Perhaps no group of animals is more familiar to us than birds. With over 10,000 bird species worldwide, and over 468 species in Sri Lanka itself, they are among the most commonly seen animals across the planet. In fact, birds are so widespread that it’s almost impossible to go a day without seeing them! Birds today are renowned for many things. Their most obvious feature is naturally their ability to take flight, which has allowed them to become the undisputed rulers of today’s skies. However, birds are also adored for their beauty, with birds such as peacocks and flamingos being admired in every corner of the world for their vibrant plumage. Birds such as eagles are widely regarded as symbols of might and power while many birds, such as cranes, have significant value in the folktales and myths and legends of numerous cultures. Birds such as parrots and crows are even well known for their impressive intelligence and problem solving capabilities. There is hardly a place on Earth not filled with the sight or sound of birds but this very omnipresence makes it easy for us to overlook their value. Many of us may not take the time to appreciate the simple value of seeing a bird flying overhead or a bird perched on the branch of a tree. Yet, a world without birds is impossible to imagine and their value cannot be overstated. Despite their overwhelming abundance today, birds are actually far more special and far more unique then we could ever imagine and this becomes easier to understand when we look at their history.
Even the evolutionary history of birds showcases how special they are. Many of us may have heard through Jurassic Park that birds are actually the direct descendants of dinosaurs and this is completely true. In fact, birds are actual dinosaurs the same way humans are primates, and are descended from a group of bipedal, mostly carnivorous dinosaurs called theropods. This group includes the iconic T. rex as well as the famous Velociraptor, with the latter being very closely related to birds. There is significant fossil evidence proving birds and theropod dinosaurs share a huge number of similarities in a combination not shared with any other group of animal. These similarities include bipedal posture, three fingered hands, three toed feet, an elevated ankle, wishbone, half-moon shaped wrist bone and an internal system of air sacs. The eggs and embryos of many theropods are also identical in structure and development to those of birds and many dinosaur skeletons have even been preserved sitting over their nests like nesting birds. However, perhaps the most obvious similarity is in their feathers since bird like feathers have been preserved in the skeletons of several theropod dinosaurs, including relatives of both T. rex and Velociraptor. Velociraptor even has structures on its arms called quill knobs, which are also seen in birds today, and are attachment points for wing feathers. Overall, birds and theropod dinosaurs share so many features that the chances of all these similarities being simply due to coincidence is absurdly low. Further, most features seen in birds today, including their feathers and even certain behaviours, are all inherited from dinosaurs! Therefore, dinosaurs live on in birds today and that alone is an enormously amazing realisation! However, this isn’t what makes birds so special. Birds are not special simply because they are dinosaurs but because they are the only dinosaurs to have survived to the present day. Furthermore, when we look at how abundant and diverse dinosaurs used to be, it becomes clear just how lucky we are to have birds at all!
Non-bird dinosaurs first appeared around 230 million years ago, only going extinct when an unfathomably immense asteroid crashed into Earth 66 million years ago, causing the second worst mass extinction in the history of the planet. However, up until the asteroid impact, non-bird dinosaurs had thrived for a period of almost 170 million years, which is a staggeringly enormous amount of time. To put this into perspective, we humans have only existed for around 0.3 million years! Throughout their reign, dinosaurs evolved into every possible shape and size and occupied almost every habitat in every corner of the planet, including both the Arctic and Antarctica. The diversity of non-bird dinosaurs cannot be overstated and we’ve already been able to identify over 1000 species in the fossil record! However, since dinosaurs existed for 170 million years and because the preservation of fossils is an extremely rare phenomenon, even the 1000 species we’ve discovered so far is only a minuscule portion of the total number of species that would have existed. I say all of this to emphasise that, out of all these dinosaur groups, the only group that has survived to the present day is the birds and this is one of the reasons why birds are so special. Out of the staggering number of dinosaur groups, only one group survived past 66 million years and they are still with us today. Thus, our coexistence with birds is a blessing we should never overlook! However, there is another equally poignant reason for why birds are so valuable. Interestingly, the thing that makes birds so unique is also the very thing that has made them so iconic: their feathers.
