Longisquama

Longisquama is an extinct genus of small Triassic reptile known from a fossil bearing elongated, featherlike structures along its back. The structures’ anatomy and relationship to feathers remain disputed.

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Longisquama insignis: The species named from the holotype fossil of Longisquama, a small Triassic reptile with elongated dorsal appendages. This is the named species represented by the specimen at the center of debate.
Feather: A branched epidermal structure that forms the characteristic covering of birds and some other dinosaurs. The Longisquama appendages have been proposed as feather-like, but their identity as feathers is disputed.
Diapsid: A member of a major reptile lineage traditionally defined by two openings on each side of the skull. Longisquama is commonly discussed within the broad evolutionary context of diapsid reptiles.
Sinosauropteryx: A small theropod dinosaur from the Early Cretaceous of China, preserved with filamentous integument. Its fossilized filaments provide a better-supported dinosaur example of feather-like covering.
Origin of feathers: The evolutionary history of feathers, including their development before the origin of birds. Longisquama has figured in arguments over whether feather-like structures predated dinosaurs.
Holotype: The single specimen designated as the name-bearing reference for a species or subspecies. The interpretation of Longisquama rests largely on its designated name-bearing fossil.
Homology: Similarity between biological structures because they were inherited from a common ancestor. Whether its appendages are homologous to feathers is central to the evolutionary controversy.
Archosauromorpha: A major group of reptiles that includes archosaurs and their close extinct relatives. Some proposed classifications place Longisquama among early archosauromorph reptiles.
Microraptor: A small feathered dromaeosaurid dinosaur from the Early Cretaceous of China. Its flight-related feathers contrast with the disputed appendages of Longisquama.
Bird origins: The evolutionary emergence of birds from theropod dinosaurs and the traits that distinguish early birds. A proposed link between its appendages and feathers could alter narratives of bird evolution.