Stop, then go! Rapid acceleration offsets the costs of intermittent locomotion when turning in Florida scrub lizards.

Intermittent locomotion is a common locomotor mode in small vertebrates. Pausing is thought to aid in locating a predator or prey, enhancing crypsis, lowering energy costs, and/or maneuvering around obstacles or toward a refuge. Many lizards flee predators by turning into potential refugia and subsequently pausing, presumably to conceal themselves. Intermittent locomotion may be associated with turning by allowing an animal time to assess its surroundings and/or decreasing the likelihood of losing its footing. In this study, we quantify locomotor performance and the use of intermittent locomotion in Florida scrub lizards (Sceloporus woodi) when navigating either a 45° or 90° turn. Lizards paused in 92.91% of all trials, and yet despite pausing, instantaneous speed was not different entering or exiting the turn. This result suggests that turning comes at minimal cost to forward speed for lizards under these conditions. Pausing during a turn, however, did slow speed in the turn. Interestingly, the speed in the turn did not differ in trials with a pause before the turn versus trials without a pause. The angle of the turn also had no effect on whether lizards paused. We found that lizards increase peak acceleration following pauses to compensate for lost speed during the pause, providing a mechanism that may minimize negative fitness effects associated with slow running speeds and allow intermittent locomotion to be such a common strategy in lizards.

When Food Fights Back: Skull Morphology and Feeding Behavior of Centipede-Eating Snakes.

Feeding is a complex process that involves an integrated response of multiple functional systems. Animals evolve phenotypic integration of complex morphological traits to covary and maximize performance of feeding behaviors. Specialization, such as feeding on dangerous prey, can further shape the integration of behavior and morphology as traits are expected to evolve and maintain function in parallel. Feeding on centipedes, with their powerful forcipules that pinch and inject venom, has evolved multiple times within snakes, including the genus Tantilla. However, the behavioral and morphological adaptations used to consume this dangerous prey are poorly understood. By studying snakes with varying degrees of dietary specialization, we can test the integration of diet, morphology, and behavior to better understand the evolution of consuming difficult prey. We studied the prey preference and feeding behavior of Tantilla using the flat-headed snake (T. gracilis) and the crowned snake (T. coronata), which differ in the percentage of centipedes in their diet. We then quantified cranial anatomy using geometric morphometric data from CT scans. To test prey preference, we offered multiple types of prey and recorded snake behavior. Both species of snakes showed interest in multiple prey types, but only struck or consumed centipedes. To subdue centipedes, crowned snakes used coiling and holding (envenomation) immediately after striking, while flat-headed snakes used the novel behavior of pausing and holding onto centipedes for a prolonged time prior to the completion of swallowing. Each skull element differed in shape after removing the effects of size, position, and orientation. The rear fang was larger in crowned snakes, but the mechanical advantage of the lower jaw was greater in flat-headed snakes. Our results suggest that the integration of behavioral and morphological adaptations is important for the success of subduing and consuming dangerous prey.

DNA Methylation and Counterdirectional Pigmentation Change following Immune Challenge in a Small Ectotherm.

AbstractBy allowing for increased absorption or reflectance of solar radiation, changes in pigmentation may assist ectotherms in responding to immune challenges by enabling a more precise regulation of behavioral fever or hypothermia. Variation in epigenetic characteristics may also assist in regulating immune-induced pigmentation changes and managing the body's energetic reserves following infection. Here, we explore how dorsal pigmentation, metabolic rate, and DNA methylation in the Florida scrub lizard (Sceloporus woodi) respond to two levels of immune challenge across two habitat types. We found changes in pigmentation that are suggestive of efforts to assist in behavioral fever and hypothermia depending on the intensity of immune challenge. We also found correlations between DNA methylation in liver tissue and pigmentation change along the dorsum, indicating that color transitions may be part of a multifaceted immune response across tissue types. The relationship between immune response and metabolic rate supports the idea that energetic reserves may be conserved for the costs associated with behavioral fever when immune challenge is low and the immune functions when immune challenge is high. While immune response appeared to be unaffected by habitat type, we found differences in metabolic activity between habitats, suggesting differences in the energetic costs associated with each. To our knowledge, these results present the first potential evidence of pigmentation change in ectotherms in association with immune response. The relationship between immune response, DNA methylation, and pigmentation change also highlights the importance of epigenetic mechanisms in organism physiology.

