EARLY CAMBRIAN PERIOD to LATE PERMIAN PERIOD: 570 million - 230 million years ago
Trilobites are hard-shelled, segmented creatures that lived hundreds of millions of years ago in the Earth's ancient seas. They are considered to be one of our planet's earliest complex life-forms and are one of the key signature creatures of the Paleozoic Era. Trilobites went extinct before dinosaurs even existed. The name 'TRILOBITE' means 'three lobed" and is derived from the fact these animals had bodies featuring three longitudinal lobes, not lateral (head, body, tail) as is often thought. The lateral division of three parts is shared by many arthropods, not just trilobites.
Next to dinosaur fossils, trilobites command a dedicated and passionate following amongst both scientists and fossil collectors, alike. In a relatively short time-frame (scientifically speaking, of course), we have the emergence and subsequent extinction of these fascinating creatures. Still most baffling is the incredible diversity of sizes and features that made up the trilobite group. Many bizarre species co-existed with highly specialized body parts that defy the theories of evolution in their "sudden" emergence and diversity during the Early Cambrian Period in what is known as the 'Cambrian Explosion'.
Trilobites were among the world's first arthropods, a phylum of hard-shelled creatures with multiple body segments and jointed legs (although the legs, antennae and other finer structures of trilobites only very rarely are preserved). They constitute an extinct class of arthropods, Trilobita, that is comprised of over 15,000 known species. It has been reported that every year, four to five new species are discovered in the Atlas and Anti-Atlas Mountain regions in Morocco, alone! This desolate northern fringe of the Sahara Desert was once covered by a prehistoric ocean and its fossil deposits can be considered amongst the world's richest and most diverse source of these ancient sea creatures.
Trilobites are the single most diverse group of extinct organisms that ever existed, period! The smallest known trilobite is just three millimeters long, while the largest type grew to a length of 70 centimeters (over two feet long!). The most common fossil of trilobites is the mineralized dorsal exoskeleton of the creature. This is found in partial form from molting (shedding the shell as it grows) or in complete form when the animal was buried and died intact. The soft parts of the underside are rarely preserved. Trilobite fossils are collected by locating a fossil-bearing layer in rock and then breaking boulder or splitting rock sheet to reveal a cross-section of the preserved trilobite carapace in the break or to reveal an imprint in the sheet. Once the fossil is located, the pieces are then reassembled and delicate preparation then ensues to remove the surrounding rock above and around the trilobite to expose the fossil.
Much of what we hypothesize about trilobites comes from our knowledge of modern arthropods and marine crustaceans. Scientists believe they reproduced sexually, molted and underwent a series of life stages. We know trilobites lived in a variety of marine environments over the course of their existence on our planet. Feeding habits are believed to have been varied including predators, scavengers, filter-feeders and parasites, depending on both type of trilobite and life stage. The majority are believed to have been predator / scavengers due to the presence of a calcified mouthpart called a 'hypostome'. Rare fossils of trilobites showing detailed preserved anatomy under the carapace indicates they had a series of jointed legs and gill structures. Considerable study has been done on trilobites as a whole organism. Even more fascinating though, is the research done on a microscopic level with regards to trilobite morphology. Radiographs have captured incredible detail of complete and fully articulated antennae and underparts like legs and gills, preserved in the host rock of some fossilized specimens. Perhaps the most impressive and classic feature of trilobites that comes to mind is the eyes. Microscopic studies of trilobite eye structures have also revealed marvelous adaptation and very high degrees of specialization in vision.
It seems that the more we learn about trilobites, the unfolding of their mystery is stranger than fiction. Certainly we gain a greater appreciation with each new discovery of these strange and highly advanced but now extinct 'butterflies of the ancient seas'. Unfortunately, fakes plague the fossil market and both ignorance and dishonesty on the supply side continues to facilitate the increasing appearance of fakes in the fossil market and especially, the trilobite market. Education and vigilance is needed.