Archosauromorpha
Clade of reptiles more closely related to archosaurs than to lepidosaurs.
Wikipedia / Wikimedia Commons
Archosauromorpha, meaning "ruling lizard forms," is a group of diapsid reptiles that includes all reptiles more closely related to archosaurs—like crocodilians, dinosaurs, and birds—than to lepidosaurs, such as tuataras, lizards, and snakes. These animals first appeared in the fossil record during the late Middle Permian or Late Permian, but they became far more widespread and varied in the Triassic period. The name was coined in 1946 by Friedrich von Huene, but it wasn't until the 1980s, with the rise of cladistics, that the group's membership was firmly established.
Archosauromorpha currently includes four main reptile groups: the robust, plant-eating allokotosaurs and rhynchosaurs; the highly diverse Archosauriformes; and a polyphyletic collection of long-necked reptiles like *Protorosaurus* and tanystropheids. Some researchers also place pantestudines (turtles and their extinct relatives) and the semiaquatic choristoderes within this clade. Despite their variety, archosauromorphs share several skeletal features, including laminae on the vertebrae, a posterodorsal process on the premaxilla, no notochordal canals, and the loss of the entepicondylar foramen in the humerus.
The term Archosauromorpha was first used by von Huene in 1946 to describe reptiles closer to archosaurs than to lepidosaurs, but it saw little use for decades due to a lack of consensus on ancient reptile relationships. Cladistics helped clarify that a split between the archosaur and lepidosaur lineages occurred sometime in the Permian. Jacques Gauthier revived the term in 1982 at a meeting of the American Society of Zoologists, and later in his 1984 Ph.D. thesis, grouping Rhynchosauria, "Prolacertiformes," "Trilophosauria," and Archosauria (now roughly Archosauriformes). Gauthier, along with Michael J. Benton and Susan E. Evans, applied this scheme in large reptile studies during the 1980s.
Michel Laurin defined Archosauromorpha in 1991 as a node-based clade containing the most recent common ancestor of *Prolacerta*, *Trilophosaurus*, *Hyperodapedon*, and all its descendants. David Dilkes offered a broader, branch-based definition in 1998, including *Protorosaurus* and all saurians closer to it than to Lepidosauria. In 2020, Gauthier and co-authors redefined it as a node-based clade containing *Gallus*, *Alligator*, *Mesosuchus*, *Trilophosaurus*, *Prolacerta*, and *Pro
- first_appeared
- late Middle Permian or Late Permian
- peak_diversity
- Triassic period
- term_coined
- 1946 by Friedrich von Huene
- membership_established
- 1980s
- key_groups
- Allokotosaurs, Rhynchosaurs, Archosauriformes, long-necked reptiles (Protorosaurus, tanystropheids)
- defining_features
- laminae on vertebrae, posterodorsal process of premaxilla, lack of notochordal canals, loss of entepicondylar foramen of humerus
Lore & Background
The term Archosauromorpha was first used by Friedrich von Huene in 1946 to refer to reptiles more closely related to archosaurs than to lepidosaurs. However, little consensus on ancient reptile relationships existed prior to the late 20th century, so the term was seldom used until many years later. The advent of cladistics helped sort out relationships within Reptilia, revealing a split between the archosaur and lepidosaur lineages in the Permian. Jacques Gauthier reused the term at the 1982 annual meeting of the American Society of Zoologists and later in his 1984 Ph.D. thesis, including Rhynchosauria, 'Prolacertiformes,' 'Trilophosauria,' and Archosauria (not Archosauriformes). Note that Gauthier's original grouping used Archosauria, which roughly corresponds to what is now called Archosauriformes, but the two terms are distinct and should not be conflated.
Reader's Guide
Archosauromorpha is one of the most diverse groups of reptiles, encompassing stocky herbivores like rhynchosaurs and allokotosaurs, the hugely diverse Archosauriformes (including dinosaurs, pterosaurs, crocodilians, and birds), and a polyphyletic grouping of long-necked reptiles such as Protorosaurus and tanystropheids. Its members share several skeletal characteristics, including laminae on the vertebrae and loss of the entepicondylar foramen. The clade's definition has evolved: Michel Laurin (1991) defined it as a node-based clade, while David Dilkes (1998) formulated a more inclusive branch-based definition. In 2016, Martin Ezcurra named the subgroup Crocopoda. Disputed members include Choristodera, drepanosaurs, thalattosaurs, kuehneosaurids, and pantestudines (turtles and their relatives), with genetic studies sometimes placing turtles within Archosauromorpha as part of the clade Archelosauria, though anatomical data disagrees.
Did You Know?
- Archosauromorpha means 'ruling lizard forms' in Greek.
- The term was first used by Friedrich von Huene in 1946 but did not gain wide use until the 1980s.
- Archosauromorphs first appeared during the late Middle Permian or Late Permian.
- The subgroup Crocopoda was named in 2016 by Martin Ezcurra.
More in Extinct Archosaurs 1-24
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