An elephant shark’s skeleton is made up largely of cartilage, not bone. Now, researchers have found a possible explanation that could help in the development of treatments for bone diseases like osteoporosis.

By sequencing the shark’s genome, the scientists learned that it was missing several genes crucial to bone development, said Byrappa Venkatesh, a genome scientist at the Institute of Molecular and Cell Biology in Singapore who led the research. They tested the finding by removing the same genes in laboratory zebrafish; that resulted in a significant reduction in bone formation.

Image Credit... Chris Gash

The elephant shark is among about 1,000 species of cartilaginous fish, including sharks, rays, skates and chimaeras, that diverged from bony vertebrates about 450 million years ago. Some cartilaginous fish, like the dogfish, have genomes twice the size of humans’; the researchers decided to sequence the elephant shark’s genome because it was relatively small.