At the heart of the Greater Yellowstone ecosystem is Yellowstone National Park and its nearly 3,500 square miles of forests, canyons, rivers and steaming geothermal areas. Equally impressive are the hundreds of animals that make their home here.

However, keep in mind that this is not a petting zoo. Get too close and wildlife can be very dangerous. The National Park Service recommends staying at least 100 yards from bears and wolves at all times, and at least 25 yards from all other wildlife.

Here you can see some of the rarest, most beautiful, and most exciting animals in Yellowstone.

1. Grizzly Bear

Distinctive features: Raised shoulders, brown fur, round ears

Where to View: The northeastern part of the park, such as the meadows and hillsides of Lamar Valley (pictured), or Hayden Valley Lake north of Yellowstone in the center of the park, especially when trout spawn in late spring.

When to watch: Spring, when animals emerge from hibernation. Or fall, when they're busy fattening up for a winter nap.

Chances of sighting: Not much, unless you're in a remote area.

2. Moose

Distinguishing features: On males, broad antler stand can grow to 6 feet wide; fleshy dewlap hangs like a bell under neck

Where to See: Pond edges and wet, lush valley floors, where moose feed on willows and aquatic plants. Or you can try Willow Park Wetlands (driving south of Mammoth Hot Springs on Grand Loop Road in the northwest corner of the park) or Yellowstone Lake and Hayden Valley in the center of the park.

When to see: Year round - but antlers are most at their peak during their summer and early fall

Sighting Chance: Moderate

3. Bighorn Sheep

Distinguishing Features: Stout, taupe body with white rump; males are curled horns, females are square

Where to View: The best option is to climb Mount Washburn (Chittenden Rd. parking lot, Dunraven Pass Trailhead near the Grand Canyon in north central Yellowstone). Or among the petrified trees at Specimen Ridge (entered from the Yellowstone River picnic area near the North Tower Roosevelt area).

When to see: Year-round, but during winter, animals tend to stop at lower elevations near the Yellowstone, Lamar, and Gardner rivers

Sighting Opportunities: Fair, due to remote animal habitat and relatively small population in the park.

4. Wolf

Distinguishing features: Dog-like but huge (about 3 feet at the shoulder), with rounded ears and long legs; coyotes are smaller, with thinner legs and pointed ears

Where to View: Lamar Valley, northeast of the park, where gray wolves are like paparazzi monitoring wildlife with binoculars and scopes.

When to View: Year-round; dawn and dusk are the most active times of the day for wolves.

Sighting chance: Very small for the average tourist. Although the wolf population has boomed since its reintroduction to Yellowstone in 1995, there are still fewer than 100 in the entire park.

5. Bison Bison

Distinguishing features: Large, furry head and burly body, seemingly docile, they will attack if approached.

Viewing Locations: Central Hayden Valley, Swamp Pelican Valley near East Entrance Road, Madison River Area near West Entrance, The geyser area near Old Faithful and the Fire Hole River, and anywhere else there is grass to chew on and ponds to roll in.

Viewing time: all year round

Sighting opportunities: Many; bison is one of the most common large mammals in Yellowstone.

6. Elk

Distinguishing features: Large antlers on males (which shed antlers every spring); taupe body, chestnut head, shaggy mane, short tail, and tan patches on the rump.

Where to View: Throughout the park; sightings are especially common near the north entrance to the Mammoth Hot Springs area, where elk often rest on the plaza lawn near Yellowstone and the Mammoth Springs Hotel.

When to see: Year-round, but the summer herds are the largest (up to 20,000)

Sighting Chances: Almost guaranteed - Elk are the most common large animals in the park

7. Pronghorn

Distinguishing Features: Short black horns, tan and white body, black accent stripes

Where to View: Lamar Valley in the northeast, near the North Entrance of Yellowstone National Park (in Gardiner, Montana), where pronghorns often graze, pictured above (that's Electric Peak in the background)

When to see: Year-round; however, in winter, pronghorns tend to head toward the park's far north

Sighting chance: Great, but pronghorns can be difficult to photograph - they're timid and can run away at 45 mph