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Dikelocephalus
''Dikelocephalus'' is a genus of very large trilobites of up to long, that lived during the last 3 million years of the Cambrian (Sunwaptan). Their fossils are commonly found as disarticulated sclerites, in the upper Mississippi Valley (northeastern Iowa, southeastern Wisconsin, central to western Wisconsin) and in Canada (Alberta). The exoskeleton is rounded anteriorly, with the thorax and sides of the tailshield (or pygidium) slightly tapering to about ⅔× of the width across the base of the spines at the back of the headshield (or cephalon). At the side corners of the pygidium there may be triangular or hooked spines, pointing backwards, while between the spines the posterior margin is at a 30-75° angle with the lateral margin, gently convex or nearly straight. If pygidial spines are lacking, the margin is gradually rounded. The thorax has 12 segments.
== Distribution ==
The oldest known specimens of ''Dikelocephalus'' have been found in the upper part of the Tunnel City Group. Some of these early specimens, and only those, have been assigned to ''D. freeburgensis''. These specimens may or may not be outside the wide morphological range of ''D. minnesotensis'', but the analysis to establish this could not yet be done due to the absence of a sufficiently large collection from the collection site. Other specimen from the same deposit have confidently been assigned to ''D. minnesotensis'' however. ''D. minnesotensis'' also occurs in the Reno Member of the Lone Rock formation. The most common location of the species is the St. Laurence Formation, which directly overlies the deposits of the Tunnel City Group. The youngest know finds come from the Van Oser Member of the Jordan Formation, that in turn overlies the St. Laurence Formation.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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