Old Earth Ministries Online Dinosaur Curriculum
Free online curriculum for homeschools and private schools
From Old Earth Ministries (We Believe in an Old Earth...and God!)
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Lesson 74 - Mosasaurs
Mosasaurs (from Latin Mosa meaning the 'Meuse river',
and Greek sauros meaning 'lizard') are large extinct marine
lizards. The first fossil remains were discovered in a
limestone quarry at
Maastricht on the Meuse in 1764. Mosasaurs
are now considered to be the closest relatives of snakes, due to cladistic
analyses that have taken into account similarities in jaw and skull
anatomies. Mosasaurs were
varanoids closely related to terrestrial
monitor lizards. They
probably evolved from semi-aquatic
squamates known as
aigialosaurs, which were more similar in
appearance to modern-day
monitor lizards, in the Early Cretaceous.
During the last 20 million years of the Cretaceous Period (Turonian-Maastrichtian),
with the extinction of the
pliosaurs, mosasaurs became the dominant
Length: Smallest species was about 10 feet, largest species was 57 feet
Date Range: 85 - 65 Ma, Cretaceous Period
|Mosasaurus hoffmannii skeleton, Natural History Museum of Maastricht, The Netherlands (Picture Source)|
Mosasaurs breathed air, were powerful swimmers, and were well-adapted to living in the warm, shallow epicontinental seas prevalent during the Late Cretaceous Period. Mosasaurs
The smallest-known mosasaur was Carinodens belgicus, which was about 3.0 metres (9.8 ft) to 3.5 metres (11 ft) long and probably lived in shallow waters near shore, cracking mollusks and sea urchins with its bulbous teeth. Larger mosasaurs were more typical: mosasaurs ranged in size up to 17 metres (56 ft). Tylosaurus holds the record for longest mosasaur, at 17.5 metres (57 ft).
Mosasaurs had a body shape similar to that of modern-day monitor lizards (varanids), but
Mosasaurs had a double-hinged jaw
and flexible skull (much like that of a snake),
which enabled them to gulp down their prey almost whole, a snakelike habit
which helped identify the unmasticated gut contents fossilized within
mosasaur skeletons. A skeleton of
Tylosaurus proriger from
South Dakota included remains of the diving
Hesperornis, a marine
bony fish, a possible
shark and another, smaller mosasaur
(Clidastes). Mosasaur bones have also been found with shark teeth embedded
Despite the relatively high number of mosasaur remains collected worldwide, knowledge of the nature of their skin coverings remains in its early stages. An incredibly small amount of mosasaurid specimens collected from around the world retain fossilized scale imprints; this
More recently, a well preserved
has been found that preserves not only skin impressions, but also internal
organs. There are several reddish areas in the fossil that may represent the
heart, lungs, and kidneys. The trachea is also preserved along with part of
what may be the
retina in the eye. The
placement of the kidneys is farther forward in the abdomen than it is in
monitor lizards, and is more similar to that of
cetaceans. As in cetaceans, the
leading to the lungs run parallel to each other instead of splitting apart
from one another as in monitors and other terrestrial reptiles. In
mosasaurs, these features may be internal adaptations to a fully marine
Sea levels were high during the Cretaceous Period, causing marine transgressions in many parts of the world and a great inland seaway in what is now North America. Mosasaur fossils have been found in the Netherlands, Belgium, Denmark, Portugal, Sweden, the United Kingdom, Angola, Morocco, Australia, New Zealand, and on Vega Island off the coast of Antarctica. Mosasaurs have been found in Canada in Manitoba and Saskatchewan and in much of the contiguous United States. Complete or partial specimens have been found in Alabama, Mississippi, Tennessee, and Georgia -- as well as in states covered by the Cretaceous seaway: Texas, southwest Arkansas, New Mexico, Kansas, Colorado, Nebrask, South Dakota, Montana, and the Pierre Shale/Fox Hills formations of North Dakota. Lastly, mosasaur bones and teeth are also known from California, Mexico, and Peru.
Many of the so-called 'dinosaur' remains found on New Zealand are actually mosasaurs and plesiosaurs, both being Mesozoic predatory marine reptiles.
Based on features such as the loosely-hinged jaw, modified/reduced limbs and probable locomotion, many researchers believe that snakes share a common marine ancestry with mosasaurs, a suggestion advanced in 1869, by Edward Drinker Cope, who coined the term "Pythonomorpha" to unite them. The idea lay dormant for more than a century, to be revived in the 1990s. Recently, the discovery of Najash rionegrina, a fossorial snake from South America cast doubt on the marine origin theory.
In 2005, research reported in Netherlands Journal of Geosciences, confirmed that the recently uncovered Dallasaurus turneri is an early link between land-based monitor lizards (such as the Komodo dragon) and the aquatic mosasaurs.
In popular culture
Mosasaurs appear in the BBC television series Sea Monsters. Mosasaurs also feature heavily in the ITV television series Primeval. In this show, the mosasaurs are depicted incorrectly as having skin more like a crocodile's. A highly evolved mosasaur appeared in an episode of Godzilla: The Series. It was inhabiting Loch Ness as the legendary Loch Ness Monster.
The IMAX 3D film "Sea Monsters"
features several mosasaurs (including Tylosaurus and
Platecarpus) with detailed animated
recreations of their movements and activities.
Return to the Old Earth Ministries Online Dinosaur Curriculum homepage.
Bay State Replicas - T-rex teeth, claws, skulls, jaws, foot, rib, femur, complete skeleton (1/20 scale), brain cavity
Black Hills Institute - Full size skulls, skeletons, 1/6th scale disartictulated skull, teeth, arm, leg, femur, foot, claws. Wall-mounted half-skull.