Rare Agnostid Trilobites Association

Ptychagnostus michaeli

Trilobites Order Agnostida, Family Ptychagnostidae

Hypagnostus parvifrons

Trilobites Order Agnostida, Family Spinagnostidae

Geological Time: Middle Cambrian

Size: 4mm and 6mm

Fossil Site: Marjum Formation, Millard County, Utah

Agnostid Trilobites Ptychagnostus michaeli Hypagnostus parvifronsOrder 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 the cephalon and pygidium are of essentially the same size.

Ptychagnostus michaeli, with its five spines, is one of the rarest agnostids found in the Marjum Formation, and only recently have good specimens been found. Hypagnostus hypagnostus is of moderate rarety.

In all, a very nice Cambrian trilobite association plate with two rare Ptychagnostus michaeli and a Hypagnostus parvifrons.

click fossil pictures to enlarge

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