In this week’s Trilobite Tuesday, we present a brief history of the ebb and flow of trilobite evolution. These amazing arthropods existed for nearly 300 million years of earth history, during which time they produced over 25,000 different scientifically recognized species. But the fact is that after presenting a dizzying array of species during the Cambrian, Ordovician and Silurian periods, by thetime the trilobite line reached the Devonian some 400 million years ago, their species count had dwindled down to a precious few. And by the time the Mississippian began, their was ostensibly only one order of trilobites left—the Proetids. Here is an attractive example of a “double” Ameropiltonia lauradanae from the Mississippian-age shale of Missouri. These proetids were among the last survivors of the noble trilobite lineage.
cavoliamari drew 12, Clara, and Danny, and took photos of them around Florence for me, cardinalcapaldi, and escapaldi. We did our best to return the favor as we took a hike to Webster’s Falls. Cardinal drew top, I drew bottom, and Nehs wrote a story below:
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Clara and Danny poked their heads out of the TARDIS and looked around. Everything seemed normal, terrestrial, making it an interesting change of pace.
“Okay, what’s the catch?” Clara asked as they stepped out. “This looks like plain old ordinary Earth.”
“That’s because it is plain old ordinary Earth,” the Doctor frowned. He closed the door to the TARDIS behind him and shoved his hands in his pockets. “I thought you’d like to just see something normal for a change.”
“Normal’s good,” Danny nodded. He looked around at the lush green forest and the craggy rocks. “So, uh, where is normal today?”
The Doctor remained oddly quiet as he took in the scenery. “The Niagara Escarpment…?” Clara looked at the Doctor with a straight, unimpressed expression. He scowled back as if to challenge her. “What? You doubt me? Look at the sign over there.”
By the Ordovician time period, approximately 460 million years ago, trilobite eyes had developed into an almost dizzying array of sizes and shapes. Some, like those attached to species such as Asaphus kowalewski (pictured) and Cybele panderi, sat atop spindly “stalks” up to three inches long. This feature presumably allowed the trilobite a better view of the world around it, even when it may have been lurking under a thick layer of silt or mud along the sea bottom. Other trilobites of the time period, such as the aptly named Cyclopyge bohemica, developed huge wrap-around holochroal eyes featuring over a thousand small, tightly packed lenses that allowed a virtually uninterrupted view of the ocean surrounding it.