For more than 250 million years, the primeval oceans of the Paleozoic teemed with trilobites. These hardy invertebrates evolved into an astonishing array of separate species—more than 25,000 at last count—and much remains unknown about these once-ubiquitous creatures. Fossil enthusiasts are captivated by trilobites’ diversity and adaptability, enthralled by the possibility of catching a glimpse of a transcendently strange past.Andy Secher—one of the most prolific trilobite collecto...

Trilobites are among the most remarkable lifeforms ever to exist. First emerging 521 million years ago, these organisms—animals with highly developed eyes, sturdy walking legs, and protective outer shells—evolved into more than 25,000 scientifically recognized species. During their 270 million years of inhabiting the ancient seas, trilobites proliferated into an ever more fanciful cast of characters, from graceful Cambrian olenellids to robust Ordovician asaphids to spine-covered Devonian ...

Ammonites swam in Earth’s ancient seas for nearly 400 million years. These prolific cephalopods diversified into more than 10,000 species before meeting their demise during the end-Cretaceous mass extinction. Today, these spiral-shelled invertebrates are among the most abundant fossils in the geologic record, found from snowcapped Himalayan peaks to parched South American arroyos. People around the world have long been drawn to the mystery and beauty of ammonite fossils. These preternatura...