Conservation and Management Strategies Create Opportunities for Integrative Organismal Research.

Conservation and management activities are geared toward the achievement of particular goals for a specific species, or groups of species, at the population level or higher. Conversely, organismal or functional research is typically organized by hypothesis tests or descriptive work that examines a broader theory studying individual organismal traits. Here, we outline how integrative organismal biologists might conduct mutually beneficial and meaningful research to inform or assist conservation and management biologists. We argue that studies of non-target species are very useful to both groups because non-target species can meet the goals of managers and organismal biologists alike, while also informing the other. We highlight our work on a threatened lizard species' thermal physiology, behavior, and color pattern-all of which are impacted by species management plans for sympatric, threatened, bird species. We show that management practices affect activity time, thermal adaptation, and substrate use, while also altering predation rates, crypsis, ectoparasite load, and sexual coloration in the study species. These case studies exemplify the challenges of conservation and management efforts for threatened or endangered species in that non-target species can be both positively and negatively affected by those efforts. Yet, the collaboration of organismal biologists with conservation and management efforts provides a productive system for mutually informative research.

Mite load predicts the quality of sexual color and locomotor performance in a sexually dichromatic lizard.

Since Darwin, the maintenance of bright sexual colors has recurrently been linked to mate preference. However, the mechanisms underpinning such preferences for bright colors would not be resolved for another century. Likely, the idea of selection for colors that could decrease the chances of survival (e.g., flashy colors that can inadvertently attract predators) was perceived as counterintuitive. It is now widely accepted that these extreme colors often communicate to mates the ability to survive despite a "handicap" and act as honest signals of individual quality when they are correlated with the quality of other traits that are directly linked to individual fitness. Sexual colors in males are frequently perceived as indicators of infection resistance, in particular. Still, there remains considerable discord among studies attempting to parse the relationships between the variables associating sexual color and infection resistance, such as habitat type and body size. This discord may arise from complex interactions between these variables. Here, we ask if sexual color in male Florida scrub lizards (Sceloporus woodi) is an honest signal of resistance to chigger mite infection. To this end, we use linear modeling to explore relationships between mite load, different components of sexual color, ecological performance, body size, and habitat type. Our data show that that the brightness of sexual color in scrub lizards is negatively associated with the interaction between mite load and body size, and scrub lizards suffer decreased endurance capacity with increases in mite load. Our data also indicate that mite load, performance, and sexual color in male scrub lizards can vary between habitat types. Collectively, these results suggest that sexual color in scrub lizards is an honest indicator of individual quality and further underscore the importance of considering multiple factors when testing hypotheses related to the maintenance of sexual color.

Acclimatization in the physiological performance of an introduced ectotherm.

Phenotypic flexibility may facilitate range expansion by allowing organisms to maintain high levels of performance when introduced to novel environments. Phenotypic flexibility, such as reversible acclimatization, permits organisms to achieve high performance over a wide range of environmental conditions, without the costly allocation or acquisition tradeoffs associated with behavioral thermoregulation, which may expedite range expansion in introduced species. The northern curly-tailed lizard, Leiocephalus carinatus, was introduced to the USA in the 1940s and is now established in southern Florida. We measured bite force and the thermal sensitivity of sprinting of L. carinatus during the winter and spring to determine how morphology and performance varied seasonally. We found evidence of seasonal variation in several aspects of physiological performance. Lizards sampled in spring sprinted faster and tolerated higher temperatures, while lizards sampled in winter had high performance over a wider range of temperatures. Furthermore, seasonal differences in physiology were only detected after generating thermal reaction norms. Both sprint and bite force performance did not differ seasonally when solely comparing performance at a common temperature. No seasonal relationships between morphology and performance were detected. Our results suggest that L. carinatus may use reversible acclimatization to maintain high levels of performance across seasons not typically experienced within their native range. Thermal physiology plasticity may ameliorate the impacts of sub-optimal temperatures on performance without the cost of behavioral thermoregulation. Our work highlights the importance of utilizing reaction norms when evaluating performance and the potential ecological impacts of introduced species.

Resolving tradeoffs among crypsis, escape behavior, and microhabitat use in sexually dichromatic species.

