An illustration of Archaeopteryx
Mark Witton.
About 150 million years ago, a small, feathered dinosaur was negotiating one of the most consequential transitions in vertebrate evolution: getting airborne and remaining there under its own power. Archaeopteryx, with its feathered wings, toothed jaws, clawed fingers and long, bony tail, combined features that creationists prefer to imagine belong in separate, independently created categories. It also lived almost 150 million years before the supposed ‘Creation Week’ of young-Earth creationism. Both its anatomy and its antiquity present awkward problems for anyone trying to compress the history of life into a literal reading of Genesis.
Now, a paper in Developmental Biology, by Erik A. Meilak and colleagues, addresses a particularly interesting question: how could an animal with a less specialised flight apparatus than that of modern birds get off the ground? Their modelling suggests that powerful hindlimbs could have supplied the answer. A succession of forward leaps, potentially assisted by a wingbeat between jumps, could have built up sufficient speed for flapping flight.
For a modelled Archaeopteryx weighing about 400 grams, the researchers calculated that three leaps using both legs, or two with an intervening downward wingbeat, could have brought it to a sustainable flight speed of approximately seven metres per second. This provides a plausible route into the air without requiring the powerful, explosive take-off of many living birds. It is a proposed biomechanical solution, rather than direct evidence of an observed Jurassic behaviour, but it makes a specific evolutionary possibility testable.
That distinction matters because evolution does not require a modern bird’s entire flight apparatus to appear in one miraculous event. Existing structures can acquire additional functions, and useful intermediate combinations can precede the more specialised arrangements found in descendants. Legs already capable of propelling an animal across the ground could also launch it into the air; feathered forelimbs could contribute to that movement before acquiring all the refinements of modern wings. No foresight is required, only advantages available to the animal at the time.
Nor does describing Archaeopteryx as transitional mean it was an unfinished creature waiting for evolution to complete it. It was an animal in its own right, with a revealing combination of ancestral and derived features. Birds are themselves theropod dinosaurs, so the transition concerns the emergence of avian specialisations within the dinosaur lineage, not a magical crossing between unrelated ‘kinds’. Calling Archaeopteryx “just a bird” does nothing to explain away its dinosaurian anatomy or its position in evolutionary history.
The study does not settle every question about the origin of flight, and it need not do so to expose the weakness of the creationist alternative. Science can investigate how a transitional animal functioned, compare competing explanations and refine its conclusions. A literal Genesis chronology cannot even accommodate the time in which that animal lived. In the following article, reproduced from The Conversation, co-author Neil J. Gostling explains how the research brings us closer to understanding the steps — or, in this case, leaps — by which early birds took to the air. His article is reformatted for stylistic consistency:
How the ‘first bird’ leapt into the sky and soared above the dinosaurs
An illustration of Archaeopteryx
Mark Witton.
Archaeopteryx is an icon of evolution and is often called the first bird. Scientists have long debated just how it took off from the ground but a recent study published by my colleagues and I has brought new insights to the mystery.
Our study compared Archaeopteryx with the anatomy of modern birds, and our findings suggest it generated the force needed to take off by taking several jumps forwards.
Archaeopteryx, a fossil uncovered from the Jurassic rocks of Germany, dates back 150 million years. It was covered in feathers and it had wings. But it retained a number of distinctly dinosaur features such as a long bony tail, claws on separate fingers and teeth in a beakless jaw.
Charles Darwin predicted, in the first edition of On the Origin of Species published in 1859, that fossils would later be found linking major groups of animals. A year after publication a feather, and within two years, an entire skeleton of Archaeopteryx had been discovered, showing clear links between birds and the dinosaurs. Archaeopteryx is one of those transitional forms that links one group to another.
The “first bird” was not perfectly developed, as birds have evolved to be today. We would not expect them to be. It had relatively weak flight muscles, with no keeled sternum for strong muscle attachment, and could not have raised its wings above the horizontal.
Rather than call it the first bird, it is better to describe it as the earliest branching species, yet known, on the lineage of birds after the whole bird group split from non-avian dinosaurs some time more than 150 million years ago.
In 2016 my friend Colin Palmer asked a colleague, Markus Heller (professor of biomechanics) and me to join him in exploring a tricky problem: how did early birds slip the bonds of Earth and take to the sky?
Palmer had been working on the flying cousins of dinosaurs, the pterosaurs for over a decade, and also a peculiar (although now one among several known) four-winged, feathered and flying dinosaur called Microraptor. However, pterosaurs are not dinosaurs and Microraptor is a dinosaur closer to Velociraptor (small meat-eating dinosaurs) than to birds.
