When I think of zoo animals, elephants lions, tigers and bears come to mind. Those magnificent animals undoubtedly are some of the most popular with zoo visitors.

A closeup of the naked mole rat. While it probably won't win any beauty contests, the small mammal is a heary survivor.

But when it comes to animal care, all creatures great and small get annual exams at the Pittsburgh Zoo & PPG Aquarium. On a recent day, I was fortunate to be invited into the zoo's veterinary exam room, which the general public never gets to see. Dr. Priscilla Joyner was doing check ups on naked mole rats.

"Are they generally clothed?" asked my co-worker and husband, Michael A. Fuoco, when we compared assignments for the day.

"No they're always naked," I explained.

"Naked" is a bit of a misnomer, for none of the zoo animals wear clothes. Hairless would be a better way to describe these creatures, who are actually neither moles nor rats. The tiny mammals are more closely related to guinea pigs, porcupines and chinchillas.

They're about three inches long and weigh 1 to 2 ounces. Their hairless pink and grey skin is wrinkled. Their eyes are tiny and squinty. In short, they are not the cutest animals in the zoo, but they are interesting. They live in the Discovery Building in Kids Kingdom.

Four naked mole rats traveled to the exam room in a plastic picnic cooler. At the bottom of the cooler were heat packs to keep them warm during their brief journey. Inside the picnic cooler each naked mole rat snuggled inside his or her own cardboard tube -- recycled from rolls of toilet paper or paper towels. .....

"They like the tubes because they are like the burrows" they live in, Dr. Joyner said.

She gently handled the animals, one at a time. She used a small pediatric stethoscope to check their hearts and a tiny scale to get their weight in grams. This was no small feat, for the animals wiggle and squirm. Zoo animals are not pets, and the handling of zoo animals is kept to a minimum, such as when they need veterinary care or checkups.

Dr. Joyner was looking for weight gain or loss and for any injuries or skin problems.

She checked their front teeth -- which grow continuously -- to make sure they had not grown too long. In their native habitat in sub-Sahara portions of Africa, naked mole rats use their teeth to dig burrows in the dirt. Because their zoo "burrows" are plastic tubes, naked mole rats have to have their teeth trimmed, on occasion. But not at this checkup.

The four members of this colony were born in 1995, which makes them really old, for the life span of this mammal is thought to be 10 to 12 years.

It's hard to say how long they would live in the wild, for they are very low on the food chain. They spend virtually their entire lives in underground burrows, where their main enemies/predators are snakes. In the wild, naked mole rats eat plants, roots and tubers. At the zoo they eat sweet potatoes, lettuce, apples, animal biscuits and white potatoes, cut into tiny pieces. They receive all the fluids they need from the foods they eat.

Because of their venerable age, these four "rats" are semiretired, and don't live on exhibit in the Kid's Kingdom. They're used for occasional education programs. The Pittsburgh Zoo has 23 naked mole rats, and there are generally nine or 10 on exhibit in the Discovery Building.

Zoo veterinarians are special, in my book, because they deal with so many kinds of animals. I had to ask Dr. Joyner if she had ever handled, studied or treated naked mole rats in veterinary school at the University of Glasgow in Scotland.

"Actually, no," she said with a chuckle.

And as an interesting aside, she said scientists did not discover naked mole rats until the 1970s.

All four naked mole rats passed their exams with flying colors.

The smallest zoo animals were packed into their cooler and Dr. Joyner left the exam room to make a house call for the zoo's largest animals, the elephants.