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FIG. 2. Responses of adult Regal Horned Lizards (Phrynosoma solare)to presentation of encounters with ophidian predators. A) body-flip responseto an approaching Coachwhip (Masticophis flagellum). B) continuedholding of a body-flip response to a M. flagellum following retractionand hiding of the snake. C) running response (lower right) to a tubedWestern Diamond-backed Rattlesnake (Crotalus atrox) (upper left/center).dog encounters, and 75% of encounters with a native canid(Sherbrooke and Middendorf 2001, 2004). Assuming humans werenot a selective force in the evolution of blood squirting (nor in theevolution of body-flipping/immobility behavior in P. solare), thesesignificant differences in frequency of horned lizards employingantipredator defenses at humans versus at predators suggest thathumans present confounding stimuli that may sometimes erroneouslyelicit defensive behaviors evolved as defenses against othercategories of organisms.Ingestion of horned lizards by gape-limited predators such assnakes involves significant risk of death to the predator (Holteand Houck 2000; Sherbrooke 1981, 2003; Vorhies 1948). Becauseof this, features of the P. solare body-flip and immobility displaymay inhibit the likelihood of further attack, depending on the relativesize of the snake and the lizard, the experience of the snake,and the snake’s level of hunger (Aubret et al. 2007). And, if asnake initiates an attack, the flipped and immobile lizard is in aposition for maintaining a stance that maximizes the effectivenessof its physical defenses against such a predator. Rattlesnakes possesssimilar size-related ingestion limitations as do whipsnakes,but envenomation may reduce some features of resistance to captureand ingestion, such as leg rigidity, but not others, such ashorn erection (Sherbrooke and May 2008). A body-flip and immobileresponse offers little defense against envenomation by arattlesnake, but a running response distances the lizard from a strikeby this predator that does not rapidly pursue fleeing prey.Phrynosoma solare responses to M. flagellum were initiated ata distance of 5–70 cm, suggesting a visual identification of thepredator as a precursor to subsequent reactions. Tilting was themost common response (98%). This was followed by body-flipping(92%) and horn raising (54%). We suggest that followingvisual identification of predator type (as non-venomous rather thanvenomous; breadth and characteristics of these predator categorieshave not yet been determined), the lizard adjusts its body defensivelywith a tilting of its dorsal surface toward the predator,with a raising of the horns in many cases, and then, or even beforethese reactions, it executes a body-flip.Once body-flipping behavior has instantaneously inverted a P.solare, still located at the site of its encounter with a M. flagellum,its appearance has been visually altered. This may startle (Edmund1974; Ruxton et al. 2004) a non-venomous snake enough to preventan immediate jaw-grasping attack. During body-flipping thelizard’s cryptically-colored and disruptively-patterned dorsal surface(visually fragmented) is replaced by a nearly pure white (sometimeswith small gray spots; Fig. 2, B) ventral surface. This surfaceis broadly oval with a row of lateral fringe scales (jagged inappearance) along each side of the abdomen, four laterally-splayedlimbs, and an extended tail. This suddenly appearing new visionmay advertise to the snake that its potential prey possesses a broaddimension and extended sharp structures, which present potentialdifficulties for ingestion (Inbar and Lev-Yadun 2005; Speed andRuxton 2005). The wide-taxonomic occurrence of uniformly-whiteventral surfaces in iguanid lizards suggests that this character isplesiomorphic in the clade. Therefore the uniform-white color ofventral surfaces exposed during body-flip/immobility displays ofP. solare may have evolved as an exaptation.If body-flip and immobility displays do not successfully thwartsubjugation and consumption by a relatively large M. flagellum, itmay be unlikely that an attempted running escape would enhancesurvival. Limb length is short and sprint speed is low inPhrynosoma (Bonine and Garland 1999; Pianka and Parker 1975),virtually assuring capture by a pursuing M. flagellum. Fleeing preyoften elicit chase and capture responses by predators (Cyr 1972),and running horned lizards 1) may not easily visually monitor themovements of a pursuing snake, 2) may provide a horizontallyflattenedtarget for the vertically-grasping jaws of whipsnakes(Sherbrooke 2008), and 3) may be unable to display their morphologicalfeatures that are threats to whole-prey ingestion.The best defense of a P. solare against a M. flagellum appears tobe remaining stationary (flipped and immobile), thus visually in-160 Herpetological Review 39(2), 2008