Plesiosaur

Unveiling the Mysteries of Plesiosaurs: The Mesozoic Marine Giants

The Enigmatic Plesiosaurs

Plesiosaurs, those ancient marine reptiles that roamed the oceans during the Mesozoic Era, are a fascinating subject for both scientists and enthusiasts. Imagine these creatures gliding through the waters with their four flippers, their long necks reaching out to catch unsuspecting prey. But how much do we really know about them? Let’s dive into the world of plesiosaurs and uncover some of their secrets.

Origins and Discovery

The Plesiosauria order is an extinct group of marine reptiles that emerged around 203 million years ago during the Triassic Period. These creatures thrived until their extinction at the end of the Cretaceous Period, about 66 million years ago. They had a worldwide oceanic distribution and some species even inhabited freshwater environments. The first plesiosaur was discovered in 1821, leading to the naming of Plesiosaurus. This discovery marked the beginning of our understanding of these fascinating creatures.

Adaptations for Life at Sea

Plesiosaurs had a broad flat body and short tail, with two pairs of limbs evolving into large flippers. The flipper arrangement was unusual for aquatic animals, with all four limbs used to propel the animal through the water by up-and-down movements. This unique adaptation allowed them to navigate both shallow coastal waters and deep oceanic environments.

Neck and Head Variations

The plesiosaurs varied in their neck form and size, with ‘plesiosauromorphs’ having long necks and small heads, while ‘pliosaurs’ had shorter necks and larger heads. The number of cervical vertebrae was not directly correlated to the length of the neck but rather an increase in the number of joints allowed for flexibility.

Feeding Habits

Plesiosaurs likely ate fish, cephalopods, and possibly bony fish. They were likely visual hunters using their large eyes and directional sense of olfaction. One hypothesis suggests they surprised schools of fish with their long necks, while another proposes they were bottom feeders ploughing the sea floor.

Swimming and Movement

The four-flippered body shape has sparked debate about flipper movement, with comparisons to birds and sea turtles being made. By the mid-19th century, it was assumed plesiosaurs rowed using horizontal flippers; however, early 20th-century researchers suggested a flying movement like birds and turtles. In 1905, Eberhard Fraas proposed this theory, followed by Othenio Abel in 1908. The model described a vertical flipper movement with an oval or ‘8’ path, generating thrust through Bernoulli’s principle.

Reproduction and Social Behavior

Fossil finds of ichthyosaur embryos showed that at least one group of marine reptiles had borne live young. The first reported discovery of plesiosaur embryos was by Harry Govier Seeley, but it was later revealed to be a ‘doctored’ fossil. An actual plesiosaur specimen found in 1987 proved that plesiosaurs gave birth to live young, with a single large juvenile born and likely parental care from the mother.

Evolutionary Relationships

Theoretical work has increased since the 1950s, using cladistics to calculate evolutionary relationships and test hypotheses about hunting and swimming behaviors. Plesiosaurs have their origins within Sauropterygia, a group of archelosaurian reptiles that returned to the sea.

Modern Research

Recent discoveries include 17 new sex plesiosaurs in the 1990s and about three or four plesiosaurs named each year in the early 21st century. Notable discoveries include the ‘Monster of Aramberri’ (2002), originally classified as a dinosaur but later found to be a large plesiosaur, and the intact juvenile plesiosaur fossil (2004) in Somerset, UK.

Conclusion

The study of plesiosaurs continues to evolve with new discoveries and research. From their origins within Sauropterygia to their extinction at the end of the Cretaceous Period, these marine reptiles have captivated our imagination for centuries. As we continue to uncover more about them, one thing is certain: Plesiosaurs remain a fascinating subject in paleontology.