Yongjiacaris
Extinct freshwater shrimp from the Early Cretaceous of China.
Yongjiacaris is an extinct shrimp genus containing a single species, *Yongjiacaris zhejiangensis*. It is only the second known example of a freshwater caridean shrimp from the Mesozoic era. The genus name comes from Yongjia County in China’s Zhejiang Province, and the species name refers to the province itself. Alessandro Garassino, Shen Yanbin, Frederick R. Schram, and Rod S. Taylor formally described it in 2002, based on 138 specimens from two locations in southeastern China: the C Member of the Moshishan Formation in Yongjia County, and the Showchang Formation near Jiande. Both rock units date to the Barremian stage of the Early Cretaceous, with volcanic rocks in the C Member dated to 120 million years old and those in the Showchang Formation to 118 million years ago. The C Member is a mix of sandstone, shale, tuff, conglomerate, and rhyolite, while the Showchang Formation consists mainly of sandstone and mudstone. Plant fossils from both units—abundant ferns and Bennettitales, with rare Ginkgoaceae—along with leaf shapes and cuticle thickness, point to a hot, dry climate. These formations also contain remains of plants, charophytes, bivalves, ostracods, conchostracans, and insects. Although other Palaemonidae shrimp are known from the Aptian stage of the Early Cretaceous, Yongjiacaris is the first from the Barremian. Adults measured between 1.5 and 2 centimeters (0.6 to 0.8 inches) in length.
Quick Facts
- Genus
- Yongjiacaris
- Species
- zhejiangensis
Facts from the source article.
Lore & Background
Yongjiacaris was formally described in 2002 by Alessandro Garassino, Shen Yanbin, Frederick R. Schram, and Rod S. Taylor. The genus name refers to Yongjia County in Zhejiang Province, China, while the species name Y. zhejiangensis is derived from the province name. 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, both in southeastern China. These two correlative rock units date to the Barremian age of the Early Cretaceous; volcanic rocks in the C Member are dated to 120 million years old, and volcanic rocks in the Showchang Formation are dated to 118 million years ago. The C Member is a heterogeneous rock unit including sandstone, shale, tuff, conglomerate, and rhyolite, while the Showchang Formation is dominantly sandstone and mudstone. The types of plants present in both units (relatively abundant ferns and Bennettitales, rare members of the Ginkgoaceae) and characteristics such as leaf form and cuticle thickness indicate a relatively hot and dry climate. The two rock units have fossil assemblages including plants, charophytes, bivalves, ostracods, conchostracans, and insects.
Reader's Guide
Yongjiacaris is notable as the second report of freshwater caridean shrimp from the Mesozoic and the first member of the family Palaemonidae described from the Barremian age, while other genera from the family are known from the Aptian age. Its discovery in two correlative rock units in southeastern China provides a snapshot of Early Cretaceous freshwater environments. The associated plant fossils indicate a relatively hot and dry climate, and the diverse fossil assemblages—including plants, charophytes, bivalves, ostracods, conchostracans, and insects—help contextualize the ecosystem in which Yongjiacaris lived. The species measured only 1.5 to 2 centimetres in length, making it a small shrimp. Its formal description in 2002 by an international team of paleontologists added to the understanding of Mesozoic freshwater shrimp diversity and the geographic range of the family Palaemonidae during the Early Cretaceous.
Frequently Asked Questions
What is Yongjiacaris?
Yongjiacaris is an extinct freshwater shrimp genus that includes just one known species, *Yongjiacaris zhejiangensis*. It inhabited inland waters during the Barremian stage of the Early Cretaceous, roughly 118 to 120 million years ago, in what is now southeastern China.
What made Yongjiacaris so rare in the fossil record?
It is only the second confirmed freshwater caridean shrimp ever identified from the entire Mesozoic, which makes it a vanishingly small sample of that era's inland aquatic life. The animal itself was tiny, measuring just 1.5 to 2 centimetres, yet its taxonomic placement gave it outsized importance for reconstructing shrimp biogeography.
Where and by whom was Yongjiacaris formally described?
The 138 type specimens came from two Early Cretaceous rock units in Zhejiang Province: the C Member of the Moshishan Formation in Yongjia County and the Showchang Formation near Jiande. Alessandro Garassino, Shen Yanbin, Frederick R. Schram, and Rod S. Taylor published the formal description in 2002.
Why does Yongjiacaris matter to shrimp researchers?
Because so few Mesozoic freshwater carideans are known, every new find like this one sharpens our picture of when and how shrimp lineages moved out of marine settings into rivers and lakes. The name also encodes its provenance: the genus honours Yongjia County, and the species epithet points to Zhejiang Province itself.
What happened to Yongjiacaris in the end?
The genus is fully extinct, with no living descendants recognised in today's fauna. Its last trace in the rock record sits in Barremian-age volcanic deposits, meaning it vanished from the fossil record around 118 million years ago, long before the modern shrimp radiation took off.
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