''Yongjiacaris'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

shrimp Shrimp are crustaceans (a form of shellfish) with elongated bodies and a primarily swimming mode of locomotion – most commonly Caridea and Dendrobranchiata of the decapod order, although some crustaceans outside of this order are refer ...

, which had only one species, ''Yongjiacaris zhejiangensis''. ''Yongjiacaris'' represents the second report of

freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does include ...

caridean shrimp The Caridea, commonly known as caridean shrimp or true shrimp, are an infraorder of shrimp within the order Decapoda. This infraorder contains all species of true shrimp. They are found widely around the world in both fresh and salt water. Many ...

from the

Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceo ...

. The name of the genus ''Yongjiacaris'' refers to

Yongjia County Yongjia County (; Wenzhou dialect: yon2ko1/ yu3 ''ion ko'') is a county in Wenzhou in the southeast of Zhejiang province, People's Republic of China, located north of the city proper of Wenzhou Wenzhou (pronounced ; Wenzhounese: Yuziou �y33 ...

, in the

Zhejiang Zhejiang ( or , ; , also romanized as Chekiang) is an eastern, coastal province of the People's Republic of China. Its capital and largest city is Hangzhou, and other notable cities include Ningbo and Wenzhou. Zhejiang is bordered by Jiang ...

Province of

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 ...

, while the species name ''Y. zhejiangensis'' is derived from the province name. ''Yonjiacaris'' was formally described by Alessandro Garassino, Shen Yanbin, Frederick R. Schram, and Rod S. Taylor in 2002. It is described from 138 specimens discovered in the C Member of the Moshishan Formation of Yongjia County, and from specimens found in the Showchang Formation near

Jiande is a county-level city of Zhejiang Province, East China, it is under the administration of the prefecture-level city of Hangzhou. History During the Ming and Qing Dynasties, Jiande was the capital of Yanzhou Prefecture. On account of this, Jiand ...

, both in southeastern China. These two correlative rock units date to the

Barremian The Barremian is an age in the geologic timescale (or a chronostratigraphic stage) between 129.4 ± 1.5 Ma (million years ago) and 121.4 ± 1.0 Ma). It is a subdivision of the Early Cretaceous Epoch (or Lower Cretaceous Series). It is preceded ...

age of the

Early Cretaceous The Early Cretaceous ( geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma. Geology Pro ...

; volcanic rocks in the C Member of the Moshishan Formation are dated to 120 million years old, and volcanic rocks in the Showchang Formation are dated to 118 million years ago. The C Member of the Moshishan Formation is a heterogeneous rock unit including

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...

tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock cont ...

, conglomerate, and

rhyolite Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained groundmass. The mineral ...

, while the Showchang Formation is dominantly sandstone and

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...

. The types of plants present in the C Member and the Showchang Formation (relatively abundant

fern A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes except t ...

s and

Bennettitales Bennettitales (also known as cycadeoids) is an extinct order of seed plants that first appeared in the Permian period and became extinct in most areas toward the end of the Cretaceous. Bennettitales are among the most common Mesozoic seed plants ...

, rare members of the

Ginkgoaceae The Ginkgoaceae is a family of gymnosperms which appeared during the Mesozoic Era, of which the only extant representative is ''Ginkgo biloba'', which is for this reason sometimes regarded as a living fossil A living fossil is an extant tax ...

) and characteristics of the plants, such as leaf form and cuticle thickness, indicate a relatively hot and dry climate. The two rock units have fossil assemblages including plants,

charophytes Charophyta () is a group of freshwater green algae, called charophytes (), sometimes treated as a phylum, division, yet also as a superdivision or an unranked clade. The terrestrial plants, the Embryophyta emerged within Charophyta, possibly fro ...

bivalves Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...

ostracod Ostracods, or ostracodes, are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 70,000 species (only 13,000 of which are extant) have been identified, grouped into several orders. They are small crustaceans, typic ...

conchostracans Clam shrimp are a group of bivalved branchiopod crustaceans that resemble the unrelated Bivalvia, bivalved molluscs. They are extant and also known from the fossil record, from at least the Devonian period and perhaps before. They were originally ...

, and insects. While other genera from the family

Palaemonidae Palaemonidae is a family of shrimp in the order Decapoda. Many species are carnivores that eat small invertebrates, and can be found in any aquatic habitat except the deep sea. One significant genus is ''Macrobrachium'', which contains commerc ...

are known from the

Aptian The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous Epoch or Series and encompasses the time from 121.4 ± 1.0 Ma to 113.0 ± 1.0 Ma (million years ago), a ...

age in the lower Cretaceous period, ''Yongjiacaris'' represents the first member described from the Barremian age. It measured from in length.

References

{{Taxonbar, from=Q8055017 Palaemonoidea Prehistoric arthropod genera Monotypic decapod genera Early Cretaceous crustaceans Fossils of China Early Cretaceous arthropods of Asia Cretaceous China Barremian genera Fossil taxa described in 2002