Elasmosaurus platyurus

Overview

This marine reptile had a small head on a long neck and four flippers beside its body. Elasmosaurus platyurus is a plesiosaur representing the seas of the dinosaur age. Each bone forming its long neck also carries a story of discovery.^[1][4]

Key facts

Humans and giraffes usually have seven neck vertebrae. In this animal’s fossils, researchers identified as many as 72. Consider how lengthening individual bones and increasing their number can produce very different bodies.^[1][5]

Time and place

It lived in Late Cretaceous seas around 80 million years ago. The type fossil came from the Sharon Springs Member in present-day western Kansas, United States. Marine sediments preserved in today’s interior reveal the sea life of that time.^[1][2]

The time range describes source context, not the complete duration of this species.

Size, form and skeleton

A neck conspicuously longer than the trunk and a small head are characteristic. Its limbs had become the four flippers typical of plesiosaurs, aiding underwater movement. A 2013 study reexamined the vertebral boundary between neck and trunk and identified 72 neck vertebrae.^[1][4]

Habitat and reproduction

Plesiosaurs were marine reptiles with flippers suited to aquatic life. Experiments suggest that coordinating foreflipper and hind flipper movements could enable efficient swimming. Consider how the long neck, small head, and four flippers moved together underwater.^[4]

Fossil discovery

When first reporting it in 1868, Cope misread the long neck as a tail. In 1870, Leidy pointed out this reversed interpretation. Research continued, and in 2013 separately stored neck-vertebra fragments were compared again to reassess the vertebral count.^[1]

References

1. Sachs, Kear & Everhart (2013), Revised Vertebral Count in the Long-Necked Plesiosaurian Elasmosaurus platyurus, PLOS ONE 8(8):e70877.
2. Paleobiology Database — Fossil occurrence records for Elasmosaurus platyurus
3. Sachs, Kear & Everhart (2013) — Revised Vertebral Count in Elasmosaurus platyurus
4. NHM — What is a plesiosaur?
5. University of Cambridge — How sloths got their long neck
6. Elasmosaurid body-length comparison, AMEGHINIANA2016 Table2

Research questions

Where does the neck end and the trunk begin? The attachment position of ribs on vertebrae provides a clue to this boundary. Even a famous long neck requires careful reading of bone counts and boundaries to understand it.^[1]

Observation

Move your gaze from the small head along the neck to the trunk and four flippers.^[1][4]