Sunday, 23 May 2010

Squamates Part III

The last of the lizards, and a couple of mosasaurs, before I begin on the snakes. Families represented here are the Varanidae, Scincidae, and Mosasauridae (order Squamata; class Sauropsida; phylum Chordata).

Mangrove monitor
Varanus indicus (Daudin, 1802) - Varanidae
Jardin des Plantes, Paris
January 2010

Monitor lizards are a group of large to enormous Old World lizards, including the largest of them all - the Komodo dragon (Varanus komodoensis - see below). They are found in a variety of habitats, from the most arid deserts to lush tropical rainforests, and take to the trees and water as well as dry land. The mangrove monitor is a widely distributed species from southeast Asia, parts of Australia, and many islands of the western Pacific Ocean. Although the specific epithet is 'indicus', it does not range as far west as India - the name supposedly refers to the Indies, which was the generic name given to most of southeast Asia in colonial times. True to its vernacular, it does frequent mangrove forests, as well as inland freshwater bodies.

Philippine water monitor
Varanus cumingi Martin, 1839 - Varanidae
London Zoo
December 2009

The water monitor (V. salvator) is a large and widely distributed monitor lizard from southeast Asia. Some of its more distinctive races, including V. s. cumingi, were recently split from it taxonomically, becoming species in their own right. This new species, known as the Philippine water monitor, originates from three of the larger Philippine islands, and is known for having more yellow markings than any other monitor.

Peach-throated monitor
Varanus jobiensis Ahl, 1932 - Varanidae
London Zoo
November 2008

Closely related to the mangrove monitor, and it has only recently been separated from it, the peach-throated monitor is native to New Guinea. It is indeed sympatric with the mangrove monitor, meaning that they both occur in the same region and habitat, suggesting that they are taxonomically distinct. Its throat is not always peach, ranging from white through to red.

Nile monitor
Varanus niloticus (Linnaeus, 1758) - Varanidae
Colchester Zoo
June 2009

The Nile monitor is a large monitor lizard distributed throughout much of tropical Africa. They are the largest lizards in Africa, and are among the largest of the monitors.

Komodo dragon (or Komodo Island monitor)
Varanus komodoensis Ouwens, 1912 - Varanidae
London Zoo
December 2009

The largest of the lizards, and one of the most familiar of the monitors, the Komodo dragon is restricted to a few tiny islands in Indonesia. Their huge size has been attributed to the phenomenon known as insular gigantism, whereby animals on islands become larger than their mainland counterparts, due to an available large predator niche which needs filling. The Komodo dragon is the only terrestrial predator on the islands in which it lives.

Juvenile Komodo dragon
London Zoo
June 2007

It was recently discovered that female Komodo dragons can reproduce without having mated. This virgin birth phenomenon is known as parthenogenesis, and until it was discovered in this species, it was previously only known in a few lizards and snakes. The other recent discovery concerning Komodo dragons is the verification that they are venomous - it has been known for a long time that they can bring down animals as large as fully grown water buffalo, but the mechanism involved was thought to be restricted to bacteria present in the lizard's mouth which cause infection. It is now known that they actively produce venom, albeit not in huge amounts, and it takes prey animals several days to die.

Juvenile Bosc's monitors
Varanus exanthematicus (Bosc, 1792) - Varanidae
Crews Hill, Enfield
May 2009

The Bosc's, or savannah, monitor is a fairly large terrestrial species from the savannahs of sub-Saharan Africa. It is smaller than the closely related rock monitor (V. albigularis) and the Nile monitor, with which the Bosc's monitor is sometimes confused.

Emerald tree monitor
Varanus prasinus Schlegel, 1839 - Varanidae
London Zoo
December 2009

One of the smallest monitor lizards, the emerald tree monitor is also one of the most striking in colour. There are many similar species under the same complex, grouped together as 'green tree monitors'. This species is restricted to the island of New Guinea, while others are found in surrounding areas.

Australian ridge-tailed monitor
Varanus acanthurus Boulenger, 1885 - Varanidae
Edinburgh Zoo
July 2005

Australia has a great variety of monitor lizards. Most of the mid-sized ones are colloquially called goannas, and the biggest of them all is the perentie (V. giganteus). The ridge-tailed monitor is a small species, never reaching more than around 60 cm (2').

Plioplatecarpus primaevus Russell, 1967 - Mosasauridae
Oxford Museum of Natural History
July 2008

Mosasaurs were a group of mostly very large marine lizards. They were closely related to the monitor lizards, and probably shared a common ancestor during the mid to late Mesozoic era. Plioplatecarpus lived in Laurasian seas, as fossils have been found in both North America and Europe - during the late Cretaceous, these two continents would have been very close together.

Mosasaurus hoffmanni Mantell, 1829 - Mosasauridae
Natural History Museum, London
February 2008

This is one of the original specimens of the entire group of mosasaurs. Gideon Mantell, the man who discovered and identified the remains of Iguanodon, named this, the type species of the genus.

Ocellated skink
Chalcides ocellatus Forsskål, 1775 - Scincidae
Jardin des Plantes
January 2010

Skinks are a widespread family of lizards distributed in every continent but Antarctica. There are few species in Europe, many of them having reduced limbs. The ocellated skink is related to the three-toed skink (C. chalcides), which is one of those with very small vestigial limbs, and tiny toes.

Tiliqua rugosa (Gray, 1825) - Scincidae
London Zoo
November 2008

The head of this reptile is on the right: the tail is used for defence by the skink as a decoy. Like other members of the genus Tiliqua, T. rugosa has a dark blue tongue which it flashes at potential threats. It is reputed to have the most vernacular names of any lizard, including bobtail skink, stump-tailed skink, bogeyes, pinecone lizard, and Australian sleepy lizard.

Gidgee skink
Egernia stokesii (Gray, 1845) - Scincidae
London Zoo
December 2009

Another Australian skink, recognisable for its very rough scales and pinecone-like tail. It is found in arid areas of central Australia.

Giant blue-tongued skink
Tiliqua gigas (Schneider, 1801) - Scincidae
Shepreth Wildlife Park, Cambridgeshire
September 2008

This is the only member of the genus Tiliqua not to be found in Australia - it originates from New Guinea. As its name suggests, it is larger than the other species, and does indeed have a blue tongue.

The squamate parade continues with snakes, next time.


Zachary said...

I almost sort of kinda want a pet water monitor. I've heard that, if you get them young, they are very docile and dog-like. But they also get very large.

Mo Hassan said...

Yes, they get HUGE! It would be cool though, a bit like having your very own modern-day mosasaur!

Neha AM said...

very interesting work Mo..i see u excelling in nxt years 2 come..All the best!