A basalt shoreline teeming with large resting iguanas looks nothing short of the Jurassic. When I first saw these striking creatures in the Galapagos, I was struck by their placidity. Undeterred by humans, they spend long, sunny days basking in the equatorial sun like scaly house cats, sometimes in droves, between foraging missions at sea to feed on kelp.

Charles Darwin was not impressed with this rare marine lizard. “It is a hideous-looking creature,” he wrote in the journey of the beagle“stupid and slow in his movements.”

However, since those encounters, iguanas have conquered many scientists. “I enjoy them because they seem very friendly and calm,” says Amy MacLeod, a conservation biologist at the University of Leipzig who studies marine iguana populations. “They are quite gangly on land but very graceful in the water.”

Surviving almost entirely on algae, some of which are over four feet long, these lizards developed flat tails for swimming and glands that filter and remove excess salt (which they expel through their noses when sneezing). They can also absorb their own bone marrow and shrink to help them survive famine when warmer waters during El Niño events make seaweed scarce. However, despite such adaptations, marine iguana populations are vulnerable. Wild dogs, cats, and even rats have taken a bite out of their number. Increased development on these attractive islands is also a threat. So are oil slicks, El Niño events intensified by climate change, and plastic debris.

But the severity of the risk to the lizards remains a mystery. “We don’t have enough data on population trajectories,” says MacLeod. One reason is that for years it was assumed that iguanas, unlike Darwin’s famous Galapagos finches, were fairly uniform across islands, making the risks to the animal lower, even if a population seemed to be wavering. But recent genetic research by MacLeod and others has revealed 11 distinct subspecies, each requiring individualized conservation efforts. MacLeod and his colleagues have launched a program known as Iguanas From Above, in which they fly drones to get a better picture of these populations and recruit the public to help count the lizards.

MacLeod is encouraged by the thriving populations of marine iguanas on Fernandina, the westernmost of the main Galapagos islands, where human impact is minimal and the waters produce abundant fodder for these graceful swimmers. “The colonies there are a delight to behold,” he says, “because they give the impression of a land before time.”