Here be dragons
VulcanSpirit
Richard & Alison Brunstrom
Tue 24 Apr 2012 21:48
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Readers of this Blog may recall that ancestors of
the Galapagos Marine Iguanas Amblyrhynchus cristatus arrived in the
archipelago as terrestrial iguanas from South America at least 11 million
years ago. That's a long time ago - as a reference point the last common
ancestor of humans and chimpanzees lived about 6 million years ago. So the
iguanas have had plenty of time to evolve to their current form. But
interestingly the marine form, once developed, seems to have been remarkably
stable for millions of years. They have found an ecological niche and filled it
and have not speciated further, unlike much of Galapagos life.
Marine iguanas are unique. There are no other
marine lizards, and there never have been, ever. They are entirely vegetarian,
living on marine algae which they dive to eat off the rocks beneath the tide
line. The water here is relatively cold, and as reptiles these are cold blooded
animals, so they cannot stay in the water long. As a result they spend much of
the day on the coastline soaking up the equatorial sun, often in huge numbers.
Here are a few males on a rock at the top of a 50m vertical cliff - why they
have climbed up here is a mystery as other seem happy to sunbathe at the
bottom.
 These animals are large, with older males reaching
well over a metre. They do look like sea dragons, but are utterly docile as far
as humans are concerned and can be closely observed. Here is a male in
breeding colours:
 And here a smaller female, also in breeding
colours, greener in her case (these animals are from Espanola Island where
their colours are especially vivid; most are simply black all over, probably to
help in absorbing the sun's warmth after a cold dive):
 As you can see she's higher up the shore amongst
the vegeation because its the nesting season now and she's been laying eggs.
Finding a nice sandy spot above sea level on an island composed entirely of lava
is not easy and there is fierce competition for the best sites. Females will
fight, sometimes continuously for 24 hours to get the prime real estate - but
interestingly they never disturb eggs already laid even though the few really
good nest sites are very heavily used.
Marine iguanas have skin parasites like most
animals, and lava lizards are allowed to act as skin cleaners, running over the
resting iguanas (and sealions) picking off juicy ticks and the like. Here is a
male lava lizard using an iguana as both a food source and a handy vantage point
from which to display. Both lizards do so by bobbing their heads - sometime in
unison which looks really comic:
 As you might guess I have rather a lot of iguana
pictures but the cost of transmitting them by satellite phone is prohibitive so
you are spared the rest. I'll use the money 'saved' to load up some pictures
illustrating the truly amazing tortoise story, and the nesting albatrosses, and
and and. It really is an amazing place.
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