Platynota
Encyclopedia
Platynota is a group of anguimorph
lizards. Since it was named in 1839, it has included several groups, including monitor lizard
s, snake
s, mosasaur
s, and helodermatids. Its taxonomic use still varies, as it is sometimes considered equivalent to the group Varanoidea
and other times viewed as a distinct group. It is phylogenetically defined as a clade
containing Varanidae
(the monitor lizards) and Helodermatidae (the beaded lizard and Gila monster). It includes many other extinct species as well.
and nasal bone
s on the tops of their skulls (in other lizards, these bones are separated into pairs). Some platynotan features that are not seen in the skeleton, and therefore only known from living species, include a deeply forked tongue and a venom gland called the gland of Gabe.
included the groups Varanoidea
and Mosasauroidea
, or monitor lizards and mosasaurs (a group of large marine reptile
s from the Cretaceous
). A close relationship between mosasaurs and snakes, which together formed the group Pythonomorpha
, gained favor in the following years. Consequently, some researchers also included snakes in Platynota.
A more restricted definition was proposed by herpetologists Samuel Booker McDowell and Charles Mitchill Bogert
in 1954. Within Platynota, they included only monitor lizards, helodermatids, and their closest extinct relatives. Their use of Platynota made it essentially equivalent to Varanoidea
, a taxon that included monitor lizards and helodermatids that had been in use for many years. McDowell and Bogert's usage of Platynota gained favor in the following decades, although it was substituted by the name Varanoidea in some studies.
Platynota was given a phylogenetic definition in 1997. It was erected as a stem-based clade that included Heloderma
(the Gila monster and Beaded lizard), Lanthanotus (the Earless monitor lizard), and Varanus (monitor lizards), and all lizards that are more closely related to them than to other anguimorphs. These other anguimorphs were traditionally called Diploglossa, and include Anguidae
, Anniellidae (American legless lizards), and Xenosauridae
(knob-scaled lizards). A node-based definition was first given in 1998 in which Platynota included the last common ancestor
of Monstersauria
(helodermatids) and Varanidae
(monitor lizards) and all of its descendants. Under this definition, Platynota includes the same forms as Varanoidea in its traditional sense. Varanoidea, however, has been redefined as a node-based clade including the extinct Telmasaurus
and varanids.
Molecular evidence from DNA and other molecules conflicts with the commonly held classification of platynotans. A 2004 molecular study of living anguimorph lizards found a close relationship between helodermatids and xenosaurids, but not between helodermatids and varanids. Similarly, a 2005 study found a close relationship between Anniella pulchra
(the California legless lizard) and helodermatids.
of Mongolia
, living around 80 million years ago. They include forms that are similar in appearance to living monitor lizards, such as Paravaranus, Proplatynotia
, Gobiderma
, Cherminotus
, Telmasaurus
, and Saniwides. Although they lived in close association with each other, they represent a diversity of different anguimorphs. The earliest and most generalized platynotans were once called necrosaurians after the genus Necrosaurus.
Anguimorpha
Anguimorphs of the infraorder Anguimorpha include the anguids , monitor lizards, the extinct mosasaurs, and helodermatids . The infraorder was named by Fürbringer in 1900 to include all autarchoglossans closer to Varanus and Anguis than Scincus...
lizards. Since it was named in 1839, it has included several groups, including monitor lizard
Monitor lizard
Monitor lizards are usually large reptiles, although some can be as small as in length. They have long necks, powerful tails and claws, and well-developed limbs. Most species are terrestrial, but arboreal and semiaquatic monitors are also known...
s, snake
Snake
Snakes are elongate, 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...
s, mosasaur
Mosasaur
Mosasaurs are large extinct marine lizards. The first fossil remains were discovered in a limestone quarry at Maastricht on the Meuse in 1764...
s, and helodermatids. Its taxonomic use still varies, as it is sometimes considered equivalent to the group Varanoidea
Varanoidea
Varanoidea is a superfamily of lizards, including the well-known family Varanidae . Also included in the Varanoidea are such extinct marine and semi-aquatic forms as mosasaurs and dolichosaurs, the venomous helodermatids , the Lanthanotidae , and the extinct Necrosauridae.Throughout their long...
and other times viewed as a distinct group. It is phylogenetically defined as a clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
containing Varanidae
Varanidae
Varanidae is a group of lizards of the superfamily Varanoidea. The family is a group of carnivorous lizards which includes the largest living lizard, the Komodo dragon, and the crocodile monitor. Varanidae contains the living genus Varanus and a number of extinct taxa...
