LIZARD ENERGETICS AND DIET' F. HARVEY POUGH Section of Ecology and Systematics, Langmuir Laboratory, Cornell University Ithaca, NY 14850

Abstract. In the families Agamidae, Gerrhosauridae, Iguanidae, and Scincidae, species that weigh more than 300 g are almost all herbivores, whereas those weighing less than 50-100 g are carnivores. Juveniles of large herbivorous species tend to be carnivorous until they reach body weights of 50-300 g. Diet is compared to metabolic expenditure in these lizards. Although smaller animals have higher weight-specific metabolic rates, the greater total metabolic rate of larger animals requires a greater caloric intake. Juvenile animals and species of small body size are primarily insectivorous. It is postulated that larger animals of these families are unable to meet caloric demands on a diet of insects, have no practical alternative animal prey, and rely instead on vegetation. The families Anguidae, Chamaeleontidae, Helodermatidae, Teiidae, and Varanidae do not include herbivorous species, although each family has species that weigh more than 300 g. Morphological, ecological, and physiological specializations in these families account for the absence of herbivorous species. For an unspecialized lizard, evolution of large body size both requires and permits an herbivorous diet.

INTRODUCTION and Old World respectively and are very similar in and behavior. Agamid dentition There are strikingly few herbivores among living gross morphology however, lizards, particularly in comparison to the large her- is more differentiated than that of iguanids, (Uro- bivorous reptilian faunas that lived during the Meso- and in at least one genus of agamid herbivores mastix) is highly specialized. There is less specializa- zoic. Of some 2,500 species of living lizards, fewer iguanids. If than 50 are predominantly herbivorous. Explanations tion of dentition in most herbivorous fragments is of this phenomenon have been based on the premise grinding plant material into digestible would that lizards are unable to chew or digest plant food a great problem for herbivorous lizards, one spe- efficiently. Szarski (1962) suggested that poor assim- expect that agamids with their differentiated and the ilation of vegetation reduced the energy herbivorous cialized teeth would be better able to cope with this were true, there should lizards had available for reproduction, leading to re- problem than iguanids. If than among productive rates lower than those of carnivorous liz- be smaller herbivores among the agamids dentition would reduce ards. Thus, he hypothesized, lizards require some iguanids, since specialized data I have been able mechanism to reduce predation in order to exploit the effort of chewing. All the that this is not the case; the small- an herbivorous niche successfully. Ostrom (1963) to gather indicate are almost felt that the loss of the lower temporal arch in mod- est herbivorous iguanids and agamids ern lizards (compared to the fully diapsid condition exactly the same size. are considered of Mesozoic reptilian herbivores) and the resulting Symbiotic micro-organisms generally of all herbivorous reptiles mobility of the quadrate bone prevented the evolu- to be absent from the guts 1971). This assumption may be tion of an efficient plant-grinding mechanism. Sokol (Szarski 1962, Nagy cases. The caeca of the herbivorous (1967) pointed out that most herbivorous lizards incorrect in some Uromastix (El-Toubi and Bishai 1959) and are large and suggested that because of an inefficient lizards much larger than the cae- chewing mechanism only large lizards are able to Iguana are proportionally Tupinambis (Beattie 1926) reduce plant matter to digestible fragments. These cum of the carnivorous Agama agama (Harris 1963). explanations rest on the assumption that thorough or the insectivorous caecum of Uromastix grinding of vegetation is a necessary preliminary to Dubuis et al. (1971) found the with worms. Inasmuch as this digestion. This may not be true; the completely her- acanthinurus packed bivorous chuckwalla (Sauromalus obesus) does not was the common condition in the specimens they grind its food (Nagy 1971). Furthermore, the mor- examined and the lizards seemed healthy, they sug- phology of teeth and jaw muscles differs from family gested that the worms might play a role in the lizards' to family among lizards. For example, iguanids and digestion. In Iguana iguana the caecum is propor- agamids occupy similar ecological niches in the New tionally smaller in adults than in hatchlings although its absolute size increased tenfold. At present there l Received November 27, 1972; accepted January 15, 1973. seems no reason to believe that the absolute dimen- 838 F. HARVEY POUGH Ecology, Vol. 54, No. 4 sions of the gut determine a lizard's ability to digest 5000 plant food. Szarski (1962) suggested that insular species of lizards could be herbivorous because of the absence of predators from island habitats. It is true that the /~~~~~ ground iguanas of the Caribbean and Galapagos are herbivorous, but they are also among the largest liv- 1000 S ing lizards. On the mainland, lizards of comparable size are also herbivores. Lack of predators on islands probably permits the large iguanids to be terrestrial instead of arboreal, but probably does not influence their diet. There are many insular species of small insectivorous lizards, and none is known to be carniv- *0 orous on the mainland and herbivorous on an island. A factor not previously considered is the relation- E -ao | 0oooo. ship between diet and body size per se. Metabolic rate is a function of body size; small organisms have smaller total energy requirements than do larger ones, but the energy requirement per unit of body weight is greater for a small animal. Because an an- imal's food intake must be adequate to maintain its metabolic rate, it seems likely that body size will have a bearing on the efficiency with which various energy 10 - sources can be utilized. In this paper I have assembled data on body size and dietary habits of a number of species from nine families of lizards and examined the relationship between these characters.

