A Comparative Study of Facial Expressions of Two Species of Pinnipeds

Fur seals Arctocephalus forsteri and walruses Odobenus rosmarus show similar facial expressions in a variety of social and non-social contexts. In non-social settings, both species modify the facial appearance by erecting the mystacial vibrissae while grooming the forequarters, while yawning, and during olfactory/tactile investigation of objects. During naso-nasal greetings, vibrissae are often erected in fur seals, and are erected and moved against the interactant's mystacial pads in walruses. Highly submissive animals show: for A. forsteri, erection of the vibrissae, wide gape, relaxed lips, posterior retraction of the corners of the mouth, wide-eyed stare; for walruses, dorsomedial drawing up of the mystacial pads and erection of the vibrissae, imparting a 'pig snout' appearance. In high intensity threat, both species show facial expressions involving: for A. forsteri, slight lateral expansion of the mystacial pads, slight to moderate opening of the mouth, direct or oblique visual orientation from a head-up posture; for O. rosinarus, lateral and dorsoventral expansion of the mystacial pads, attendant exposure and stretching of the skin of the upper lip, especially around the bases of the tusks, and inflation of the rostrum posterolateral to the nostrils. The similarities of form and context of facial expressions used by the two species suggest common causation, but a greater number of those of A. forsteri is considered communicative, in agreement with known ecological and social characteristics of the two species.