A "standard" species of weasel in Algeria has evolved such bizarre physical traits that it's practically a different animal.
April 16, 2026
Original Paper
Evidence of phenotypic polymorphism in Mustela nivalis (Carnivora: Mustelidae) in Algeria
SSRN · 6576051
The Takeaway
We thought we had a handle on the "least weasel," a common carnivore found across the globe. But researchers in Algeria just discovered specimens with unique penile bones and tail lengths that don't match any other weasel on Earth. This "phenotypic polymorphism" means that even in well-known species, there are ghost variations hiding in plain sight. It’s a reminder that nature is far more weird and diverse than our field guides suggest. For regular people, it means there are still "new" types of animals to discover even in well-studied areas—if you know exactly what to look for.
From the abstract
The least weasel, Mustela nivalis, is a small, rare carnivorous mammal found in Algeria. Having encountered weasels of varying shapes and sizes, many believe that another species, besides M. nivalis, exists in Algeria and suspect the presence of the stoat, M. erminea. To fill this gap in knowledge and having observed marked but still unexplored individual variation, or phenotypic polymorphism, within this species, we examined the phenotype, morphometrics, cranial measurements, and the length and