Carusioidea is a

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

lizard Lizard is the common name used for all Squamata, squamate reptiles other than snakes (and to a lesser extent amphisbaenians), encompassing over 7,000 species, ranging across all continents except Antarctica, as well as most Island#Oceanic isla ...

s that includes the family

Xenosauridae Xenosauridae is a family of anguimorph lizards whose only living representative is the genus '' Xenosaurus'', which is native to Central America. Xenosauridae also includes the extinct genera '' Exostinus'' and '' Restes''. Also known as knob-sca ...

(knob-scaled lizards) from Central America and the extinct genus '' Carusia'' from the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...

of Mongolia. It was named in 1998 after a sister-group relationship was found between ''Carusia'' and Xenosauridae.

Phylogenetic analysis In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical data ...

indicates that Carusioidea is the most basal clade within

Anguimorpha The Anguimorpha is a suborder of Squamata, squamates. The group was named by Fürbringer in 1900 to include all autarchoglossans closer to ''Varanus'' and ''Anguis'' than ''Scincus''. These lizards, along with iguanians and snakes, constitute the ...

. Features that help define Carusioidea include closely spaced

orbits In celestial mechanics, an orbit (also known as orbital revolution) is the curved trajectory of an physical body, object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an satellite, artificia ...

or eye sockets separated by fused

frontal bone In the human skull, the frontal bone or sincipital bone is an unpaired bone which consists of two portions.'' Gray's Anatomy'' (1918) These are the vertically oriented squamous part, and the horizontally oriented orbital part, making up the bo ...

s, a connection between the

jugal The jugal is a skull bone found in most reptiles, amphibians and birds. In mammals, the jugal is often called the malar or zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species. Anatomy ...

and

squamosal bone The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and quadratojugal bones form the cheek series of the skull. The bone forms an ancestral ...

s below the supratemporal arch, and a covering of bony

osteoderm Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of extant and extinct reptiles and amphibians, including lizards, crocodilians, frogs, temnospondyls (extinct amph ...

s over the

skull roof The skull roof or the roofing bones of the skull are a set of bones covering the brain, eyes and nostrils in bony fishes, including land-living vertebrates. The bones are derived from dermal bone and are part of the dermatocranium. In com ...

. Below is a

cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...

showing the phylogenetic relationships of carusioids from Gao and Norell (1998):

References

Anguimorpha Tetrapod unranked clades Extant Campanian first appearances {{lizard-stub