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Often it's the tiniest organisms that do the most harm. One example is microscopic algae, which can grow rapidly to form harmful algal blooms . Such blooms (some are called "red tides") create unhealthy...
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Evidence shows that life probably began in the ocean at least 3.5 billion years...
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Monodontids, the group of whales that includes the belugas and narwhals...
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The whales that we see in today's world can broadly be split into two groups:...

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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...
The foot-long extinct shark Falcatus falcatus lived during the early Carboniferous period around 325 million years ago. The species, known from fossils in the Bear Gulch formation of Montana , was...
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...
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 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...
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...
Evidence shows that life probably began in the ocean at least 3.5 billion years ago. Photosynthesis began more than 2.5 billion years ago—the Great Oxidation Event. But it took hundreds of millions...
Opabinia was a strange looking creature: it had five mushroom-like eyes that allowed it to see predators approaching from many directions.
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...
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...
The Wiwaxia corrugata may have molted its scales in order to grow past these hard boundaries.
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...
Earth’s first animals had soft bodies. This illustration shows a community of soft-bodied Ediacaran (edi-A-karan) animals. Some species resemble living ocean creatures. Others are unlike any known...
What makes a top predator? Razor-sharp teeth? Speed? Strength? Size? Who is the most fearsome hunter? It depends on where and when you look.
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...
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...
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 Haplophrentis carinatus had two oar-like appendages (called “helens”) used to stabilize the creature and help it move along the ocean bottom.
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