Elasmosaurus

Elasmosaurus: The Longest Neck in the Plesiosaur Family

Imagine a creature with an incredibly long neck, so long that it could almost touch its own tail if stretched out straight. That’s Elasmosaurus, a genus of plesiosaur that lived during the Late Cretaceous period, approximately 80.5 million years ago in North America. How did such a creature evolve and what can we learn from its discovery?

The Discovery and Naming

In 1867, near Fort Wallace, Kansas, the first specimen of Elasmosaurus was discovered. Edward Drinker Cope named it E. platyurus, which means ‘thin-plate reptile’ and ‘flat-tailed,’ referring to its unique vertebrae structure. But little did anyone know that this discovery would spark a scientific controversy that would last for decades.

A Scientific Controversy

Cope’s initial reconstruction of Elasmosaurus showed a short neck and long tail, which was later disputed by Joseph Leidy. Cope attempted to recall copies of his preprint article and printed a corrected version with a new skeletal reconstruction that placed the head on the neck. This mistake led to a rivalry between Cope and Othniel Charles Marsh, known as the ‘Bone Wars.’ The argument was widely publicized in the 1890s, but it has been questioned why Cope would make such an obvious anatomical error.

The Holotype Specimen

The incomplete holotype specimen of Elasmosaurus is now stored in a cabinet with other assigned fragments. Sven Sachs redescribed it in detail in 2005, noting that the skeleton consists of premaxillae, right maxilla fragments, teeth, dentaries, jaw fragments, cranial fragments, cervical vertebrae (72), pectoral vertebrae (3), back vertebrae (6), sacral vertebrae (4), tail vertebrae (18), ribs and rib fragments. A neck vertebra was rediscovered in 2013.

Adaptations for Aquatic Life

Elasmosaurus had a streamlined body with paddle-like limbs, a short tail, a small head, and an extremely long neck measuring 7.1 meters (23 ft) long. The skull was slender and triangular, with large fang-like teeth at the front and smaller teeth towards the back. These adaptations made Elasmosaurus well suited for aquatic life, probably eating small fish and marine invertebrates.

Neck Vertebrae and Function

The 72 neck vertebrae of Elasmosaurus were compressed sideways, especially at the middle of the neck. A crest ran longitudinally along the side of the neck vertebrae, visible from the third to the fifty-fifth vertebrae. The neural spine was low and directed upwards and back. The centra of the atlas and axis were of equal length, and had a quadratic shape in side view.

Back and Tail Vertebrae

The back vertebrae had rib facets level with the neural canal, and distinct ridges on their margins. Elasmosaurus had four sacral vertebrae, a number typical of elasmosaurids. The transverse processes were short and rib facets increased in size from the first to the fourth sacral vertebra. A ridge ran along the top of these vertebrae, and the lower sides of the centra were rounded, bearing pairs of nutritive foramina.

Species and Taxonomy

Cope named several species based on fragmentary remains, including E. platyurus, E. orientalis, E. constrictus, E. serpentinus, E. intermedius, E. snowii, and E. nobilis. However, most of these species are now considered dubious or moved to other genera.

Ecology and Predation

The unusual body structure of elasmosaurids limited their speed, with paddles moving in an oar-like motion and held rigidly. Plesiosaurs could maintain high body temperature, allowing sustained swimming. A 2015 study found that fore-flippers controlled locomotion, while hind-flippers provided maneuverability. Elasmosaurid remains show evidence of predation by sharks and pliosaurs.

Reproduction

The neck of elasmosaurids was incapable of raising its head above the water due to weight and musculature limitations. Neck movement and function are unknown, but may have been important for hunting or as a snorkel. Plesiosaurs likely gave live-birth due to rigid paddles. Elasmosaurid fossils show evidence of viviparity, with one fossil containing a single fetus inside.

Feeding Habits

The flexion ranges of Elasmosaurus necks allowed it to employ various hunting methods, including benthic grazing and active hunting in the pelagic zone. Elasmosaurids likely preyed on animals between 30 cm and 2 meters long, with stomach contents suggesting they hunted sharks, fish, mosasaurs, and cephalopods. They probably ate small bony fish and marine invertebrates, swallowing their prey whole due to their adapted teeth.

Conclusion

Elasmosaurus, with its incredibly long neck, is a fascinating creature that has captivated scientists for over 150 years. From its initial discovery to the ongoing debates about its anatomy and relationships, Elasmosaurus continues to be a subject of great interest in paleontology. Its unique adaptations and lifestyle offer valuable insights into the evolution and ecology of plesiosaurs during the Late Cretaceous period.