Why penguin skeleton is different from other birds and land animals? – Technology Org

All vertebrate animals – including humans, dogs, or penguins – have similar skeletons. However, the skeletal system of penguins has some particularities that make their bone structure unique.


Penguins. Image credit: Djwosa via Pixabay, free license

Number of bones in penguin skeleton

While humans have 206 bones, penguins have just 112. However, they share nearly all main skeletal features with us, despite being visually very different from people from other animals. Penguins also have a skull, a neck, and a vertebral column. They also have knees and elbows – just to name a few similarities.

These non-flying birds also have one of the fastest bone growth rates in the animal kingdom.

Penguins are birds, but why their bones are different?

As birds learned to fly, they evolved to have fewer bones, which allowed them to weigh less. For example, humans have two ankle bones, while birds have one long leg bone that connects to their feet and toes. Their bones in the spine are also joined together in one structure. That lets them fly or swim in a horizontal position. The bones of birds are lighter than these of other animals, as they are filled with spaces for air.

A king penguin feeding its chick.

A king penguin feeding its chick. Image credit: heidemsy via Pixabay, free license

But, besides these traits of the skeleton of birds, penguins have their own particularities. They do not fly but spend most of their time in the ocean; therefore, they have heavier bones than other birds. They have developed dense bones with no air pockets contrary to their flying relatives.

The weight of bones keeps penguins from floating up to the water’s surface. That is a useful ability, as penguins can easily dive as deep as 1,500 feet (460 meters). The deepest known penguin dive is 564 meters (1850 feet), with a duration of up to 32.2 minutes.

Their wings are adapted to swimming and not for flying. They look like short, flat fins and do not bend but act like paddles and let penguins swim fast. In fact, penguins can reach a speed of 22 mph, which is the velocity of a relatively fast-moving bike.

A swimming penguin.

A swimming penguin. Image credit: Pixabay, free license

When did penguins first appear on earth?

The first flightless penguins emerged approximately 66 million years ago, right after the great mass extinction event.

It is thought that penguin predecessors were capable of flying. Then, an intermediary evolutionary stage followed, during which these animals learned to swim and dive, but also kept their ability to perform aerial flights. And the current form of penguins is the one in which they became highly efficient in swimming and diving; They, however, do not fly anymore but use their wings to propel themselves in water.

Scientists, however, have not found any fossils proving this three-stage theory of penguin evolution. So how do they know that such a transition likely happened? Or, what was the reason for such a change?

Why did penguins evolve differently from other birds?

The most popular theory says that at some stage of their existence, penguins simply became more efficient at diving than flying. This difference in their abilities slowly grew until they were no longer capable of getting off the ground. Furthermore, there was no incentive not to dive, because the seas were always full of food and it was easier to catch than in the air.

Paleontologists did histological bone microstructure investigations based on discovered bones of ancient penguins. Analysis results show uneven distribution of bone hardening, which suggests that this transition to the flightless stage did not occur at the same time in different parts of the skeleton.

Some ancient penguin skeletons are larger compared to current specimens. It is known that in diving birds, both dive duration and maximum depth are proportionally related to their body size. This means that those earliest possible species were able to reach even greater depths and longer diving durations.

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