I mentioned earlier that the feathers of birds are inherited from theropod dinosaurs similar to Velociraptor. However, the very evolution of feathers in the first place, especially flight feathers, is actually a unique adaptation. When we look through Earth’s natural history, it becomes clear that flight feathers are not only rare but downright bizarre and theropod dinosaurs are the only animals to have ever evolved them. In fact, these feathers probably didn’t even evolve for flight in the first place but instead evolved either as display structures to attract mates or for insulation. This seems to be supported by several dinosaur skeletons showing feathers that were useless for flying but may have been very useful for courtship or keeping warm. The group of dinosaurs that led to birds are a unique case where feathers developed over millions of years to assist in gliding and eventually flying. This is not seen in any other group of flying animal and illustrates how incredibly special birds are. Although there are many other vertebrates in our world today that are capable of flight, all of them use membranous sheets of skin called a patagium instead. For example, bats don’t have wings made of hair but instead possess a large sheet of skin over each wing. Other flying mammals today; such as flying squirrels, flying phalangers, anomalures and the Malayan colugo; all glide using sheets of skin that stretch between their front and back legs. Some reptiles and amphibians have also taken to the skies today but they too use skin instead.
For instance, the flying lizards called Draco can glide because they have extremely long ribs that are supported by a sheet of skin. Meanwhile, flying frogs use expanded sheets of webbed skin between their feet to help them glide. Flying geckos also have increased webbing on their feet but also possess flaps of skin along their flanks. On the other hand, flying snakes simply flare out their ribs when leaping from tree to tree. Even most extinct animals possessed membranous wings instead of feathers. A group of extinct reptiles called weigeltisaurids had bony rods extending from their bodies which were then supported by skin to help them glide. Most famous of all extinct flying animals are the pterosaurs, popularly called pterodactyls, and they had massive, membranous wings more like those of bats than any bird. This is particularly important since pterosaurs are very closely related to dinosaurs and show evidence of actually having feathers on their bodies but not on their wings. Even some theropod dinosaurs had wings made of skin instead of feathers. Yi qi is a theropod with bird like feathers covering its body but with sheets of skin over its wings like a bat. Yi qi and its close relatives, called scansoriopterygids, are actually the only dinosaurs known to have had membranous wings instead of feathers.
Overall, the history of life on our planet shows us that membranous wings are the default method for flying and not feathers. This is because membranous wings are much easier to evolve, only requiring an area of skin to expand with modifications in the arms. By comparison, flight feathers are among the strangest and most complex innovations seen in any vertebrate animal! The feathered wings of birds that we’re so familiar with today are actually extremely strange and highly unusual structures not seen anywhere else in nature. The fact that flight feathers are now present in 10,000 bird species is a testament to the extraordinary success of birds as a group and further highlights how incredibly special they really are. However, this also brings to light a very important but somewhat grim understanding. If birds were ever to go extinct, then it is very likely that feathered wings may never evolve again.
While membranous wings have evolved multiple times across the history of life, and are likely to continue reappearing, feathered wings have only ever evolved once. The flight feathers of theropod dinosaurs, that still remain in birds today, are the only time feathered wings have ever appeared in the history of the planet. While evolution has repeatedly proven that membranous wings are relatively easy to evolve, feathered wings have only appeared once and only once. Therefore, if birds were ever to disappear, the unique beauty and brilliance of their feathered wings would probably be lost forever. This is why it’s so important that we never take them for granted. Birds are living wonders of nature and we are beyond blessed to live in an age where the world is filled with their fantastic, feathered wings! It would also be the most shameful loss if we were to let them go extinct.
The non-bird dinosaurs were wiped out by an asteroid 15 kilometres wide; they faced an extinction that was impossible to survive and could do nothing to prepare or protect themselves. However, for better or worse, the threats facing birds today are entirely of our own doing. Thankfully, all is not lost and these threats are all threats that we can fix. Today, we have all the power and potential to address these issues and build a better tomorrow, so let us not wait for the loss of birds to remind us of their value. Let us recognise the value and privilege of seeing birds today and do what we can, in our own way, to ensure they continue to grace our skies for many generations to come. Even simple things, such as not littering in natural environments and not throwing garbage into water bodies, would contribute so much towards protecting birds and their habitats. Sri Lanka itself is home to over 468 species of birds, including 34 endemic species, all of which are amazingly wondrous in their own way. Even the most common birds, like pigeons, crows or sparrows, are every bit as remarkable and miraculous as peacocks, eagles or flamingos. The non-bird dinosaurs may be gone, but we can prevent their descendants from meeting the same fate. The next time we spot a sparrow, or hear the caw of a crow, let us remember to cherish the value of such sights and sounds and do what we can to ensure that we and our children may continue to experience them for the foreseeable future and beyond.
Writer David Jeevathithan Ambalavanar is a twenty four year old from Jaffna who has been fascinated with the natural world and its history. He is currently reading for his Bachelor of Science Honoure degree at Monash University Malaysia.
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