Manatees, large herbivorous marine mammals classified as sirenians, possess teeth, though not in the way most people imagine. They have evolved a highly specialized dental system perfectly adapted to grazing on aquatic vegetation. This arrangement allows them to process the tough, abrasive foods that make up their diet.
The Manatee’s Unique Dental Arrangement
Manatees are homodonts, meaning all their teeth are similar in shape and function. They lack the incisors and canines found in many other species, possessing only a series of large, cylindrical cheek teeth, which are exclusively molars. These molars feature broad, flat surfaces with two or three roots, designed specifically for grinding. A mature manatee typically has five to eight molars in contact (occlusion) along each side of the upper and lower jaws. This composition reflects their diet, which requires mechanical force to break down the fibrous cell walls of aquatic plants.
The Phenomenon of Marching Molars
The most fascinating aspect of manatee teeth is their continuous replacement system, known as “marching molars.” This horizontal dental succession replaces teeth from the back of the jaw to the front. New molars form and erupt at the posterior end of the dental row, gradually moving forward along the jawbone like a conveyor belt.
As the molars drift forward, they are subjected to wear from chewing, which reduces their crown height. Once a tooth reaches the front and is worn down, its roots are resorbed, and the tooth falls out, making way for the next one. Teeth drift approximately one millimeter per month, ensuring a functional grinding surface. This adaptation is necessary because their diet of sea grasses often contains abrasive materials like sand, grit, and hard silicate particles (phytoliths), which rapidly erode the teeth.
Oral Anatomy and Feeding Behavior
The efficiency of the manatee’s teeth is supported by specialized structures in their mouth. The manatee uses its highly prehensile, split upper lip to grasp and manipulate vegetation, pulling plants into the oral cavity. This muscular, bristly lip functions much like a short trunk.
The jaws also feature tough, keratinized dental pads at the front. These dense pads work with the lips to tear or clip vegetation before it is passed back to the molars for crushing. Since the food source is fibrous and often covered in sediment, the powerful grinding action of the marching molars is essential for extracting nutrients.