Variation in color pattern between populations of cryptic animals is common and typically attributed to selection pressures from visual predators combined with variation in substrate composition. However, little is known about how cryptic color pattern relates to varied rates of predation, and few studies simultaneously analyze patterns of escape behavior and microhabitat use along with variation in color pattern, even though these traits evolve in tandem. Here, we use a combination of calibrated photographs and spectrometry to examine the influence of spatial heterogeneity in rates of predation on dorsal brightness in the Florida scrub lizard (Sceloporus woodi), a cryptic and sexually dimorphic species. Simultaneously, we analyze patterns of escape behavior and microhabitat use measured in the field. The results of this study indicate that populations inhabiting environments of increased predation have less color variation and more closely match the color of local substrate than populations sampled in environments of relaxed predation. Populations exposed to increased predation also show more pronounced escape behavior and are more selective in their use of microhabitat. Interestingly, geographic variation of dorsal brightness, escape behavior, and microhabitat use were greater for females than for males. Our results not only provide empirical evidence for theories of adaptive coloration, but suggest that sexual dichromatism can be maintained by selection pressures related to predation.

Forelimb position affects facultative bipedal locomotion in lizards.

Recent work indicates that bipedal posture in lizards is advantageous during obstacle negotiation. However, little is known about how bipedalism occurs beyond a lizard's acceleratory threshold. Furthermore, no study to date has examined the effects of forelimb position on the body center of mass (BCoM) in the context of bipedalism. This study quantified the frequency of bipedalism when sprinting with versus without an obstacle at 0.8 m from the start of a sprint. Forelimb positions were quantified during bipedal running at the start of a sprint and when crossing an obstacle. Two species with contrasting body forms (and thus different BCoM) were studied (Sceloporus woodi and Aspidoscelis sexlineata) to assess potential variation due to body plan and obstacle-crossing behavior. No significant difference in frequency of bipedalism was observed in S. woodi with or without an obstacle. However, A. sexlineata primarily used a bipedal posture when sprinting. Forelimb positions were variable in S. woodi and stereotyped in A. sexlineata Caudal extension of the forelimbs helped shift the BCoM posteriorly and transition to, or maintain, a bipedal posture in A. sexlineata, but not in S. woodi The posterior shift in BCoM, aided by more caudally placed forelimbs, helps raise the trunk from the ground, regardless of obstacle presence. The body plan, specifically the length of the trunk and tail, and forelimb position work together with acceleration to shift the BCoM posteriorly to transition to a bipedal posture. Thus, species exhibit morphological and behavioral adjustments to transition to and maintain facultative bipedalism while sprinting.

The effects of multiple obstacles on the locomotor behavior and performance of a terrestrial lizard.

Negotiation of variable terrain is important for many small terrestrial vertebrates. Variation in the running surface resulting from obstacles (woody debris, vegetation, rocks) can alter escape paths and running performance. The ability to navigate obstacles likely influences survivorship through predator evasion success and other key ecological tasks (finding mates, acquiring food). Earlier work established that running posture and sprint performance are altered when organisms face an obstacle, and yet studies involving multiple obstacles are limited. Indeed, some habitats are cluttered with obstacles, whereas others are not. For many species, obstacle density may be important in predator escape and/or colonization potential by conspecifics. This study examines how multiple obstacles influence running behavior and locomotor posture in lizards. We predict that an increasing number of obstacles will increase the frequency of pausing and decrease sprint velocity. Furthermore, bipedal running over multiple obstacles is predicted to maintain greater mean sprint velocity compared with quadrupedal running, thereby revealing a potential advantage of bipedalism. Lizards were filmed running through a racetrack with zero, one or two obstacles. Bipedal running posture over one obstacle was significantly faster than quadrupedal posture. Bipedal running trials contained fewer total strides than quadrupedal ones. But on addition of a second obstacle, the number of bipedal strides decreased. Increasing obstacle number led to slower and more intermittent locomotion. Bipedalism provided clear advantages for one obstacle, but was not associated with further benefits for an additional obstacle. Hence, bipedalism helps mitigate obstacle negotiation, but not when numerous obstacles are encountered in succession.

The ontogeny of escape behavior, locomotor performance, and the hind limb in Sceloporus woodi.

