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Curly-tailed lizard
Leiocephalus carinatus
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	Squamata
Suborder:	Iguania
Clade:	Pleurodonta
Family:	Leiocephalidae Frost & Etheridge, 1989
Genus:	Leiocephalus Gray, 1827[1]

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Leiocephalidae, also known as the curlytail lizards or curly-tailed lizards, is a family of iguanian lizards restricted to the West Indies. One of the defining features of these lizards is that their tail often curls over. They were previously regarded as members of the subfamily Leiocephalinae within the family Tropiduridae. There are presently 30 known species, all in the genus Leiocephalus.

Phylogenetic evidence supports Leiocephalidae being the most basal extant member of the clade Pleurodonta, with it diverging from the rest of the suborder as early as the Late Cretaceous, about 91 million years ago.^[2] As with many other higher-order taxa endemic to the Caribbean, it likely colonized the Antilles from South America during the Cenozoic; however, its deep divergence time from other lizards supports a much more complex and less straightforward history in the West Indies compared to other modern taxa.^[3]

Phylogenetic analysis on the genus supports some members of the now-extinct Lesser Antillean Leiocephalus radiation being the most basal of the recent Leiocephalus, with the last-surviving members of this group, L. herminieri and L. roquetus, sharing traits not present in other curlytail lizards from the Greater Antilles and other areas, such as the absence of enlarged snout scales. The second most basal of the recent curlytail lizards is another recently extinct species, L. eremitus from Navassa, followed by all other members of the genus from the Bahamas and Greater Antilles. Another extinct species from the Lesser Antilles known only from fossil remains, L. cuneus of Antigua and Barbuda, is thought to be more closely related to more derived Leiocephalus from the Bahamas and Greater Antilles, such as L. carinatus, L. greenwayi and L. punctatus, than to the other, more basal Lesser Antillean and Navassa species.^[3]

Curlytail lizards are native to the West Indies, with the extant (living) species in the Bahamas, Turks and Caicos, Cayman Islands, Cuba, Hispaniola (Haiti and the Dominican Republic) and nearby small islands.^[4][5] Additionally, Leiocephalus carinatus and Leiocephalus schreibersii have been introduced to Florida.^[6]

The curly-tailed lizards vary in size depending on species, but typically are approximately 9 cm (3.5 in) in snout-to-vent length. These lizards have no femoral pores, pterygoid teeth, or palatine teeth. Additionally, these lizards are observed to have overlapping scales.^[4]

The curly-tailed lizards mostly forage on arthropods such as insects, but also commonly take flowers and fruits.^[4][8] Large individuals will eat small vertebrates, including anoles.^[8][9]

As suggested by their name, most species of this family often lift their tail and curl it. This is done both when a potential predator is present and when not present, although in some curly-tailed lizard species it increases when a predator is present. It shows the fitness of the lizard to a would-be predator and—in the case of an attack—draws attention to the tail, which increases the lizard's chance of escaping.^[10][11] Although it has been suggested that it also functions as a territorial display,^[6] studies have been unable to find support for this, as the tail curling does not vary when another member of the same species is present.^[11]

The conservation status of the species in this family varies greatly. Several species, for example Leiocephalus carinatus, are common and widespread. Others are rare and highly threatened, especially those restricted to a single small island or a single location on a larger island, like the critically endangered Leiocephalus (barahonensis) altavelensis from Alto Velo Island and critically endangered Leiocephalus onaneyi from Guantánamo Province in Cuba.^[5] Primary threats to their survival are habitat loss (for example, expanding agriculture, charcoal production and grazing goats) and introduced predators (for example, small Indian mongoose).^[12][13][14]

Several species of Leiocephalus are already extinct, including all of the Jamaican, Puerto Rican and Lesser Antillean members of the genus.^[7][15] Some of these are only known from fossil or subfossil remains and became extinct in the Pleistocene or pre-Columbian era, but others such as two Lesser Antillean species and one from Navassa survived until comparatively recently, during the 19th century. Leiocephalus is the only known squamate genus to be entirely wiped out from the Lesser Antilles following European colonization; other reptilian genera that have also seen significant extirpations in the Lesser Antilles, such as Boa or Diploglossus, still retain relict populations on at least some islands, such as Dominica and Montserrat. This mass disappearance of Leiocephalus from the Lesser Antilles may be due to their inhabiting dry forests in littoral areas that were heavily exploited and deforested by early colonists. Few confirmed Leiocephalus fossil remains from after the early Holocene are known from the Lesser Antilles, which has raised doubts about their being only recently extirpated from this area; however, Leiocephalus fossil bones are small and closely resemble those of other lizard species, which may explain the lack of detection of Leiocephalus fossil bones from these areas aside from by the most highly trained palaeo-herpetologists.^[3]

In modern times, three species, Leiocephalus endomychus, Leiocephalus pratensis and Leiocephalus rhutidira, have not been seen since the 1960s and 1970s and are recognized as critically endangered, possibly extinct, by the IUCN. They are among the "most wanted" EDGE species.^[13][14][16]

Lizards of this family are diurnal and mostly inhabit fairly open habitats in a generally well-studied part of the world. Consequently, the majority of the species and subspecies already were scientifically described several decades ago. In 2016, the first new curly-tailed lizard since the early 1980s was described. The species was found in the coastal dunes of Bahía de las Calderas in the southwestern Dominican Republic. This species differs from the rest within Leiocephalidae in that its bony parietal table is U-shaped versus V-shaped, the males have 3–4 enlarged post-postcloacal scales versus 2, and there are specific sexual dimorphism trails.^[17]

The following species and subspecies, listed alphabetically by scientific name, are recognized as being valid by the Reptile Database.^[18]