An expedition in northwest Peru turned up four new mammal species, including this amphibious mouse. Ronald Diaz/Conservation International When scientists embarked on a biological survey where the rugged Andes mountains meet the dense Amazonian rainforests in northwest Peru, they didnt have high hopes of discovering much biodiversity. Most of their study sites, after all, are located near heavily populated areas where deforestation, agricultural expansion and illegal hunting and fishing have threatened local ecosystems.To their surprise and delight, the scientists encountered an ecological richness that far exceeded their expectations. By the end of their 38-day expedition through the Alto Mayo Landscape, theyd uncovered 27 species new to science, including four mammals, among them an extremely rare amphibious mouse with webbed feet that thrives in swampy areas dominated by palm trees.Discovering four new mammals in any expedition is surprising finding them in a region with significant human populations is extraordinary, Trond Larsen, the leader of the expedition, said in a statement. This is a vibrant, dynamic mosaic of ecosystems, both natural and anthropogenic, that we must maintain and restore if we hope to protect the species found there.The mouse belongs to a group of semi-aquatic rodents that have been observed by scientists only a handful of times. However, this little swimmer represents just one of many thrilling finds made during the Rapid Assessment Program expedition sponsored by ecological nonprofit Conservation International, which released the results on Friday. The program, as its name suggests, sends experts on relatively short expeditions to critically important field sites worldwide to deepen understanding the overlap of biodiversity, healthy ecosystems and human societies.Scientists surveying Peru's Alto Mayo Landscape called this "blob headed" fish a shocking discovery ... [+] due to its unusual look.Robinson Olivera/Conservation InternationalMORE FOR YOUOther standout discoveries included a strange type of bristlemouth armored catfish with an enlarged blob-like head that serves an as-yet unknown purpose. The fish specialists on the team had never seen such a creature before, though Indigenous Awajn people who accompanied them on the journey had.Overall, the team of 13 scientists and seven locals recorded more than 2,000 species, from mammals to birds to reptiles, amphibians, insects and plants, using methods like camera traps, bioacoustic sensors and DNA collected from water. The International Union for the Conservation of Nature considers 49 of those species to be at risk of extinction.In addition to the swimming mouse and the bizarre blob-headed fish, other newly described species include a narrow-mouthed frog, a tropical climbing salamander spotted in a unique white-sand forest, 12 butterflies and two beetles. More species may be declared new to science pending further study, Conservation International says.Scientists spotted an abundant number of this new species of salamander, but only within a small ... [+] patch of unique white sand forest.Trond Larsen/Conservation InternationalThe organization, which is headquartered in Arlington County, Virginia, says the data collected during the Rapid Assessment Program expedition will help it develop a new conservation corridor linking two existing protected areas: the Alto Mayo Protection Forest and the Cordillera Escalera Regional Conservation Area. The nonprofit is now working with the local government and indigenous communities to identify areas that should be prioritized for protection and restoration.The Alto Mayo Landscape covers an area of about 1.9 million acres and includes a broad range of habitats and ecosystems. While past research in the region has concentrated on the protected forest in the northwest and other safeguarded areas, this survey set out to its, a largely unstudied area.We found that areas closer to cities and towns still support incredibly high biodiversity, including species found nowhere else, Larsen said.Members of indigenous Awajn communities helped the scientists with their survey, throwing cast nets ... [+] to capture fish for example.Trond Larsen/Conservation International