Plotopteridae

A long time ago, special birds lived in the sea.

These birds could not fly in the sky. Instead, they used their short wings to swim. They were like penguins, but they lived in a different place.

Some of these birds were very large. They lived on cold islands. They moved south as sea plants grew. Later, other sea animals like seals arrived. These birds then went away forever. They are part of history now.

Plotopteridae were a family of birds that lived long ago.

These birds could not fly in the sky. Instead, they used their short wings to swim deep under the water. This is called wing-propelled pursuit diving. This is the same way penguins swim today.

Some people called them the "Northern Hemisphere's penguins." They lived in the North Pacific. This is far from where penguins live today. They may look like penguins, but they are not close relatives. Some scientists think they are related to cormorants or darters.

These birds lived on cold islands. They moved south as kelp forests grew. Some were very big. One type had legs twice as long as an emperor penguin. Most lived during the Oligocene time. They went extinct during the Miocene. This happened when seals and dolphins grew in number. Some think these new sea animals caused the birds to go away. Fossils have been found in many places. These include Japan, Washington, and California.

Plotopteridae were a family of extinct seabirds. These birds could not fly through the air. Instead, they lived in the ocean. They used their short wings to swim deep under the water. This way of moving is called wing-propelled pursuit diving.

This is the same way penguins swim today. Some people called them the "Northern Hemisphere's penguins." They lived in the North Pacific. This is on the other side of the world from real penguins. They were not close relatives, even if they looked similar.

These birds had a very special way of living. They likely evolved on cold islands during the mid-Eocene time. As kelp forests grew, the birds spread south. They used their wings to hunt for food underwater. Their bodies were built for the sea. Their skeletons were similar to a bird called a darter.

Some fossils show tiny holes in the bird bones. These holes were made by a marine bone-eating worm named Osedax. This shows how even dead bones became part of the ocean.

Scientists have spent a long time studying these birds. They want to know exactly where they belong in the bird family tree. Some think they are related to darters or cormorants. Other theories suggest they might share an ancestor with penguins.

However, recent studies show big differences. The shoulder and chest bones of plotopterids are not like penguin bones. This means they might not work exactly the same way. Finding these fossils helps us understand how different animals solve the same problems.

We know many details about where they lived and how big they were. Fossils have been found in California, Oregon, and Washington. They were also found in British Columbia and parts of Japan. These places include Hokkaido, Tōhoku, Chūbu, and Kyushu.

Some species were quite large. One bird had a leg bone twice as long as an emperor penguin. Another species, Tonsala hildegardae, was found in the Pysht Formation in Washington. The earliest known member was called Phocavis maritimus.

Most plotopterids lived during the Oligocene time. They eventually went extinct during the early to mid-Miocene. This happened around the same time as the giant penguins.

At this time, seals and dolphins were also spreading across the seas. Some people think these new marine mammals might be why the birds disappeared. This idea has not been formally tested yet. It is a mystery that scientists are still looking at today. The history of these birds shows us how life in the ocean changes over time.

Plotopteridae was a family of extinct seabirds that lived long ago. These birds were flightless, meaning they could not fly through the air. Instead, they were highly adapted for life in the ocean. They used a method called wing-propelled pursuit diving to hunt. This means they used their wings to swim through the water to catch prey.

Because they lived in the North Pacific, they were sometimes called the "Northern Hemisphere's penguins." However, they were not closely related to modern penguins. They are an example of convergent evolution. This happens when different animals develop similar traits because they live in similar environments.

The way these birds moved was very specialized. They had shortened wings that were optimized for diving deep underwater. Their body skeletons were quite similar to those of the darter, which is a type of water bird.

Some scientists have looked closely at their anatomy to find their relatives. There is a theory that they might share a common ancestor with penguins. This idea comes from similarities in their brain morphology and forelimbs. However, recent studies have challenged this idea. Researchers found that the shoulder-girdle, forelimb, and sternum differ significantly from penguins. The sternum is the breastbone that connects to the wings. These differences suggest their functional mechanics might not be exactly like a penguin's.

Plotopterids are currently placed in different ways by scientists. Many researchers consider them members of the order Suliformes. This order includes birds like cormorants and darters. Some studies suggest they are closely related to the Anhingidae family, which are darters. Others link them to the Phalacrocoracidae family, which are cormorants. Interestingly, the hallux of these birds provides another clue. The hallux is the big toe on a bird's foot. In plotopterids, this toe was more similar to frigatebirds than to cormorants. This suggests they may have evolved from a highly aerial ancestor that could fly well.

We can trace the history of these birds through the fossil record. The earliest known member of the family was Phocavis maritimus. This species lived during the late Eocene epoch. Most other known species lived during the Oligocene epoch.

They likely evolved on arctic islands during the mid-Eocene. As kelp forests formed, these birds spread southwards. Eventually, the family became extinct during the early to mid-Miocene. This extinction happened around the same time as the extinction of giant penguins in the Southern Hemisphere. Some scientists speculate that the radiation of marine mammals, such as seals and dolphins, caused this extinction. However, this theory has not been formally tested yet.

Fossils of plotopterids have been found in many different locations. In North America, they were found in California, Oregon, and Washington. They were also discovered in British Columbia.

In Asia, fossils have been found in Japan. These include the regions of Hokkaido, Tōhoku, Chūbu, and Kyushu. One specific species, Tonsala hildegardae, was identified from rocks in Washington State. These fossils were found in the lower part of the Pysht Formation. This formation dates back to the late Oligocene. These locations show that plotopterids had a wide geographic range across the North Pacific.

These birds came in many different sizes. Some were only as large as a large cormorant, such as a Brandt's cormorant. Other members of the family were much larger. For example, some species had a femur length twice as long as an emperor penguin. The femur is the large bone in the upper leg.

Finding these large fossils helps scientists understand the scale of these ancient birds. It also shows how much they varied within their own family.

Scientific discoveries involving these birds also reveal how the ocean works. Some fossils of Tonsala hildegardae include very interesting details. They contain some of the first known examples of borings made by Osedax. Osedax is a type of marine bone-eating worm. These worms create holes in bones that have fallen to the ocean floor.

This tells us how nutrients move through the marine ecosystem. Even after a bird died, its bones provided food for other life forms. This connects the study of extinct birds to the study of deep-sea biology.