Different dietary habits of mammalian groups are reflected in the size and importance of the three major salivary glands (the parotid, sublingual, and submandibular glands ; Fig. 1) and the viscosity of the saliva they produce.
Fig. 1: Human salivary glands .
The paratoid glands generally produce a serous (watery) saliva. The glands are larger, more developed in herbivores and humans than in carnivores . This is due to the fact that the plant matter that herbivores, especially browsers and grazers, consume is often quite dry and requires extensive chewing before swallowing .
The saliva secreted by the submandibular glands of carnivores is mucous, while that of herbivores, rodents and humans is mostly serous . The mucous saliva of carnivores is helpful as they tend to swallow chunks of meat whole or after minimal chewing. In omnivores, the submandibular glands produce mixed (seromucous) saliva.
What about humans?
With large, well-developed parotid glands and submandibular glands that produce a mostly serous saliva, humans share more traits with herbivores.
 Tucker, Abigail S., and Isabelle Miletich, eds. Salivary glands: development, adaptations and disease. Vol. 14. Karger Medical and Scientific Publishers, 2010.
 Blausen.com staff. “Blausen gallery 2014”. Wikiversity Journal of Medicine (2014).