How did penguins become the "King of Antarctica"?

According to the New York Times website and Reuters news agency recently reported, it is difficult to imagine penguins living elsewhere. But fossils of ancient penguins appeared near the equator, and many of these prehistoric seabirds predate the formation of antarctic ice sheets.

Few animals have evolved like penguins to survive in the brutal Antarctic. Species like the emperor penguin have cascading insulation feathers, tightly packed blood vessels to maintain body temperature, and an abdomen large enough to withstand wind chills approaching minus 80 degrees Fahrenheit (about minus 62 degrees Celsius).

With all of these abilities to adapt to cold weather, it's hard to imagine penguins living elsewhere. But fossils of ancient penguins appeared near the equator, and many of these prehistoric seabirds predate the formation of antarctic ice sheets. Daniel Kesepka, a paleontologist at the Bruce Museum in the United States, said: "They experienced the hottest period in Earth's history, when the equator was 5 degrees Fahrenheit higher than it is now. They basically evolved in an ice-free environment. ”

To determine how penguins transitioned from warm tropical waters to the polar oceans, Kesepka and his colleagues recently analyzed the genomes of all extant penguins. However, the genes of modern penguins tell researchers only so much. Most modern lineages date only a few million years ago, giving much of the penguin's 60-million-year long evolutionary journey.

Fossil record

More than three-quarters of penguin species are "now extinct," Kesepka said. He added: "You have to study the fossil record or you can only see part of the matter." ”

To supplement modern data, the researchers studied a variety of ancient seabird fossils. Some prehistoric penguins traveled through the tropical waters near Peru, using their spear-like beaks to fork fish. Other penguins have long legs, with the largest probably 7 feet (about 2.1 meters) tall. Some even have rusty red feathers.

By comparing the genomes of modern penguins and penguin fossils, the team was able to reconstruct the penguins' evolutionary processes. In the findings, published Tuesday in Nature Communications, the researchers identified genes that help penguins transition from warm waters to the polar regions. Some of these genes help penguins gain fat, while others shape their shrunken wings into streamlined flippers. Some genes even boost penguins' immune systems or help them tolerate low oxygen while diving in the deep sea.

At the Natural History Museum in Lima, Peru, paleontologist Rudolf Salas studied the skull of a fossilized giant penguin that lived 36 million years ago, which is about 5 feet tall and weighs 130 pounds (about 59 kilograms).

The researchers also found genes that help fine-tune the penguins' eyes, which can be seen in the cold depths. Most birds have four types of cone cells, and one of the penguins' cone cells is inactive, which hinders their ability to see green and red. Instead, their eyes have adapted to the blue of the ocean.

Some of the missing genes have puzzled the researchers. While modern penguins eat krill, the team found evidence that their ancestors lacked genes that help break down crustacean shells. This may be evidence that ancient penguins preyed on larger prey, such as fish and squid. Penguins have limited mouth sensation and limited taste. Their taste receptors can only feel salty and sour, and Kesepka said, "If you're eating fish, that's pretty good." That's probably why they love sardines. ”

Change is slow

When these changes happened to ancient penguins, they were in trouble. Genetic analysis shows that penguins tend to evolve at the slowest rate of any bird. Because they look so peculiar, such a slow rate of change seems surprising. But it reveals how successful the penguin's plump, streamlined body structure is —for millions of years, its change has been a slow process. But the emperor penguins that breed during the cold Antarctic winters are the fastest of all penguins, leading the researchers to deduce that lower temperatures somehow accelerated the evolution of penguins.

