Well, that´s absolutely incorrect. The term “Megafauna” is neither any direct connection to animals of the Ice Age nor is it restricted to mammals. I includes in general just any large animal in an ecosystem which is “big”, no matter if it is a mammal, a bird, a reptile or another animal. Animals don´t have to be giant to be part of the megafauna, it includes even comparably small species, depending on the definition of the term. An African elephant is part of the megafauna, as well as an ostrich, an alligator or a giant tortoise from the Seychelles. The evolution of large to giant body size has also no direct connection to the Ice Age. In some cases the Ice Age variants of some species were indeed larger than those in more southern regions, but in other cases, for example the wooly mammoth, it was the opposite. Most of the giant animals which are in general associated with the Ice Age, were already of similar size when the last Ice Age had not even started.