Measuring 10.3 meters (34 ft) long, Elasmosaurus modernus has a streamlined body with paddle-like limbs, a short tail, a small head, and an extremely long neck. The neck alone is around 7.1 meters (23 ft) long. Along with its relative Albertonectes, it is one of the longest-necked animals to have lived, with the largest number of neck vertebrae known, 72. The skull is slender and triangular, with large, fang-like teeth at the front, and smaller teeth towards the back. It has six teeth in each premaxilla of the upper jaw, and 14 teeth in the maxilla and 19 in the dentary of the lower jaw. Most of the neck vertebrae are compressed sideways, and bore a longitudinal crest or keel along the sides. Elasmosaurids, including Elasmosaurus modernus, are well adapted for aquatic life, and use their flippers for swimming. Contrary to earlier depictions in fiction and outdated restorations, their necks are not very flexible, and could not be held high above the water surface. Elasmosaurus modernus mainly feeds on small fish and marine invertebrates, seizing them with their long teeth, and use gastroliths (stomach stones) to help digest their food.