METHODS

Few lizards are strictly carnivorous or herbivorous, 1 I1111111tl and most reports of feeding habits or analyses of 5 10 15 20 25 30 35 40 45 50 stomach contents are too qualitative to allow precise estimates of the relative importance of plant and Snout-vent length (cm) animal foods, particularly in view of the seasonal FIG. 1. Relationship between body weight and snout- changes in diet reported in some studies. vent length in lizards. See text for details. Open circles I classified lizards as "Carnivores," "Omnivores, indicate values from the literature. primarily carnivorous," "Omnivores, primarily her- bivorous," or "Herbivores" on the basis of descrip- dude agamids, anguids, chamaeleontids, cordylids, tions in a wide variety of primary and secondary gerrhosaurids, iguanids, lacertids, scincids, teiids, and sources and examination of stomach contents of pre- varanids. No legless species were included, and only served specimens. (Only the most important refer- lizards that appeared to be in good health and neither ences are cited in the bibliography.) unusually fat nor thin were measured. A few data In captivity most herbivorous lizards will adopt a from the literature were included. There is surpris- carnivorous diet and carnivorous lizards may accept ingly little scatter among the points for lizards weigh- plant food. Because of this dietary lability, I have ing less than 100 g. Intra-specific variation in Dipso- excluded from consideration almost all records of saurus dorsalis resulting from seasonal and sexual food habits in captivity. Wherever possible I relied differences (Minnich 1971) is very nearly as great as upon field observations of lizard food habits or on the interspecific variation. At weights greater than stomach contents of wild-caught specimens. 100 g there is more variation, probably because large Estimates of body weight were difficult to obtain; lizards purchased from dealers had lost weight in they are seldom given in ecological or taxonomic captivity. The curve was fitted by eye and used to papers. Weights were obtained from the literature, estimate the weight of lizard species for which I was from lizards I weighed, or from the relationship be- unable to obtain direct measurements. I estimated tween snout-vent length and body weight illustrated some live weights by weighing preserved specimens in Fig. 1. This relationship was derived from mea- and applying a correction factor of 0.86 obtained surements of lizards in my laboratory. The data in- by weighing 23 lizards before preservation in forma- SUmmer 1973 LIZARD ENERGETICS AND DIET 839 Iin and storage in 40% isopropyl alcohol for 6-12 vores, whereas those weighing more than 100 g are months. Assigning a weight to a particular species is predominantly herbivores. The smallest herbivorous an arbitrary judgment for any sort of animal and par- iguanids include Enyaliosaurus defensor and E. quin- ticularly so for reptiles, in which growth continues quecarinatus, which weigh about 100 g; the largest throughout life. The weights are intended only as carnivores are juvenile Amblyrhynchus cristatus and estimates of the body size of a typical adult of a Basiliscus plurnifrons, weighing between 100 and given species. 200 g. A similar relationship exists among agamids: Uro- RESULTS inastix ocellatus and U. princeps at 100 g are the [he dietary preferences of lizards in relation to smallest herbivores; the largest carnivores include body weight and estimated metabolic rate at 30'C Goniocephalus boydii (25() g) and Chlamydosaurus are shown in Fig. 2 a-e. Among iguanids, species kingi (350 g). weighing less than 100 g are predominantly carni- In the family Scincidae the switch from carnivory

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BoAdy weight ( gins) FIG. 2a-e. Body size and estimated weight-specific metabolic rate of lizards in rela- tion to diet. The solid curve is the expected metabolic rate at 3O?C for a lizard of a given size (based on Bartholomew and Tucker 1964). Lizard species are plotted at positions corresponding to the typical adult weight except where noted. Carnivorous lizards plotted below the line, herbivorous lizards above. Omnivorous species indicated by parentheses, above or below the line depending on whether they are primarily her- bivorous or carnivorous. Legless species indicated by brackets. A question mark indi- cates uncertain allocation.

