbian species, ''E. permulta'', is much smaller, averaging about only 20 millimeters, and has up to thoracic 14 segments. Because ''E. permulta'' lacks several diagnostic features of the genus it may even represent a distinct genus.
See also
*
Hypoxia (environmental)
References
External links
*
*
"Order ptychopariida" ''A Guide to the Orders of Trilobites''. Sam Gon III. 2009
{{Taxonbar, from=Q26146
Burgess Shale fossils
Alokistocaridae
Cambrian trilobites
Fossils of British Columbia
Fossils of the United States
Fossils of Georgia (U.S. state)
Cambrian genus extinctions
Wheeler Shale
Paleozoic life of Newfoundland and Labrador