Thursday, 20 May 2010

Squamates Part I

The order Squamata ('scaly ones') contains the lizards and snakes. The group used to be split into Sauria (the lizards) and Serpentes (the snakes), but this is not a natural grouping - snakes are legless, hypercarnivorous lizards. Since this is such a huge group (approaching 6000 species), with many interesting members, I shall break up the squamates into several arbitrary groups. The first contains the Agamidae, Anguidae, Chamaeleonidae, Cordylidae, and Corytophanidae (all order Squamata; class Sauropsida; phylum Chordata).

Male plumed basilisk
Basiliscus plumifrons (Cope, 1876) - Corytophanidae
Whipsnade Wild Animal Park
April 2009

The lizard called the basilisk should not be confused with the beast of the same name famed in mythology, and another similar one from the world of Harry Potter. This creature is very much real, and can't kill its prey with a single stare. It does do one rather remarkable thing though: it can run on water on its hind limbs. I bet Nagini couldn't do that.

Giant plated lizard
Gerrhosaurus validus Smith, 1849 - family Cordylidae
Colchester Zoo
June 2009

Plated lizards and sungazers are chunky, well-armoured African lizards of the family Cordylidae. They are popular pets, but not so popular as bearded dragons (see below). There are six species in the genus Gerrhosaurus, and this species can grow up to 69 cm in length.

Panther chameleon
Furcifer pardalis Cuvier, 1829 - Chamaeleonidae
Manchester Museum
July 2008

Chameleons are a very well-known group of Old World lizards reknowned for many things: their eyes which can move independently of one another; their extremely long sticky tongue used to ensnare their invertebrate prey; and most famously, their ability to change colour. The panther chameleon is a large Madagascan species (the island has a huge diversity of chameleons, from the tiny leaf chameleons of the genus Brookesia to the Oustalets' chameleon - Furcifer oustaleti) with large spots on its body which change colour accordingly dependent on the animal's surroundings and mood.

European chameleon
Chamaeleo chamaeleon Linnaeus, 1758 - Chamaeleonidae
Wild in eastern Cyprus
October 2008

There are two species of chameleon in Europe: this one occurs in Greece and many of the Aegean islands, as well as Cyprus and elsewhere. The African chameleon, C. africanus, also occurs in Greece. We spotted this individual crossing the road in the vicinity of Famagusta on the eastern coast of North Cyprus. I found it retreating into the undergrowth and attempted to catch it but it put up a fight, hissing and rocking its body from side to side as only pissed off chameleons know how to do. I had to make do with a few fuzzy photographs, and this one which captures its mood perfectly I think.

Ophisaurus apodus Pallas, 1775 - Anguidae
London Zoo
December 2009

There are several families of legless lizards - many people in Britain and Europe are familiar with slow worms (Anguis fragilis), a legless lizard which is oft mistaken for a snake. The scheltopusik is a Eurasian species, also called the glass lizard. This name originates from the common behaviour strategy amongst many lizard groups to shed their tail when stressed - a phenomenon known as caudal autotomy. This is also the origin to the specific name of the slow worm - fragilis - something which many people realise when they pick up a lizard by the tail and are left with a wriggling tail and a look of shock on their face.

Saharan uromastyx
Uromastyx geyri Muller, 1922 - Agamidae
Shepreth Wildlife Park, Cambridgeshire
September 2008

Uromastyx lizards, also called dab lizards, mastigures, or spiny-tailed lizards, are desert-dwelling reptiles from north Africa and the Middle East with fattened spiny tails. These tails are used as a fat source and a defence against would-be predators.

Philippine sailfin lizard
Hydrosaurus pustulatus (Eschscholtz, 1829) - Agamidae
Colchester Zoo
June 2009

A large tree-dwelling agamid with two conspicuous sails on its back and tail, the Philippine sailfin lizard will escape predators by plunging into the water below the tree in which it will otherwise be resting. They are good swimmers and, like the basilisk, can run on water, but quadrupedally rather than bipedally.

Frilled lizards
Chlamydosaurus kingii Gray, 1827 - Agamidae
Crews Hill, North London
May 2009

One of the best known of the agamids, the frilled lizard or frilled dragon is familiar to most people for its threat display. The fold of skin which almost completely encircles its neck is erected, the mouth is opened, and the lizard runs on its hind legs towards its attacker. This is usually enough to deter its predators, which in the Australian outback would include dingos, monitor lizards, quolls, and birds of prey. The frill around the neck also features on the Dilophosaurus in the first Jurassic Park movie - there is no evidence for this, nor its ability to spit venom in the faces of dinosaur DNA thieves.

Laudakia stellio (Linnaeus, 1758) - Agamidae
Wild at Bellapais Abbey, North Cyprus
April 2009

The family Agamidae is distributed in the Old World, with many species found in Africa, Asia, and Australasia. It is represented only by Laudakia stellio in Europe, and only marginally at that. It is one of the most common reptiles in Cyprus, and large and small individuals abound wherever there is a sunny spot to bask. It is also the largest lizard present on the island.

Juvenile agama
Wild at Bellapais Abbey
October 2008

Young agamas are more brightly patterned than the adults, as the above individual shows. They commonly have a diamondback pattern and a banded tail.

Bearded dragon ("Mr. Gibbs")
Pogona sp. Storr, 1982 - Agamidae
Photographs courtesy of Jason Kay

The bearded dragon is probably everyone's favourite agamid... it certainly is a popular pet, and rightly so. It can be a charming, friendly, and inquisitive companion, isn't very demanding in its needs, and gets to a manageable size. Best of all, you can handle them - you can't do that to amphibians.

There are seven species in the genus Pogona, and most them do appear in the pet trade from time to time. Since they differ only in very small ways, it can be difficult to tell which species any given individual is. The majority probably belong to P. vitticeps (Ahl, 1926), the inland bearded dragon, which is the most common in the wild, although Lawson's dragons - P. henrylawsoni Wells & Wellington, 1985 - are popular too.

It has been observed that some species, including P. barbata, have vestigial venom glands from the ancestral squamate from which all lizards and snakes evolved. Not only is venom present in snakes, but also in two groups of lizards - the monitors and the beaded lizards - it could be found to be present in other lineages too. Of course, bearded dragons are completely safe to handle - the venom glands are not ducted and they do not have fangs.

More lizards to come...


Albertonykus said...

Frilled lizards, chameleons, and basilisks were some of my favorite creatures when I was younger.

Also, I didn't realize that the sailfin lizard runs on water as a quadruped! That's new to me.

Zachary said...

I'm kept two chameleon's (Jackson's) and can tell you that they are very difficult to keep. The first one died of old age, but he was an irritable old lizard. The second didn't live past his sixth month. He had a parasite infection that we didn't know about until it was too late. I've since read that chameleons are not the hardiest of lizards.

I desperately want a beardie, though. My wife won't have it. Nothing bigger than my first chameleon, I'm afraid.