Archosauromorpha
Clade of reptiles more related to archosaurs than lepidosaurs.
Archosauromorpha (Greek for 'ruling lizard forms') is a clade of diapsid reptiles containing all reptiles more closely related to archosaurs (such as crocodilians and dinosaurs, including birds) than lepidosaurs (such as tuataras, lizards, and snakes). Archosauromorphs first appeared during the late Middle Permian or Late Permian, though they became much more common and diverse during the Triassic period.
- First appeared
- late Middle Permian or Late Permian
- Diversity peak
- Triassic period
- Modern definition established
- 1980s
- Key subgroups
- Allokotosaurs, rhynchosaurs, Archosauriformes, and long-necked reptiles (e.g., Protorosaurus, tanystropheids, Prolacerta)
- Surviving members
- Crocodilians and birds
Lore & Background
However, little consensus on ancient reptile relationships existed prior to the late 20th century, so the term was seldom used until many years later. Gauthier's classification included four main groups: Rhynchosauria, 'Prolacertiformes', 'Trilophosauria', and Archosauria (now equivalent to Archosauriformes).
Reader's Guide
Archosauromorpha is one of the most diverse groups of reptiles, united by several shared skeletal characteristics including laminae on the vertebrae, a posterodorsal process of the premaxilla, a lack of notochordal canals, and the loss of the entepicondylar foramen of the humerus. The clade encompasses four main groups: the stocky, herbivorous allokotosaurs and rhynchosaurs; the hugely diverse Archosauriformes (including dinosaurs, pterosaurs, crocodilians, and birds); and a polyphyletic grouping of long-necked reptiles such as Protorosaurus, tanystropheids, and Prolacerta. Disputed members include choristoderes, drepanosaurs, thalattosaurs, kuehneosaurids, and pantestudines (turtles and their extinct relatives). Genetic studies have suggested turtles are part of basal Archosauromorpha, forming a clade called Archelosauria, though anatomical data disagrees. The group's legacy is profound: archosauriforms survived the Triassic-Jurassic extinction and continue to dominate, with crocodilians and birds as living representatives.
Did You Know?
- Archosauromorpha means 'ruling lizard forms' in Greek.
- Archosauromorphs first appeared during the late Middle Permian or Late Permian.
- Living members include crocodilians and birds.
Frequently Asked Questions
What is Archosauromorpha?
Archosauromorpha is a clade of diapsid reptiles whose Greek-derived name means 'ruling lizard forms.' It encompasses every reptile lineage that is more closely related to archosaurs (crocodilians, dinosaurs, birds) than to lepidosaurs (lizards, snakes, tuataras).
When did Archosauromorpha first appear in the fossil record?
The earliest known archosauromorphs date to the late Middle Permian or Late Permian, around 260 million years ago. They went on to become far more diverse and widespread during the Triassic, filling many ecological roles after the end-Permian extinction.
What major subgroups make up Archosauromorpha?
Key branches include allokotosaurs, rhynchosaurs, the archosauriform lineage, and long-necked reptiles such as Protorosaurus, tanystropheids, and Prolacerta. Together these groups span a broad range of body plans from the Permian through the Mesozoic.
Which modern animals still belong to Archosauromorpha?
Two lineages persist today: crocodilians (crocodiles, alligators, gharials, caimans) and birds. Both descend from archosaurs, which sit within the broader archosauromorph clade.
Why is Archosauromorpha important in paleontology?
It provides the evolutionary framework connecting early Permian reptiles to the dominant Mesozoic fauna and ultimately to living birds and crocodilians. The modern clade definition was formalized in the 1980s, giving researchers a clear node for tracing relationships across hundreds of millions of years.
More in Prehistoric Extinct Animals 1-24
Elsewhere in the Prehistoric Extinct Animals universe
Spotted an error? Know more?
This is a living reference — every entry is fact-audited, and reader corrections feed straight into our audit queue. Suggest an edit · See this site's audit record