mammals are vertebrates
some mammals have a large larynx and thus a lowpitched voice namely the hammerheaded bat hypsignathus monstrosus where the larynx can take up the entirety of the thoracic cavity while pushing the lungs heart and trachea into the abdomen
 most if not all are thought to have remained nocturnal the nocturnal bottleneck accounting for much of the typical mammalian traits