Quick, what's the largest land mammal ever? If you guessed the elephant or woolly mammoth you're wrong. If you guessed the whale, read the question again. Land mammal. If you guessed Indricotherium, and who wouldn't guess that, you would be right.

What? You never heard of the Indricotherium. That's hard to believe.

The Indricotherium looked like an extra-large version of the modern rhinoceros, and it roamed around Asia and Eurasia 25 million to 55 million years ago, more or less. It could grow to up to 18 feet tall and 26 feet long, more or less.

If you want to see one today, you need only go to the Rochester Museum and Science Center. It's the first exhibit you will see as part of the museum's four-month exhibition, "Extreme Mammals."

The exhibition, organized by the American Museum of Natural History in New York, began two days before Christmas and runs until tax day, April 15. The California Academy of Sciences in San Francisco, the Canadian Museum of Nature in Ottawa and the Cleveland Museum of Natural History all contributed to the traveling exhibition. RMSC added a few items from its own collection for the showing in Rochester.

The Indricotherium is located on the first floor of the museum, near the main entrance. Most of the exhibition is on the third floor.

Up there you'll see a pangolin, an anteater that grows up to 3 feet long and lives in East Africa and Southern India.

And the skeleton of a kinkajou, a relative of the raccoon and found in South and Central America. And the shell of a Glyptodont big enough for children to crawl through. It became extinct at the end of the last Ice Age; its closest living descendant is the armadillo. It existed mostly in Western South America.

There are more than 100 items in the exhibition, some tiny, like a bumblebee bat the size of a dime, and some giant, like the blue whale, at 200 tons the largest animal, mammal or otherwise, ever.

Much of the explanatory signage focuses on extinction. One sign notes that in the last 500 years, more than 75 mammal species have died out. One in four mammal species existing today is "threatened with extinction."

Sometimes humans cause the extinction. Sometimes humans save a species from extinction. In the 1800s, one exhibit explains, the American bison was killed by the millions and by 1890 only about 1,000 remained on the Great Plains. In the early 1900s, however, "captured herds" were reintroduced to the plains and special preserves were set aside to protect them. It was the first-ever mammal reintroduction, and today a half-million bison exist on ranches and another 20,000 roam free in places like Yellowstone National Park.

Part of the exhibition is devoted to explaining exactly what a mammal is. The key is that mammals nurse their young with milk, but other characteristics of mammals include having three middle ear bones, a diaphragm for breathing and a palate that allows the animal to breathe and eat at the same time.

You would be wrong if you assume that all mammals reproduce by live birth. Of the 5,400 mammal species alive today, about 300 don't give live birth. The platypus, for example, lays eggs.

Humans make it into the exhibition because they (we) are extreme because of their (our) large brains, compared with body size, and the ability to walk upright on two legs. Most other mammals that get around on two legs don't walk, they hop, like kangaroos.

As usually happens with special exhibits, the museum gift shop is selling theme-related items. Caution: The prices may seem extreme -- about $25 for a T-shirt, twice that for a sweat shirt. In the basement, there's a restaurant serving burgers, fries and some chicken dishes. Nothing extreme on the menu.

Admission to the special exhibit includes admission to the full museum. About half of the second floor is devoted to Native American cultures in North and South America. Also on that floor is a sizable display of exhibits depicting Rochester's sizable role in the pre-Civil War Underground Railroad and early black settlers in the area.

On the first floor is an Adventure Zone, aimed at younger museum visitors. It includes a wall climb, a ride in a spaceship and other interactive things that will appeal mostly to preteens. On another part of the first floor are a walk-through glacier and exhibits showing what the Rochester area was like during the last Ice Age.

In a separate building on the museum grounds is the Strasenburgh Planetarium. There is a separate admission charge for the planetarium, although combined admission tickets for both the museum and planetarium are available.

> If you go:

Take the Thruway (I-90) to I-490 (at the LeRoy exit), go east through downtown Rochester, exit at Culver Road, go north on Culver, turn left on East Avenue, go about one mile. The museum will be on your left. There is lots of free parking on museum grounds.

Admission for "Extreme Mammals" is $15; $14 for seniors and college students; $13 for children 3 to 18. Admission for children under 3 is $3. Admission to the planetarium ranges from $7 to $10. Combined, reduced price tickets are available.

Admission to the special exhibit includes admission to the entire museum.