Trilobites

Their body plan was highly distinctive, consisting of three main sections: the cephalon (head), thorax (a trunk of multiple articulated segments), and pygidium (tail). The thorax was flexible, allowing some species to curl into a defensive ball (enrollment), while others evolved protective spines.Trilobites exhibited diverse ecological strategies. Many were bottom-dwellers feeding on organic detritus, while others adapted as swimmers, burrowers, filter-feeders, or predators. More than 20,000 species are currently recognized, representing one of the most successful early arthropod radiations. Although most fossils preserve only the hard exoskeleton, rare specimens have revealed internal organs, including digestive tracts and even specialized stomach pouches (crop), offering valuable insights into their anatomy and physiology. Recent discoveries continue to expand our understanding of their diversity—for example, the identification of a new species, Toledodiscus valverdi, from Spain, dated to about 520 million years ago, with no known equivalent elsewhere. Beyond their biological significance, trilobites are also key biostratigraphic markers, widely used to correlate rock layers and refine the geological timescale of the Paleozoic.