14 DAY TRIAL // In case you ever wondered how come penguins are not cold, even after they take a bath in the icy waters of the Antarctic, you should know they have a secret weapon, that apparently they developed when they still lived in warm climates.
A team of researchers from the University of Cape Town in South Africa concluded that penguins developed their humeral arterial plexus while they lived in warmer waters, some 49 million years ago.
The humeral arterial plexus is a crucial adaptation that helped penguins survive the cold waters of Antarctica, for the past 16 million years.
It is a network of blood vessels that limits heat loss through the wings, by routing blood coming into the body from the wings past the blood traveling from the body to the wings.
This way, the cooler blood gets heated by the warmer blood from the body and penguins manage to preserve their body heat, even if they swim in cold waters.
The earliest known penguins that had the plexus were living on the lost continent of Gondwana – what is today Seymour Island in Antarctica.
Back then, the waters there were far warmer than today, with an average temperature of 15ºC (59ºF), whereas the current temperature of the water is 1ºC (34ºF).
Even if this might seem odd, scientists can actually calculate ancient temperatures by looking at the chemistry of fossils — like magnesium levels in the shells of certain organisms that rise as temperatures go up.
The plexus must have evolved at first to help penguins save energy during long foraging trips in the cold water, at the same time as their skeleton (which helps them float and reduces drag) transformed to allow them to deep-dive and swim long distances.
Once the waters started cooling down, the plexus assumed a protection role that allowed penguins to invade the Antarctic ice sheets.
The researchers analyzed 7 live penguins and 19 fossilized ones, and concluded that the plexus that leaves behind grooves in the upper arm bone in live penguins also appeared in extinct penguin species from the fossil record.
So they concluded that the plexus appeared some 49 million years ago (at least), in a time when the planet went through a global warming period probably caused by gases released into the atmosphere by volcanoes.
Researcher Daniel Thomas, a paleontologist at the University of Cape Town in South Africa, told LiveScience that he “began this work thinking we would relate heat retention in penguins to the global cooling that took place at the Eocene-Oligocene boundary – about 34 million years ago, whereas in fact, penguins were cold-water-tolerant millions of years earlier.”
“Penguins have occupied much of the Southern Hemisphere in the last 40 million years because of their tolerance for cold water," Thomas added.
Thomas worked on this research with his colleagues Dan Ksepka and Ewan Fordyce, and their findings are detailed online in the journal Biology Letters.
