ungulates, as has been said, are a highly specialized type of Mammals, and although they walked on the nails of five digits instead of only one, a vast amount of Evolution would be required to bring them even to this point, from that whence all Mammals are said to have started.
"The Old Riddle and the Newest Answer"
John Gerard
But, so far as we know, the first ungulates made their appearance upon earth quite as soon as did any other mammals from which they could possibly have sprung.
"The Old Riddle and the Newest Answer"
John Gerard
Tundras then spread over the meadow-lands and remnants of forests, whilst arctic animals replaced the large ungulates and carnivores which had wandered far away from their native southern home.
"The History of the European Fauna"
R. F. Scharff