The Last Trilobites
The last trilobites, those of the proetid order that lived during the Mississippian, Pennsylvanian and Permian periods, were certainly not the biggest, baddest or boldest examples of their class. Yet even considering their diminutive size (usually an inch of less) and their modest, generally ovate body plan -- a design that allowed them to burrow beneath the sea floor mud in order to avoid the constant threat of predation -- these trilobites still contributed significantly to their kind's lingering legacy. They may have been a far cry from the foot-long, spinose trilobite “monsters” that inhabited the Ordovician and Silurian seas, but in look, design and lifestyle they were still very much quintessential trilobites.
The fossilized evidence of these last trilobites can be found in numerous spots across the face of the planet. The 360 million year old Mississippian-age outposts of Missouri, for example, have long been a favorite of collectors in search of such species as Ameropiltonia lauradanae and Comptonaspis swallowi. Over the last two decades, New Mexico has also emerged as a Mississippian hotspot, where 23 species have now been scientifically identified from the Caballero and Lake Valley formations, including the likes of Piltonia carlakertisae, Namuropyge newmexicoensis and Pudoproetus fernglenensis. These trilobites are often preserved in a dark brown or black calcite which contrasts dramatically against a reddish-pink matrix. Another important Mississippian-age trilobite location can be found in Antoing, Belgium, where for more than a century, well-preserved examples of such species as Piltonia kuehnei, Witrydes rosmerta and Bollandia globiceps have been found in the hard black mudstone rocks of the area. At the start of the Pennsylvanian, roughly 323 million years ago, trilobites were clearly continuing their decline in the fossil record, yet the proetid order still managed to produce an interesting array of species including such notable American varieties as Ditomopyge olsoni, Ameua major and the highly pustulated Brachymetopus nodusus. In recent years, a number of species from the remote Ulutau mountains region of Kazakhstan have invaded the world market, with many of these dolomitic specimens (including Ditomopyge kumpani and Griffithides praepermicus) being fossilized along-side other fauna, including brachiopods and crinoids, providing an interesting view of life at this stage of the evolutionary game.
By the time the Permian rolled around, 298 million years ago, the limited available fossil material provides glaring evidence that trilobites were barely hanging on within their ever-changing aquatic world. Their size had shrunk to an average of a centimeter, and their speciation had reached a critical low. Yet despite their apparent difficulties, the distribution of Paraphilipsia sp. and Acropyge multisegmenta was surprisingly cosmopolitan, with the generally disarticulated remains of these trilo types being found within sedimentary layers in such disparate locations as present-day Hungary, China, Pakistan, Russia and Japan.
These end-of-the-line trilobites apparently filled a wide variety of oceanic habitats -- ranging from deep open water to shallow continental shelves. Yet their versatility wasn't enough to save them from their eventual fate. As life on our ever-changing planet has continually proven, nothing lasts forever, and for reasons that continue to both confound and fascinate scientists, the end of the Permian also signaled the end of trilobites… along with 90 percent of life around the globe, an event which represents the greatest mass extinction in the history of Planet Earth.
Here's a look at some of the last member of the trilobite class:
At 5 cm, Pudoproetus fernglenensis was large for a Mississippian trilobite.
Witrydes rosmerta, found in Belgium, displays the classic proetid shape.
The Pennsylvanian-age proetid, Ameura major, was fossilized in a distinctive white calcite.
Ditomopyge olsoni is one of the most commonly found Pennsylvanian trilobites.
Ditomopyge kumpani was preserved in a dolomitic limestone.