Background The phylogenetic relationships of fossil birds near the origin of the avian crown group remain debated, in part due to a limited amount of character evidence from incomplete fossils. The av...

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Air space proportion (ASP), the volume fraction in bone that is occupied by air, is frequently applied as a measure for quantifying the extent of skeletal pneumaticity in extant and fossil archosaurs....

Fossils reveal how birds survived the killer asteroid and became today’s only living dinosaurs.

We devised novel staging criteria for near-hatching embryos of the Mallard (Anas platyrhynchos) and Swan Goose (Anser cygnoides) based on four easily measurable morphological traits. We show that our...