Flight initiation distance describes the distance at which an animal flees during the approach of a predator. This distance presumably reflects the tradeoff between the benefits of fleeing versus the benefits of remaining stationary. Throughout ontogeny, the costs and benefits of flight may change substantially due to growth-related changes in sprint speed; thus ontogenetic variation in flight initiation distance may be substantial. If escape velocity is essential for surviving predator encounters, then juveniles should either tolerate short flight initiation distances and rely on crypsis, or should have high flight initiation distances to remain far away from their predators. We examined this hypothesis in a small, short-lived lizard (Sceloporus woodi). Flight initiation distance and escape velocity were recorded on an ontogenetic series of lizards in the field. Maximal running velocity was also quantified in a laboratory raceway to establish if escape velocities in the field compared with maximal velocities as measured in the lab. Finally a subset of individuals was used to quantify how muscle and limb size scale with body size throughout ontogeny. Flight initiation distance increased with body size; larger animals had higher flight initiation distances. Small lizards had short flight initiation distances and remained immobile longer, thus relying on crypsis for concealment. Escape velocity in the field did not vary with body size, yet maximum velocity in the lab did increase with size. Hind limb morphology scaled isometrically with body size. Isometric scaling of the hind limb elements and its musculature, coupled with similarities in sprint and escape velocity across ontogeny, demonstrate that smaller S. woodi must rely on crypsis to avoid predator encounters, whereas adults alter their behavior via larger flight initiation distance and lower (presumably less expensive) escape velocities.

Rock-dwelling lizards exhibit less sensitivity of sprint speed to increases in substrate rugosity.

Effectively moving across variable substrates is important to all terrestrial animals. The effects of substrates on lizard performance have ecological ramifications including the partitioning of habitat according to sprinting ability on different surfaces. This phenomenon is known as sprint sensitivity, or the decrease in sprint speed due to change in substrate. However, sprint sensitivity has been characterized only in arboreal Anolis lizards. Our study measured sensitivity to substrate rugosity among six lizard species that occupy rocky, sandy, and/or arboreal habitats. Lizards that use rocky habitats are less sensitive to changes in substrate rugosity, followed by arboreal lizards, and then by lizards that use sandy habitats. We infer from comparative phylogenetic analysis that forelimb, chest, and tail dimensions are important external morphological features related to sensitivity to changes in substrate rugosity.

The correlation between locomotor performance and hindlimb kinematics during burst locomotion in the Florida scrub lizard, Sceloporus woodi.

Burst locomotion is thought to be closely linked to an organism's ability to survive and reproduce. During the burst, animals start from a standstill and then rapidly accelerate to near-maximum running speeds. Many previous studies have described the functional predictors of maximum running speed; however, only recently has work emerged that describes the morphological, functional and biomechanical underpinnings of acceleration capacity. Herein we present data on the three-dimensional hindlimb kinematics during burst locomotion, and the relationship between burst locomotor kinematics and locomotor performance in a small terrestrial lizard (Sceloporus woodi). We focus only on stance phase joint angular kinematics. Sceloporus woodi exhibited considerable variation in hindlimb kinematics and performance across the first three strides of burst locomotion. Stride 1 was defined by larger joint angular excursions at the knee and ankle; by stride 3, the knee and ankle showed smaller joint angular excursions. The hip swept through similar arcs across all strides, with most of the motion caused by femoral retraction and rotation. Metatarsophalangeal (MTP) kinematics exhibited smaller maximum angles in stride 1 compared with strides 2 and 3. The significant correlations between angular kinematics and locomotor performance were different across the first three strides. For stride 1, MTP kinematics predicted final maximum running speed; this correlation is likely explained by a correlation between stride 1 MTP kinematics and stride 2 acceleration performance. For stride 3, several aspects of joint kinematics at each joint predicted maximum running speed. Overall, S. woodi exhibits markedly different kinematics, performance and kinematics-performance correlations across the first three strides. This finding suggests that future studies of burst locomotion and acceleration performance should perform analyses on a stride-by-stride basis and avoid combining data from different strides across the burst locomotor event. Finally, the kinematics-performance correlations observed in S. woodi were quite different from those described for other species, suggesting that there is not a single kinematic pattern that is optimal for high burst performance.

Performance and three-dimensional kinematics of bipedal lizards during obstacle negotiation.

