Elasmosaur


An elasmosaur paddle bone found in Sumter County. Elasmosaur Paddle BoneElasmosaurs belong to the family Elasmosauridae, a classification of extinct marine reptiles that belong to the order Plesiosauria. The name "plesiosaur" means "near-lizard" in reference to the fact that these animals were taxonomically close to living reptiles. Plesiosaurs first evolved in the late Triassic (beginning about 205 million years ago), diversified during the Jurassic period (beginning about 145 million years ago), and survived into the late Cretaceous period (ending about 66 million years ago). Elasmosaur fossils are found worldwide and are notable for their extremely long necks and their paddle-shaped appendages. In Alabama, most of the elasmosaur material that has been found comes from sediments from the Campanian stage of the late Cretaceous (83.6–72.1 million years ago) in rock formations in Hale, Greene, Dallas, and Montgomery counties. The name roughly translates as "thin-plate lizard," in reference to the thin, platelike bones in the animal's pelvis.

“The Snake-necked Elasmosaurus” by Charles R. Knight appeared Elasmosaur Painting Elasmosaurs have the longest necks of all plesiosaurs discovered thus far. By the late Cretaceous, the animals had reached what would be their peak length of 14 meters (46 feet) and weighed more than two tons. Their long necks were comprised of anywhere between 32 and 76 cervical (neck) vertebrae. These marine reptiles probably could lift their heads only slightly above water to breath, as their necks were too long and heavy to raise very high outside the water. Elasmosaurs preyed primarily on fish and prehistoric cephalopods (a class that includes present-day squids and octopuses) such as belemnites and ammonites. Scientists believe that elasmosaurs were relatively slow-moving ambush predators that used their long necks and thin, pointed teeth to catch their prey.

During the Cretaceous, a large body of water known as the Western Interior Seaway covered most of what is now the central United States (including a large portion of Alabama) and Canada from the Gulf of Mexico up to the Arctic Ocean. Thus, the Southeast is rich in marine fossils; at least five genera of elasmosaurs have been identified from fossils discovered in the region, including Elasmosaurus, Styxosaurus, Libonectes, Thalassomedon, and Hydralmosaurus. The identification of elasmosaurs at the genus and species level is difficult because it requires diagnostic bones such as skull fragments or bones from the shoulder, including the scapula and clavicle, which together form the pectoral girdle. Because none of these bones have been found for the specimens recovered from Alabama, the animals have not been identified beyond the higher taxonomic classifications.

This side view of an elasmosaur vertebra shows Elasmosaur VertebraElasmosaur fossils are rare in the late Cretaceous sediments of Alabama compared with those of other marine reptiles, such as mosasaurs (large animals related to modern snakes) and sea turtles. Large predacious mosasaurs were plentiful in the waters along the Gulf Coast during the late Cretaceous and most likely outcompeted the less powerful elasmosaurs locally. Elasmosaur vertebrae can be easily distinguished from mosasaur vertebrae by their large size, oval or heart-shaped appearance. Elasmosaur vertebrae are relatively flat on the front and back surfaces that contact the other vertebrae in the backbone. In contrast, mosasaur vertebrae are procoelous, meaning that the front surface of the vertebra is concave (like the back of a spoon) and the back surface is convex (like the front of a spoon).

This elasmosaur tooth was discovered in Greene County Elasmosaur ToothAlabama state paleontologist Winnie McGlamery acquired the first set of vertebrae, comprised of about 12 bones, in the 1930s from the Black Belt region of Alabama. In the early 1960s, a second set of vertebrae, comprised of about 20 bones, was collected by two high school students in Montgomery County. High-school student Noah Traylor discovered the most recent set of vertebrae during the Alabama Museum of Natural History's 2013 summer field expedition to search for fossils in Greene County. This specimen is also comprised of about 20 bones and is on display at the Alabama Museum of Natural History on the campus of the University of Alabama in Tuscaloosa, Tuscaloosa County. Other specimens in the collections of the Alabama Museum of Natural History include isolated teeth and paddle bones, and three sets of associated vertebrae.

Additional Resources  

Carpenter, Kenneth. "Revision of North American Elasmosaurs from the Cretaceous of the Western Interior." Paludicola 2 (June 1999): 148-73.

Sachs, Sven, Benjamin Kear, and Michael J. Everhart. "Revised Vertebral Count in the ‘Longest-Necked Vertebrate' Elasmosaurus platyurus Cope 1868, and Clarification of the Cervical-Dorsal Transition in Plesiosauria." PLOS One 8 (August 5, 2013): e70877.

Vincent, Peggy, et al. "New Plesiosaur Specimens from the Maastrichtian Phosphates of Morocco and Their Implications for the Ecology of the latest Cretaceous Marine Apex Predators." Gondwana Research 24 (September 2013): 796-805.

Dana Ehret
Alabama Museum of Natural History


Published January 24, 2014
Last updated June 24, 2014