The fastest land animal on the North American continent, the pronghorn antelope is believed to have evolved its great speed to escape the now-extinct American cheetah. However, the construction of fences, roads, and railroads, and the encroachment of mesquite, tarbush, creosote and other invasive brush species, has hemmed in its fast runs and long migrations, contributing to steep declines in its Texas population in the first decade of the 21st century.