Sauriurae

Sauriurae is an obsolete taxonomic group that was historically used in avian classification. The term, literally meaning "lizard tails," was initially used to group birds possessing long, reptile-like tails, particularly those with unfused caudal vertebrae.

In the late 19th and early 20th centuries, Sauriurae was often contrasted with Ornithurae, which encompassed all other birds possessing shortened tails composed of a pygostyle (fused caudal vertebrae). Archaeopteryx, a transitional fossil exhibiting both reptilian and avian features, was a key member of Sauriurae and a defining characteristic of the group.

The concept of Sauriurae reflects an early understanding of avian evolution and the relationship between birds and reptiles. This older classification system emphasized morphological characteristics, particularly the tail structure. However, with advancements in phylogenetic analysis and the discovery of numerous fossil bird species, the Sauriurae/Ornithurae dichotomy has been superseded by more refined and accurate classifications based on cladistics and evolutionary relationships.

Modern phylogenetic studies demonstrate that the evolutionary history of birds is more complex than the simple division proposed by the Sauriurae/Ornithurae framework. While Archaeopteryx retains its significance as a crucial transitional fossil, the term Sauriurae is no longer considered a valid taxonomic group in current ornithological or paleontological classification systems. The birds formerly placed within Sauriurae are now understood to be part of a broader lineage of early avian forms that exhibit a mosaic of ancestral and derived traits.