As we made our way westward, the landscape of the Texas Panhandle changed dramatically. Flat terrain abruptly dipped and rose, marking our entrance into the Caprock escarpment. Erosion and formation of sedimentary rock continues to shape the badlands, as it has for the past 230 million years. The deepest layers are a vibrant red-orange color, primarily red clay and shale, interspersed by fibrous sheets of gypsum crystals. Deposition of gypsum dates back to the Permian, the result of periodic evaporation at the sea’s edges when it receded from the inland. It was spectacular to see contiguous gypsum veins stretch infinitely along the lowest crevices of the canyon, each jagged turn representing shifts of large land masses or the crashing of sediment when erosion made the peaks ever so precarious. Above these layers lie multicolored sandstones and mudstones of the Triassic, where phytosaurs and giant amphibians (e.g., Anaschisma) once roamed the swamps. Finally, the higher layers of Caprock were markedly different in color and composition, a dusty white caliche covering an assortment of opalite and silicate rocks from the Tertiary.
The semi-arid climate of Caprock Canyons is brimming with life, yet in the dry season most animals remain hidden in wait of rain. Few birds were calling, no colubrid snakes could be found wandering the terrain, and the air was so empty that a rare dragonfly or butterfly was noteworthy. During early March, most plant life was on the cusp of blooming, and even a brief drizzle brought forth all kinds of insects and lizards to try to make the most of the moisture. No doubt I would love to return to this ecosystem when the vegetation reaches its full potential. What makes Caprock unique from adjacent badlands, such as in Palo Duro, is the presence of free-roaming plains bison. In the late 19th century, near the end of the tragic declines of wild bison, five orphan calves were captured from the southern herd. Over generations on a ranch, the bison reproduced and grew to hundreds of individuals before falling to just 36. In 1997, they were released into Caprock and have expanded their domain as a herd of more than 200 bison. However, the extreme population bottleneck and low genetic diversity does not fare well for persistence of Caprock bison as it stands. It appears that managed breeding with the northern plains bison will be necessary to prevent the collapse of the Caprock herd.
Megafauna like bison substantially remodel the landscape they inhabit. During my brief visits to Caprock and Palo Duro, their differences were astonishing. Along the tops of the sandstone plateaus of Caprock, bison had cleared out the vegetation from large swathes of land, barren trails permeated through the ridges, and large piles of dung were visible at every turn. By consuming primarily graminoids, bison limit the abundance of these competitively superior species, thereby increasing the diversity of plants, arthropods, and birds. Another more specialized way bison impact the environment is through their wallowing behavior. Bison will roll back and forth on the ground, creating large circular depressions of compacted soil. These areas offer entirely distinct patchy microhabitats across the semi-arid environment. Moisture collects more readily, which attracts amphibians to breed and provides nesting habitat for an astonishing diversity of bees and wasps. Even in abandoned wallows, higher water retention supports plant and arthropod taxa that are scarce elsewhere. Species interactions between the big (bison) and small (insects) may seem unlikely at first thought, but it’s an important reminder that organisms have both far-reaching and cascading effects in ecosystems. Conservation and management of natural areas, such as in Caprock, beautifully illustrate the interconnectivity of living things, and by the same token, how sensitive they all are to anthropogenic change.
Lizards that inhabit Caprock are all well-adapted for hot and dry conditions. Eight of the most common species include:
1) the side-blotched lizard (Uta stansburiana); also called the rock-paper-scissors lizard due to its male-male competitive dynamics that involve three color morphs,
2) three species of whiptail; the checkered (Aspidoscelis tesselatus), spotted (A. gularis), and six-lined (A. sexlineatus),
3) the prairie lizard (Sceloporus consobrinus), males characterized by iridescent blue on the throat and belly,
4) the collared lizard (Crotaphytus collaris), pastel orange and turquoise in color,
5) the Texas horned lizard (Phrynosoma cornutum), iconic for its blood-shooting antipredator behavior and ant-eating habits, and
6) the greater earless lizard (Cophosaurus texanus).
Earless lizards are specialists of open rocky habitats in xeric environments. As ambush foragers, they will perch on rocks in the heat of the day and shuttle off to pick up wandering arthropods. Grasshoppers, bees/wasps, flies, spiders, butterflies and ants are preferred prey items, and their reliance on each is dependent on seasonal and geographic abundance. In comparison to side-blotched and spiny lizards, Cophosaurus has a higher optimal body temperature. Since high elevations in the badlands are hotter and more sunlit, earless lizards perform better in these locations. Accordingly, their activity tends to be more concentrated high up the ridges, and this is exactly what I observed in Caprock. Cophosaurus is also known to make use of flat limestone and sandstone in stream beds, but surprisingly, I did not observe a single one during my several day stay. It’s possible that once the spring rains begin, insects will convene in those locations and attract their lizard predators.
Cophosaurus are “earless” because they lack an external tympanum, but yet another cool aspect of their morphology has earned them a second common name, the zebra-tailed lizard. The underside of the tail is conspicuously striped black and white, but most of the time remains hidden from view. It wasn’t until I finally observed one display, that I was awestruck. When threatened, it dashed away, came to a halt, then raised and waved its tail from side to side about four or five times. As I kept pursuing it, the lizard repeatedly performed this behavior, apparently some sort of deimatic display. My friend Josh witnessed the same behavior when he was off searching for hymenopterans, and later recounted it to me with a super cool explanation. Both of us had encountered eight western diamondback rattlesnakes in Oklahoma a few days before, and he said that the black and white pattern resembled the rattlesnakes’ bicolored tails— even making him stop to think twice! If you follow my blog, you know I love stories of mimicry, and whether or not it holds true, I think it was the most exciting natural history observation we shared during our road trip.