The animal that arrived at Hannah Huckabay’s barn this past summer had been advertised as a mule, but it didn’t look like any mule she’d ever seen. She had bought it cheaply online from a livestock auction with thoughts of reselling it or putting it up for adoption, as she does with many last-chance equines at her stables in Aurora, Colo.

It had a broom-bristle mane and a wedge-shaped head, an equine silhouette more often found in a cave painting than on a ranch. “I looked at him, with my daughters, and we thought, ‘Is he a Przewalski's?’ Or however you say it?” Ms. Huckabay later said. “But that seemed very impossible — those horses are critically endangered.”

It couldn’t be, could it? The Przewalski’s — most commonly pronounced che-VAL-ski’s — is so rare that the horse, native to Mongolia, was once extinct in the wild. Its scant bloodlines are tracked by zoos, and individual animals are part of multinational conservation efforts. These precious few horses don’t typically knock around auctions in the western United States.

“POV,” one of her daughters wrote on a TikTok video. “You accidentally rescue a purebred Przewalski.”

But the seemingly impossible had actually happened twice: Soon after, Ms. Huckabay’s daughters found a TikTok post by a woman from Utah named Kelsey Bjorklund. She had taken in an identical animal after it was given up by an auction buyer.