The oldest trilobites had babies with large heads and long spines

Trilobites are the most iconic inhabitants of the Paleozoic seas. These arthropods possess an exoskeleton that was hardened by calcium carbonate shortly after they hatched from the egg. Owing to this fact, their developmental stages are often preserved in the fossil record. In their new paper, Lukáš Laibl with his colleagues from Freie Universität Berlin described the development of trilobite Fritzolenellus lapworthi from Cambrian strata of Newfoundland, from tiny individuals smaller than one millimeter up to the nearly 20 cm long adults. Juveniles of Fritzolenellus show a large cephalon and distinct spines on their body. Based on a detailed comparison of Fritzolenellus babies with those of other Cambrian trilobites, the authors showed that features seen in Fritzolenellus have the original morphology inherited from the last common ancestor and can be thus used as a reference group when studying the ontogeny of other trilobites. For additional information click here.