to herbivory also begins at a body weight near 100 g: oxygen/g hr. Juveniles of large herbivorous species Macroscinus is the smallest herbivore I found, and are in the same bioenergetic situation as adults of Eurneces schneideri at 125 g is the largest carnivore. small lizard species and are more carnivorous than Scincopus fasciatus (100 g) may be herbivorous adults. An ontogenetic change in diet from carnivory (Anderson 1898). to herbivory has been noted in Amblyrhynchus cris- Among the gerrhosaurids and cordylids there ap- tatus (Wilhoft 1958), Basiliscus plumifrons (Hirth pear to be only two herbivores. Angolosaurus skoogi 1963a), Cyclura macleayi (Carey 1966), Iguana (75 g) is the smallest herbivore and Gerrhosaurus iguana (Swanson 1950, Hirth 1963b), Uromastix sp. l'alidis, the largest species of gerrhosaurid, is an her- (Mertens 1960) and Uromastix hardwicki (Minton bivore. 1966). The family Teiidae contains no herbivores, al- In the genus Agama the transition between car- though Tupinamnbisis said to be omnivorous in cap- nivory and herbivory can be examined in some detail tivity (Sokol 1971). Other families of lizards in by the use of Minton's (1966) observations. He di- which no herbivores are found, although some spe- vided the Agama of West Pakistan into two groups: cies weigh well over 300 g, are the Anguidae, Cha- large montane species (nupta, mnelanura,tuberculata, maeleontidae, Helodermatidae, and Varanidae. himalayana, caucasica, and agrorensis) weighing 40- 140 g, and medium size terrestrial species (agilis, DISCUSSION megalonyx, minor, ruderata, and rubigularis) which weigh 5-35 g. His records of the lizards' feeding Size and dietary habits habits indicate that the large species are predom- In the families Agamidae, Scincidae, lguanidae, inantly herbivorous as adults but the small species Gerrhosauridae a similar relation- Cordylidae, and are carnivorous. Juveniles of the large species are ship exists between body size and dietary habits: carnivorous. lizards weighing less than 50-100 g are almost all carnivorous, whereas those larger than 300 g are Metabolic rate and diet almost all herbivores. These weights correspond to The oxygen consumption per unit weight of an estimated metabolic rates at 30?C of 0.20-0.10 ml organism is inversely related to its body size. The 842 F. HARVEY POUGH Ecology, Vol. 54, No. 4 relationship between body size and resting metabolic lower energy content of plant matter and its lower rate at 30'C for 18 species of lizards in five families digestibility. was calculated to be Few precise data are available on exactly what parts of plants herbivorous lizards eat. Flowers and ml 02/ g hr = 0.82W-- 0.38 fruit may be preferred, but, except in tropical areas where W - weight in g (Bartholomew and Tucker with no pronounced dry season, fruit and flowers are 1964). This relationship applied to all the families of available only at certain times of the ycar. The ma- lizards examined. joritv of herbivorous lizards probably depend largely The metabolic rate per g of a 100-g lizard is 1/6 upon leaves and small stems. For plant material of that of a l-g lizard, while a lizard weighing 1 kg this sort the energy content is 3,600-4,200 cal/g would have an estimated weight-specific metabolic of dry weight (Golley 1961. 1969). In contrast, ver- rate about 1/2 that of a 100-g lizard. In other words, tebrate animal tissue contains 5.200 cal/g and in- small lizards have higher energy requirements in pro- sects 5.400 cal/g (Golley 1961). In addition, the portion to their body weight. In contrast, large liz- assimilation efficiency (cal ingested less cal excreted) ards have higher total energy expenditures. A 1-kg may be greater for insectivorous lizards than her- lizard has a daily energy requirement five times as bivorous ones. Mueller ( 1970) reported an efficiency large as a 100-g lizard and nearly 20 times that of a of 83 /,; for mealworm larvae caten by Sceloporuis, 1O-g lizard. Avery (1971) found 89%( efficiency in Lacerta, and The energetic cost of obtaining food must also be Kitchell and Windell ( 1972) 79.7-82.0% in A nolis considered. An insect or small vertebrate represents cwrolit1n'si.s. Licht and Jones (1967) found assimila- a package of energy to a predator. To be energetically tion efficiencies in Atnolikscarolinecnsi~s of 54.4%, for advantageous the package must contain more energy I'encbrio beetles. 