Phys.org has a story about a new Cambrian arthropod.  Erratus sperare was discovered in the Chenjiang Fossil Site in Yunnan, China.  That site dates to about 520 million years ago during the Cambrian Period.  The researchers were looking for evidence of the evolution of biramous limbs from specialized flaps.   In both cases, the limbs are used for locomotion and as gill structures.  E. sperare has both.  The research was published in the journal Philosophical Transactions of the Royal Society B: Biological Sciences.

University of Manchester research fellow David Legg, in collaboration with a team of international scientists from China, Switzerland, and Sweden, has today announced a new fossil that reveals the origin of gills in arthropods.

Arthropods, the group of animals that includes creepy crawlies like spiders and woodlice, are the largest phylum in the animal kingdom and are found everywhere from the deepest ocean trench to the top of Mount Everest.

Research published today shows the newest addition to the group is a 520-million-year-old (about 5 times as old as the dinosaurs) organism called Erratus sperare. Erratus sperare was discovered in the Chengjiang Fossil Site, a UNESCO World Heritage Site located in Yunnan, China. The Chengjiang Fossil Site preserves an ancient underwater ecosystem which included the relatives of some well-known arthropod fossils like trilobites and anomalocarids.

Modern water dwelling arthropods have biramous limbs, legs that have two parts—one for breathing and one for walking—but how such specialized limbs evolved was a mystery. Some of the earliest fossil arthropods, like Anomalocaris, had swimming flaps that may have doubled as gills, but until now researchers didn’t know how arthropods made the jump from these specialized flaps to the biramous limbs of modern arthropods.

Erratus sperare provides the missing link between arthropods that used such specialized flaps and arthropods with biramous limbs. It has both legs and flaps.