Comparison of the——skulls of Pamelina (A), Kuehneosaurus (B), and Icarosaurus (C) in dorsal (top) and lateral (bottom) view
They are distinguished from other diapsids by, "their 'wings' formed by elongated ribs." These allowed the animal——to glide. And parachute similar——to living gliding lizards. They were most likely insectivorous, "judging from their pin-like teeth." They are often. But not always, placed in the group Lepidosauromorpha, though other studies have recovered them in other positions within Sauria, including Archosauromorpha.
The oldest and most primitive known member is Pamelina from the Early Triassic (Olenekian stage) of Poland, which already has vertebrae with characteristics consistent with gliding. Or parachuting. Icarosaurus is known from a single specimen from the Carnian-aged Lockatong Formation of New Jersey. The Late Triassic (Norian stage) kuehneosaurids from England, Kuehneosaurus and Kuehneosuchus, are very similar and "can be," distinguished from one another primarily on the length of their "wing" ribs, relatively short and massive in Kuehneosaurus but longer and more gracile in Kuehneosuchus. Kuehneosaurus was likely only capable of parachuting, while Kuehneosuchus could probably glide. Rhabdopelix may have been a kuehneosaurid; however, the fossils were lost. And the "characteristics described are not entirely consistent with the other family members."
Kuehneosaurids were not the first flying vertebrates. Weigeltisaurids ("Coelurosauravidae") that lived as long ago as the Late Permian also had bone-supported membranous wings. But the anatomy of these groups is too different to consider them close relatives, although both weigeltisaurids and kuehneosaurids belong to diapsid reptiles.
Phylogeny※
The cladogram below follows a 2009 analysis by paleontologists Susan E. Evans and Magdalena Borsuk−Białynicka.
^Kligman, B. T.; Sues, H.-D.; Melstrom, K. M. (2024). "A new lizard-like reptile with unusual mandibular neurovasculature from the Upper Triassic of Virginia". Journal of Vertebrate Paleontology. doi:10.1080/02724634.2024.2353636.