88.9'( for Teiebrio larvae, and than the predator expends in its capture. For a 20-g 69.5%6 for crickets. In contrast. Nagy (1971) found lizard it is energetically feasible to run several meters digestive efficiencies of 50-55%lS for plant material to catch an insect, but that is less true of a 2- or 3-kg eaten by Dipsosauirims and Sauromaoliis. (Throckmor- iguana. Large lizards are less adept at catching small ton's [19711 value of 82%/, assimilation for Ctetio- prey than are little lizards. Furthermore, a large liz- saIIra eating sweet potatoes probably reflects the low ard must move a greater mass in pursuit of prey, and cellulose content of the tuber.) These figures suggest the energy cost of capture cuts into the energetic that insectivorous lizards may obtain more than twice profit derived from the prey. Assuming that a lizard as much energy pcr gram of food ingested than do must exert itself to the limit of its aerobic metabolic herbivores. scope to run 10 m at 2 m/sec, the cost of that ac- Supporting this hypothesis is an observation that tivity would be 30 times as great for a 2-kg iguana lizards apparently do obtain more energy from a car- as for a 20-g Cnemidophorus. These figures are based nivorous diet than an herbivorous one. Mayhew on metabolic scope values reported by Moberly (1963) noted that when a juVCenilC Sauroinallus obe- (1968) and Asplund (1970). The metabolic scope stSy switched from an herbivorous to an insectivorous of Dipsosaurus is similar to that of Cnemnidophorius diet, its rate of increase in snout-vent length increased (A. F. Bennett and W. R. Dawson, personal comn- from 2 mmi/ month to 9 mm/month and its weight mnunication). This calculation is undoubtedly an un- increase rose from 2 g 'month to 20 g/month. How- derestimate because it considers only the aerobic ever. in the same cage two other juvenile chuckwal- scope; more energy is derived from anaerobic me- las that continued to eat plants did not grow appre- tabolism in such a situation than from aerobic. Large ciably. Parker ( 1972) noted that juvenile Dipso- lizards' ineptness at catching small, fast-moving in- saumis dborsalis grew more slowly than julveniles of sects is probably at least as important as the energetic five sympatric species of insectivorous lizards. Gib- cost of each pursuit. Every failure adds to the cost bons ( 1967) found a similar effect of diet on growth of the next successful capture. From the viewpoint rate in painted turtles (ClrvxseniYsl picta) . Turtles of energy balance, it seems better for a large lizard from the Kalamazoo River were largely carnivorous to walk to an immobile clump of plants and eat its and grew faster than those from other populations fill. that were omnivorous (intermediate growth rate) or A large lizard expends more calories in a day than herbivorous (slowest growth rate). does a small one. Since it is energetically inefficient to capture numerous small packets of energy, the Large ccarntivores (uid snall herhivoresi lizard must utilize plant material, which is readily The consistency of the relationship between body available in most habitats and requires little expen- size and diet among species in the four families of diture of energy to ingest. Such an alternative is prob- lizards cited is striking. These species occur in very ably not available to small lizards because of the different habitats and differ in evolutionary history Summer 1973 LIZARD ENERGETICS AND DIET 843 and morphology. Metabolic rate is the character Leglessness is a common morphological specializa- which is most similar in the four families and ap- tion, particularly in the families Anguidae, Gerrho- pears to provide the most generally applicable ex- sauridae, and Scincidae. Some legless lizards weigh planation for the small insectivore-large herbivore considerably more than 300 g, but all are carnivores. relationship (Pough 1971). There are exceptions to Snakes may be regarded as the most highly special- this generalization, and an examination of them is ized legless lizards, and all snakes are carnivores. instructive. I think that any departure from the basic Legless squamates seldom chase their prey. lizard pattern of physiology, morphology, or ecology Ecological specializations may contribute to devi- may permit carnivory to be retained in lizards larger ation from the relationship between body size and than would normally be expected. diet postulated. For example, Dipsosaurus