Ancient Seas

The water and sea basins we know today have been on Earth for much longer than the first humans. Clues from the ocean (in the form of seafloor or ice cores, and fossils) can help us learn about how the oceans reached their current state.

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For a long time, scientists thought that some small tentacled fossils were early ancestors of jellyfish. But a new study has found that these ancient animals are actually related to an entirely different group...
Sirenians , or seacows, are a group of marine mammals that include manatees and...
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One of the ocean's tiniest organisms often does the most harm. Microscopic...
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Evidence shows that life probably began in the ocean at least 3.5 billion years...

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Offshore Peru, during the Eocene (~56-34 million years ago), showing three archaeocetes (ancient whales), along with a previously described fossil penguin. Top to bottom: Perudyptes devriesi , unnamed protocetid, Ocucajea...
These "elevator" rudists, an ancient bivalve, used one long heavy valve to...
How long have jellyfish lived in the ocean? This jellyfish fossil is from...

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Whales swim, but their ancestors walked. Whales are mammals (like us) whose ancestors lived on land. Life probably began in...
Sirenians , or seacows, are a group of marine mammals that include manatees and dugongs . Currently, only a single species of seacow is found anywhere in the world. However, the fossil record of...
The peaceful Archaeocyatha lived during the most recent part of the Cambrian period. They separated into many families and were the Earth’s first reef-building animals.
Lenticulina secans -- this foram lives on the seafloor. This specimen was collected from ocean sediments in southeast Tanzania. It comes from a time over 92 million years ago when both the polar...
The basic body plans of all modern animals were set during the Cambrian Period, 542 - 488 million years ago. Your friends, family, and pet turtle may not look much like the creatures here. But we and...
During the late Cretaceous period, Kansas was covered by a vast sea. There, scientists have found fossils of Squalicorax sharks (also called crow sharks) that lived 70-80 million years ago. They were...
The Haplophrentis carinatus had two oar-like appendages (called “helens”) used to stabilize the creature and help it move along the ocean bottom.
For a long time, scientists thought that some small tentacled fossils were early ancestors of jellyfish. But a new study has found that these ancient animals are actually related to an entirely...
This illustration shows one old idea of what the ancient shark Helicoprion might have looked like. There once was room for many ideas—some more plausible than others—because the only fossils of the...
How long have jellyfish lived in the ocean? This jellyfish fossil is from the Cambrian period, more than 500 million years ago. It was found buried in Utah —an area that used to be underwater,...
The evolution of whales represents one of the great stories in macroevolution. It's a narrative that has mostly benefitted from an extraordinary series of fossils recovered from rocks around the...
About 100 million years ago, during the heyday of the dinosaurs , reefs were built by mollusks called rudist clams . They looked very different from today's coral reefs . Discover more about the...
Where ocean currents were strong, ancient rudist “recliners” lay unattached on the seabed. Notice the pink tentacles, which were used to filter feed. Learn more about ocean life throughout deep time...
When you're standing in a museum surrounded by fossils, you can almost imagine drifting through time to when long-extinct creatures swam the ocean. Found all over the world, these fossils can be read...
400 to 1,000 year old bones from an endangered seabird, the Hawaiian petrel. Bones such as these provide a window into the lives of seabirds before and after human arrival in the open ocean...
Offshore Peru, during the Eocene (~56-34 million years ago), showing three archaeocetes (ancient whales), along with a previously described fossil penguin. Top to bottom: Perudyptes devriesi ,...
Not all fossils from the Cambrian period became amulets; instead the extinct Hallucigenia sparsa was notable for its spines.
This rendering shows life at the end of the Cretaceous Period, before the impact of a 6.2 mi (10 km) asteroid triggered mass extinctions on land and sea. Dinosaurs are the most famous victims of the...
These "elevator" rudists, an ancient bivalve, used one long heavy valve to anchor themselves in the sediment. They used their tentacles (shown here in pink) to filter food from the sea water. And...
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