Brought to you by the “Mythic Creatures” traveling exhibition (seen at the Denver Museum of Nature and Science), it’s an odd concoction called a Feejee Mermaid:
Back in the days of traveling carnivals, freak shows were all the rage, and a variety of odd creations was put together in order to extract money from people. P. T. Barnum was notorious for these sideshow attractions, and was the first to exhibit a “Feejee Mermaid” in 1842 (although such creations were apparently common things in southeast Asia at the time). It was built from the head of a monkey and tail of a fish (with various other supporting elements), but billed as being a mummified mermaid caught in the “Feejee” Islands.
This particular object was re-discovered in the Peabody Museum of Archaeology and Ethnology in 1973, and it dates to the mid- to late-19th century, but is of unknown origin.