Mosasaur
A mosasaur was not a dinosaur, but rather an
ocean-dwelling serpentine marine reptile more closely related to
snakes than to monitor lizards (Lee 1997). These predators evolved
from terrestrial ancestors in the early Cretaceous and dominated
the oceanic food chain during the late Cretaceous Period.
Genera included Mosasaurus, Tylosaurus, and Platecarpus.
An etching of a
Mosasaur
Description
Mosasaurs breathed air, but were powerful swimmers, so well adapted
to living in shallow seas that they gave birth to live young,
rather than return to the shoreline to lay eggs, as sea turtles do.
Mosasaurs likely descended from varanid lizards.
The smallest known mosasaur is Carinodens belgicus, which was about 3
to 3.5 m long and probably lived on the sea floor cracking mollusks
and sea urchins with its bulbous teeth. Larger mosasaurs were more
typical: mosasaurs ranged in size up to 17 m: Hainosaurus holds the record for
longest mosasaur, at 17.5 m.
A mosasaur had a body form similar to that of a crocodile, although
streamlined for fast swimming in marine waters. Their front leg
bones were reduced in length, their paddles strengthened by long
finger-bones. Their rear legs were atrophied. Their powerful tails,
lashed side to side crocodile-fashion, provided locomotion.
Mosasaurs had a loosely-hinged jaw which enabled them to gulp down
their prey almost whole, a snakelike habit that has helped identify
the stomach contents fossilized within a Mosasaur skeleton, which
included the diving seabird Hesperornis, a marine bony fish, a
shark, and part of a smaller mosasaur. Mosasaur bones have been
found with embedded shark teeth.
Based on features such as the loosely-hinged jaw, modified/reduced
limbs and probable locomation, many researchers believe that snakes
may be descended from mosasaurs, a suggestion advanced in 1869, by
Edward Drinker Cope, who coined the term "Pythonomorpha" to include
them. The idea lay dormant for more than a century, to be revived
in the 1990s.
Environment
Sea-levels were high during the Cretaceous, causing marine
ingressions in many parts of the world, and a great inland seaway
in North America. Mosasaur fossils have been found in the
Netherlands and Sweden, in Africa, in Australia, New Zealand, and
Vega Island off the coast of Antarctica. In Canada and the United
States, complete or partial specimens have been found in Alabama
and Georgia and in almost all the states covered by the seaway:
Texas, southwest Arkansas, New Mexico, Kansas, Colorado, the
Dakotas and Montana.
The "dinosaurs" of New Zealand, a volcanic island arc that has
never been part of a continent, are a unique series of mosasaurs
and plesiosaurs, another group of predatory marine reptiles of the
Mesozoic era.
Discovery
The first publicized discovery of a fossil mosasaur preceded any
dinosaur fossil discoveries, and drew The Enlightenment's attention
to the existence of fossilized animals; the specimen was discovered
in 1780 by quarry-workers in a subterranean gallery who quickly
alerted Doctor C. K. Hoffman, a surgeon of Maastricht and
fossil-hunter though rights of ownership lay with a canon of
Maastricht, as owner of the overlying land.
Discovery of the first Mosasaur
(Mosasaurus hoffmani), at a Maastricht limestone quarry, 1780. An
engraving by G. R. Levillaire.
Dr. Hoffman's correspondence among men of science made the find
famous. When the Revolutionary forces occupied Maastricht, the
carefully-hidden fossil was uncovered, betrayed, it is said, by a
case of wine, and transported to Paris, where Georges Cuvier was
able to describe it for science, though le grand animal fossile de Maastricht
was not described as a Mosasaur ("Meuse reptile") until 1822, and
not given its official name, Mosasaurus hoffmani, until 1829. A
Mosasaur skull that had actually been discovered at Maastricht
earlier, has recently been reidentified in the Teylers Museum,
Haarlem.
The Maastricht limestone beds were rendered so famous they have
given their name to the ultimate 6-million-year epoch of the
Cretaceous: the Maastrichtian.
Conservation status: Fossil
Issue #180
