By Hans-Dieter Sues
In recent years, discoveries of a spectacular array of Jurassic and Early Cretaceous “missing links,” mostly from China, have allowed scientists to map the evolutionary transition from small predatory dinosaurs to birds in astonishing detail.
The ancient lake deposits of the Yixian Formation in the northeastern corner of China have yielded a particularly rich treasure trove of exquisitely preserved fossils of birds and other animals. They date from the Early Cretaceous, some 120 to 125 million years before present.
Confuciusornis sanctus is the most common bird species from the Yixian Formation.
Photo by Captmondo/Wikimedia Commons
In addition to birds, particularly important fossils from the Yixian Formation include the oldest known flowering plants, dinosaurs, and mammals. Many of these specimens preserve extensive traces of soft tissues like feathers or hair.
These birds are remarkably diverse in terms of both their places on the evolutionary tree and modes of life. One skeleton of Jeholornis prima had an intact mass of about 50 seeds in its gut region, documenting the earliest known case of feeding on fruits in birds.
However, even newer finds show that much remains to be learned about these animals.
A recent paper in the Journal of Vertebrate Paleontology by a group of Chinese and American researchers reports on a new Early Cretaceous bird from the Yixian Formation. The new species, named Longicrusavis houi (“Hou’s long-shinned bird”), is known from an almost complete skeleton.
Longicrusavis can be assigned to a major group of birds known as Ornithuromorpha, which are more closely related to present-day birds than are most of the other Early Cretaceous birds from the Yixian Formation.
Along with Hongshanornis longicresta, a species from the same formation reported five years earlier, Longicrusavis provides evidence for the existence of a previously unknown, specialized group of small birds during the Early Cretaceous.
The remarkably long legs of Longicrusavis suggest that it was a wader and spent much of its time feeding in shallow lake water.
Previously undescribed feather impressions for Hongshanornis indicate that both it and Longicrusavis had a fan-shaped tail. They are the oldest known birds to have such a tail fan, which probably improved flight performance.
Hans-Dieter (Hans) Sues is a vertebrate paleontologist based at the National Museum of Natural History in Washington, D.C. He is interested in the evolutionary history and paleobiology of vertebrates, especially dinosaurs and their relatives, and the history of ecosystems through time.
A former member of the National Geographic Committee for Research and Exploration, Hans has traveled widely in his quest for fossils and loves to share his passion for ancient life through lectures, writings, and blogging.