Meriwether Lewis and William Clark are known as trailblazing explorers of the American West, not pioneering scientists. But during their 8,000-mile journey from Missouri to the Pacific Ocean and back between 1804-1806, Lewis and Clark discovered 122 animal species, including iconic American animals like the grizzly bear, coyote, prairie dog and bighorn sheep.

When President Thomas Jefferson first charged his assistant Lewis with the mission of finding a passable river route to the Pacific, he included an assignment to “[observe] the animals of the country generally, & especially those not known in the U.S. the remains and accounts of any which may [be] deemed rare or extinct.”

Jefferson was especially enticed by fossils recovered of mastodons and a type of giant land sloth he dubbed the megalonyx (“big claw”). Unsure of what species the men would encounter in the wilds beyond Missouri, Lewis took crash courses in botany, zoology and specimen collection and preservation from the best scientific minds in Philadelphia.

One of the most remarkable periods of the expedition (zoologically speaking) occurred between September 4 and September 24, 1804 during a 263-mile trek from the Niobrara River in Nebraska to the Teton River in modern-day Pierre, South Dakota. In a span of just over two weeks, Lewis and Clark encountered four classic Western animals for the first time: the prairie dog, pronghorn, coyote and the jack rabbit.

In his September 7, 1804 journal entry, Clark describes a “Village of Small animals” discovered in Boyd County, Nebraska. The men found a sloping hillside containing “great numbers of holes on top of which these little animals Set erect make a Whistling noise and whin alarmed Step into their hole.”

Anxious to capture a live specimen, the men tried digging down into the burrows, but after reaching a depth of six feet, they switched tactics and attempted to flush the critters out.

“They spent an entire day hauling buckets of water up from the Missouri River and dumping them down the holes,” says Jay Buckley, a history professor at Brigham Young University and author of several books on Lewis and Clark, and Western exploration. “Eventually they flushed one out, put it in a cage and sent it to Jefferson. Incredibly, it made the trip alive.

There was some disagreement over what to name the curious creatures. Lewis called them “barking squirrels” while Clark referred to them as “ground rats” or “burrowing squirrels.” It was Sergeant John Ordway, an Army volunteer, who first called them prairie dogs.

On September 14, 1804, near Chamberlain, South Dakota, one of the men killed a large white hare whose long, donkey-like ears inspired the name “jackass rabbit,” later shortened to jack rabbit. In his journal, Lewis marveled at the jack rabbit’s flexible ears, which the animal could “dilate and throw… forward, or contract and fold... back at pleasure.” He observed the jack rabbit could leap 18 to 20 feet in a single bound.

On the very same day near the mouth of Ball Creek in South Dakota, Clark shot a “Buck Goat” of an intriguing species of deer. In his journal, Lewis described the striking animal as having forked horns or “prongs” and its “brains of the back of his head.” Consulting his eight-volume A New and Complete Dictionary of Arts and Sciences, published in 1764 by W. Owen, Lewis concluded that “he is more like the Antilope or Gazelle of Africa than any other Species of Goat.”

In fact, the pronghorn is neither goat, antelope or deer, and belongs to its own family, Antilocapridae. The pronghorn is also the fastest four-legged species in North America, reaching top sprinting speeds of 60 mph. Lewis and Clark stuffed two pronghorn, one male and one female, and shipped them back East to Jefferson.

The mournful wails and yelps of coyotes followed Lewis and Clark to the Pacific and back, but the team shot and identified the first of this new species on September 18, 1804 near Chamberlain, South Dakota, and Clark called it a “Prairie Wolff.”

“I killed a Prairie Wolff, about the size of a gray fox, bushy tail head and ears like a Wolf, Some fur burrows in the ground and barks like a Small Dog,” wrote Clark.

Not all of Lewis and Clark’s animal encounters were so calm and collected.

“One of my favorite moments is when Lewis is all alone at the Great Falls in Montana,” says Buckley. “In a 24-hour period, he’s nearly bitten by a rattlesnake, attacked by a wolverine, charged by a bison and eaten by a grizzly bear. That night, in his journal he says, ‘The entire animal kingdom has conspired against me!’”

As for grizzlies, Lewis and Clark were skeptical at first of the native Mandan and Hidatsa’s accounts of “white bears” weighing over 1,000 pounds, and the explorers scoffed at the war paint and other “supersticious rights” the Indians performed before setting out to hunt the mythical beasts.

But later, while traversing Montana, Lewis and Clark became believers. In his trademark creative spelling, Lewis described “a most tremendious looking anamal, and extreemly hard to kill notwithstanding he had five balls through his lungs and five others in various parts… and made the most tremendous roaring from the moment he was shot.”

When Lewis had his close call with a grizzly in Great Falls, he described a massive bear chasing him “open mouthed and full speed” into the river. With nowhere to run, Lewis spun around to face the grizzly armed only with his spear-headed “espontoon.” To his great relief, the animal retreated.

“So it was, and I feelt myself not a little gratifyed that he had declined the combat,” wrote Lewis.

Despite the great care taken by Lewis and Clark to collect specimens and include detailed descriptions and measurements of plants and animals in their journals, the men never achieved scientific fame in their lifetimes. After their triumphant return in 1806, Lewis planned to write a three-volume account of their expedition with an entire volume dedicated “exclusively to scientific research, and principally to the natural history of those hitherto unknown regions.”

But Lewis, overburdened in his new post as governor of Louisiana, died suddenly in 1809, and when the expedition journals were finally published in 1814, the editors left out almost all of the zoological and scientific reports. It wasn’t until 1893 that a new edition of the journals was published by naturalist Elliott Coues, who correctly credited Lewis and Clark as scientific trailblazers as well as daring American explorers.