Feels like the animal kingdom opposite of the panda--adults weigh upwards of 300 pounds, but baby panda birth weights are just under 1/3 of a pound.
A male Red Kangaroo can weigh upwards of 92kg and stand around the 1.8m (6 feet) mark. Some are over two metres tall. I’ve seen a couple giants, well over two metres and biceps as big as my thigh. Anyways, kangaroo sucklings typically way less than one gram.
Although they are special case of mammal.
Kangaroos are also comically dumb.