Figure 1. Here is one sad Brontosaurus.
Cartoon animals have been a staple of animation since well before Mickey Mouse. Winsor McCay’s "Gertie the Dinosaur" (Figure 1) made her debut in 1914, and right from the start this gigantic animated sauropod was depicted with very human expressions, like joy and sadness.
Dinosaurs, like all reptiles, have no facial musculature whatsoever. It would never occur to the viewer, however, to question the “rightness” of McKay's expressive creation; our human bias is overwhelmingly in favor of accepting animal faces as capable of expressing emotion in the same manner as human faces.
19th century French sculptor, Antoine-Louis Bayre, was called the “Michelangelo of the Menagerie” specifically for the vigorous action and dramatic qualities of his animal sculptures which included human-like facial expressions, as in the scowl and down-turned mouth of the dog in Figure 2. Audiences found Bayre's animal sculptures more convincing, rather than less, with the inclusion of such familiar emotional clues. Ironically, the portrait of Bayre in Figure 3, painted from a photograph after his death, shows Bayre with a scowl and frowning mouth highly reminiscent of his dog sculpture. Is this a coincidence, or was Bayre his own model?
Peter Paul Rubens, renowned 17th century Flemish painter, excelled in painting huge canvasses depicting battles and hunts. Within a whirlwind composition called, "The Lion Hunt," filled with attacking hunters and charging horses, the wounded lion (see Figure 4) is even angrier-looking than the fierce dog by Bayre above; a facial expression appropriate for both the creature and the situation. No viewer would question the realism of the lion's expression, in spite of the fact that lions can’t make such a face – compare this painted lion with the photo of a wounded lion in the midst of live action in Figure 5. With the "real" lion, note the absence of a frowning brow, and the lack of lift (snarl) in the mouth corner, both elements that Rubens imaginatively and effectively added to his "fake" lion. Both lions are fighting for their lives. Which lion looks angrier?
When animal faces are stylized, there seems to be few limits, other than the structure of the animal head, to our acceptance and enjoyment of seeing them express human emotions, and exaggeration is not a problem.
The John Tenniel illustrations for "Alice's Adventures in Wonderland" are considered classics. In Figure 6, the dramatic exposure of eye white above the iris, plus the oblique upper lid margin, effectively expresses the White Rabbit’s anxiety about being late for a tea party. Note the lack of any exposed eye white in the real hare's eyes (Figure 7); no animal besides humans shows eye white; this is a big part of what makes our faces so expressive.
CG animation introduced the novel combination of photo-realist textures with extremely stylized characters. This has allowed invented animals to look "convincing", no matter what their design. The characters from the "Big Buck Bunny" movie poster (see Figure 8) demonstrate some of the possibilities. The mouse on the left is basically a human face (note the close counterpart in Figure 9) pasted on top of a mouse head - not my favorite approach. I find it a bit creepy, like a man wearing a mask. Much better is the name-that-creature on the right, which has no real world counterpart, two unmatched eyes, and an asymmetrical big tooth for good measure. The net result is that it is much funnier and more appealing than the stylized mouse. It also demonstrates the natural fit between extreme stylization of a face, and a facial expression that pushes the boundaries of the plausible.
Stylization is a matter of degree. In the movie "Happy Feet," the baby Emperor Penguin (Figure 11) has larger, more closely-set, and more readable, higher-contrast eyes than its real-world counterpart (Figure 12). The character designers also shrank the beak and gave it a lighter tone and the capability to smile. The stylized baby penguin is meant to seem cute, funny, and appealing. Instead, it falls into an uncomfortable middle ground between realism and exaggeration, like those notorious paintings of big-eyed children.