It is already a questionable idea to return the long-extinct dire wolf—a creature 25 percent bigger than the modern gray wolf, whose enormous teeth once slew horses and bison across the primordial American plains—to the modern world.

A genetically modified wolf juvenile, one of three successfully bred by reconstructing a genome from the ancient DNA of fossils from dire wolves that had been extinct for over 12,500 years by Colossal Biosciences,