An African pancake tortoise is recovering after an operation to remove a bladder stone the size of a small egg which could have killed her.
A team of expert veterinarians at Bristol Zoo performed an hour-long operation on Polly the pancake tortoise after discovering the bladder stone during a routine health check up.
During the procedure, vets had to cut away a hole in the bottom of Polly's shell to remove the stone, which could have killed her within weeks.
The bladder stone weighed 19g and measured 3.7cm (1.5 inches) by 3cm (1.2 inches) and Polly measures just 14cm (5.5 inches) long from head to tail.
The five-year old tortoise is now bandaged up and recovering well in the zoo's Reptile House, but will be off-show to visitors until she has fully recovered.
Sharon Redrobe, head of veterinary services, said: "We x-rayed the tortoise as part of a standard health check, and were amazed when we saw the size of the bladder stone.
Anaesthetising a tortoise is quite tricky and requires specialist training, but she is likely to have been in some discomfort so we took the decision to remove the stone as soon as possible.
"I've performed bladder stone operations on tortoises before, but never on a pancake tortoise and never with a bladder stone this big.
"Despite initial concerns that we might not be able to get the bladder stone out of the hole we made in the shell, the operation went very well and there were no complications."
African pancake tortoises are classed as a vulnerable species by the International Union for Conservation of Nature and Natural Resources (IUCN), which mean they are at high risk of facing extinction in the wild in future.
Bristol zoo manages a breeding programme for the species with other UK and European zoos.
Several pancake tortoises have been hatched successfully in Bristol Zoo's incubators.