''Cedaria'' is a small, rather flat trilobite with an oval outline, a headshield and tailshield of approximately the same size, 7 articulating segments in the middle part of the body and spines at the back edges of the headshield that reach halflength of the body. ''Cedaria'' lived during the early part of the Upper Cambrian (
Dresbachian
The Dresbachian is a Maentwrogian regional stage of North America, lasting from 501 to 497 million years ago. It is part of the Upper Cambrian and is defined by four trilobite zones. It overlaps with the International Commission on Stratigraphy, IC ...
), and is especially abundant in the Weeks Formation.
Description
''Cedaria'' has an ovate outline of long on average (maximum size 2.5 cm) and ¾ as wide between the tips of the genal spines. The headshield (or
cephalon
Cephalon, Inc. was an American biopharmaceutical company co-founded in 1987 by pharmacologist Frank Baldino, Jr., neuroscientist Michael Lewis, and organic chemist James C. Kauer—all three former scientists with the DuPont Company. Baldino s ...
) is parabolic in shape with a well defined wide, and typically darker colored border of about 10% of the glabellar length or equal to a thorax segment. The well-defined central raised area (or
glabella
The glabella, in humans, is the area of skin between the eyebrows and above the nose. The term also refers to the underlying bone that is slightly depressed, and joins the two brow ridges. It is a cephalometric landmark that is just superior t ...
) tapers slightly forward with a rounded front, but lateral furrows are weakly defined. The backward occipital ring is well defined. The distance between the glabella and the border (or preglabellar field) is ±¼ as long as the glabella or 2× the width of the border. The eyes are kidney-shaped, ±¼ as long as the glabella and midlength of the glabella, and close to the glabella (at ⅓ of the width of the glabella). The remaining parts of the cephalon, called fixed and free cheeks (or fixigenae and librigenae) are flat. The fracture lines (or
sutures) that in moulting separate the librigenae from the fixigenae are divergent just in front of the eyes, becoming parallel near the border furrow and slightly convergent at margin. From the back of the eyes the sutures bends outward and slightly backward, curving backward at the lateral border furrow and cutting the posterior margin in the inner bend of the spine (or
opisthoparian sutures). The articulating middle part of the body (or
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 c ...
) has 7 segments, the outer tips bending backwards, pointed and darker. The tailshield (or
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 ...
) is semicircular, straight or almost indented and has a long, low, tapering axis with 5 or 6 rings, and 4 or 5 pleural furrows. The border in the pygidium is as wide as in the cephalon and is also often darker, but the border furrow is very shallow or absent.
Taxonomy
''Bonneterrina'', ''Carinamala'', ''Cedaria'', ''Cedarina'', ''Paracedaria'', ''Jimachongia'' and ''Vernaculina'' together comprise the family Cedariidae.
Reassigned species
* ''C. buttsi''
= ?''Crepicephalus''
* ''C. woosteri''
= ?
Distribution
* ''C. minor'' appears in the Upper Cambrian of the United States (between 200 m above the base of the Weeks Formation 15 m into the Big Horse Limestone Member, Orr Formation,
House Range
The House Range is a north-south trending mountain range in Millard County, of west-central Utah. The House Range was named in 1859 by James H. Simpson. It was named by Simpson because "...of its well-defined stratification and the resemblance ...
,
Millard County
Millard County ( ) is a county in the U.S. state of Utah. As of the 2010 United States Census, the population was 12,503. Its county seat is Fillmore, and the largest city is Delta.
History
The Utah Territory legislature created the county o ...
, Utah), Canada (Rabbitkettle Formation, Mackenzie Mountains), and Greenland.
* ''Cedaria'' is also reported in the
Warrior Formation in Pennsylvania.
[Tasch, Paul, 1951, Fauna and Paleoecology of the Upper Cambrian Warrior Formation of Central Pennsylvania, Journal of Paleontology, Vol. 25, No. 3, pp. 275-306, pls. 44-47, May 195]
abstract
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References
{{Taxonbar, from=Q15738362
Ptychopariida genera
Cambrian trilobites
Wheeler Shale
Paleozoic life of the Northwest Territories
Paleozoic life of Yukon