Researchers in Scotland have found species of dolphins with classic markers of Alzheimer's disease in their brains.
Alzheimer's is a neurodegenerative disease which causes brain cell connections and brain cells to degenerate and die, destroying memory and other mental functions.
The disease had been thought to be unique to humans, although there are other animals that develop similar aspects of Alzheimer-like pathology.
Toothed whales (which includes orcas, dolphins and other whales with teeth) share traits with humans that, according to the researchers' study, suggests they are susceptible to Alzheimer's disease.
Researchers studied the brains of 22 stranded toothed whales, which included five different species.
In the brains of four of the animals, which were all different species, hallmark signs of Alzheimer's disease were found.
Three of those animals in particular, which were all of old age, had a number of dementia-related pathologies in their brains.
The three with the most hallmark signs of Alzheimer's consisted of a long-finned pilot whale, a white-beaked dolphin and a bottlenose dolphin.
The researchers said the findings might explain what caused the unexplained stranding of some of the animals.
Tara Spires-Jones, from the University of Edinburgh, explained in a statement how fascinated they were to see brain changes in aged dolphins which were similar to those in ageing humans and those with Alzheimer's disease.
"Whether these pathological changes contribute to these animals stranding is an interesting and important question for future work," she said.
Mark Dagleish, from the University of Glasgow, said more research was needed to better understand what was happening to the animals.
