Plesiosauridae
Plesiosaurs, marine reptiles from the Early Cretaceous period (around 110 million years ago), were discovered
| Andamooka Sea Monster (Plesie) | |
 | |
| Classification | |
| Genus | Unknown |
| Species | Unknown |
| Habitat | |
| Diet | Likely fish |
in Andamooka, South Australia, among other fossils in the Marree Formation. In 1983, miners John St. Alban and Stephen Bilka uncovered the largest opalized vertebrate fossil in this region while working on Lunatic Hill—a plesiosaur nicknamed 'Plesie' by locals. This specimen, adapted for aquatic life, had limbs transformed into paddle-like structures, making it less suited for terrestrial movement. It likely featured a long neck and a small head, distinguishing it from the related pliosauroids, such as Kronosaurus from Queensland, which had shorter necks and larger heads.
These reptiles used their broad paddles for swimming, similar to the motion of sea turtles or the rowing action of oars, generating thrust on the backstroke and lift during the recovery stroke. Plesiosaurs ingested stones, possibly to manage buoyancy by offsetting the air in their lungs or to help grind food, much like birds use 'crop stones.' Their flexible spine suggests they could expand their lungs, potentially allowing some to come ashore—comparable to seals or sea turtles—for activities like giving birth, laying eggs, or resting. The paddle structure of plesiosaurs, adapted from tetrapod limbs, displays hyperphalangy, meaning an increased number of bones in each digit, which expanded the paddle's surface area for better swimming efficiency.
Globally distributed and primarily marine, though some adapted to freshwater environments, plesiosaurs are identified by their distinctive vertebrae, which include paired paddle bones on the underside, unlike other reptiles. Their digits contain more bones than those of typical vertebrates, differing from ichthyosaurs. In the shallow, cool sea covering parts of ancient Australia during the Early Cretaceous, the Andamooka plesiosaur and its young lived, with adults collecting seabed stones—often found in their fossilized remains—while juveniles likely fed on schools of fish, a primary food source for the species.[1]
References
- Kadimakara Extinct Vertebrates of Australia, By P.V.Rich, 1985, P.143,144.
