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Credit: Stephanie Abramowicz Source: ScienceDaily |
Would you believe it! Another one of those non-existent transitional fossils has turned up again, this time in a 125 million years ago Cretaceous rock from Spain. And just when creationists were getting used to dismissing all the ones from China as 'forgeries', despite there being no evidence for the claim!
In as clear an example as you could wish for of the transition from dinosaurs to birds, a paper published by an international group of palaeontologists shows that a fossil of a tiny feathered dinosaur proto-bird from Spain has unmistakeable evidence that it had the musculature for sophisticated flight, by being able to control individual flight feathers in its wings.
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Abstract
Despite a wealth of fossils of Mesozoic birds revealing evidence of plumage and other soft-tissue structures, the epidermal and dermal anatomy of their wing’s patagia remain largely unknown. We describe a distal forelimb of an enantiornithine bird from the Lower Cretaceous limestones of Las Hoyas, Spain, which reveals the overall morphology of the integument of the wing and other connective structures associated with the insertion of flight feathers. The integumentary anatomy, and myological and arthrological organization of the new fossil is remarkably similar to that of modern birds, in which a system of small muscles, tendons and ligaments attaches to the follicles of the remigial feathers and maintains the functional integrity of the wing during flight. The new fossil documents the oldest known occurrence of connective tissues in association with the flight feathers of birds. Furthermore, the presence of an essentially modern connective arrangement in the wing of enantiornithines supports the interpretation of these primitive birds as competent fliers.
Soft-tissue and dermal arrangement in the wing of an Early Cretaceous bird: Implications for the evolution of avian flight
Guillermo Navalón, Jesús Marugán-Lobón, Luis M. Chiappe, José Luis Sanz & Ángela D. Buscalioni
Scientific Reports 5, Article number: 14864 (2015) doi:10.1038/srep14864
Copyright © 2015, Rights Managed by Nature Publishing Group. Reprinted under Creative Commons CC-BY license
It's becoming increasingly clear now that birds should more properly be regarded as modern dinosaurs and that they have emerged from a group of feathered theropod dinosaurs which was diversifying even while other dinosaurs were lumbering about below them. The evidence of this paper suggests that flight dexterity was such an advantage to this group that it evolved in some very early on in the musculature and mechanism of fine control. The main driver for flight evolution would then have become achieving this more efficiently by remodelling of the underlying skeleton rather than improving on the ability itself.
The anatomical match between the muscle network preserved in the fossil and those that characterize the wings of living birds strongly indicates that some of the earliest birds were capable of aerodynamic prowess like many present-day birds...
The new fossil provides us with a unique glimpse into the anatomy of the wing of the birds that lived amongst some of the largest dinosaurs... Fossils such as this are allowing scientists to dissect the most intricate aspects of the early evolution of the flight of birds.
There is of course no obligation on evolution to proceed by what seems intuitively to be the most logical route. There is no plan; the only test of fitness is whether it gives an advantage over and above the 'cost' of the change. If it does, the adaptation will spread in the genepool; if it doesn't, it'll be quickly eliminated. Once this fine structure in soft tissues had evolved, there would have been an advantage in adaptations in the skeleton which enabled it to be used more efficiently.The new fossil provides us with a unique glimpse into the anatomy of the wing of the birds that lived amongst some of the largest dinosaurs... Fossils such as this are allowing scientists to dissect the most intricate aspects of the early evolution of the flight of birds.
Luis M. Chiappe
But the important point here is that early birds were not some newly-evolved order which appeared from nowhere; they were dinosaurs, plain and simple. Modern birds are the descendants of an order which once dominated the land and occupied the major niches, including the air and, with flight, the canopies of the forests.
Like the early mammals, they were warm-blooded and able, with feathers which served the same function as the fur of mammals, to survive the cataclysmic climate change which would have followed a meteor strike which cause the mass extinction that put an end to the dominance of the terrestrial dinosaurs. This extinction cleared the way for the expansion of mammals into the niches terrestrial dinosaurs once occupied, whilst the aerial dinosaurs occupied the air and shared the forest canopy with the arboreal mammals. Bats, probably because they lack the fine flight control that birds get from feathers, have never come close to competing with the birds in terms of flight control and mastery of the air.
Those bipedal theropods which preyed on those long-extinct lumbering giants, are with us still and have been getting better at flying for at least 125 million years.
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