Sci-News has an article about a distinctive, but enigmatic, group of arthropods called Cyclidans. Cyclidans appeared during the Carboniferous and hung around until the Late Cretaceous. The Mazon Creek biota includes a few species – Cyclus americanus, Cyclus obelus, and Halicyne max. A new species, Yunnanocyclus fortis, has been described in the journal Papers in Palaeontology. This animal dates to the Early Triassic and lived about 251 years ago in what is now China’s Guizhou province. This discovery gives us a glimpse into the Earth’s recovery after the Permian-Triassic mass extinction, which eliminated more than 80% of marine species. All three specimens preserve a pair of strongly developed mandibles, an uncommon feature of cyclidan fossils.

Cyclidans are a distinctive group of arthropods that first appeared in the Carboniferous period and survived until the Late Cretaceous.

Their fossil record is sparse, and most finds preserve only the animals’ carapaces (hard shells), leaving many aspects of their anatomy poorly understood.

“Cyclida is an order of arthropods in the Guiyang biota,” said Dr. Xiaoyuan Sun from the China University of Geosciences and his colleagues from China and the United States.

“As an enigmatic and specialized group of crustaceans, they originated in the Mississippian (359 to 323 million years ago) and became extinct in the Late Cretaceous Maastrichtian (73 to 66 million years ago).”

“They are classified as Crustacea on the basis of the possession of features such as antennules, antennae, mandibles, maxillae and maxillipeds.”

“However, our knowledge of cyclidan crustaceans is very limited due to their rarity in the fossil record.”

“Usually, only the hard carapaces are preserved, while their antennules and appendages are extremely rare.”