Oklahoma Trilobites

Interestingly, the Devonian trilobites of Oklahoma have look-a-likes found in the Atlas Mountains of Morocco. While today on continents separated by thousands of miles, such was not the case during Devonian-time. During the Devonian, present-day Morocco was part of the Eastern continental shelf of Gondwana, and present-day Oklahoma was part of the Southern continental shelf of Euramerica. These locations were adjacent and at essentially equal latitudes and probably had nearly identical environments. Thus, each of the comparable species undoubtedly shares a common ancestry and is classified in the same genera. The Table below lists the species found in Devonian of Oklahoma, as well as information on classification and relative frequency.

Mr. Robert Carroll has operated one of the commercial quarries in the area for the past dozen years. Actually, he works several quarries that have exposures of both the Haragan and Bois d' Arc Formations. I have hunted in these quarries, and the process is markedly different from hunting the Great Basin in the Western U.S. While surface hunting is possible for trilobites weathering out of matrix, if your goal is an exquisite specimen, you'll have to do a lot of rock splitting. The trilobites are discovered by their very thin cross sections (hence, the trilobite will already be in two or more pieces). Expert eyes like Bob's are usually required to ID the species and to estimate whether it is possible that the matrix may contain a complete specimen. Most are not complete. If it can not be determined that it is incomplete, the next step is to take it back to the prep lab and rough it out with a pneumatic chisel. The exception is the complete specimen which is then finished using air abrasive tools. The trilobites that come from Bob's lab are exquisite in every respect, and each one represents prodigious hours of preparation. The good news is that the limestone matrix melts away under AlO2 grit at 100 psi pressure, yielding a life-like specimen that is a darker brown than the matrix.The picture below shows Bob setting by his circa 1953 White air abrasion machine. As old as it is, it is meticulously maintained. Bob's preparation is a source a pride, and examples of his work can, for example be found in Riccardo Levi-Setti's book, Trilobites.

The Table below lists the 19 species found to occur in the Devonian, Haragan and Bois d' Arc Formations, and I thank Bob Carroll for providing this information; links are also provided where you will find pictures for many of the species. Some of these are exceedingly rare and no complete specimens have been found. Cysphaspis carrolli, a diminuative Aulocopleurid, is named for Bob Carroll. Bob is also credited for the discovery of a rare petite lichid which is still undescribed, and which Bob has affectionately named Bug X. As previously mentioned, Morroco and Oklahoma were proximal during Devonian time, such that some trilobite genera are common to both Coal County and the Moroccan Atlas Mountains. The Oklohoma species tend to be smaller and, I believe, more elegant. A perfect example is the highly sought Odontopleurid, Dicranurus. The Morrocan species is named Monstrosus, and the Oklahoma species Elegantus - it appears that the names pretty much tell it all.

Uncle Darwin