The beginning of our discussion of the Premaxillary Bone consisted of reading about Goethe's suggestion that humans do in fact have the bone. Since seemingly all other animals had the bone, Goethe insisted, in accordance with his theory of universality in nature, that humans must have it as well. Many other scientists of the time disagreed with Goethe's assertion, but as it turns out, Goethe was actually right.
Given that humans do have the bone – although it's seemingly difficult/impossible to distinguish – I was most interested in the Premaxillary Bones of monkeys. Conveniently, I was sitting in front of two Macaques, a baby from 1925, and an adult from 1873. Not to my surprise, I found it hard to distinguish the Premaxillary Bone from the Maxillary Bone in both Macaques, but I noticed a significantly larger split in the roof of the mouth of the baby Macaque. If my estimation of where the Premaxillary Bone ends and the Maxillary Bone begins is accurate, it appears that the Premax was 1 cm in the baby Macaque and 1.5-2 cm in the adult Macaque.
I was determined to see a more blatant Premax following the Macaques, and the one I found to be the easiest to see was in the Harbor Porpoise, which appeared to have a defined Premaxillary Bone of about 18 cm long. At this point I figured that whether an animal had the Premax or not depended on whether or not it had teeth (We had learned that the anteater, which does not have teeth, does not have the Premaxillary Bone). I then saw, however, that the Humpback Whale had a significant Premax, but also does not have teeth, so based on the lab and what we have learned about the Premax thus far, I don't think that there is a definite determiner in whether or not an animal has the Premaxillary Bone.
Humpback Whale Premaxilla