(the monitor lizards) and Helodermatidae (the beaded lizard and Gila monster). It includes many other extinct species as well.
Description
Many skeletal features support the grouping of monitor lizards, helodermatids, and several extinct species in Platynota. All platynotans have a hinged upper jaw. The teeth are widely spaced, and each has a large base. They also erupt from behind existing teeth. The teeth are plicidentine, meaning that they have highly folded layers of dentine in their centers. Many have fused frontalFrontal bone
The frontal bone is a bone in the human skull that resembles a cockleshell in form, and consists of two portions:* a vertical portion, the squama frontalis, corresponding with the region of the forehead....
and nasal bone
Nasal bone
The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face, and form, by their junction, "the bridge" of the nose.Each has two surfaces and four borders....
s on the tops of their skulls (in other lizards, these bones are separated into pairs). Some platynotan features that are not seen in the skeleton, and therefore only known from living species, include a deeply forked tongue and a venom gland called the gland of Gabe.
History and classification
Platynota was first used as a superfamily of anguimorph lizards. In 1923, Charles Lewis CampCharles Lewis Camp
Charles Lewis Camp was a notable palaeontologist and zoologist, working from the University of California, Berkeley...
included the groups Varanoidea
Varanoidea
Varanoidea is a superfamily of lizards, including the well-known family Varanidae . Also included in the Varanoidea are such extinct marine and semi-aquatic forms as mosasaurs and dolichosaurs, the venomous helodermatids , the Lanthanotidae , and the extinct Necrosauridae.Throughout their long...
and Mosasauroidea
Mosasauroidea
Mosasauroidea is an extinct superfamily of Late Cretaceous lizards that includes the highly-marine mosasaurs and their relatives the "aigialosaurs"....
, or monitor lizards and mosasaurs (a group of large marine reptile
Marine reptile
Marine reptiles are reptiles which have become secondarily adapted for an aquatic or semi-aquatic life in a marine environment.The earliest marine reptiles arose in the Permian period during the Paleozoic era...
s from the Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
). A close relationship between mosasaurs and snakes, which together formed the group Pythonomorpha
Pythonomorpha
Pythonomorpha was originally proposed by paleontologist Edward Drinker Cope as a reptilian order comprising snakes and mosasaurs. Cope wrote, "In the mosasauroids, we almost realize the fictions of snake-like dragons and sea-serpents, in which men have been ever prone to indulge...
, gained favor in the following years. Consequently, some researchers also included snakes in Platynota.
A more restricted definition was proposed by herpetologists Samuel Booker McDowell and Charles Mitchill Bogert
Charles Mitchill Bogert
Charles Mitchill Bogert was an American herpetologist, and curator of herpetology and researcher for the American Museum of Natural History.-Early life and education:...
in 1954. Within Platynota, they included only monitor lizards, helodermatids, and their closest extinct relatives. Their use of Platynota made it essentially equivalent to Varanoidea
Varanoidea
Varanoidea is a superfamily of lizards, including the well-known family Varanidae . Also included in the Varanoidea are such extinct marine and semi-aquatic forms as mosasaurs and dolichosaurs, the venomous helodermatids , the Lanthanotidae , and the extinct Necrosauridae.Throughout their long...
, a taxon that included monitor lizards and helodermatids that had been in use for many years. McDowell and Bogert's usage of Platynota gained favor in the following decades, although it was substituted by the name Varanoidea in some studies.
Platynota was given a phylogenetic definition in 1997. It was erected as a stem-based clade that included Heloderma
Heloderma
Heloderma, the only genus of the family Helodermatidae, consists of venomous lizards native to the southwestern United States, Mexico and as far south as Guatemala. It includes two separate species, with six subspecies...
