Longrich challenges some of the established wisdom in his field. ‘A standard approach in evolutionary biology is that macroevolution is just lots of microevolution — I question that.’ Evolution didn’t just happen automatically and rhythmically, Longrich argues. ‘Over very long timescales, unusual things happened. The evolution of flight, for instance, occurred repeatedly but in the last half-billion years, it only happened four to five times.’ He describes the wonder that is flight. ‘It’s an amazing adaptation, given how birds are very successful beings, widespread, diverse and long-lived — but avian flight only evolved once. Some other things evolved flight, like bats, insects and certain snakes which went halfway.’ Even as you ponder the charms of flying snakes, Longrich continues, ‘But the avian evolution of flight was extremely rare. You needed the right adaptations, happening in the right order, the most suited environment, the right ecological niches. Everything had to come into alignment or it couldn’t happen — that involves improbability or unpredictability.’
I CAN DO IT TOO! Squirrels can achieve some flight with their arms and bushy tail (Photo: Getty images & iStock)
Avian flight has its roots in the Jurassic era. Longrich describes, ‘First, there were probably just dinosaurs, jumping between branches. To stabilise themselves, they’d possibly have thrown their arms out on the side, like a sky diver. This would make them descend more slowly. Next, the integument, the feathers and skin, could have expanded to make larger surfaces which could con trol descent more effectively. We see an incipient version of this in squirrels actually which have some membrane on their arms. Evolution could then start elaborating with feathers.’
THEN & NOW: The archaeopteryx fossil (above), the first bird dating back 145 million years, was discovered in Germany in 1861 — showing a complete set of wings, it is not too different from birds seen today, like the Hoatzin (R) (Photo: Getty images & iStock)
Dino feathers wouldn’t have looked too polished. ‘Initially, these would have been quite crude,’ Longrich explains, ‘Instead of bird feathers, these would have been more hair-like, meant mostly for insulation. But packed together, like the collected bristles of a paintbrush, they’d allow you to control descent and steer. As these grew bigger, species could generate enough lift to descend at an angle — so, you’re not just coming down, you’re doing so and going forward. Creatures would also develop control over landing — they’d have large structures on their tail to stabilise this, like an arrow’s flight. Squirrels have a big bushy tail — this is an aerodynamic stabiliser which prevents them from tumbling. Dinosaurs possibly also evolved a big bushy tail alongside gliding and finally flapping.’
Again, the chances of all this happening were slim. Longrich says, ‘Dinosaurs began by gliding between trees — then, one lineage evolved which could flap its wings. Dinosaurs likely experimented with flight more than once. A fossil found in China has gliding membranes but these are not like those of birds — this could have been an independent evo lution which didn’t go further. While they experimented, only one lineage of dinosaurs got lucky.’
Longrich’s own research on the archaeopteryx has been path-breaking.
(Photo: Getty images & iStock)
‘The archaeopteryx is an early bird,’ he describes, ‘It dates back 145 million years. The skeleton is similar to a dinosaur’s, almost like a non-avian Velociraptor, but smaller. This has very modern feathers. It has pointed wings, tail feathers and little feathers on the hind limbs that act like a pair of extra wings. It could flap its wings and fly,’ Longrich pauses, then emphasises, ‘Perhaps not very well but it could fly.’
He describes his study of the archaeopteryx fossil, ‘I wanted to reconstruct the wings in detail. So, I started to draw, tracing, barb by barb, every shaft and structure — I then realised much of the conventional reconstruction didn’t work. You had these series of feathers that alternate with the wing feathers. They were so regular. Why was every other feather displaced rather than just one or two? How did everything else about these wings look perfect? I found we were actually looking at two different series of feathers — one was the main wing feathers. The other was the coverts.’ You can hear Longrich’s amusement as he says, ‘When you sit down and draw something, it forces you to let the fossil talk, instead of superimposing your preconceptions on it.’
Birds began evolving from the midJurassic period. The process was slow, taking time — millions of years — to get the right mutations. ‘Meanwhile,’ Longrich says, enthusiastically, ‘There was a big extinction event during the Triassic era and another in the later Jurassic. All those also caused diversifications. This is when we tend to see evolution being its most innovative — things start moving in the wake of a mass extinction. After the asteroid impact which wiped out most dinosaurs, bats started evolving. Then came mammals.’
As birds, the successors of dinosaurs, evolved, their wings diversified. ‘There is a huge range of wings now. Some, like the albatross, are very long. Duck wings are really short. Some are specialised for soaring, some for diving. Some are even used as weapons, certain plovers, for instance, having stabbing spurs on their wings while geese have knobs on theirs to punch with. With evolution,’ Longrich smiles gently, ‘One feature might develop for a certain purpose — but then, it turns out to be useful for something else as well.’ Yet, the basic arrangement of bird wings hasn’t changed in the last 100 million years. Longrich says, ‘There is something very close to a modern bird wing in the Jurassic archaeopteryx. The feathers are primitive but in a few more million years, you’d have had basically a modern bird wing. So, a bird wing today is actually a living fossil — it hasn’t changed much. That’s also since it is as good as it can be.’
I’M ACTUALLY PERFECT: Being superb, bird wings have not altered much over 145 million years (Photo: Getty images & iStock)
Source : Times of India
