The occasionally marine iguana

by Greg Mayer

Matthew sent me and Jerry this Tweet from PADI, of a wonderful video clip by Turtle & Ray Productions in Curaçao. It reminded Matthew of mosasaurs, an extinct group of giant marine lizards from the Mesozoic.

The common green iguana (Iguana iguana iguana) is widespread in Central and South America, and has also been introduced to a number of other places, including South Florida, where it is flourishing. It’s long been known that they readily take to water, both fresh and salt. I saw and photographed one in the harbor at Charlotte Amalie on St. Thomas in the Virgin Islands, but I’ve never gotten to see one from an underwater perspective! My friend and colleague James D. “Skip” Lazell, Jr., published this field sketch he made of a swimming iguana in his monograph on the genus Iguana in the West Indies. (This is Iguana delicatissima, a species endemic to the northern Lesser Antilles).

Field sketch by Skip Lazell of Iguana delicatissima swimming, Woodford Hill, Dominica (Lazell, 1973).

I immediately thought of the marine iguana, Amblyrhynchus cristatus, endemic to the Galapagos, where it lives along the coasts, and feeds on algae in the sea. Like the green iguana, in person I have only seen them from above the water. The following video, from Scuba Hank NYC, shows them underwater, both swimming and feeding. Upon seeing these lovely beasts lining the shores of the Galapagos, Darwin is said to have leaned over the the bow rail of the Beagle and exclaimed, “Wow, lizard city!

In looking for an appropriate marine iguana video, I came across this intriguing video, of a kayaker rescuing a green iguana four miles at sea off the Florida Keys. Besides being a wonderful story, and a testament to the kayaker’s humanity and, the iguana’s tenacity and ingenuity in figuring out that staying with the boat and jumping on, despite the presence of a man, was a good move, it helps to show how iguanas may have gotten to the Galapagos: they readily enter into, and can survive for some time, in the sea. Though not capable of directed swimming over great distances, this would make it more likely than landlubbing lizards that they could be carried off to a distant landfall, by what Darwin called “occasional means of transport.

Lazell, J.D. 1973. The lizard genus Iguana in the Lesser Antilles. Bulletin of the Museum of Comparative Zoology 145:1-28. BHL

Neill, W.T. 1958. The occurrence of amphibians and reptiles in saltwater areas, and a bibliography. Bulletin of Marine Science of the Gulf and Caribbean 8:1-97. pdf


  1. Jenny Haniver
    Posted April 3, 2019 at 10:05 am | Permalink

    I’m glad to see this at last, instead of the code that constituted the first email announcement of the post.

    Very cool to watch these iguanas slither through the sea and munch on sea vegetables.

  2. Posted April 3, 2019 at 10:52 am | Permalink

    “Wow! Lizard city!” Now I am giggling uncontrollably, and have to go teach my class. Hope I get thru it.

  3. Posted April 3, 2019 at 11:25 am | Permalink

    I thought iguanas ate flies and other insects? If so, why are they into swimming?

    • Posted April 3, 2019 at 12:11 pm | Permalink

      It is a large group (family?) but these general types of iguana are vegetarian. The big green iguanas will eat bananas, for example.

  4. Dominic
    Posted April 3, 2019 at 11:27 am | Permalink

    Very nice…

    Greg – did you see this?//
    “Here, we report apparent facultative oviparity by a viviparous female of the bimodally reproductive skink Saiphos equalis—the first report of different parity modes within a vertebrate clutch. Eggs oviposited facultatively possess shell characteristics of both viviparous and oviparous S. equalis, demonstrating that egg coverings for viviparous embryos are produced by the same machinery as those for oviparous individuals. “

  5. ThyroidPlanet
    Posted April 3, 2019 at 11:39 am | Permalink


    There’s a joke there somewhere but I’ll leave it alone.

  6. Curt Nelson
    Posted April 3, 2019 at 12:39 pm | Permalink

    That undulating swimming style reminds me of good podcast I just heard (Sean Carroll’s Mindscape with guest Malcolm MacIver) in which the study of electric fish, that swim forward and backward via undulating fins, helped him conclude that it was movement onto land that induced animals to evolve big brains – because in water animals mostly react (instead of plan) due to short visibility (sensoria), but on land the greater visibility makes planning possible.

  7. Nicolaas Stempels
    Posted April 3, 2019 at 12:51 pm | Permalink

    IIRC there was an observation of iguanas floating on an ‘island’ of plant debris yo other ‘real’ islands in the Caribbean. I even think Dawkins mentioned it in one (or more) of his books.

    • Posted April 3, 2019 at 8:20 pm | Permalink

      Yes– absolutely! Iguanas from Guadeloupe, apparently blown out to sea on large trees by a hurricane, fetched up on Anguilla in 1995. They floated over 175 miles, taking a month or more, clinging to the floating trees. The piece de resistance was when a sign labeled “Parque Nacional de Guadeloupe” washed up with the trees, indicating exactly where they came from. Ellen Censky, then at the Carnegie Museum, and now president of the Milwaukee Public Museum, documented the event. Here’s an early account by her; and two later news concerning her paper in Nature from 1998 are here and here. It was even covered in the glossy travel magazine Islands! (I had a copy, but can’t find it 😦 .) I can’t immediately find a link to her Nature paper, but it wouldn’t be hard to find with a bit more searching.


  8. rickflick
    Posted April 3, 2019 at 1:03 pm | Permalink

    I saw the marine iguana in the Galapagos, but not from underwater, unfortunately. Mostly they were sleeping on rocks.

  9. Daniel
    Posted April 3, 2019 at 1:08 pm | Permalink

    Legalize marineiguana

    • Curt Nelson
      Posted April 3, 2019 at 2:16 pm | Permalink

      Good one.

  10. Posted April 3, 2019 at 1:45 pm | Permalink

    It is an impressive swimmer for a land animal!

  11. infiniteimprobabilit
    Posted April 3, 2019 at 5:38 pm | Permalink

    That land iguana was a lot more graceful than the rather fat Galapagos ones.

    But how does it hold its breath for so long? It didn’t look like it was going to surface any time soon.


  12. Mark R.
    Posted April 3, 2019 at 6:55 pm | Permalink

    Thanks for this fun post…it wasn’t working yesterday.

    I knew someone in college who kept his pet iguana in the bathroom of his apartment- a large and handsome male. The entire bathroom was the iguana’s “cage”- it had branches to climb on, water in the tub to lounge in…quite a nice habitat. It was strange going to the bathroom though, and I doubt the landlord would have approved. 😉

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