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 phacopids. Their fossil remains, which today can be found on every continent, testify to the astonishing breadth and scope of trilobite heterogeneity. Trilobites A to Z is the ultimate reference guide to these incredible invertebrates. It features reader-friendly, concise yet information-packed introductions to nearly 1,500 trilobite species, each accompanied by a full-color photograph. Grouped according to periods within the Paleozoic era, the book illuminates the similarities and differences among trilobite specimens from around the globe, bringing to life the complexity and beauty of these long-extinct creatures in all their variety. Andy Secher—one of the world’s leading trilobite collectors—also offers practical guidance for readers seeking to identify specimens of their own. Comprehensive and entertainingly written, this essential encyclopedia will inform and delight trilobite enthusiasts and collectors as well as students and scholars of invertebrate paleontology.