Complex sentence: The original specimen was lost or destroyed, and by the late 19th century, all mention of the Robust redhorse had ceased; it was thought to be extinct until several unidentified fish specimens were collected from the Savannah River and Pee Dee River in 1980 and 1985.
Split into simpler sentences: The original specimen was lost or destroyed, and by the late 19th century, all mention of the Robust Redhorse had ceased. It was thought to be extinct until several unidentified fish specimens were collected from the Savannah River and Pee Dee River in 1980 and 1985.