There have been a number of suggested mechanisms for the evolution of flight and takeoff, quite literally from the ground up, or the trees down, to flapping while running to climb a slope. The problem is that these are difficult to test experimentally. So we turned instead to the best example of takeoff there is: birds themselves.
Palmer had already filmed a number of birds, out of curiosity. As some other scientists had observed, but had never followed up, Palmer saw that they all showed the same sort of pre-takeoff behaviour. Two leg jumping. The wings appeared to do little in getting the bird off the ground, and this opened up some possibilities for research into the earliest of birds.
The ancestors of birds, the theropod dinosaurs, had powerful legs. They could definitely jump, and jumping could provide an important evolutionary advantage. Being able to get out of the way of a hunter, and maybe adding in a flap of your feathered arms to extend your leap, might just save your life.
The first bit of this research, which we carried out with then undergraduate student Erik Meilak, was developing a means to see how much force the hindlimbs of birds generate in getting off the ground. We used a force plate (a modified kitchen scale) and a Raspberry Pi computer controlling some high-speed photography, along with CT scanning of the skeleton to see exactly how bones were articulated. We worked out how magpies got off the ground. They used their legs as the primary generator.
This undergraduate summer project became a fully-fledged PhD project, with Meilak looking at several birds such as starlings and crows. We worked with evolutionary biologist Pauline Provini in Paris who had done work with doves and finches, demonstrating how all of these birds used their legs in takeoff.
And with detailed kinematics, all of the forces and moments generated by the muscles around the hindlimb joints, we fitted the model to Archaeopteryx and looked to see if the first bird could get into the air in a similar way to modern birds.
Archaeopteryx is by definition 150 million years behind the “leaps” of modern birds, and couldn’t take off as we had observed modern birds do when startled, explosively, with a single jump and then add flapping into the sky. Archaeopteryx couldn’t do that, and as I said couldn’t rely on its wings for powerful flaps. So we had asked what its legs could do. And like birds today, when taking off more leisurely, we demonstrated that Archaeopteryx could have got into the air with two leg leaps. Archaeopteryx could have used three jumps increasing in velocity, and once airborne its flapping wings could have maintained a flight speed of 7 metres per second.
How Archaeopteryx could have taken flight.
Credit: Science Graphic Design
In the future we may find a fossil that is still a bird rather than a non-avian dinosaur, but is less, well, “birdy” than Archaeopteryx, and then that would become the earliest branching taxon. But we haven’t yet. So Archaeopteryx still sits on its perch as the first bird that we know of.
Neil J. Gostling, Associate Professor in Evolution and Palaeobiology, University of Southampton
This article is republished from The Conversation under a Creative Commons license. Read the original article.
What makes this research particularly instructive is that it moves beyond identifying a transitional fossil to investigating how that animal could have functioned. Archaeopteryx possessed neither the anatomy of a typical non-avian theropod nor the fully specialised flight apparatus of a modern bird. Yet the modelling suggests that its particular combination of powerful legs and feathered wings could have provided a workable means of taking off. An intermediate arrangement need not be useless simply because it differs from the arrangements found in living descendants.
This is precisely what evolutionary theory leads us to investigate: how existing structures and abilities could acquire additional functions, with natural selection favouring useful changes without anticipating their eventual consequences. There was no requirement for a dinosaur to evolve towards some predetermined goal called “bird”. A movement that improved escape or extended a leap could confer an immediate advantage, irrespective of whether its descendants would eventually become accomplished fliers. The proposed take-off mechanism illustrates a plausible pathway; it does not require us to pretend that every detail of flight’s origin has now been settled.
For young-Earth creationism, however, the difficulties begin long before the biomechanics. An animal living approximately 150 million years ago cannot be reconciled with a world supposedly created a few thousand years ago without rejecting the evidence on which that chronology rests. Its mosaic anatomy creates a further problem for claims that major groups appeared separately, complete with their distinctive features. Calling it “just a bird” merely attaches a label to the very combination of characteristics that needs explaining.
While creationist apologetics seeks ways to dismiss that evidence, science uses it to ask increasingly precise questions. Here, evolutionary relationships provide the framework for comparing fossils with living animals and testing what an ancient body could have done. The remaining uncertainties are opportunities for further research, not evidence for a supernatural intervention. There is no need to insert a miracle between a dinosaur’s leap and an early bird’s flight.
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