[1] Seaman was purchased in 1803 specifically for the expedition by Captain Meriwether Lewis, while he was in Pittsburgh, Pennsylvania, awaiting completion of the boats for the voyage.

He chose a Newfoundland, whose estimated weight is 150 pounds (68 kg) and for which he paid the high price of $20 (equivalent to $407 in 2023): half a month's pay for an Army captain.

Working dogs, strong and easy to handle—Lewis describes Seaman as "docile"[2]—, he chose a Newfoundland because they do well on boats, are good swimmers, and can assist in water rescues.

"[7]: 65 During the expedition, around May 14, 1805, Captains Meriwether Lewis and William Clark performed surgery on one of Seaman's arteries in his hind leg that had been severed by a beaver bite.

[6] The final reference to Seaman in the expedition journals, recorded by Lewis on July 15, 1806, states that "[T]he musquetoes continue to infest us in such manner that we can scarcely exist... My dog even howls with the torture he experiences from them.

[12]According to the same historian, in 1814 Seaman's collar was in an Alexandria, D.C., museum and bore the inscription: Due to a transcription error in Lewis' journals, the dog was once thought to have been named Scannon.