The supply list created at the start of the journey includes two horses. Because the expedition set out by boat, it was far more practical to buy the horses they needed along the way. One of these purchases includes the horses that Sacajawea helped negotiate from the Shoshone Nation. This reunion and negotiation has fired the imaginations of artists and has been the subject of many paintings.
In preparation for the journey Meriwether Lewis purchased a dog "... of the Newfoundland breed very active strong and docile." The dog was named Seaman and, by all accounts, proved himself to be a great asset. At the start he hunted and retrieved game. In grizzly country he patrolled the campsite to help protect the men from the bears. Along the way he suffered the privations along with the men. The last mention of Seaman is on July 15, 1806, when the men, and Seaman, were suffering from the mosquitoes at Great Falls, Montana.
The Lewis and Clark Corps of Discovery also bought dogs for food along the way. During the journey along the Columbia River, the expedition's documents show there were times of great hunger when the men bought dogs from the native peoples along the way and used them as food. Although it was recorded that in times of hunger the expedition ate their horses and these dogs, no mention is ever made that anyone ever contemplated using Seaman in this manner.
One of the stated purposes of the journey was to document the flora and fauna of the land to the west. In that the expedition was a great success, documenting more than 122 animals not previously recorded and sending back a number of specimens, including the first live prairie dog ever seen back east. Among the species newly recorded are many we now have come to associate with the western United State, including bighorn sheep, antelope, coyote, mountain goat, steelhead and cutthroat trout, prairie dogs the grizzly bears. Lewis's woodpecker, Melanerpes lewis, is named after Meriweather Lewis and Clark's nutcracker, Nacifraga columbiana, is named after William Clark. The expedition also documented 178 new and different species of plants.