Arthropods, the group of animals that includes such individuals as spiders and mealybugs, are the largest phylum in the animal kingdom and are found everywhere from the world’s deepest ocean trench to the top of Mount Everest.
Now, Manchester University scientist David Legg, in collaboration with a team of international experts from China, Switzerland and Sweden, has announced a new fossil that reveals the origin of gills in arthropods. It is a new species of marine arthropod that has been named Erratus sperare and had unique trunk appendages that represent an intermediate stage in the evolution of biramic limbs.
Modern water-dwelling arthropods have biramic limbs, that is, legs that have two parts, one for breathing and one for walking, but how such specialized limbs evolved was a mystery. Until now, researchers didn’t know how arthropods made the jump from these specialized fins to the biramic limbs of modern arthropods.
A missing link appears among arthropods
The study, which has been published in the Philosophical Transactions of the Royal Society B Biological Sciences journal, shows that the latest addition to the group is an organism 520 million years old (about 10 times the age of the dinosaurs).
The creature, Erratus speare , was discovered at the Chengjiang Fossil Bed, a UNESCO World Heritage Site located in Yunnan, China; place that preserves an ancient underwater ecosystem with some of the most well-known arthropod fossils such as trilobites (the most characteristic fossils of the Paleozoic period and of which nearly 20,000 species have been described) and anomalocarids (which existed in the early-mid Cambrian period , until about 510 million years ago).
Erratus sperar e has legs and a projection that protects the gills, which shows that fish are not the only organisms that have gills. The difference is that arthropods have gills on their legs. Until now it was unknown where the gills of arthropods came from. A mystery that this missing link has helped bring to light.
“Thanks to this new fossil, Erratus sperare , we now have a much clearer picture. These gills also probably evolved into the wings of insects and the lungs of terrestrial arthropods such as spiders, so they were a very important innovation,” says David Legg, leader of the work.
Referencia: Dongjing Fu, David A. Legg, Allison C. Daley, Graham E. Budd, Yu Wu and Xingliang Zhang. 2022. The evolution of biramous appendages revealed by a carapace-bearing Cambrian arthropod. 7 February 2022, Philosophical Transactions of the Royal Society B Biological Sciences.
DOI: 10.1098/rstb.2021.0034
