Are birds classified as reptiles in cladistics?

In modern cladistic taxonomy, birds are considered reptiles because genetic and paleontological evidence shows they are nested within the dinosaur clade and share a most recent common ancestor with crocodilians. Traditional evolutionary taxonomy treats reptiles as a paraphyletic group excluding birds, but strict cladistics requires that all descendants of an ancestral group remain within it. Consequently, many cladistic systems redefine Reptilia to include birds.

What we know

• Modern cladistic taxonomy considers traditional reptile groups to be paraphyletic because birds are the surviving group of dinosaurs. [2]
• Birds are nested among reptiles under the clade Archosauria from a phylogenetic perspective. [2]
• In a strict cladistic framework, all descendants stay in their overarching ancestral clade, meaning birds are considered reptiles. [3, 4]
• Many cladistic systems redefine Reptilia as a clade that includes birds, though the precise definition varies between authors. [2]

Still open

• The precise definition and membership boundaries of the redefined Reptilia clade vary between different authors.

Where to go next

• how it workedHow does cladistic classification work?
• compared withWhat are the closest living relatives of birds?
• what caused itHow did birds evolve from dinosaurs?
• the bigger pictureWhat defines traditional reptile orders?
• whenWhen did the Cretaceous-Paleogene extinction occur?
• an unexpected connectionWhy would strict cladistics imply that fish or worms include humans?Because cladistic rules dictate that all descendants must stay in their ancestral group, traditional grades like fish or worms would technically have to include human beings if applied strictly.

Sources

• [1]Reptilia (Wikidata Q10811) · CC0 1.0
• [2]Reptile · CC BY-SA 4.0
• [3]List of reptiles · CC BY-SA 4.0
• [4]Cladistics · CC BY-SA 4.0
• [5]Bird · CC BY-SA 4.0