The contrast between the deterrent lion with open mouth and luxurious mane and the peaceful antelope is striking, so more since the antelope is represented in profile while the lion, on the contrary, fully obeys the artistic law of frontality which is one of the most characteristic features of Palmyrene art.² Only early examples of Palmyrene sculpture from the first century B.C. and the beginning of the first century A.D. still show representations of human beings in profile.
Source: wiktionary