(the Gila monster and Beaded lizard), Lanthanotus (the Earless monitor lizard), and Varanus (monitor lizards), and all lizards that are more closely related to them than to other anguimorphs. These other anguimorphs were traditionally called Diploglossa, and include Anguidae
Anguidae
The Anguidae is a large and diverse family of lizards native to the northern hemisphere. The group includes the slowworms, glass lizards, and alligator lizards, among others. Anguidae is divided into three subfamilies and contains 94 species in eight genera. Their closest living relatives are the...
, Anniellidae (American legless lizards), and Xenosauridae
Xenosauridae
The Xenosauridae is a family of lizards native to Central America and China. Also known as knob-scaled lizards, they have rounded, bumpy scales and osteoderms. Most species prefer moist or semi-aquatic habitats, although they are widespread within their native regions, with some even inhabiting...
(knob-scaled lizards). A node-based definition was first given in 1998 in which Platynota included the last common ancestor
Most recent common ancestor
In genetics, the most recent common ancestor of any set of organisms is the most recent individual from which all organisms in the group are directly descended...
of Monstersauria
Monstersauria
Monstersauria is a clade of Varanoid lizards, defined as all taxa more closely related to Heloderma than Varanus. It includes Heloderma, as well as several extinct taxa, such as Estesia and Gobiderma....
(helodermatids) and Varanidae
Varanidae
Varanidae is a group of lizards of the superfamily Varanoidea. The family is a group of carnivorous lizards which includes the largest living lizard, the Komodo dragon, and the crocodile monitor. Varanidae contains the living genus Varanus and a number of extinct taxa...
(monitor lizards) and all of its descendants. Under this definition, Platynota includes the same forms as Varanoidea in its traditional sense. Varanoidea, however, has been redefined as a node-based clade including the extinct Telmasaurus
Telmasaurus
Telmasaurus is an extinct genus of varanoid lizard from the Late Cretaceous of Mongolia. Fossils have been found from the Djadokha and Barun Goyot Formations that date between the early and middle Campanian stage from approximately 80 to 75 million years ago. The type species T...
and varanids.
Molecular evidence from DNA and other molecules conflicts with the commonly held classification of platynotans. A 2004 molecular study of living anguimorph lizards found a close relationship between helodermatids and xenosaurids, but not between helodermatids and varanids. Similarly, a 2005 study found a close relationship between Anniella pulchra
Anniella pulchra
The California Legless Lizard is a limbless, burrowing lizard often mistaken for a snake.-Description:These lizards are around long from snout to vent...
(the California legless lizard) and helodermatids.
Evolution
The oldest platynotans are from the Late CretaceousLate Cretaceous
The Late Cretaceous 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...
of Mongolia
Mongolia
Mongolia is a landlocked country in East and Central Asia. It is bordered by Russia to the north and China to the south, east and west. Although Mongolia does not share a border with Kazakhstan, its western-most point is only from Kazakhstan's eastern tip. Ulan Bator, the capital and largest...
, living around 80 million years ago. They include forms that are similar in appearance to living monitor lizards, such as Paravaranus, Proplatynotia
Proplatynotia
Proplatynotia is an extinct genus of varanoid lizard from the Late Cretaceous of Mongolia. Fossils have been found in the Barun Goyot Formation, which is mid-Campanian in age. The type and only species, P. longirostratia, was named in 1984....
, Gobiderma
Gobiderma
Gobiderma is an extinct genus of Late Cretaceous lizard whose fossils are known from the Gobi Desert in southern Mongolia. It was first discovered as a result of a joint Polish-Mongolian Paleontological Expedition, and formally named in 1984...
, Cherminotus
Cherminotus
Cherminotus is an extinct genus of monitor lizard from the Late Cretaceous of Mongolia. The type and only species, C. longifrons, was named in 1984.-Description and history:...
, Telmasaurus
Telmasaurus
Telmasaurus is an extinct genus of varanoid lizard from the Late Cretaceous of Mongolia. Fossils have been found from the Djadokha and Barun Goyot Formations that date between the early and middle Campanian stage from approximately 80 to 75 million years ago. The type species T...
, and Saniwides. Although they lived in close association with each other, they represent a diversity of different anguimorphs. The earliest and most generalized platynotans were once called necrosaurians after the genus Necrosaurus.