Agnostida: Tiny, Blind (Mostly) Trilobites

I generally wade in blind and trust to fate and instinct to see me through. –Peter Straub

Goniagnostus nathorsti, Maya Formation, Cambrian Period, Lena River region, Siberia, Russia
Goniagnostus nathorsti, Maya Formation, Cambrian Period, Lena River region, Siberia, Russia. Trilobite is 10 mm long.

Agnostids are quite familiar to collectors of North American trilobites from the Cambrian of Utah, especially the Wheeler and Marjum Formations. How many trilobite collectors (or geologists for that matter) got their start when a parent or grandparent bought them an agnostid from Utah at a museum gift shop for a buck or two?

Baltagnostus eurypx, Wheeler Shale, Millard County, Utah
Baltagnostus eurypx, Wheeler Shale, Cambrian Period, Millard County, Utah. Trilobite is 4 mm long.

A quick perusal of the Treatise, however, reveals a bewildering variety of similar forms from the Cambrian and Ordovician of the world. Something about this small, blind, isopygous morphotype allowed for great success in the oceans of the early Paleozoic Era.

Peronopsis interstricta, Wheeler Shale, Cambrian Period, Millard County, Utah
A Typical Introduction to the World of Fossil Collecting: Peronopsis interstricta, Wheeler Shale, Cambrian Period, Millard County, Utah. Trilobite is 7 mm long.

The Order Agnostida contains two suborders, the Agnostina and Eodiscina. Agnostina are the more common and familiar to most collectors: These are all blind and have two thoracic segments. Some Eodiscina have eyes and possess two or three thoracic segments. The relationship between these groups has been controversial, some even arguing that the two suborders share no close relationship, their affinities resting with other trilobites.

Ptychagnostus michaeli, Marjum Formation, Millard Coounty, Utah
Ptychagnostus michaeli, Marjum Formation, Millard County, Utah. A spiny agnostid? Sure enough. Trilobite is 7 mm long (exclusive of spines).

As is the case with most trilobite groups, the mode of life of these little creatures is a matter for speculation. Some believe these trilobites occupied a planktonic niche. Whatever the case, agnostids (except for the rare ones from exotic locales like the Goniagnostus above) provide an easy entrée into the fascinating world of fossil collecting for children and adults alike.

Cephalopyge notibilis, Jbel Wawrmast Formation, upper Lower Cambrian, Taroudant, Morocco
Cephalopyge notibilis, a blind eodiscoid (Family Weymouthiidae), Jbel Wawrmast Formation, upper Lower Cambrian Epoch, Taroudant, Morocco. Trilobite is 9 mm long.

©2017 Christopher R. Cunningham. All rights reserved. No text or images may be duplicated or distributed without permission.

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