Scuba Diving club,
Southern California
Sea Sabres
Plesiosaur
"near-reptile"
By Richard Forrest
EARLY JURASSIC TO CRETACEOUS
PERIOD
220 million - 65 million
years ago
Plesiosaurs were magnificent
ocean-dwelling reptiles that "flew" gracefully through the water with
massive paddles. They were around almost as long as the dinosaurs from the
Triassic period 220 million years ago until the end of the Cretaceous 65
million years ago. Their remains have
been found on every continent. First discovered in the Jurassic formation of
Lyme Regis in England in 1820, the name meaning "near-reptile" was
meant to differentiate the understanding that these creatures were more
reptilian than the fish-like Ichthyosaurs discovered in the same region.
The
order Plesiosauria are a large and varied group which have been broadly divided
into two superfamilies based on their overall body structure. The long-necked, small-headed
PLESIOSAURS make up one superfamily named Plesiosauroidea and the short-necked,
large-headed PLIOSAURS comprise the other superfamily named Pliosauroidea.
Plesiosaurs
were one of the first kinds of extinct animal known to science, and were described
as early as 1821. The smallest were about 2m long as adults, the largest were
enormous pliosaurs up to 20m long, comparable in size or even bigger than sperm
whales ( Physeter ). They were possibly the biggest predators of all time,
though remains of these giants are rare and fragmentary, and much research
remains to be done.
Pliosaurs
first emerged in the Early Jurassic Period. They were among the chief predators
of the ancient seas, attacking large sharks, ichthyosaurs and
even their relatives, plesiosaurs.
Pliosaurs
had a large head with very strong teeth and jaws. Their teeth are deeply rooted
in powerful jaws backed by extremely large jaw muscles.
An
immediately obvious difference between pliosaurs and plesiosaurs is the
pliosaurs have bodies streamlined for speed and possess a very short neck when
compared to the super long necks of the plesiosaurs. Some pliosaurs had as few
as only 13 neck vertebra whereas the shortest-necked plesiosaur had 28
vertebrae! The body size of the pliosaurs developed into larger sizes than the
plesiosaurs making them a formidable enemy to anything that lived in the ocean
during their reign.
We
can learn about what they ate from the fossils. Occasionally stomach contents
are found with well-preserved specimens, showing that some at least fed on
belemnites and ammonites. Other specimens show bite marks from larger predatory
forms. There is a wide range in tooth shape, showing that they were adapted to
feeding on different types of prey. Long, slender teeth may have been used to
rake through sea-floor sediments in the way a swan dabbles on pond bottoms.
Larger, more robust teeth seem to be adapted for feeding on armored fish and
cephalopods. Some of the bigger
pliosaurs had enormous, dagger-like teeth which were used to attack their
smaller relatives.
A
plesiosaur used stones in it's stomach known as gastroliths. These made it possible for them to swallow their
food whole, letting the gastrolith grind the food. The stones may also have
served as ballast or weight for deep diving.
Common
misspellings: Pleosaur, Pleosaurus, Plyosaur, Plisiosaur, Pliosor, Plesiosor.
Find out about a man who finds ansestor to
Nessie on shore of Loch Ness
Posted September 2, 2003
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