Species Yet to Be Discovered Are More Threatened and Have Smaller Ranges

ABSTRACT Aim To assess whether newly described species are more likely to be threatened and have smaller ranges than known species. Location Global. Methods In this study, we focus on the timing of species acceptance. We compare two global taxonomic assessments of birds, mammals and amphibians conducted approximately 10 years apart. Our approach allows us to isolate the most recently accepted species, a methodological improvement from earlier studies that depended on the recency of authority year to address similar questions. Instead, we categorised all currently accepted species into four groups: (1) Discovered species; (2) Raised species; (3) Restricted species; and (4) Identical species, with category 1 representing de novo discovered species between the taxonomic assessments, category 4 representing unchanged species, and categories 2 and 3 representing changes in taxonomic treatment of known populations. Results We find that species accepted earlier tend to be widespread and less threatened, while more recently accepted species often have smaller ranges and face a higher risk of extinction. We also find that taxonomic splits typically leave the original name with a widespread species, while newly split species tend to be range‐restricted and more likely to be assessed as threatened. Main Conclusions Our results suggest that many species not yet formally recognised may already be at risk of extinction. This highlights the urgent need for more fieldwork in understudied areas to help prevent extinctions before new species are formally described.