''Yicaris dianensis'' is a species of

microscopic The microscopic scale () is the scale of objects and events smaller than those that can easily be seen by the naked eye, requiring a lens (optics), lens or microscope to see them clearly. In physics, the microscopic scale is sometimes regarded a ...

pancrustacean Pancrustacea is the clade that comprises all crustaceans and Hexapoda, hexapods. This grouping is contrary to the Atelocerata hypothesis, in which Myriapoda and Hexapoda are sister taxon, sister taxa, and Crustacea are only more distantly relate ...

found in the Yu’anshan Formation,

Yunnan Yunnan , () is a landlocked Provinces of China, province in Southwest China, the southwest of the People's Republic of China. The province spans approximately and has a population of 48.3 million (as of 2018). The capital of the province is ...

Province,

China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...

. ''Yicaris''' discovery is notable because its age suggests that true crustaceans already existed as far back in time as

Early Cambrian The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ago ( ...

, much earlier than other fossils known from the Middle and Late Cambrian. Its closest living relatives are believed to be

Cephalocarida The Cephalocarida are a class in the subphylum Crustacea comprising only 12 benthic species. They were discovered in 1955 by Howard L. Sanders, and are commonly referred to as horseshoe shrimp. They have been grouped together with the Remipedi ...

ns.

Etymology

The name ''Yicaris dianensis'' honors the ethnic minority Yi people of Yunnan Province, while

Dian Dian may refer to: Places * Dian Kingdom, ancient kingdom in modern Yunnan province, China * ''Diān'' (滇), an official abbreviation for Yunnan province * Lake Dian, a lake in Yunnan * Dian, Armenia, a village * People * Dian (given name), a lis ...

is an ancient kingdom of southern China. The suffix —caris refers to shrimp in Latin.

Description

''Yicaris''' body consists of a

cephalothorax The cephalothorax, also called prosoma in some groups, is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. (The terms ''prosoma'' and ''opisthosoma'' are equivalent to ''cepha ...

covered by a head shield and limb-bearing segments. Out of the thirty-four specimens examined, six consecutive growth stages are known, the smallest one being 460 μm while the largest fossil, though fragmentary, reaches 1.8 mm long. Yicaris is also notable for the leaf-like structures on its limbs called epipodites. The developmental origin of epipodites is thought to be enigmatic, but Yicaris' discovery shows that early crustaceans already possessed a set of three epipodites on their limbs. This structure is considered important due to its potential significance in the evolution of wings in insects, which evolved from within

Pancrustacea Pancrustacea is the clade that comprises all crustaceans and hexapods. This grouping is contrary to the Atelocerata hypothesis, in which Myriapoda and Hexapoda are sister taxa, and Crustacea are only more distantly related. As of 2010, the Pan ...

References

Microscopic animals Crustaceans {{Arthropod-stub