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It is not uncommon to find swans in rivers and lakes today dividing their time between pulling aquatic plants and punishing the foolish with the mighty blows of their bony elbowed wings.
But eleven million years ago, in what is now Japan, swans did something unexpected: They went to the oceans. In article published In this week’s Gunma Natural History Museum Bulletin, Japanese paleontologists have officially described this family or genus of swans, the Annakacygna, with long, filter-fed heads, small wings, and seriously odd hips—all of them researchers, that “ultimate bird.”
The first set of Annakacygna remains – an almost articulated skeleton in a stone slab from a riverbed in Japan’s Gunma Prefecture – was excavated in 2000 by a Japanese fossil hunter. After the fossil hunter donated the remains to the Gunma Museum of Natural History, museum director Hasegawa Yoshikazu summoned paleontologist Hiroshige Matsuoka to examine them.
Initially, Dr. Matsuoka thought he was looking at a strange duck, perhaps an animal that dove in the oceans just off the then-nascent Japanese Archipelago. But when the bones on the plate were cleaned, he concluded that the short-winged skeleton belonged to a flightless swan.
He and his co-author Dr. The species, which Yoshikazu named Annakacygna hajimei, was about four feet long, as large as the modern black swan. Another group of remains from a related species, which they named A. yoshiiensis, suggested a bird as tall as the 5½-foot trumpeter swan, the largest living swan species.
Dr. Both birds were “fatter and heavier than these modern swans,” Matsuoka said. When he compared its remains to the dismembered body of a common swan, he found that the birds differed in other ways as well. Their tails were extremely mobile. Their hips were unusually broad and strong, and their bones were thicker than usual for a waterfowl, which helped them ride low in the water.
The weirdest were the wings. Dr. Flightless birds often lose some of the benefits of their wings, Matsuoka said, which is called degeneration. In Annakacygna, however, the shoulder joints and muscle attachments that pull the arms back were unexpectedly well developed, with the fingers and with them the uniquely shaped wrists that kept the wings permanently bent.
At first, these wings surprised the team. However, Dr. Matsuoka had a brainwave while watching a video of a mute swan holding a chick on its back. Many modern swans habitually carry their young backs, holding their wings back and up to protect the chicks, he said. This stance in Ananakacygna’s modern relatives suggested a new possibility: flightless swans may have built this behavior into their anatomy, transforming their curved wings and broad hips into cradles specially adapted for carrying chicks safely in saltwater.
The swans were also well adapted to the coastal lifestyle in another way: their long, filter-fed beaks similar to that of rowing ducks allowed them to tinker with plankton in the cool, rich seas of the Japanese coast. Unlike modern swans, they have flat, plant-gnawing beaks.
It is not unusual for waterfowl to be unable to fly; modern steamship ducks, several species of teal, and several extinct species of geese have left the sky for water. Some of these waterfowl reached remarkable sizes: Malta’s Pleistocene giant swan, which some researchers suggest was land-bound, was 30 percent larger than a living mute swan.
But despite being smaller, Dr. Matsuoko said that Annakacygna is in a league of its own. “I think all wild animals live for two purposes,” he said, namely, to sustain himself (by eating) and the species (by breeding). it is something special.
“It’s the best form of survival as an animal,” he said. “That’s why we call it the ‘ultimate bird’.”
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