This is Trilobite Tuesday post #15.
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Both the American Museum of Natural History and Trilobites.info have pages on "The Last Trilobites". By the end of the Permian, trilobites had existed for nearly 300 million years. That stretch of time spread from the lower Cambrian to the mass extinction events at the end of the Permian. Their highest diversity was during the Ordovician. After that, they endured through multiple mass extinction events. Their diversity had dwindled by the end, with only a few families still around. It was the Permian mass extinction that took them out, along with more than 90% of all life on Earth at that time.
The AMNH's page on the last trilobites has a nice write up and some pictures.
At 5 cm, Pudoproetus fernglenensis was large for a Mississippian trilobite.
The Pennsylvanian-age proetid, Ameura major, was fossilized in a distinctive white calcite.
Witrydes rosmerta, found in Belgium, displays the classic proetid shape.
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.
Trilobites.info has a table of the last genus and when they are thought to go extinct.
Although the Trilobita went entirely extinct at the end of the Permian (251 million years ago [mya]), when >90% of all species on the planet were extinguished, the pattern of decline for trilobites had been significant since the end of the Ordovocian. By the end of the Devonian (359 mya), the last of the Phacopidae went extinct, ending the order Phacopida. All of the orders of trilobites had gone extinct, except for one: the Proetida. This order persisted into the Carboniferous (with two superfamilies represented: Aulacopleuroidea and Proetoidea. There was even a major adaptive radiation among the family Phillipsiidae (especially various subfamilies such as Phillipsiinae and Ditomopyginae) in the early Carboniferous, as changes in the world's continents created expanding habitat opportunities. But the number of taxa fell dramatically after the Mid-Carboniferous, and by the start of the Permian (299 mya), only the families Brachymetopidae, Phillipsiidae, and Proetidae remained. The table below lists all of the trilobite genera that existed in the Permian, and indicates when these genera became extinct.
And, they address a theory on what the last species was.
Owens (2003) reviewed the last trilobites to go extinct during the Permian, and revealed that five genera of trilobites persisted until the great extinction crisis at the end of the Permian. This event was perhaps the largest extinction event in Earth's history, wherein >90% of all species were extinguished. However, the fossil record reveals that for trilobites, there were two crises during the Permian, one during the Middle Permian (266 million years ago, in the Late Guadalupian Epoch), in which over half of the trilobite genera extant at the time were lost (see the numerous "Middle Permian" extinctions in the table above). Of those that remained, only five persisted to the end Permian event: Cheiropyge (an aulacopleuroid in the family Brachymetopidae), Kathwaia (a proetoid in the family Phillipsiidae, subfamily Bollandiinae), Paraphillipsia (Phillipsiidae, Cummingellinae), Acropyge (Phillipsiidae, Ditomopyginae), and Pseudophillipsia (also Ditomopyginae). Specimens of these genera are shown at right: These are the last genera of the trilobites, and are found in various localities today including Pakistan, China, Russia, Hungary, and Japan.
Reconstructions of three of these Permian trilobite species are presented at bottom right: Leftmost: Cheiropyge koizumii (Japan, Brachymetopidae); Middle: Pseudophillipsia sumatrensis (Malaysia, Proetidae); Far right: Paraphillipsia karpinskyii (Ukraine, Proetidae)
