Hidden diversity: Scientists now recognize nearly 6,800 living mammal species, a 25% increase since 2005

The update draws on the Mammal Diversity Database, which compiles taxonomic and distribution information about mammals worldwide. Since 2005’s “Mammal Species of the World, Volume 3,” scientists have identified 1,579 new distinct species: 805 newly described and 774 splits of previously recognized taxa. Meanwhile, 226 species were removed or merged, resulting in a net gain of 1,353 species, roughly 65 new recognized mammals per year.

New species appear across 20 of the 27 mammal orders and 98 of 167 families, illustrating that nearly every major group of mammals, from rodents to whales, is part of this discovery surge. For example, rodents gained 595 species (a 21.7% jump), bats 410 species (27.6%), shrews and moles 166 (27.7%), and primates 161 (30.8%).

Lead researcher Nathan Upham, Assistant Professor at ASU’s School of Life Sciences, notes: “Every week, new papers come out that change what we know about mammal diversity. Sometimes it is a brand-new species to science, and sometimes it is realizing that what we thought was one species is actually two or five.”

The growth in recognized diversity is being driven by new technologies such as genomics, morphological imaging, and computational tools, along with broader global collaboration. Many new species come from mountainous and tropical regions such as Madagascar, the Andes, Indonesia, and the Philippines, where complex terrain promotes isolation and divergence.

However, the study, published in the Journal of Mammalogy, also highlights a conservation concern: about 25% of mammal species fall into the “Data Deficient” or “Not Evaluated” categories under the International Union for Conservation of Nature (IUCN) system. This means many species are poorly known even as they are newly recognized.

The findings show that our catalog of mammal biodiversity is far from complete, and that estimates of extinction risk, ecosystem roles, and conservation status may be underinformed. Better taxonomic frameworks such as the Mammal Diversity Database allow scientists, conservationists, and policymakers to “speak the same language” about species, track changes over time, and make more effective biodiversity decisions. Recognizing more species also emphasizes how much remains to be explored and protected, especially in understudied regions facing increasing pressures from logging, land conversion, and climate change.

The researchers project that at the current pace, the number of living mammal species recognized could exceed 8,000 by 2050. They call for stronger integration of taxonomic databases with conservation systems such as the IUCN Red List, NatureServe, and iNaturalist to ensure newly recognized diversity does not fall through the cracks. Greater global collaboration, especially involving scientists in biodiversity-rich but resource-constrained regions, is also key.

The research appears in the Journal of Mammalogy and is based on a comprehensive update of the Mammal Diversity Database, which aggregates taxonomic changes over nearly three centuries of scientific history.