Bipedal running is common among lizard species, but although the kinematics and performance of this gait have been well characterized, the advantages in biologically relevant situations are still unclear. Obstacle negotiation is a task that is ecologically relevant to many animals while moving at high speeds, such as during bipedal running, yet little is known about how obstacles impact locomotion and performance. We examined the effects of obstacle negotiation on the kinematics and performance of lizards during bipedal locomotion. We quantified three-dimensional kinematics from high-speed video (500 Hz) of six-lined racerunners (Aspidoscelis sexlineata) running on a 3 m racetrack both with and without an obstacle spanning the width of the track. The lizards did not alter their kinematics prior to contacting the obstacle. Although contact with the obstacle caused changes to the hindlimb kinematics, mean forward speed did not differ between treatments. The deviation of the vertical position of the body center of mass did not differ between treatments, suggesting that in the absence of a cost to overall performance, lizards forgo maintaining normal kinematics while negotiating obstacles in favor of a steady body center of mass height to avoid destabilizing locomotion.

Effects of training and testosterone on muscle fiber types and locomotor performance in male six-lined racerunners (Aspidoscelis sexlineata).

Testosterone (T) is thought to affect a variety of traits important for fitness, including coloration, the size of sexual ornaments, aggression, and locomotor performance. Here, we investigated the effects of experimentally elevated T and locomotor training on muscle physiology and running performance in a nonterritorial male lizard species (Aspidoscelis sexlineata). Additionally, several morphological attributes were quantified to examine other characters that are likely affected by T and/or a training regimen. Neither training alone nor training with T supplementation resulted in increased locomotor performance. Instead, we found that T and training resulted in a decrease in each of three locomotor performance variables as well as in hematocrit, ventral coloration, and testis size. Strikingly, neither the size nor the fiber composition of the iliofibularis or gastrocnemius muscles was different among the two treatments or a group of untrained control animals. Hence, the relationships among T, training, and associated characters are not clear. Our results offer important insights for those hoping to conduct laboratory manipulations on nonmodel organisms and highlight the challenges of studying both training effects and the effects of steroid hormones on locomotor performance.

How muscles define maximum running performance in lizards: an analysis using swing- and stance-phase muscles.

Maximum locomotor performance is crucial for capturing prey, escaping predators and many other behaviors. However, we know little about what defines maximum performance in vertebrates. Muscles drive the movement of the limbs during locomotion, and thus likely play a major role in defining locomotor capacity. For lizards, the iliofibularis, a swing-phase muscle, is often linked to ecology and/or performance. However, stance-phase muscles likely limit performance given that they propel the animal. Using a small semi-arboreal lizard (Sceloporus woodi), we compared how swing- and stance-phase muscles relate to maximum running speed and acceleration. We employed both a level and vertical trackway to elicit ecologically relevant locomotor performance. Six individuals were filmed at 250 frames s⁻¹ in lateral view. Following performance trials, upper and lower hindlimbs were sectioned and assessed using histochemistry. Fast glycolytic, fast oxidative and slow oxidative fibers were detected and counted in the gastrocnemius (GA; stance phase) and iliofibularis (IF; swing phase) muscles. In addition, the mean fiber diameter for each fiber type in each muscle was determined, as was the fiber cross-sectional area. We found that properties of the GA, but not the IF, were positively correlated with performance. Interestingly, certain attributes of the GA were correlated with maximum vertical locomotion whereas others were correlated with maximum level locomotion. We conclude that stance phase, not swing phase, limits maximum performance in this species of lizard. In addition, we highlight the need to include properties of stance-phase muscles and a spectrum of ecologically relevant behaviors when attempting to correlate locomotor physiology with ecology and/or performance.

Getting up to speed: acceleration strategies in the Florida scrub lizard, Sceloporus woodi.

Small animals typically rely on quick bursts and intermittent pauses when moving in the wild. Hence, the study of acceleration capacity is important for understanding the ecology and evolution of locomotor performance. In this study, we investigate intraspecific variation in the acceleration capacity of a small lizard (Sceloporus woodi). To quantify animal acceleration performance, the momentum-impulse theorem is applied to data collected from high-speed video recordings of individuals accelerating from a standstill and over a subsequent distance of 0.4 m. Unlike earlier studies, the momentum-impulse approach allows one to directly and precisely quantify the per step contribution to acceleration capacity. Like other small vertebrates, we show that S. woodi is capable of accelerating to near maximum speeds (approximately 2 m s(-1)) within approximately 0.4 m and needs only a few steps (at least five) to achieve maximum speed. However, considerable intraspecific variation in acceleration capacity exists; individuals take different numbers of steps (two to five steps) over the first 0.4 m, and only some individuals (10 of 19) reach their maximum speed over the first 0.4 m. Only acceleration performance in steps 1 and 2 is predictive of running speed at 0.4 m; accelerations in steps 3, 4, and 5 are not related to individual differences in speed. Individual variation in acceleration strategy is considerable, with individuals using one of three strategies to reach maximum speed. Muscle mass-specific power during acceleration approaches the maximum power output measured for lizard hindlimb musculature ( approximately 900 W kg(-1)), suggesting that S. woodi accelerations approach the limit of their musculoskeletal system. This study highlights the utility of the momentum-impulse approach to study acceleration performance and the importance of elucidating the per step contribution to acceleration capacity.

