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INTRODUCTION TO THE ICHTHYOSAURIA


A specimen of the Jurassic icthyosaur Ichthyosaurus intermedius, found in
Somerset County, England. Photo by Sara Rieboldt, © UC Museum of Paleontology.

Some really cool information on ichthyosaurs has been put together by Ryosuke
Motani, a former post-doc in Kevin Padian's lab.

While dinosaurs ruled the land, the ichthyosaurs, classified variously in the
Ichthyosauria or in the Ichthyopterygia, shared the seas of the world with the
other great groups of large marine reptiles, the plesiosaurs and mosasaurs.
"Ichthyosaur" means "fish lizard," while "Ichthyopterygia" means "fish paddle."
Both names are apt. The earliest ichthyosaurs had long, flexible bodies and
probably swam by undulating, like living eels. More advanced ichthyosaurs — like
the one shown above, on display at the Senckenberg Museum in Frankfurt, Germany
— had compact, very fishlike bodies with crescent-shaped tails. The shape of
these ichthyosaurs is like that of living tunas and mackerels, which are the
fastest fish in the ocean; like them, the later ichthyosaurs were built for
speed. Note the paddles with which ichthyosaurs swam; they have the same basic
plan as your hand and arm, but the arm bones are very short, while the fingers
have lengthened by developing many more bones than the three that make up each
of your fingers.


Reconstruction of Ichthyosaurus.
 

Rare fossils have been found that show ichthyosaurs actually giving birth to
live, well-developed young; ichthyosaurs never had to leave the water to lay
eggs. In fact, from their streamlined, fishlike bodies, it seems almost certain
that ichthyosaurs could not leave the water. Yet they still breathed air and
lacked gills, like modern whales.

Ichthyosaurs were not dinosaurs, but represent a separate group of marine
vertebrates. Because ichthyosaurs were so specialized and modified for life in
the ocean, we don't really know which group of vertebrates were their closest
relatives. They might have been an offshoot of the diapsids — the great
vertebrate group that includes the dinosaurs and birds, the pterosaurs, the
lizards and snakes, and many other vertebrates. On the other hand, some have
suggested that the ichthyosaurs were descended from a distant relative of the
turtles.

The first ichthyosaurs appeared in the Triassic. In the Jurassic, ichthyosaurs
reached their highest diversity, and then began to decline. The last
ichthyosaurs disappeared in the Cretaceous — several million years before the
last dinosaurs died out. Whatever caused the extinction of the dinosaurs did not
cause the ichthyosaurs to die out.

An on-line article by paleontologist Richard Cowen, "Locomotion and respiration
in marine air-breathing vertebrates," describes how ichthyosaurs — and many
other marine vertebrates — lived and breathed.

Berlin-Ichthyosaur State Park, near Gabbs, Nevada, includes a partial excavation
of some of the largest and best-preserved ichthyosaurs anywhere in the world.

Read about the Saurian Expedition of 1905 on which UCMP benefactress Annie
Alexander collected many ichthyosaurs.