Watch: Genetically Modified Dire Wolves Double In Size In 6 Months

The genetically modified "dire wolf" pups are now six months old and have doubled in size, as per a new video by a Texas startup, Colossal Biosciences. Romulus and Remus weigh around 40.8 kgs, and Khaleesi weighs approximately 15.9 kgs. The company said that the dire wolves are growing rapidly.

In April, Colossal Biosciences gained attention worldwide after they released footage of canines they claimed were dire wolves, a species that vanished more than 12,000 years ago. The wolves were born of both grey wolf and extinct dire wolf DNA.

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Watch the video here:

The pups underwent 20 genetic edits across 14 genes to replicate the physical traits of their extinct ancestors, making them nearly 20% heavier than average grey wolves. They exhibit classic dire wolf traits, including thick white fur, broad heads and hefty builds.

"So today, Romulus and Remus, at a little more than six months old, weigh a little more than 90 pounds [40.8 kilograms], which is about 20 percent larger than a standard gray wolf," Matt James, Colossal's Chief Animal Officer, said in the video.

"So, we can really tell that the dire wolf genes are kicking in, and we're getting these nice large wolves that are much more representative of what we saw in the ancient specimens."

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James said Khaleesi is "a little smaller, a little younger [...] She weighs about 35 pounds [15.9 kilograms], but she's still tracking about 10, 15 percent larger than what we've seen in gray wolves."

Colossal Biosciences aims to use genetic modification technology to aid in conservation efforts, such as saving the critically endangered red wolf and northern white rhino. But the project has sparked debate, with some critics questioning the term "de-extinction" and the ethics of genetic modification. The process also faced criticism that these wolves are not exactly dire wolves, but just pose some similarities.

"To truly de-extinct something, you would have to clone it," Associate Professor Nic Rawlence of the Otago Palaeogenetics Lab at the University of Otago said while speaking to the New Zealand Science Media Centre. "The problem is we can't clone extinct animals because the DNA is not well enough preserved."