Seasonal variation in testosterone and performance in males of a non-territorial lizard species.

The ability to perform key behaviors, particularly those associated with reproduction, has been linked to reproductive success. However, it remains unclear as to which underlying mechanisms govern variation in the performance capacities of these behaviors. Due to its ability to mediate physiological and morphological changes, the steroid hormone testosterone has been hypothesized to influence performance. This hypothesis, however, has not been tested in a broad range of taxa or mating systems. In this study, seasonal patterns of bite force and locomotor performance were quantified concurrently with circulating testosterone levels in males of a non-territorial polygynous lizard species (Aspidoscelis sexlineata). Bite force and one measure of locomotor performance were significantly greater in the breeding season than in the post-breeding season, and this seasonal variation in performance was correlated with seasonal changes in testosterone levels. These results suggest that the performance capacities of behaviors important for acquiring mating opportunities in this species are maximized during the breeding season by elevated testosterone levels.

Concordance between locomotor morphology and foraging mode in lacertid lizards.

Foraging behaviors exist along a continuum from highly sedentary, ambush foraging, to more continuous searching, or active foraging. Foraging strategies, or modes, are defined based upon locomotor behaviors (e.g. percent time moving, moves per minute). In lizards, traits correlated with ambush and active foraging have been of interest for some time; however, general patterns of correlated evolution between locomotor morphology and locomotor behavior have only recently begun to be quantified. In this study, variation in hindlimb morphology is investigated in a model group of lizard species that vary between active foraging and more sedentary (or mixed) foraging mode. Canonical variates analysis reveals that the two active foraging species occupy similar regions of the morphospace, while the two more sedentary species occupy different regions. The active foraging species have a narrow pelvis with shorter tibia and femora. The more sedentary species have a wide pelvis, long tibia and femora, and slightly longer metatarsals. Phylogenetic patterns of trait variation were examined through ancestral character state reconstruction and show morphological shifts in concert with foraging mode in these species. The observed shifts in locomotor morphology are discussed in light of published data on sprint speed and endurance in these species. Together, the data show that linking morphological variation to variation in stride length and stride frequency is critical to understanding the evolution of locomotor performance. Much more stride length and frequency data are needed among ambush, mixed, and active foraging species because these parameters, and their morphological components, are likely correlated with variation in food acquisition mode.

Testing amniote models of prey transport kinematics: a quantitative analysis of mouth opening patterns in lizards.

Two models have been proposed to describe the prey transport kinematics of terrestrial vertebrates (Bramble and Wake, 1985; Reilly and Lauder, 1990). The critical difference between the models is the presence or absence of a slow open-II phase (SO-II) in the gape profile during mouth opening. Each of these models has been applied to lizards, however to date, lizard feeding kinematics have not been adequately quantified to assess the utility of these models for this clade. Neither model has been sufficiently tested due to the lack of a methodology to assess the specific differences between the models. We describe a method that uses explicit mathematical criteria to define the kinematic phases in tetrapod feeding. This "slope analysis& is used to precisely quantify and compare the transport kinematics of seven lizard species. Lizard transport kinematics were highly variable both within and across taxa. However, several common gape cycle patterns were identified. The predominant patterns were slow-fast opening (37.3%), fast opening only (22.9%) and slow opening only (21.2%). The most common pattern explicitly fits the prediction of the Reilly and Lauder model while the other two are similar to patterns observed in salamanders. Thus, lizards possess both the slow opening-fast opening pattern predicted for amniotes and the more primitive, simple opening pattern characteristic of more basal tetrapods. Plateau phases were found in only 12.8% of the profiles and only a fourth of these (3.4% of the total) explicitly fit the Bramble and Wake model (slow opening, plateau, fast opening) and two species never exhibited plateaus in their gape cycles. Thus, it is clear that the Bramble and Wake model is not supported as a generalized model for lizards or generalized tetrapods.