Plesiosaurus
Early Jurassic marine reptile with a long neck and small head.
Plesiosaurus, whose name translates from Greek as "near lizard," was a marine reptile of the Early Jurassic period, known from nearly complete skeletons unearthed in the Lias Group of England. It reached about 3.5 meters in length and is distinguished by a small head, an exceptionally long and slender neck, a broad body reminiscent of a turtle, a short tail, and two pairs of large, elongated paddles. As the namesake of the order Plesiosauria, it represents an early and fairly typical member of that group. The genus contains only one valid species, the type species *Plesiosaurus dolichodeirus*.
The first complete skeleton was discovered in December 1823 by the renowned fossil hunter Mary Anning in Sinemurian-age rocks of the lower Lias Group near Lyme Regis, Dorset, England. Although less complete remains had been used by Henry De la Beche and William Conybeare to name the species two years earlier in 1821, Anning’s specimen became the holotype. The discovery generated great excitement in 19th-century England as one of the first "antediluvian reptiles" found. Conybeare and De la Beche coined the genus name to indicate it was more lizard-like than the *Ichthyosaurus* found in the same strata. Additional fossils were collected from the Lias Group of Dorset until quarrying ceased early in the 20th century. Several species once assigned to *Plesiosaurus*, such as *P. brachypterygius* and *P. guilielmiimperatoris*, have since been reclassified into other genera.
The skull of *Plesiosaurus* is small, narrow, and bluntly triangular, widest just behind the eyes. Its external nostrils are positioned closer to the eyes than the snout tip, and the roughly circular eye sockets face upward and sideways. The lower jaws meet at a robust, fused symphysis, forming a shallow, scoop-like shape. The teeth are simple, needle-like cones, slightly curved and circular in cross-section, with fine striations. They point forward, becoming nearly horizontal at the front of the skull, with 20 to 25 teeth in each upper jaw and 24 in each lower jaw. The vertebral column includes about 40 neck vertebrae, with the centra being slightly longer than tall and wider than long. The neck ribs are hatchet-shaped with two heads, while the dorsal ribs are thick and single-headed. The body also possesses gastralia, or belly ribs, with nine or more sets present between the shoulder and pelvis.
- field
- Paleontology
- known_for
- Archetypical genus of Plesiosauria; first complete skeleton discovered by Mary Anning
- length
- 2.87–3.5 m (9.4–11.5 ft)
- time_period
- Early Jurassic (Sinemurian)
- type_species
- Plesiosaurus dolichodeirus
Lore & Background
The first complete skeleton of Plesiosaurus was discovered by early paleontologist and fossil hunter Mary Anning in Sinemurian (Early Jurassic)-age rocks of the lower Lias Group in December 1823 near Lyme Regis in Dorset, England. Additional fossils were found in rocks of the Lias Group of Dorset for many years. Less complete remains were used by Henry De la Beche and William Conybeare to name the species two years earlier in 1821, but Conybeare's remains were not the holotype; Anning's were. Plesiosaurus was one of the first of the 'antediluvian reptiles' to be discovered and excited great interest in 19th-century England. It was so-named ('near lizard') by William Conybeare and Henry De la Beche, to indicate that it was more like a normal reptile than Ichthyosaurus. Conybeare and De la Beche coined the name for scattered finds from the Bristol region, Dorset, and Lyme Regis in 1821. The type species, P. dolichodeirus, was named and described by Conybeare in 1824 on the basis of Anning's original finds.
Reader's Guide
Plesiosaurus had a small head, with a skull much narrower than long. The anterior portion was 'bluntly triangular'. The external nostrils were not at the tip of the snout but farther back, nearer the eyes. The orbits were roughly circular and positioned about halfway along the skull. The teeth were simple, needle-like cones, slightly curved, with fine striations, and pointed forward. There were 20 to 25 teeth per upper jaw tooth row and 24 per lower jaw tooth row. The neck had approximately 40 cervical vertebrae. The body had about 21 dorsal vertebrae, three or more sacral vertebrae, and at least 28 caudal vertebrae. The forelimbs were elongate and relatively narrow; the hindlimbs were long and narrow, and in adults much smaller than the forelimbs. Both fore and hind paddles had five digits. Plesiosaurus is thought to have eaten belemnites, fish and other prey, using its U-shaped jaw and sharp teeth like a fish trap. It propelled itself by the paddles.
Did You Know?
- Plesiosaurus means 'near lizard' in Greek, named to indicate it was more like a normal reptile than Ichthyosaurus.
- The first complete skeleton was discovered by Mary Anning in December 1823 in Lyme Regis, England.
- Plesiosaurus has historically been a wastebasket taxon, with many species later reassigned to other genera.
- The type species Plesiosaurus dolichodeirus was named and described by Conybeare in 1824.
Common Misconceptions (Editorial)
Some people mistakenly believe that Plesiosaurus was a dinosaur or a fish, but it was actually a marine sauropterygian reptile. Another common error is that it had a snake-like neck that could coil or lift high out of the water like a Loch Ness monster; in reality, its neck was long but slender and supported by a broad, turtle-like body, and the known anatomy does not suggest such extreme flexibility or posture. Additionally, while the name “plesiosaur” is often used broadly for long-necked marine reptiles, the facts show that *Plesiosaurus* is a specific genus, with the type species *Plesiosaurus dolichodeirus* named in 1824, and it lends its name to the entire order Plesiosauria.
Why It Matters (Editorial)
*Plesiosaurus* endures as a touchstone of paleontology because its nearly complete skeletons, first uncovered by pioneering fossil hunter Mary Anning, helped establish our understanding of marine reptile evolution in the Early Jurassic. Its distinctive, almost paradoxical build—a small head on an impossibly long neck attached to a turtle-like body—continues to capture the imagination, making it a symbol of how ancient life can defy modern expectations.
Frequently Asked Questions
What is Plesiosaurus?
Plesiosaurus is a genus of large, aquatic sauropterygian reptile that swam in the oceans during the Early Jurassic. It is one of the earliest recognized members of the plesiosaur lineage and actually gave the entire order Plesiosauria its name.
What does Plesiosaurus look like?
It had a very small skull perched at the end of a long, slender neck, a broad and flattened body somewhat like a turtle's, a notably short tail, and two pairs of large, elongated flippers for propulsion through water.
How big was Plesiosaurus?
Adult specimens measured roughly 2.87 to 3.5 meters (about 9.4 to 11.5 feet) in total length. That made it a sizeable marine predator for the Early Jurassic, though considerably smaller than many later plesiosaurs.
Who discovered the first complete Plesiosaurus skeleton?
The pioneering fossil collector Mary Anning unearthed the first nearly complete skeleton in the Lias rock beds of England. Her find became one of the landmark specimens that helped establish early paleontology as a science.
Why is Plesiosaurus important to paleontology?
It serves as the type genus for the order Plesiosauria, so it acts as the baseline reference for how the group is defined. Because it represents a fairly typical early body plan, it helps researchers understand the foundational anatomy from which later, more extreme plesiosaurs evolved.
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