Plesiosaurus dolichodeirus

Overview

Plesiosaurus dolichodeirus was a marine reptile with a small head, a long neck and four flippers. It reveals an unfamiliar body plan from Jurassic seas. Its story is also closely tied to Mary Anning's discoveries.^[1][2][3]

Key facts

The fossil was once too large to be carried up to a learned society's meeting room. When the slab arrived in London in 1824, it would not fit through the narrow staircase. The new marine reptile was therefore discussed as people examined the fossil in the corridor.^[2]

Time and place

It lived in Early Jurassic seas around 190 million years ago. Important fossils were found at Lyme Regis in what is now southern England. Today's coastal cliffs expose the strata of an ancient sea.^[1][3]

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

Size, form and skeleton

A small head sits at the end of a long neck, and four flippers extend from a broad trunk. Guides to the genus Plesiosaurus describe a body length of about 3.5 m. Looking at the proportions of the neck, trunk and front and rear flippers together reveals its distinctive form.^[1][3]

Habitat and reproduction

Unlike land-dwelling dinosaurs, this reptile was adapted to life at sea. Its four flipper-like limbs were used to move through the water. Other marine reptiles, including ichthyosaurs, are also known from the Jurassic seas of Lyme Bay.^[1][3]

Fossil discovery

In December 1823, Mary Anning discovered a fossil with its bones still articulated. The following year, William Conybeare presented a detailed account to the scientific society. The connections between the bones were important evidence in identifying an animal that was unfamiliar at the time.^[2][3]

References

1. Natural History Museum — Introducing plesiosaurs
2. Geological Society — Mary Anning’s discovery of Plesiosaurus in 1823
3. Lyme Regis Museum — Discovery and body of Plesiosaurus
4. Sachs, Kear & Everhart (2013) — Revised Vertebral Count in Elasmosaurus platyurus
5. NHM — What is a plesiosaur?
6. O’Gorman (2016), “New Insights on the Aristonectes parvidens Holotype: News on an Old Specimen,” Ameghiniana 53(4):397–417. DOI 10.5710/AMGH.24.11.2015.2921.
7. Benson, Evans & Druckenmiller (2012) — High Diversity, Low Disparity and Small Body Size in Plesiosaurs
8. Study — Plesiosaurs of the Posidonia Shale
9. Benson, Evans & Druckenmiller (2012) — High Diversity, Low Disparity and Small Body Size in Plesiosaurs
10. What is a plesiosaur? · NHM

Research questions

How might the long neck and four flippers have moved together underwater? Researchers compare plesiosaur neck vertebrae, trunks and limbs to explore their locomotion. Looking only at the small head raises different questions from examining the whole body.^[1]

Observation

Follow the long neck from the small head to the broad trunk and four flippers. Look at the positions of the front and rear flippers alongside the proportions of the neck and trunk.^[1][3]