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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Most people have never heard of the Hawaiian petrel , an endangered, crow-sized seabird that spends the majority of its life searching for food over the North Pacific Ocean. Nevertheless, this bird is no...
How long have jellyfish lived in the ocean? This jellyfish fossil is from the...
Like the modern nautilus, this relative of modern squid hunted from inside the...
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What makes a top predator? Razor-sharp teeth? Speed? Strength? Size? Who is the...

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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...

DIVE DEEPER

When you're standing in a museum surrounded by fossils, you can almost imagine drifting through time to when long-extinct...
Ocean Overtime Timeline.
Crinoids (echinoderms related to sea stars and sea urchins) dominate the Paleozoic shallow water habitat in this illustration. They evolved a variety of stalk heights, which enabled them to capture...
This early whale was well suited to life at sea. But it also may have spent time on land. An ancestor of the right whale , Maiacetus lived 49-40 million years ago. It had flipper-like limbs and...
A life-sized model suspended over visitors at the San Diego Natural History Museum shows what an ancient shark, the Giant Megatooth ( Carcharodon megalodon ), might have looked like. More about the...
One of the ocean's tiniest organisms often does the most harm. Microscopic algae can grow rapidly to form harmful algal blooms (sometimes called "red tides"), which create unhealthy water conditions...
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.
Long before great white sharks appeared, much larger ancestors roamed the ocean. This giant ancient shark -- the Giant Megatooth ( Carcharodon megalodon ) -- was probably big enough to eat a whale.
Globotruncana falsostuarti -- a foram that lived about 75 million years ago, during the Cretaceous Period, from southeastern Tanzania. By measuring the chemistry in the shell, scientists can estimate...
Dugongs , along with manatees , make up a group of marine mammals called sirenians or seacows . In the modern world, only one species of seacow is found in any one place in the world. However, the...
A scientific illustration of the most powerful fish of its time, Carcharodon megalodon , which swam the ocean 30 million years ago. This shark may have reached a size of 20 meters/66 feet. Meet other...
This illustration shows the edge of a warm inland sea during the Cretaceous Period, heyday of the dinosaurs. Constantly shifting sediment supported new groups of organisms, including rudist clams—...
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 Wiwaxia corrugata may have molted its scales in order to grow past these hard boundaries.
Rudist clams are mollusks that went extinct about 65 million years ago. They were the reef builders of the Cretaceous Period, the heyday of the dinosaurs. Today corals have taken over the role...
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...
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...
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...
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