Animals such as giant ground sloths, peccaries, and hairy, elephant-like mastodons roamed what is now Missouri. Femur bone and tusk of an American Mastodon on display at the Mastodon State Historic Site. Bones of mastodons and other now-extinct animals were first found in the early 1800s in what is now known as the Kimmswick Bone Bed. Excavations in 1839 and the early 1900s revealed a great many well-preserved bones. The area became known as one of the most extensive Pleistocene bone beds in the country and attracted archaeological and paleontological interest worldwide.
Archaeologists theorize that the area was once swampy and contained mineral springs.
Large mammals that came to the spring may have become trapped in the mud, which helped preserve their bones. Other bones may have been washed in by streams. Early American Indians also had reached present-day Missouri by at least 12,000 years ago. For a brief period at the end of the Pleistocene ice age, the lives of humans and mastodons intertwined. Bones from more than 60 mastodons reportedly were taken from the pit.