Live plesiosaurs: weighing the evidence

Plesiosaur evidence

The past existence of plesiosaurs is evident from the wealth of fossilized skeletal remains unearthed worldwide. From the skeletons and from our knowledge of structure and function of various body types from presently living animals, these creatures have been reconstructed, to give us an idea of their appearance and how they may have lived.

Plesiosaurs were marine dwelling reptiles, and based on skeletons found to date they ranged in size from more than 2 meters (7 feet) for Plesiosaurus to about 14 meters (46 feet) for Elasmosaurus.16, 17

The order Plesiosauria has been divided into two Superfamilies16: Plesiosauroidea, such as Cryptoclidus (sometimes spelt Cryptocleidus, Figures 1, 2b), characterized by long necks, with 28–71 vertebrae, and small heads, and Pliosauroidea, whose members had large heads and short necks with as few as 13 vertebrae. A huge pliosaur was Kronosaurus (Fig. 2a), whose skull alone was 2.4 meters (8 feet) long.

Plesiosaurs possessed deep bodies and flipper-like limbs unique among marine reptiles, ending in phalanges consisting of five to ten bones (see Figure 1, 2b). The flippers, shaped like hydrofoils, were moved in large vertical strokes enabling the ‘subaqueous flight’ swimming style similar to sea turtles and penguins. The bones of the pectoral and pelvic girdles formed broad plates on the underside of the body to where the limbs and powerful swimming muscles were attached. A number of dense ventral, costa-like ribs connected the two plates, providing a strong, rigid base for the movement of the flippers (Figure 2a). It is also believed that plesiosaurs crawled on to beaches to lay their eggs in a similar manner to turtles, the rigid base providing the necessary support and protection.16,17

According to evolutionary dating methods they are believed to have lived in the Mesozoic Era, approximately 230–65 million years ago.