Geology Reference
In-Depth Information
Swimming in ancient seas
For millions of years in the Paleozoic, early reptiles populated the land. By 251 million
years ago, a few of them had returned to the seas. A few groups of reptiles evolved to
survive in the ancient seas of the Mesozoic earth:
Ichthyosaurs:
Icthyosaurs
were large, fish-like reptiles that looked somewhat like
modern dolphins. They gave birth to live young instead of laying eggs like most
reptiles. They were predators, at the top of the marine food chain in the Mesozoic,
eating fish and other marine creatures, including cephalopods (see Chapter 19).
Pleisosaurs:
The
plesiosaurs
were fish-eating reptiles. Some of them had short
necks, and others had very long necks, a tail, and four paddle-like feet. They
ranged in size from 4 meters to up to almost 15 meters (13 to almost 50 feet).
Mosasaurs:
Mosasaurs
evolved toward the end of the Mesozoic, during the Creta-
ceous period. They resembled large lizards with paddle-shaped limbs. Scientists
now think that mosasaurs are closely related to modern snakes, which also
evolved from early lizards.
Taking to the skies: Pterosaurs
