ABC News' Katie Kindelan and Candace Smith report:

A giant sea turtle described as "like a swimming dinosaur" is clinging to life at the New England Aquarium after it was rescued from a mud flat near the tip of Cape Cod.

The 7-foot-long, 655-pound black male leatherback turtle, an endangered species, was found late Wednesday night on a mud flat in Pamet Harbor, near the town of Truro, Mass., by staff from a local Audubon sanctuary.

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Because of darkness and the remote location, the staff had to leave the turtle until Thursday morning. Then they had to rely on a team of volunteers and a transport cart normally used to carry stranded dolphins to hoist the turtle onto a vehicle to take it to the Aquarium's marine animal care center.

Aquarium staff are now working overtime to save the turtle, only the fifth of its kind in 40 years to have been found stranded and alive on a Massachusetts beach.

"We are crossing our fingers and will do everything we can do to keep it alive," the Aquarium's Tony LaCasse told ABCNews.com.

"The feeling is to view a live leatherback up close is such a rare opportunity," he said. "The staff are keen to work with such an animal."

LaCasse described the turtle as "near death" when he arrived at the aquarium. One of its massive flippers had been partly severed, likely the result of some sort of predatory attack or a run-in with a boat, according to LaCasse.

The straight line of damaged tissue on the flipper points to a possible entanglement in a vertical line in the water, perhaps from a lobster pot or a boat mooring. Nearly 20 leatherbacks have died in New England waters this season from such accidents, according to the aquarium.

The injury to the turtle's left flipper affected its ability to forage for food and could have led to an infection. Biologists are now treating the turtle with drugs for dehydration, trauma and shock.

A leatherback rescue is so rare because the animals are open-ocean animals and cannot be kept in captivity. Even at 655 pounds, this one is actually skinny in comparison to its fellow leatherbacks which typically weigh around 1,000 pounds, according to LaCasse.

Doctors treating the turtle have not been able to confirm its age but estimate it is at least 25 to 30 years old.

Leatherbacks flock to Cape Cod and surrounding islands each June feed on the jellyfish that are abundant in the waters. They migrate south for the winter beginning this month and into October, according to the aquarium.

Officials say though they hope for the best, the leatherback's chance for a full recovery is unclear, because in order to get stranded on the mud flat where it was found it had to be critically ill.