A prehistoric fish found off New Zealand and southern Australia evolves even slower than the coelacanth, a famous "living fossil" whose DNA has barely changed over hundreds of millions of years, scientists said Wednesday.
The genome of the elephant shark "is evolving significantly slower than other vertebrates, including the coelacanth," they reported in the journal Nature.
Known as Callorhinchus milii, the elephant shark gets its moniker from a trunklike snout with which it rummages for crustaceans on the ocean floor at depths of around 200 meters.
Despite its name, the creature is not a shark. Strictly speaking, it is a chimaera, one of a small group of fishes that diverged from sharks, rays and skates 420 million years ago. Both groups have skeletons made of cartilage. They split from bony vertebrates 450 million years ago.
Comparing the genome of the elephant shark with those of other vertebrates, the study found that the genetic code of C. milii is extremely compact.
Its genome, they found, has evolved even less than that of the coelacanth — a rare fish found off South Africa that is such a success in its habitat niche that it has hardly had to change over nearly 400 million years.
"We now have the genetic blueprint of a species that is considered a critical outlier for understanding the evolution and diversity of bony vertebrates, including humans," said Wesley Warren, an associate professor of genetics at the Washington University School of Medicine in St. Louis, Missouri.
The genome could hold insights into how bones are formed, which could help the fight against the bone disease osteoporosis.
More secrets may lie in the elephant shark's simple but robust immune system.
Elephant sharks grow to around 120 cm in length. The fish is occasionally netted as by-catch by commercial trawlers but is not endangered.