Yixian Formation

The Yixian Formation is an Early Cretaceous rock unit in northeastern China, famous for preserving fossils of dinosaurs, birds, mammals, plants, and other organisms.

Sinosauropteryx: A small theropod dinosaur from the Yixian Formation, known for fossil evidence of filament-like body covering. Its preserved filaments made it an early landmark in evidence for feathered dinosaurs.
Lacustrine sediment: Sediment deposited in lakes, including mud, silt, and material washed in from surrounding land. Much of the formation accumulated in lake settings that buried organisms in fine-grained deposits.
Early Cretaceous: The first epoch of the Cretaceous Period, spanning roughly 145 to 100 million years ago. The Yixian Formation was deposited during this interval.
Feathered dinosaurs: Non-avian dinosaurs known to have feathers or feather-like integument. Yixian fossils supplied influential evidence that feathers were widespread among theropods.
Confuciusornis: An early Cretaceous bird from northeastern China, recognized by its toothless beak and fossilized flight feathers. Its abundant Yixian fossils document early bird anatomy and variation.
Volcanic ash: Fine fragments of volcanic material ejected during explosive eruptions and deposited on land or in water. Ash layers helped bury fossils and provide datable horizons within the succession.
Jehol Group: A stratigraphic group in northeastern China that includes several Early Cretaceous formations associated with the Jehol Biota. The Yixian is one of the principal formations assigned to this regional group.
Origin of birds: The evolutionary emergence of birds from theropod dinosaurs. Yixian fossils illuminate the anatomy and diversity of early birds and their relatives.
Microraptor: A small feathered dromaeosaurid dinosaur with long feathers on both its arms and legs. Yixian specimens preserve its four-winged plumage and inform debates about gliding.
Lagerstätte: A fossil deposit preserving exceptional abundance, diversity, or anatomical detail. The Yixian Formation is a classic example of exceptional fossil preservation.

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