elasmosaurids

Elasmosaurids are a family of plesiosaurs, marine reptiles within the broader group Plesiosauria. They are best known for their exceptionally long necks, a distinctive feature that set them apart from other plesiosaurs. Elasmosaurids lived during much of the Cretaceous period, from the Early to the Late Cretaceous, and their fossils have been found in oceans worldwide, with a rich record in North America’s Western Interior Seaway.

Anatomy and adaptations emphasize their necks: the neck is formed by a very high number of cervical vertebrae, often more than 50, giving them a long, flexible, reach. The skull tends to be relatively small compared to the body, and the teeth—when present—are generally slender and pointed. The fore- and hind limbs have evolved into broad, paddled flippers for efficient underwater propulsion, while the tail is comparatively short. This combination supports a lifestyle as a carnivorous piscivore or predator of cephalopods, though feeding strategies likely varied among species.

Taxonomy and notable genera: Elasmosaurus is the type genus, and other well-known members include Styxosaurus, Hydralmosaurus, and Albertonectes, the latter notable for an extremely long neck with about 72 vertebrae. Elasmosaurus platyurus, described in the late 19th century, is famous for a historic reconstruction in which the skull was initially placed at the tail end of the skeleton, a misassembly later corrected.

Paleoecology and distribution: Elasmosaurids inhabited shallow to open-marine environments and are found in Cretaceous marine deposits around the world. They coexisted with other marine reptiles and many marine invertebrates, contributing to the diverse marine ecosystems of the time before their extinction at the end of the Cretaceous.