Varanoidea is a superfamily of lizards, including the well-known family

Varanidae The Varanidae are a family of lizards in the superfamily Varanoidea within the Anguimorpha group. The family, a group of carnivorous and frugivorous lizards, includes the living genus '' Varanus'' and a number of extinct genera more closely rel ...

(the monitors and

goanna A goanna is any one of several species of lizards of the genus '' Varanus'' found in Australia and Southeast Asia. Around 70 species of ''Varanus'' are known, 25 of which are found in Australia. This varied group of carnivorous reptiles ranges ...

s). Also included in the Varanoidea are the Lanthanotidae (

earless monitor lizard The earless monitor lizard (''Lanthanotus borneensis'') is a semiaquatic, brown lizard native to the Southeast Asian island of Borneo. It is the only living species in the family Lanthanotidae and it is related to the true monitor lizards. Taxo ...

s), and the extinct Palaeovaranidae. Throughout their long

evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...

ary history, varanoids have exhibited great diversity, both in habitat and form. This superfamily includes the largest-known terrestrial lizard, Megalania (5–6 meters), and the largest extant lizard, the

Komodo dragon The Komodo dragon (''Varanus komodoensis''), also known as the Komodo monitor, is a member of the monitor lizard family Varanidae that is endemic to the Indonesian islands of Komodo, Rinca, Flores, and Gili Motang. It is the largest extant ...

(''Varanus komodoensis'', 3+ meters).

Evolution

Either synonymous with, or a subgroup of, the group

Platynota Platynota is a polyphyletic group of anguimorph lizards and thus belongs to the order Squamata of the class Reptilia. Since it was named in 1839, it has included several groups, including monitor lizards, snakes, mosasaurs, and helodermatids. ...

, the varanoids first appear in the

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

record in the latter part of Early Cretaceous, but possible varanoid ancestors have been traced back as far as

Early Jurassic The Early Jurassic Epoch (geology), Epoch (in chronostratigraphy corresponding to the Lower Jurassic series (stratigraphy), Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic-J ...

times. Among the earliest known varanoids are the monitor-like necrosaurids '' Palaeosaniwa canadensis'' from the

Campanian The Campanian is the fifth of six ages of the Late Cretaceous Epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campani ...

(roughly 71-82 mya) of North America and '' Estesia mongoliensis'' and '' Telmasaurus grangeri'', both from the Campanian of

Mongolia Mongolia; Mongolian script: , , ; lit. "Mongol Nation" or "State of Mongolia" () is a landlocked country in East Asia, bordered by Russia to the north and China to the south. It covers an area of , with a population of just 3.3 million, ...

. Varanoids survived the

Cretaceous–Paleogene extinction event The Cretaceous–Paleogene (K–Pg) extinction event (also known as the Cretaceous–Tertiary extinction) was a sudden mass extinction of three-quarters of the plant and animal species on Earth, approximately 66 million years ago. With the ...

and flourished worldwide during the

Cenozoic Era The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configu ...

. Carroll argued that the affinities of ancestral snakes suggested evolution from early aquatic or burrowing varanoid lineages, although recent evidence suggests a more distant common ancestor within

Toxicofera 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 ch ...

. Carroll characterises the varanoids as "the most advanced of all lizards in achieving large size and an active, predaceous way of life". Some

taxa In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...

, such as the extinct necrosaurids and the possibly varanoid

Gila monster The Gila monster (''Heloderma suspectum'', ) is a species of venomous lizard native to the Southwestern United States and the northwestern Mexican state of Sonora. It is a heavy, typically slow-moving reptile, up to long, and it is the only ve ...

s, were armoured with

osteoderms 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 amphi ...

(bony deposits on the skin), and many forms have hinged jaws, allowing them to open their mouths very wide when feeding (though they cannot dislocate their jaws, contrary to popular belief).Carroll, R. L. 1988. ''Vertebrate Paleontology and Evolution''. W. H. Freeman and Co. NY. p. 232

Taxonomy

According to Estes et al., 1988, which uses morphological characteristics, Varanoidea includes

Helodermatidae The Helodermatidae or beaded lizards are a small family of lizards endemic to North America today, but formerly more widespread in the ancient past. Traditionally, the Gila monster and the Mexican beaded lizard were the only species recognized, ...

, ''

Lanthanotus The earless monitor lizard (''Lanthanotus borneensis'') is a semiaquatic, brown lizard native to the Southeast Asian island of Borneo. It is the only living species in the family Lanthanotidae and it is related to the true monitor lizards. Taxo ...

'', and '' Varanus''. Gauthier et al., 2012 also groups these three groups together, where Helodermatidae evolved earlier than Varanidae (which includes ''Lanthanotus'' and ''Varanus'').

References

Anguimorpha Vertebrate superfamilies Cretaceous lizards Late Cretaceous lepidosaurs Extant Cenomanian first appearances {{lizard-stub