European beaver – Castor fiber
European beaver (Castor fiber) is a species of beaver which was once widespread in Eurasia. It was hunted to near-extinction for both its fur and castoreum; and by 1900 only 1200 beavers survived in eight relict populations in Europe and Asia. Re-introduced through much of its former range, it now occurs from Great Britain to China and Mongolia, although it is absent from Italy, Portugal, the southern Balkans and the Middle East. The fur color of Eurasian beavers varies geographically. Light, chestnut-rust is the dominant colour in Belarus. In Russia, the beavers of the Sozh River basin are predominantly blackish brown, while beavers in the Voronezh Reserve are equally distributed between brown and blackish-brown.

Eurasian beavers are one of the largest living species of rodent and are the largest rodent native to Eurasia. They weigh around 11–30 kg (24–66 lb), with an average of 18 kg (40 lb). While the largest specimen confirmed on record weighed 31.7 kg (70 lb), the Smithsonian has reported that this species can exceptionally exceed 40 kg (88 lb). Typically, the head-and-body length is 80–100 cm (31–39 in) and the tail length is 25–50 cm (9.8–19.7 in).

The Eurasian beaver is recovering from near extinction, after depredation by humans for its fur and for castoreum, a secretion of its scent gland believed to have medicinal properties. The estimated population was only 1,200 by the early 20th century. In many European nations, the beaver became extinct but reintroduction and protection has led to gradual recovery to approximately 639,000 individuals by 2003. Milishnikov found in genetic studies that beaver likely survived east of the Urals from a nineteenth-century population as low of 300 animals, and that factors contributing to their survival include their ability to maintain sufficient genetic diversity to recover from a population as low as three individuals, and that beavers are monogamous and select mates that are genetically different from themselves. 83% of Eurasian beavers live in the former Soviet Union thanks to reintroductions, however the result is that beaver in Mongolia or Siberia do not appear significantly genetically different from samples from the European part of Russia, despite the great geographical distance.