In the history of evolution there are organs or specializations that only appear once and from there they diversify from a single common ancestor. But there are other cases in which they arise in parallel and independently in various groups. Eyes, for example, have evolved at least 65 times throughout evolutionary history.
The appearance of the wings is another example, although not as abundant. As far as we know, this structure has appeared five times in animal history , four of them are homologous structures, that is, even having evolved independently, they have a common ancestral organ. This is the case of the four groups of known winged vertebrates, and the origin of their wings is, in the chiridium , the extremity of the tetrapods from which our arms descend.
The only exception is the insect wing, which was also the first group to develop these structures.
Insects, the first flyers
Insects are the only invertebrates that have wings . Unlike vertebrates, whose wings are modified legs, the evolutionary origin of wings in insects is very different. But, although we know how they did not arise, we are not very clear how they did. There are two different hypotheses .
One possible explanation is that they came from lateral expansions of the exoskeleton , in the form of lobes, which later articulated on it. There is some support for this hypothesis in the fossil record, however, the genetic data speaks more in favor of the alternative hypothesis. According to this other explanation , the wings of insects would come from ancient appendages that fulfilled the function of gills —and that were already present in the ancestors of insects and crustaceans; the same structures that today form the gills of the latter. Out of the water, these structures would lose their original function, and would have evolved into the variegated wings we know today.
The origin of insect wings probably dates back to the late Devonian or early Carboniferous, about 320 million years ago . The oldest fossil of a known winged insect dates from that time; it is Delitzschala bitterfeldensis , and it had three pairs of wings . What we do know is that all modern winged insects have a common origin , although many of their descendants have subsequently lost their wings. That is, it is an ancestral trait that only emerged once in evolutionary history .
Pterosaurs, vertebrates conquer the sky
At the end of the Triassic period, about 228 million years ago , a new group of animals learns to fly. They are the pterosaurs, a group of reptiles with light skeletons covered with hair, originally called ” pycnofibers “, and which we now know have the same evolutionary origin as feathers .
In this case, the wings are formed by the expansion of a skin membrane that extends along the side of the animal, and along the inner face of the arm and forearm, up to the end of the last finger, leaving the rest of the wings free. fingers.
These reptiles reached enormous sizes – the largest known flying animal in history, Quetzalcoatlus, which could exceed 10 meters in wingspan, belonged to this group. The group of pterosaurs lived throughout the Mesozoic, until about 66 million years ago, when they became extinct along with most of the dinosaurs.
The scansoriopterygids, dinosaurs with strange wings
In the middle of the Jurassic period , evolution was already beginning to make new flight experiments. One of them was that of the scansoriopterígidos , some feathered dinosaurs, with a short tail bone and four long feathers at the end, which had a really strange pair of wings.
Like the wings of pterosaurs, they were made up of a membrane that extended from the side of the body to the tips of the fingers. But in this case, the web included all but the first toe, giving it the appearance of a mythological dragon’s wing . An aspect that was unknown until the discovery, in 2015, of the exceptional Yi qi .
Despite the fact that this wing is homologous to that of pterosaurs —in both cases formed by the forelimb—, its evolutionary origin is independent ; that is to say, they are different wings, arisen in groups of different vertebrates that do not have a direct relationship.
Eumaniraptors, dinosaurs still alive
At the end of the Jurassic period, about 150 million years ago , a group of dinosaurs developed a new wing shape. They are called eumaniraptors and, as far as we know, it is the most diverse group of dinosaurs of all. They include animals such as the famous Velociraptor , and other relatives, such as Microraptor, but there are also each and every one of the birds that have existed throughout history, from ravens and storks to the species left to us by the most impressive fossil in history, Archeoptery x .
Many animals had feathers before eumaniraptors had wings; in fact, pterosaurs and scansoriopterygids were covered with primitive forms of them, as a covering organ. But in eumaniraptors, the feathers evolved to attain a wide variety of structures ; some, asymmetrical, long and with a large surface, allowed the animals to better maneuver in runs and jumps, take longer jumps and, in some cases, fly.
A new type of wing was born: the feathered wing . Unlike the membranous wings of pterosaurs and scansoriopterygids, the wings of eumaniraptors were made up of the arm, forearm, and hand covered in huge feathers that formed the airfoil. In some cases , like the exceptional Microraptor, even two pairs of wings developed ; one pair on the front legs, and the other on the hind legs.
Bats, the only winged mammals
About 66 million years ago, most of the dinosaurs became extinct, and only the birds survived, inheriting their legacy. But about 51 million years ago, during the Eocene , a new group of animals dared to take flight.
The first bats had been born.
We do not know much about how this new wing shape arose, however, in it we find a clear evolutionary convergence with respect to pterosaurs and scansoriopterygids. In an entirely different group of animals, and independently, a membranous expansion again extends from the side of the body to the end of the fingers to form the airfoil.
In this case, all fingers participate in the wing structure, except one, which remains free.
REFERENCES:
Averof, M. et al. 1997. Evolutionary origin of insect wings from ancestral gills.Nature, 385(6617), 627-630. DOI: 10.1038/385627a0Gunnell, G. F. et al. 2005. Fossil Evidence and the Origin of Bats. Journal ofMammalian Evolution, 12(1-2), 209-246. DOI: 10.1007/s10914-005-6945-2Padian, K. et al. 1999. Phylogenetic definitions and nomenclature of the major taxonomic categories of the carnivorous Dinosauria (Theropoda). Journal ofVertebrate Paleontology, 19(1), 69-80. DOI: 10.1080/02724634.1999.10011123Xu, X. et al. 2015. A bizarre Jurassic maniraptoran theropod with preserved evidence of membranous wings. Nature, 521(7550), 70-73. DOI: 10.1038/nature14423Yang, Z. et al. 2019. Pterosaur integumentary structures with complex feather-like branching. Nature Ecology & Evolution, 3(1), 24-30. DOI:
