Hot Dry Places - Tracks and Shadows: Field Biology as Art - page 73

interrupted by rocky cerros and farming villages. We jokingly diagnosed the scrawny
cattle as alive or dead based on verticality, then discovered that one cow sheltered three
species of lizards, her withered legs serving as handles when we checked the carcass.
And on a highway stretch that threatened to strand us without gas, as if la máquina
mala hadn't quashed my morbid fantasies, Angus hurtled us through a checkpoint in
which the soldier slept propped on his rifle. “Holy shit,” I blurted out, visualizing the
Bolivian fusillade that cut down Paul Newman and Robert Redford in ButchCassidyand
the Sundance Kid, “an octagonal red Alto means stop!”
Andean condors soared over the sparkling Pacific seashore on the last day of our month-
long circuit, but we saw little other wildlife except small birds and seedpod-eating foxes.
Although the Sechura reptiles comprise several geckos and tropidurines, the whiptail
relatives, two racerlike serpents, and one each worm-lizard, coralsnake, and pitviper,
we searched in vain for snakes and encountered only three of our elusive giant lizard
quarry. The largest monitor tegu sped across a road near Olmos (in hindsight, I realized
I should have recruited local children to search for it), and we watched another prowl
among boulders and columnar cacti, looking like a miniature version of Komodo mon-
itors I'd seen on TV. The one we caught, a handsome black male with yellow markings
found near Talara, on the continent's westernmost tip, was finally dug out from a yard-
deep, eight-foot tunnel that also contained shed skins of worm-lizards.
We didn't learn much about the big lizards, beyond admiring their long forked
tongues and pebbled skin, their jagged teeth and razor claws, but those weeks in Peru
enhanced my curiosity about adaptation. If examining preserved Tropidurusthoracicus
was thought-provoking, 14 noosing those wriggling sand-dwellers, so much like the dis-
tantly related but ecologically similar Mohave fringe-toed lizard, was downright inspir-
ing. Holding a live monitor tegu was off the charts! And beyond such impressive con-
vergent evolution, we saw never-before described behaviors. On the coast, ten-inch T.
peruvianus dashed from rocks above the tide-line down onto wet sand, scarfed up arth-
ropods, and fled back from the crashing surf; a few miles inland, dozens of herbivorous
Sechura whiptails gathered in the shade of an algarrobo tree, striped skins awash in
aquamarine hues, and vigorously hand-waved at each other—alas, to no effect, as far as
I could tell.
Soon enough we were gazing on snow-covered peaks of the continental spine glinting
off to the left throughout our four-hour flight south to Santiago. Over the coming days
Fabián would introduce us to his country, Nobel laureate Pablo Neruda's homeland,
but I couldn't shake the more general problem of specialization and kept daydream-
ing about how all North American and South American fringe-toed lizards possess ad-
aptively modified feet, implying that their respective ancestors did as well. Here was
the problem: Selection obviously can shape population genetics, but how might we test
whether that process, deep in geological time and coupled with environmental oppor-
tunity—in this case, running on sand—had favored now invariant traits in particular lin-
eages? Two other troublesome examples further stirred my thinking. 15
In the 1960s, University of Texas professor Eric Pianka initiated research on desert
reptiles, including some textbook examples of convergence. Our dozen-plus species of
horned lizards, related to other New World iguanians, are slow, tanklike, and superbly