The Pittsburgh Zoo announced today that Big Mo, a yellow-footed tortoise who was the zoo's oldest resident, died Saturday.

Big Mo's estimated age was over 70.

A necropsy showed a mass pressing against a lung. He also had been treated recently for a respiratory infection.

The tortoise was acquired by the zoo in 1972 as a wild-caught adult.

"We didn't have any birth records for him, so we made an educated estimate using his size to determine age," said Henry Kacprzyk curator of Kids Kingdoms and reptiles. "Size is indicative of age because tortoises grow throughout their entire lives," he said in a news release.

Mo weighed 86 pounds, was 29 inches long and 21 inches wide.

"Kids loved him, mainly because of his size," said Mr. Kacprzyk. "He was easy-going with staff and didn't seem to mind when visitors would continuously call his name so that he would look and they could get a picture."

Yellow-footed tortoises are named for the yellow-orange scales that appear on their front legs. They live mostly in the dense rainforests and tropical lowlands of South America. Their biggest threat is habitat destruction and though they are not classified as endangered at this time, continued habitat loss could lead to bigger population loss for the species, according to the news release.