According to a new study, fossils of a tiny sea creature with a delicately preserved nervous system solve a century-old debate over how the brain evolved in arthropods, the most species-rich group in the animal kingdom. Fossils of a tiny sea creature that died more than half a billion years ago m
Artist’s impression of an individual 525-million-year-old Cardiodictyon catenulum on the shallow coastal sea floor, emerging from the shelter of a small stromatolite built by photosynthetic bacteria. Credit: Nicholas Strausfeld/University of Arizona
belonged to an extinct group of animals known as armored lobopodians, which were abundant early during a period known as the Cambrian, when virtually all major animal lineages appeared over an extremely short time between 540 million and 500 million years ago. Lobopodians likely moved about on the sea floor using multiple pairs of soft, stubby legs that lacked the joints of their descendants, the euarthropods – Greek for “real jointed foot.
According to the authors, the finding resolves a long and heated debate about the origin and composition of the head in arthropods, the world’s most species-rich group in the animal kingdom. Arthropods include insects, crustaceans, spiders, and other arachnids, plus some other lineages such as millipedes and centipedes.
“That tells us that armored lobopodians might have been the earliest arthropods,” Strausfeld said, predating even trilobites, an iconic and diverse group of marine arthropods that went extinct around 250 million years ago. “By comparing known gene expression patterns in living species,” Hirth said, “we identified a common signature of all brains and how they are formed.”, three brain domains are each associated with a characteristic pair of head appendages and with one of the three parts of the anterior digestive system.
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