Lizard

Lizard Temporal range: Upper Triassic – present 202–0 mya

The tokay gecko, From East Timor
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Superclass:	Tetrapod
Class:	Sauropsida
Order:	Squamata
Section:	Lacertilia

Simplified classification

Traditional taxonomy

In the traditional taxonomy the Order Squamata is divided like this:

Order Squamata (the scaled reptiles)
- Suborder Serpentes (snakes)
- Suborder Lacertilia / Sauria (lizards)

Modern taxonomy

A modern view is that the snakes and lizards are all infraorders of the Squamata:^[3]^p238

Order Squamata
- Suborder Serpentes
- Suborder Iguania: Iguanas, chameleons, agamas and relatives.
- Infraorder Gekkota: Geckos, legless lizards, blind lizards.
- Suborder Scincomorpha: Skinks, wall lizards and relatives.
- Suborder Anguimorpha (Platynota, Varanoidea): Monitor lizards, Gila monsters, Slow-worms and relatives.
- Clade Lacertoidea Gymnophthalmoidea and relatives
  - Superfamily Amphisbaenia: legless burrowing worm lizards.
  - Superfamily Gymnophthalmoidea whiptailed and spectacled lizards

There are other versions, and the taxonomy will probably not settle until more molecular evidence is collected.

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Natural history

Anatomy

The skull structure of both snakes and lizards is distinctive. They can move their upper jaw relative to the braincase. Lizard skin is covered in scales. Some lizards have scales that you can easily see. Others, like geckos, have tiny scales that are challenging to see without a microscope. Some lizards use venom for attack and defense.

Evolution

The Squamates are definitely a monophyletic group; they are a sister group to the Tuatara. Judged by their fossil record, the Squamates were present in the Mesozoic, but occupied a minor place in the land ecology. Three of the six lines are recorded first in the Upper Jurassic, the others in the Cretaceous.^[3] The Mosasaurs of the Upper Cretaceous were by far the most successful of all the lizards, becoming the top predator in their ecosystem.

It is now known that lizards originated in the Upper Triassic, 237–201 million years ago.^[4]

Although snakes and lizards look so different, neither are proper clades. Snakes did descend from early lizards, so both groups together do form a monophyletic clade, the Squamata. Within that clade there is another monophyletic clade, the Toxicofera. This includes all venomous reptile species, as well as many related non-venomous species. The evidence for this is in recent molecular analyses.^[5]^[6]^[7]

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Physiology

Lizards use anti-predator defences, including venom, camouflage, and reflex bleeding. They can also sacrifice and regrow their tails.

Sight is very important for most lizards, both for finding prey and for communication. Many lizards have highly acute color vision. Most rely heavily on body language, using specific postures, gestures and movements to define territory, resolve disputes, and entice mates.

Most lizards use bright colors, but not all the time. These are usually kept out of sight, otherwise the animal would be seen by predators. The bright patches are usually hidden on the underside or between scales: they are only shown when necessary. For example, the dewlap is a brightly colored patch of skin on the throat, usually hidden between scales. When a display is needed, the lizards erect the hyoid bone of their throat. This shows a large vertical flap of brightly colored skin under its head which can be then used for communication.