He discovered the first documented remains of Tyrannosaurus during a career that made him one of the most famous fossil hunters working from the late Victorian era into the early 20th century.

Their second daughter, Alice Elizabeth, was born in 1860 in Osage County, Kansas, where the family would build a one-room cabin on top of a coal seam.

[3] As a freshman, he took a course with Samuel Wendell Williston, who then invited Brown, along with Ermine Cowles Case and Elmer S. Riggs, on a fossil collecting trip to Nebraska and South Dakota in the summer of 1894.

[5] While working in South Dakota with Williston in 1894, Brown met a crew from the American Museum of Natural History (AMNH), led by paleontologist Jacob Wortman.

[2] Brown impressed Wortman and the head curator of the AMNH's Vertebrate Paleontology Department, Henry Fairfield Osborn, with the discovery of a nearly complete Coryphodon skeleton near the Greybull River.

Brown worked a handful of years in Como Bluff, Wyoming for AMNH in the late 1890s, discovering a prominent Diplodocus specimen and introducing new jacketing and collecting procedures.

[7] He also led an expedition to the Hell Creek Formation of southeastern Montana, where, in 1902, he discovered and excavated the first documented remains of Tyrannosaurus rex.

In 1910, in one of their most significant finds, Brown's team uncovered several hind feet from a group of Albertosaurus in Dry Island Buffalo Jump Provincial Park.

In the 1990s, Dr. Phil Currie, then head of dinosaur research at the Royal Tyrrell Museum of Palaeontology in Canada, relocated the site of the bones using only an old photograph as a guide.

[10] Brown conducted his last formal field work season at the age of 83, when he returned to the Claggett Shale in Montana in 1955, where he collected a plesiosaur skeleton.

He did not recognize the significance of his find until 14 years later, when vertebrate paleontologist Edwin H. Colbert, of the AMNH, identified the fossil as a new species of primate and the earliest known anthropoid in the world.

He named the holotype Amphipithecus mogaungensis, or the "ape-like creature of Mogaung", but considerable debate remains regarding its status as a primate and the lack of fossils compounds this issue.