That's not even from my link. My link is of an ancestral genus giraffe that was not as tall which consists of 5 different species.
S. africanum Churcher, 1970
S. boissieri Forsyth-Major, 1889 (type)
S. major Bohlin, 1926
S. neumayri Rodler and Weithofer, 1890
S. sinense Bohlin, 1926
The question is whether or not these prehistoric giraffes have more basal features than modern ones, such as having a shorter neck (in lay terms), and in fact, they do have shorter necks.
If prehistoric giraffes only had longer necks, that would be problematic for evolution and would arguably disprove it (if we based our understanding of the theory only in fossils), but because there are short-necked giraffes in the fossil record, this simply supports the theory.
If evolution were hypothetically true, short necked giraffes is exactly what we would expect to find, and so it is. No necked giraffes? No. Longer necked giraffes? No. Short necked giraffes? Yes.
Same with elephants. There are bigger elephants in the fossil record, such as whooly mammoths. But prior to mammoths, there were small elephants going back to paleomastodon. If no tiny elephants existed, the theory would be in trouble. But tiny prehistoric elephants exist just as expected.
South African National Parks - SANParks - Official Website - Accommodation, Activities, Prices, Reservations
Another example, turtles. What would an ancestor turtle look like? Well, maybe a turtle with a partial shell? We ought to expect this logically, and so it is with discovery of prehistoric turtles that only have half shells.
Odontochelys - Wikipedia
If we only ever found turtles with full shells, we might be in trouble. And yet, here we are with fossil turtles that only have half a shell.
But the theory goes much deeper than these simply lay-observations. Cladistics is much more detailed and paints a much more precise picture.