There are a few different theories around how birds became what they are today, but most support the theory that the discovery of a 150-million-year-old fossil known as Archaeopteryx or “old wing” showed the world the transition from land-based dinosaurs to avian ones. Discovered in what is now Southern Germany and Portugal, the German name for this fossil is Urvogel, “first” or “original bird”, although since its discovery in 1860 older specimens of a different nature have been found, and currently the oldest by 10 million years is thought to be Aurornis from China.
The prefix ‘dino’ means great and terrible, and the suffix ‘saurus’ means lizard, or reptile.
Up in the air
A relatively new lack of agreement over whether birds are actually dinosaurs, however, is basically because so few fossils exist and more is being discovered and debated about taxonomy every day. At some point in time, when adapting for flight, many bird bones became hollow, which meant that upon death and compression in sediment, they disintegrated, and as their overall frames became lighter, they were usually crushed flat, giving palaeontologists only a 2D version of a once 3D animal. Sturdier bones of much larger animals tend to hold their structure well, often completely, allowing angles to be determined and therefore the final shape of the organism itself, not to mention the availability of vast amounts of genetic material.
There is a growing “movement” of dissenters from the long-accepted theories drawn by Darwinand Co. that birds are not descended from dinosaursat all but from another branch within the archosaur clade.
OK - I’ll back up.
The prefix ‘dino’ means great and terrible, and the suffix ‘saurus’ means lizard, or reptile. The word ‘archo’ as a prefix here means ruling, chief, extreme, as in archduke, arch enemy; sometimes as a suffix, as in matriarchy, oligarchy. The word ‘clade’ means a group of organisms believed to contain all the evolutionary descendants of a common ancestor: we are in the great ape and human clade, for instance.
Crocodilians and birds are now the only living examples of archosaurs today.
Archosauria is a clade that is referred to as a crown group, as it encompasses an awful lot of organisms that may well have had a common ancestor. Archosaurs began to exist around 245 million years ago. Dinosaurs are within the archosaur clade, and began to emerge around 233 million years ago. The term “dinosaur” is often applied to anything really, really old because of our propensity to hang onto just one word for things over time; given that the discovery of massive skeletons encased in rock have been impressing the worldsince 1824, it is easy to understand why any such bones found are instantly dubbed dinosaurs.
It is accepted by everyone that crocodilians and birds are now the only living examples of archosaurs today, and the most widely held belief about birds is that they descended from a group of dinosaurs called theropods, first seen around 231 million years ago. This is what you’ll read in practically any publication you care to browse through. However, you may come across another angle, that birds arenot living dinosaurs, in the sense that birds evolved from a separate branch within the archosaur clade; dinosaurs to the left, birds to the right kind of thing. To us, this seems to be a perfectly reasonable suggestion that will require a lot of actual physical digging, but as with all things claimed to be true for centuries, some people can be a bit stubborn. At present, anyone who argues this angle is somewhat disparagingly referred to as a member of BAND (Birds Are Not Dinosaurs) and are discounted as not knowing what they are talking about. There are empirical methods that can determine whose argument holds water and whose doesn’t, and so far, the Birds Are Dinosaurs Movement (BADM) have the upper dorsal fin. Who knows what time will reveal if anything at all?
For our purposes, we’ll just call them fossils.
It is assumed that the reason why there are so many species of birds alive today (figures lurch between 10,400 and a suggested 20,000 recently) is because of one massive asteroid about 66 million years ago that wiped out three quarters of living organisms on the planet. Bye-bye dinosaurs. However by that point, some of these reptiles had developed feathered wings, and any that weren’t in the impact radius were able to locate land that wasn’t a burning mass of molten rock and fire from above, and inhabit it. As the world cooled and plants once again regained their hold, a distinct lack of predators led to an almighty surge inadaptation as niches of all sorts began to emerge, and birds filled those niches: some began to eat fruit, insects, seeds, some tiny wee mammals that had escaped the destruction, and beaks and digestive organs adapted to the new diet, as did wings, body shape and size to efficiently find and process this food. Evolution doesn’t mean species change to become smarter, it means species change to survive, to adapt to the environment they are presented with, given half a chance. Birds now occupy almost every habitat on the planet, salt to freshwater, high to low altitudes, arid and desolate landscapes to lush and flora-filled rainforests.
The bird was alive at the same time as when the Antarctic was much warmer.
What we do know about birds today from fossils and genetic mapping is what they no longer have: heavy, tooth-filled jaws have been replaced by lightweight beaks; some bones have fused, or gone altogether; flight bones are hollow and are pneumatically operated, and density only exists in a few select places like the breastbone for flight muscles; the bladder has gone entirely, and urine and faeces are excreted as a mixed paste from the one orifice, the same one used for mating and laying eggs; the lungs have a constant flow of air and keep to the same volume, rather than deflating and expanding like ours, affecting our buoyancy in air as well as water; they’ve even lost one ovary, and all genitalia shrink during the non-breeding season. Genome mapping and DNA research has shown that during evolution, some DNA is erased altogether, never repeated, and birds have had many of these deletion events as they changed from those long, long-ago reptiles of the sky to what we see today.
At the end of October 2020, a report was published in Scientific Reports by Peter Kloess, who 5 years previously as a graduate student had been going through some fossils from Antarctica that had been stored in a museum at the University of California Berkeley since the 1980s. He found a partial jawbone of a prehistoric bird that was identified as belonging to a clade called Pelagornithidae, huge sea-going birds whose remains have been found around the world. This jawbone was found on Seymour Island in Antarctica, where fossils of penguins, and various cousins of what we call ducks and geese these days have also been found. Pelagornithids, also known as bony-toothed birds as their jaws held tooth-like pointy structures called pseudoteeth (not real teeth but in fact outgrowths of the jawbone), scoured the waters of the globe snapping up fish and squid from below around 40 million years ago. Whales and seals hadn’t become the dominant predators yet, so a lot of food was to be had, and it is now thought that the species that inhabited the Antarctic was possibly the largest bird that ever lived.
Earlier examples of fossils showed that the majority of birds had wingspans anywhere between 3.5 m and 4.5 m, but the spacing and erosion of the pseudoteeth present in this jawbone showed this bird probably had a wingspan of around 6.4 m, making this the best evidence of giant birds so far, twice the size of modern-day albatrosses. Not only was this suggestive that many more huge birds were around, the team also realised that the rock it was encased in and lichen deposits found in grooves on the bone showed this jawbone was around 10 million years older than all the other ones previously analysed. This meant these birds had actually come into being “just'' 15 million years after the asteroid that had wiped out all non-avian animals, a pretty astounding thing in palaeontology circles. This indicates that the bird was alive at the same time as when the Antarctic was much warmer, as the continent only froze over around 34 million years ago, meaning there were also land mammals such as sloths and anteaters to contend with over territory in this ecosystem. The icy wastes we know today have been shown to have supported rich and diverse fauna and flora, further backed up by the discovery of a species of frog in April 2020, the first amphibian found there.
There is much to learn about the origins of birds:potentially never enough. That they were huge and dominant and darkened the skies at some point in our collective past is now not in doubt, and logic dictates there are more astounding facts to unearth. If you are interested in bird fossils and learning more than there are many online resources, but we really like this one – just bear in mind it doesn’t matter if you are a member of the BAND or BADM club, as Einstein said, any fool can know, the point is to understand.