© 2001 S. Blair Hedges.
Adult Sphaerodactylus ariasae. The coin is 18 millimeters in diameter.
At the close of 2001, two species were tied for smallest living lizard, both geckos from the islands of the West Indies. The first, Sphaerodactylus parthenopion, was discovered¹ in the mid-1990's in the British Virgin Islands. In 2001 an equally small species was discovered² in leaf litter around a sinkhole on Isla Beata, a small island off the coast of the Dominican Republic. The latter was named Sphaerodactylus ariasae in honor of Yvonne Arias, a champion of conservation in the Dominican Republic. More at www.science.psu.edu/alert/Hedges11-2001.htm Oddly enough, one of the discoverers, Blair Hedges, is also a discoverer of the smallest frog.
A convention in describing the length of lizards is to measure from the tip of the snout to the vent, the opening through which the animal defecates. The vent is at the base of the tail, and thus the tail is not included in the length. Following this rule, the snout-vent length of the above species is about 14 to 18 millimeters. Tails add another 12 to 15 millimeters. Their weight is in the range 120 to 140 milligrams.
These two species are the smallest four-legged animals, excluding the amphibians (certain frogs are smaller).
Because they have a very large skin area in proportion to the volume of their body (see the surface-volume ratio), small animals can easily become dehydrated if, like these, they live in a semi-arid climate. Some species have special adaptations to reduce water loss, but these lizards don't seem to. Instead, they seek out humid microhabitats, for example within leaf litter.
1. Richard Thomas.
A new gecko from the Virgin Islands.
Quarterly Journal of the Florida Academy of Science, vol 28, pages
18-22 (1965).
2. S. Blair Hedges and Richard Thomas.
At the lower size limit in amniote vertebrates: A new diminutive lizard from the
West Indies.
Caribbean Journal of Science, vol 37, no. 3-4, pages 168-173 (2001).
Full text on the Web at www.caribjsci.org
The largest living lizard is the ora or Komodo dragon (Varanus komodoensis), which survives on only five islands in Indonesia. Adults can reach a length of over 3 meters and weigh about 135 kilograms (about 300 pounds).
Numerous Web sites describe the Komodo dragon. Links to many of the sites are given at www.isidore-of-seville.com/komodo. A page from the American Museum of Natural History: www.amnh.org/nationalcenter/Endangered/ora/ora.html
Many zoos with oras have an ora Web page; a good one is www.honoluluzoo.org/komodo_dragon.htm. Check out the video of the baby oras. A concise site for younger readers: www.thebigzoo.com/Animals/Komodo_Dragon.asp
The largest extinct land-dwelling lizard may be Megalania prisca (“Big Old Butcher”), which reached a length of 6 meters and a weight of 600 kilograms. Like the ora, it belonged to the group of lizards called varanids, or monitor lizards. Megalania became extinct only about 25,000 years ago, so they may have dined on a few Australians.
M. K. Hecht.
The morphology and relationships of the largest known terrestrial lizards
Megalania prisca Owen from Pleistocene of Australia.
Proceedings of the Royal Society of Victoria, vol. 87, no. 2,
pages 239-250 (1975).
Claudio Ciofi.
The Komodo Dragon.
Scientific American, March 1999.
Scientific American graciously makes this article available on the Web at The Komodo Dragon
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Last revised: 11 December 2001.