Biology:Ankyramorpha

Ankyramorpha ("anchor forms") is a proposed clade of early stem reptiles which lived between the early Cisuralian epoch (middle Sakmarian stage) and the latest Triassic period (latest Rhaetian stage) of Africa, Antarctica, Asia, Australia, Europe, North America and South America.

This clade was named in a 1996 parareptile study by Michael deBraga and Robert R. Reisz. They provided the name Ankyramorpha for a newly recognized clade encompassing "the most recent common ancestor of Procolophonia (including pareiasaurs and procolophonoids, among others) and Lanthanosuchoidea (which includes and Acleistorhinidae and Lanthanosuchidae) and all its descendants", and this clade name sees continued use among modern parareptile studies. A similar name, Hallucicrania, was provided in an earlier 1995 study by Michael S. Y. Lee, who defined it as the node-based taxon formed by the most recent common ancestor of lanthanosuchids and "pareiasauroids" (pareiasaurs + Sclerosaurus), and all its descendants. Unlike Ankyramorpha, which explicitly included procolophonoids, Hallucicrania was originally designed to exclude procolophonoids, which Lee's analysis argued to have split off prior to the divergence between lanthanosuchids and pareiasaurs. Nevertheless, purely considering the taxa encompassed by their definitions, Hallucicrania and Ankyramorpha refer to an identical grouping.

The following cladogram is simplified after the phylogenetic analysis of MacDougall and Reisz (2014) and shows the placement of Ankyramorpha within Parareptilia. Relationships within emboldened terminal clades are not shown.

Parareptilia

Mesosaurus       Millerosauria   Procolophonomorpha   Australothyris smithi   Ankyramorpha Lanthanosuchoidea   Feeserpeton oklahomensis         Colobomycter pholeter     Delorhynchus cifellii         Acleistorhinus pteroticus     Lanthanosuchus watsoni             Microleter mckinzieorum     Bolosauridae   Belebey chengi     Eudibamus cursoris     Procolophonia Pareiasauromorpha   Nycteroleteridae     Pareiasauria       Nyctiphruretidae   Abyssomedon williamsi     Nyctiphruretus acudens     Procolophonoidea   Owenettidae     Procolophonidae

Some studies from the early 2020s onward, have disputed the validity of Ankyramorpha (and Parareptilia more broadly), finding Procolophonia unrelated to bolosaurids, lanthanosuchids, and acleistorhinids. Other studies have recovered an Ankyramorpha only including Acleistorhinidae and Procolophonia as a monophyletic group, and Lanthanosuchus as not even a reptile at all.

Cladogram after Jenkins et al. 2025, with "parareptiles" highlighted in orange:

Sauropsida

†Araeoscelidia 65px       †Bolosauridae 80px       †Erpetonyx   Neoreptilia †Ankyramorpha   †Acleistorhinidae 60px   Procolophonia   †Pareiasauromorpha 60px     †Procolophonoidea 60px           †Mesosauridae 65px         †Cabarzia       †Ascendonanus     †Orovenator 60px       Parapleurota   †Millerettidae 60px   Neodiapsida   †Younginidae 60px       †Tangasauridae 60px       †Weigeltisauridae 60px       †Claudiosaurus 60px   Sauria   Lepidosauromorpha 65px     Archosauromorpha 60px

References

Template:Sauropsida Wikidata ☰ Q4766123 entry