A related genus , Glyptotherium , first appeared in the south-west of the modern USA about 2.5 million years ago as a result of the Great American Interchange . A related genus , Glyptotherium , first appeared in the south-west of the modern USA about 2.5 million years ago as a result of the Great American Interchange , a set of migrations that occurred after North and South America were connected by the rising of the volcanic Isthmus of Panama .