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Elephant what??? Meet the elephant shark

The elephant shark is a relic of a bygone age, sometimes called a living fossil, a creature alive today that has changed little since it first evolved hundreds of millions of years ago. But besides its prehistoric outward appearance—including the trunklike snout from which it gets its name—the elephant shark boasts a genome that is remarkably different from the genomes of most other living vertebrates.

Elephant sharks’ DNA hasn’t changed much in the 420 million years that bony fishes have been in existence, suggests a new analysis of the animal’s genome.

Callorhinchus milii is the first cartilaginous fish to have its genome fully sequenced. At 1 billion base pairs, the elephant shark has the smallest genetic code among sharks, rays and other similar fishes. A closer look at the animal’s genome suggests that the fish do not have many bones because they lack genes that switch on calcium-binding proteins, researchers report January 8 in Nature. They think these genes evolved after the elephant shark and its relatives split off from the other fishes that would eventually develop bones.

The elephant shark was named after its trunk-like mouth

Elephant sharks also lack a major component of the immune system called helper T cells. The discovery suggests that acquired immunity evolved in two steps — not one, as previously thought.

Because the elephant shark has changed so little from its original form—it is the slowest evolving of all known vertebrates, according to the study—this species offers a rare look into the evolutionary past.

See an elephant shark swim (with great jazz music!):

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