Luck, luck, there he was
The world 115 million years ago: Dinosaurs stomped around in fern or coniferous forests everywhere, ammonites swam in the seas, and mammals still led a niche existence. But there were already birds among them that looked like today's species.
It all started with a type of fossil mallet that Chinese paleontologists unearthed more than twenty years ago from the petrified sediment layers of a former lake in Gansu, China - 2000 kilometers west of Beijing. They recognized the remains of a bird in this foot and baptized it after the name of the province of Gansus. After that, however, the fossil fell more or less into oblivion and was ignored by science.
Wrongly so: In the meantime, colleagues of the researchers at the time dug up the remains of fifty other specimens at the same site - including skeletons that were missing nothing except for the head and whose bones were mostly not compressed. These fossils could now, if not revolutionize, at least considerably expand and shed light on the bird family tree.
Because the lives of modern members of the Aves class may have started on the water, say paleontologist Jerald Harris of Utah's Dixie State College and his colleagues. In addition to the imprints and fossils of feathers, the fine-grained sediment also preserved a very special characteristic of waterfowl: Gansus yumenensis - the full name of the species - paddled through its aquatic habitat with webbed toes.
The pelvis, knees and legs of the animals also underline this way of life, their structure is similar to that of today's loons and grebes, which skilfully and quickly hunt under water with powerful leg movements. They all have a pronounced bony crest on the walking bone below the knee, on which strong muscles are located that drive the bird - even when starting to run across the water to fly. However, the bumps on which the flexor muscles of their toes once attached are quite large in Gansus, which again suggests a relationship with herons, waders or diving ducks.
The underwater swimming abilities of Gansus yumenensis were probably more between those of divers and the slightly less agile ducks. Depending on the situation, the primeval diver probably fed on fish, aquatic insects and similar creatures or aquatic plants. But its exact eating habits will remain a mystery until science finds the birds' heads as well.
But the rest of the fossil body is enough for Harris and his colleagues to place it in the family tree of the feathered world. When Gansus yumenensis was alive, another group of birds actually predominated: the so-called Enantiornithes with their unusual joint formation in the shoulder girdle, which was exactly the opposite of that of modern birds.
However, just as these Enantiornithes were reaching their evolutionary peak during the Cretaceous, a newer lineage split off from them. In technical jargon, their representatives are called Ornithurae and, in addition to all current birds, also include their prehistoric predecessors with a similarly modern physique - with Gansus yumenensis as the nestor, because no older Ornithurae find has been found to date.
The Chinese diver shared its fondness for water with later Cretaceous ornithurae, while their enantiornithes competition dominated the land, taking the role of songbirds, griffins or woodpeckers. It is possible that modern birds were initially left with only lake and riparian ecosystems as niches in which to evolve, although a few species - ancestors of ostriches and chickens - migrated to purely terrestrial lifestyles a little later in the Cretaceous.
The real heyday of Gansus and company came after the Cretaceous-Tertiary Mass Extinction 65 million years ago, which not only wiped out dinosaurs but also the unusual Enantiornithes. Now there was room for a veritable explosion in the diversity of bird species, which now number almost 10,000 species on earth.
By the way, Gansus yumenensis has the fate of at least initial scientific disregard in common with Vegavis iaai, at least 68 million years old, which is also a relatively old duck from the late dinosaur period. Their fossil also languished in scientific collections for many years until a researcher discovered their true value - so it competes pretty badly against dinosaurs for attention. From the perspective of ducks and divers, however, the evolutionary victory is likely to be much higher.