Juliana Viana, an ecologist at the Catholic University of Chile, said the idea is consistent with penguins migrating south during global cooling. Wianna recently led a similar study but was not involved in the new study. "Their evolutionary history is closely related to climate change and glaciation in history," she said. ”

Understanding how penguins have changed in the past may provide clues as to how penguins will survive in a hotter future. Daniel Thomas, a paleontologist at Massey University in New Zealand and author of the new study, said: "Warmer temperatures will affect the biogeographic range of penguins, affecting the food species they depend on, as well as the species that prey on them. ”

Kesepka said that while the study was a comprehensive study of the penguin family, there was still one species of seabird missing — the last one that could fly. This small puffin-like bird may have lived in ancient New Zealand, but its fossils are difficult to find. "If I have a wish, that's what I want most," he said. ”

Environmentally driven

Penguins evolved from flying seabirds to flightless marine dwellers, spreading from cold Antarctica all the way to the tropical Galapagos Islands, and their evolutionary history is one of the wonders of the animal kingdom.

The researchers conducted the most detailed and in-depth study of the penguins' evolutionary history to date, including identifying a range of genes that are essential for evolution such as underwater vision, long dives, body temperature regulation, diet and body size. On Tuesday they released the results. The history of penguins dates back more than 60 million years.

The researchers sequenced genomes of 20 extant penguin species and subspecies. Since more than three-quarters of known penguin species are extinct, the researchers also analyzed 50 fossil species using skeletal data.

The researchers say penguins share a common ancestor with seabirds such as albatrosses and petrels. In the beginning, penguins evolved the ability to dive like puffins, then lost the ability to fly in the process of adapting to the marine environment, becoming excellent "swimmers" and "divers".

The earliest known penguins date back 61 million years, about 5 million years after the mass extinction event that led to the extinction of the dinosaurs.

Daniel Kesepka, a bird paleontologist at the Bruce Museum in Greenwich, Connecticut, said: "In my opinion, penguins are a classic example of a major evolutionary shift, just as the way whales evolved to live in water, and bats evolved the ability to fly. ”

"We know penguins evolved from flying birds, but this happened 60 million years ago, and we need to study the fossil record to figure out when, where, and how this evolutionary process happened," Ksepka said. In addition, penguins are a very endearing creature. They love each other, they fight, they steal, and because of their comical upright posture, it's easy to imagine that they have the same motives as humans. ”

The new study, published in Nature Communications, sheds light on how changes in global temperature and major ocean currents have become important drivers of penguin evolution.

Genetic mutations

"We estimated how the population of each penguin species has fluctuated over the past 250,000 years," Kesepka said. Changes in the size of the ice sheet have a significant impact on penguins, and species that are susceptible to melting sea ice may suffer from future global warming. ”

The researchers also found that among birds, penguins evolved at the slowest rate ever explored.

Penguins live mainly in the southern hemisphere, including species such as the Adélie penguin, which live along the coast of Antarctica. Galapagos penguins are the only penguin species found north of the equator.

Theresa Cole, a postdoctoral researcher at the University of Copenhagen and lead author of the study, said the study found multiple genes that are likely to be linked to penguins' unique physiological adaptability.

These genes exhibit genetic mutations. The mutation shifts the range of color perception of its vision toward the blue light in the spectrum. Blue light is more able to penetrate seawater than red light, reaching deeper under the surface, so this feature of penguins helps them fine-tune their vision to adapt to the underwater low-brightness environment, and their vision becomes sharper.

Penguins are active in genes that help birds distinguish between salty and sour tastes. But genes that help distinguish between bitter, sweet, and spicy tastes have lost their activity. Penguins may no longer need those genes because they feed in cold, salty waters, and they usually swallow entire prey, such as fish, shrimp and squid.

The penguin's wing bones are constantly flattened and hardened, making its flying feathers shorter and thinner, which helps it turn its wings into flippers. They also shrink hollow bones, thicken bone walls to improve diving efficiency, and enhance the ability to store more oxygen in muscles for long-term dives.

Once upon a time, penguins were much larger than species are today. Between 55 million and 60 million years ago, a penguin species living in New Zealand was about 6 feet taller than the Kumi penguin. The largest surviving penguin species, the Emperor Penguin, is about 3 feet tall.

Source: Reference News Network