query: parent_taxon aigialosauridae
supports: The Cretaceous is a geologic period and system that spans 79 million years from the end of the Jurassic Period million years ago (Mya) to the beginning of the Paleogene Period Mya. It is the last period of the Mesozoic Era. The Cretaceous Period is usually abbreviated K, for its German translation "Kreide" (chalk). Aigialosauridae ( Greek , aigialos = `` seashore '' + sauros = lizard ) is a family of Late Cretaceous semi-aquatic varanoid lizards , regarded by some paleontologists as a distinct monophyletic group and by others as an adaptive grade within the basal mosasauroids . The Late Cretaceous (100.566 Ma) is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series. The Cretaceous is named after the white limestone known as chalk which occurs widely in northern France and is seen in the white cliffs of south-eastern England, and which dates from this time. Reptiles are tetrapod (four-limbed vertebrate) animals in the class Reptilia, comprising today's turtles, crocodilians, snakes, amphisbaenians, lizards, tuatara, and their extinct relatives. The study of these traditional reptile orders, historically combined with that of modern amphibians, is called herpetology. Snakes are elongated, legless, carnivorous reptiles of the suborder Serpentes that can be distinguished from legless lizards by their lack of eyelids and external ears. Like all squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several more joints than their lizard ancestors, enabling them to swallow prey much larger than their heads with their highly mobile jaws. To accommodate their narrow bodies, snakes' paired organs (such as kidneys) appear one in front of the other instead of side by side, and most have only one functional lung. Some species retain a pelvic girdle with a pair of vestigial claws on either side of the cloaca. Toxicofera (Greek for "those who bear toxins"), is a proposed clade of scaled reptiles (squamates) that includes the Serpentes (snakes), Anguimorpha (monitor lizards, gila monster, and alligator lizards) and Iguania (iguanas, agamas, and chameleons). Toxicofera contains about 4600 species, (nearly 60%) of extant squamata. It encompasses all venomous reptile species, as well as numerous related non-venomous species. There is little morphological evidence to support this grouping, however it has been recovered by all recent molecular analyses. Lizards are a widespread group of squamate reptiles, with over 6,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group, traditionally recognized as the suborder Lacertilia, is defined as all extant members of the Lepidosauria (reptiles with overlapping scales) that are neither sphenodonts (i.e., tuatara) nor snakes  they form an evolutionary grade. While the snakes are recognized as falling phylogenetically within the Toxicofera clade from which they evolved, the sphenodonts are the sister group to the squamates, the larger monophyletic group, which includes both the lizards and the snakes. The Lepidosauria (from Greek meaning "scaled lizards") are reptiles with overlapping scales. This subclass includes Squamata and Rhynchocephalia. It is a monophyletic group and therefore contains all descendents of a common ancestor. Squamata includes snakes, lizards, and amphisbaenia. Rhynchocephalia was a widespread and diverse group 220-100 million years ago; however, it is now represented only by the genus "Sphenodon", which contains two species of tuatara, native to New Zealand. Lepidosauria is the sister taxon to Archosauria, which includes Aves and Crocodilia. Lizards and snakes are the most speciose group of Lepidosaurs and, combined, contain over 9,000 species. There are many noticeable distinguishing morphological differences between lizards, tuataras, and snakes. Tuatara are reptiles endemic to New Zealand. Although resembling most lizards, they are part of a distinct lineage, the order Rhynchocephalia. Their name derives from the Mori language, and means "peaks on the back". The single species of tuatara is the only surviving member of its order, which flourished around 200 million years ago. Their most recent common ancestor with any other extant group is with the squamates (lizards and snakes). For this reason, tuatara are of great interest in the study of the evolution of lizards and snakes, and for the reconstruction of the appearance and habits of the earliest diapsids, a group of amniote tetrapods that also includes dinosaurs, birds, and crocodilians.
candidates: anguimorpha bear gila lepidosauria lizard mya reptile rhynchocephalia squamata toxicofera
answer: squamata