Monofenestrata

Monofenestratans Temporal range: Early Jurassic – Late Cretaceous, 179–66 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Several pterosaur skulls prominently displaying the eponymous single fenestra
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Order:	†Pterosauria
Clade:	†Pterodactylomorpha
Clade:	†Monofenestrata Lü et al., 2010
Subgroups
†Archaeoistiodactylus †Melkamter †Darwinoptera †Allkaruen? †Ceoptera †Pterorhynchus †Pterodactyliformes? †Wukongopteridae †Pterodactyliformes †Changchengopterus †Douzhanopterus †Skiphosoura †Propterodactylus? †Anurognathidae? †Pterodactyloidea

Monofenestrata is a clade of pterosaurs. It includes the pterosaurs in which the nasal and antorbital fenestra (openings/holes) in the skull are merged into a single fenestra. The clade includes the pterodactyloids and their close relatives.^[1]

The clade Monofenestrata was in 2010 defined as the group consisting of Pterodactylus and all species sharing with Pterodactylus the synapomorphy of an external nostril confluent with the antorbital fenestra, the major skull opening on the side of the snout. The name is derived from Greek monos, "single", and Latin fenestra, "window". The concept was inspired by the discovery of Darwinopterus, a species combining a pterodactyloid-type skull with a more basal build of the remainder of the body.^[1] The Darwinoptera, a primitive subgroup of monofenestratans showing this transitional anatomy, was also named for Darwinopterus and defined as all descendants of its common ancestor with Pterorhynchus.^[2]

The earliest known monofenestratan fossils have been found in the Stonesfield Slate formation of the United Kingdom, which dates to the Bathonian stage of the Middle Jurassic, dated to about 166 million years ago. Identified elements include cervical vertebrae, fourth metacarpals and a possible pterodactyloid synsacrum.^[3] An earlier undescribed taxon along with the coeval and corregional Allkaruen may also belong to the group, both reported from Middle Toarcian layers of the Cañadón Asfalto Formation of Argentina.^[4][5]

Below is a cladogram showing the results of a phylogenetic analysis presented by Andres, Clark & Xu, 2014. This study found the two traditional groupings of ctenochasmatoids and kin as an early branching group (represented as the group Archaeopterodactyloidea), with all other pterodactyloids grouped into the Eupterodactyloidea.^[2]

Contrastingly, a 2024 paper by David Hone and colleagues describing the transitional taxon Skiphosoura found primitive monofenestratans to represent an evolutionary grade leading towards Pterodactyloidea, rather than a distinct darwinopteran or wukongopterid grouping. A cladogram of their results is shown below.^[6]