Casque-headed Lizard

For moderately-sized lizards that choose exposed perches on trunks and lianas, speed is a must. Basilisks will shoot up the trees clambering wildly, and frillneck lizards will use their exquisite auditory and visual senses to flee long before they are detected. A less common approach, though, is to freeze— even more so, to remain immobile when directly touched. The casque-headed lizard (Corytophanes cristatus) does just that, relying entirely on crypsis to avoid predation at any distance. As in many arboreal agamids, Corytophanes also shuffles around trunks in response to a disturbance, and I’ve had some fun observing this behavior on one occasion. However, most of the time they do not make any movement whatsoever, and when grasped they render themselves catatonic, legs stiff to the touch and sometimes gaping the mouth.

Juvenile casque-headed lizards generally have a more uniform beige color. Stripes and lighter hues will take form as they mature.

In accordance with their antipredator behaviors, Corytophanes is an obligate sit-and-wait predator, scouting terrestrial arthropods from vertical perches by slowly swaying their head side to side. Vision is their primary sensory modality, typical for iguanians, and there is no evidence that chemical discrimination contributes to their foraging behaviors. Despite the high abundance of prey in lowland and premontane tropical forests, Corytophanes is extremely selective in its choice of prey. They feed relatively infrequently on large arthropods, primarily the larvae of butterflies and beetles, and large katydids. I once observed an adult leap ~1.5 meters down to the ground, run bipedally over to a large sphingid caterpillar (Neococytius cluentius, if I remember correctly), and briskly grab the larva before ascending an adjacent tree. I was shocked to observe such a sedentary lizard behave so alertly, but indeed, activity patterns of Corytophanes involve long periods of immobility interspersed by brief and rapid foraging bouts.

Residing in a lush forest ecosystems where plants and fungi are keen to overtake you, lying still offers up a substrate conducible to all kinds of growth. Sloths are the pinnacles of blurring the lines between animal and ecosystem, essentially mobile microhabitats for thousands of invertebrates, fungi, and algae, many of which are mutualistic partners. As far as squamates go, life atop the scales is rare due to the periodic process of shedding. But surprisingly, a number of organisms have been recorded on the dorsal and lateral surfaces of Corytophanes. These include the fruiting bodies of slime molds (Myxomyceta: Physarum pusillum.. actually protists!), where they bring sporulation cycles to completion in just under a day, and also liverworts (Taxilejeunea obtusangula) that emerge from algal mats on the lizard’s casque. Whether such growths facilitate crypsis is difficult to say, but it isn’t far-reaching to speculate that Corytophanes may provide a mechanism for dispersal of these commensal organisms. In Australia, I observed two weevils hitchiking on an agamid’s tail, which may be happenstance, but I think epizoic associations with lizards are a fun research avenue that remains virtually unexplored.

All lizards in this post photographed in situ [1] unless otherwise stated

Photographed after disturbance [4]
Male brown basilisk (Basiliscus vittatus); photographed after pursuit [3]. The clade that includes basilisks, casque-headed lizards, and Laemanctus are the only bearers of dorsal casques among Iguanians.
Female plumed basilisk (Basiliscus basiliscus)
Iguanas are the closest relative to Corytophanes & Basiliscus in Costa Rica. Here a juvenile rests on grasses in a shallow swamp.

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