Trilobites Association Plate
Order Agnostida, Family Peronopsidae
Time: Middle Cambrian
mm = 1 inch): Matrix 60mm X 65mm Trilobites 5mm and 7mm
Marjum Formation, Millard County, Utah
Agnostida comprises trilobites that appeared in the Lower Cambrian,
became widespread and then declined to become rare in the Ordovician
prior to their complete extinction by the end of the Ordovician.
They are so unusual that some experts have suggested that one of
the two suborders, Agnostina, should not even be included in Class
Trilobita. Believed plantonic, they often lacked eyes, and their
cephalon and pygidium are of essentially the same size.
michaeli, with its five spines, is one of the rarest agnostids found
in the Marjum Formation, and only recently have good specimens been
plate coming from the Middle Cambrian of Millard County, Utah contains
both the rare species Ptychagnostus michaeli and the uncommon species
Peronopsis segmenta (the larger bug).
fossil pictures to enlarge