Dog faces exhibit anatomical differences in comparison to other domestic animals

Faces and their movements provide us the ability to understand parts of the evolution of communication, social behavior, cognition, and the brain (Schmidt & Cohn, 2001; Parr & Waller, 2006; Burrows, 2008). Humans and other mammals communicate using numerous signals that include visual displays, vocalizations, tactile signals, and olfactory signals (Burrows, 2008; Brecht & Freiwald, 2012; Liebal et al., 2013). Each of these signals is generated or received at least partially using the craniofacial complex. Within the visual realm, the face is the primary communication tool for terrestrial mammals and this is where facial expressions are generated. Many mammals also have facial fur of contrasting patterns and colors that are themselves used as a kind of signaling in social interactions (Santana et al., 2012, 2013; Caro et al., 2017). Human (and most mammalian) faces make facial expressions using the numerous mimetic muscles found deep to and attached to the skin of the face. These facial expressions help individuals with cohesion of social and kin groups, maintaining relationships, and potentially signal the intent and emotional state of the sender (Parr & de Waal, 1999; Parr & Waller, 2006; Burrows, 2008; Burrows & Cohn, 2014). A large majority of these studies comes from primates but recent work has increased our understanding of how some domestic mammals use facial expression in social interactions with conspecifics and humans (Wathan et al., 2015; Caeiro et al., 2017; Kaminski et al., 2017; Maglieri et al., 2020; Waller et al., 2020).