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.

Trilobite Multiples

The first law of ecology is that everything is related to everything else. –Barry Commoner

Ampyxina bellatula, Marquoketa Formation, Ordovician Period, Missouri
Ampyxina bellatula molts, Maquoketa Formation, Ordovician Period, Missouri. These trilobites lack free cheeks (note absence of long genal spines) and are therefore molts. Did these animals gather to molt communally? Largest molt is 1.0 cm long.

Associations of large numbers of monospecific trilobite molts on a single bedding surface occur worldwide throughout marine rocks of Paleozoic age. Often, it looks as though trilobites gathered to molt at a specific place and time. Sometimes it’s not easy to tell if the assemblage reflects paleobiology and not simply a hydraulic accumulation of molted exoskeletal sclerites, though.

Elrathia kingii, Wheeler Shale Formation, Cambrian Period, Utah
Elrathia kingii (multiple), Wheeler Shale Formation, Cambrian Period, Utah. Most of these trilobites have free cheeks and are probably not molts. These animals likely died at the same time, in the same place. Largest trilobite is 3.2 cm long.

Sometimes a single bedding surface may contain a monospecific (or nearly) assemblage of complete trilobite specimens. More rarely, one finds several species of complete specimens on the same bedding surface (as below).

Raymondites plate, Ordovician Period
Ceraurus globulobatus (multiple), Raymondites spiniger (center right), and Bumastoides milleri (upper left), Bobcaygeon Formation, Ordovician Period, near Brechin, Ontario. This slab contains three species of trilobites, one of which (Ceraurus) is in a variety of preservational states ranging from complete, outstretched and articulated to scattered and disarticulated. Largest Ceraurus is 3.4 cm long.

Although a complete understanding of these associations will likely forever elude us, these multi-species plates are of great interest to the collector. This is especially true if it is certain that the slab reflects a completely natural assemblage of rare or unusual species.

Raymondites plate detail, Ordovician Period
Raymondites (upper right) plate detail, Ordovician Period.

Many multiple commercial specimens from Russia and Morocco, on the other hand, are likely the product of manipulation. Large slabs may have had a pit or pits excavated into it, and trilobites or other fossils added and epoxied into place. A texture added to the surface can conceal the additions. This being the case, a collector should pay no more than he/she would for the specimens in isolation, the association being neither paleoecological nor sedimentological (i.e., scientifically meaningless).

Russian double, Ordovician Period
Asaphus cornutus (left) and Pseudoasaphus globifrons (right), Ordovician Period, St. Petersburg region, Russia. Real trilo-buddies or a composite? Most likely the latter. Larger trilobite is 8.1 cm long.

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

 

A Quality Composite Specimen of Acanthopyge haueri (Barrande, 1846) from Morocco

O’Hagen: We’re all in the same boat, fellas.
Mac: But our shenanigans are cheeky and fun.
Thorny: Yeah, his shenanigans are cruel and tragic.
Foster: Which wouldn’t make them shenanigans at all, really.
Mac: [Irish voice] Evil shenanigans!
O’Hagen: I swear to God, I’ll pistol whip the next guy that says ‘shenanigans!’—Super Troopers (2001)

Acanthopyge, Middle(?) Devonian, Morocco
Acanthopyge haueri, Middle(?) Devonian, Morocco. Specimens like this are sometimes said to come from near Mader, Morocco, but God knows where they actually originate. Trilobite is 7.5 cm long, exclusive of pygidial spines.

I have heard and read anecdotal reports of the discovery of approximately several dozen complete specimens of Acanthopyge haueri, a strange and rare lichid from the Devonian of Morocco. Many, many more apparently complete specimens than this, however, have made their way onto the commercial fossil markets.

These other specimens range in quality from sloppy out-and-out fakes to specimens such as the one above that I acquired many years ago, and which I consider to be mostly genuine, but manipulated. My specimen bears a close resemblance to the one figured on the American Museum of Natural History trilobite page, at least as far as can be judged from an image on a website.

Careful inspection of the trilobite in my possession reveals that the exoskeleton is mostly real, but with minor patching here and there with resin. As in many of the composite, or at least manipulated specimens, what is most worthy of suspicion is the matrix. The upper surface of the slab appears to be a mixture of pulverized rock, resin, and possibly plaster. This suggests some significant degree of manipulation or fakery (or dare I say shenanigans?).

Acanthopyge pygidium, Devonian Period, Morocco
Distractor: Acanthopyge haueri pygidium, Devonian Period, Morocco. The large obviously patched area of the pygidium near the center of the frame is likely designed to make potential buyers think: Oh, so that’s what repairs look like on this specimen. The rest must be perfect! Nonsense. Even the pygidium is a composite.

The relative positioning of exoskeletal sclerites also gives pause. Although the slight disarticulation here and there, as well as minor asymmetries could, I suppose, be a result of crushing. Much more likely, I think, is that this specimen was put back together on a poured slab. The parts may be from a single individual (a molt?) or a set of parts that were collected over time for this purpose.

Compositing of vertebrate specimens is a common and accepted practice, especially for museum mounts. Not so much for invertebrates. One can bemoan the questionable ethics of these trilo-fakers, but were it not for the intense commercial activities of the Moroccan diggers and preparers, such rare fossils would be far out of reach for the ordinary collector. Specimens like the one discussed here are a consequence of human nature, both to profit and to possess objects of surpassing rarity and interest.

©2016 Christopher R. Cunningham. All rights reserved. No text or images may be duplicated or distributed without permission.