What distinguishes ruminants from other mammals?

Ruminants are specifically distinguished by their unique digestive system, which features multiple stomach chambers. This system allows them to effectively break down tough plant materials, such as cellulose, which is found abundantly in grasses and other vegetation. The primary characteristic of ruminants is their possession of a complex stomach structure that generally includes four compartments: the rumen, reticulum, omasum, and abomasum.

In the rumen, for instance, microbial fermentation occurs, enabling the breakdown of fibrous plant material. After initial digestion and fermentation, ruminants can regurgitate this material as "cud" to chew it again, further aiding in digestion. This adaptation allows ruminants to extract a greater nutritional value from their herbivorous diet compared to other mammals that have simpler digestive systems.

The other options indicate misunderstandings about ruminants. For example, ruminants are well-known for their ability to digest plant materials effectively, they are not all aquatic, and they do engage in chewing their food, albeit in a unique way that involves re-chewing cud after initial consumption.