dorsalis is For example, varanid lizards are unusual physio- predominantly herbivorous although it is slightly logically in that they are able to increase aerobic smaller (25-75 g) than most herbivorous lizards. metabolism to higher levels than most lizards (Bar- Dipsosaurus is the most thermophilic of North Amer- tholomew and Tucker 1964). In some habitats vara- ican lizards; its tolerance of body temperatures ex- nids appear to occupy an ecological niche analogous ceeding 40'C allows it to be active on the desert dur- to that of small carnivorous mammals. This behavior ing midday even in summer. In this high temperature implies a more effective prey-catching ability than niche it avoids many predators and competing lizard that possessed by most lizards. The difference prob- species but there are few insects active for it to eat. ably depends at least in part on the ability of vara- I think its ecological specialization has forced it into nids to sustain the high levels of activity necessary an herbivorous diet despite its small body size. A to chase and capture active prey animals. I have ob- similar explanation may apply to some other small served small canids and felids catch rodents and have herbivorous species among the iguanids and agamids. been impressed by how much work is involved. Fre- Angolosaurus skoogi is another ecologically spe- quently a prolonged pursuit is required, with the prey cialized lizard. It inhabits sand dunes in the Namib being caught and escaping several times in the pro- Desert of South West Africa and feeds on seeds that cess. In contrast, lizards catching insects usually make blow into the dunes from vegetated areas (Hamilton a quick dash and either secure the prey or lose it and Coetzee 1969). Seeds contain more energy than beyond hope of capture; in neither case is there pro- do other parts of plants; their caloric value is approx- longed pursuit. I believe that this difference reflects imately equal to that of animal tissue. the fact that most lizards are poorly fitted physio- Carnivory would be feasible for large lizards if logically for sustained activity. Unlike mammals they there were suitable prey-large packets of energy have little capacity to increase cardiac output (Tucker that could be captured without a disproportionate 1966), and even moderate levels of activity are sus- expenditure of energy. What sorts of prey are avail- tained predominantly by anaerobic metabolism (Mo- able to a 300-g carnivorous lizard? Small (up to 20 g) berly 1968). Lizards are quickly exhausted by sus- lizards feed efficiently upon insects while larger spe- tained activity. Anyone who chased lizards as a child cies (e.g., Crotaphytus, about 40 g) move a step up knows that if a lizard can be forced into an open area the food chain by including smaller lizards in their away from escape routes and followed closely for a diets. A carnivorous lizard larger than 300 g would few minutes it finally lies inert even when approached almost certainly have to eat small vertebrates; insect- and picked up. This inability to sustain activity han- size packages of energy would not be an efficient dicaps a lizard pursuing a mammal. Varanids with diet. Few small vertebrates are available to a large their high aerobic metabolic rates are apparently an lizard. Amphibians are largely nocturnal, whereas liz- exception, and I think that it is because of the de- ards are diurnal. Furthermore, in arid regions am- velopment of this efficient predatory specialization phibians are often active for only a brief portion of that there are no herbivores in this family. the year. For both these reasons amphibians are not Lizards with morphological specializations may re- a likely food source. Adult birds and mammals are tain carnivorous habits. Chamaeleons are the most probably too agile to be caught by lizards without striking examples; some species weigh well over the predatory specializations suggested for varanids. 300 g yet all are carnivorous. In this family the de- New-born mammals, birds' eggs, and fledgling birds velopment of a protrusible tongue has surmounted are eaten by helodermatids weighing well over 300 g, the problem of having to obtain energy in small but the seasonal availability of these food items re- packets. The energetic cost to a chamaeleon of shoot- quires the lizards to store energy in the form of fat ing out its tongue must be low compared to the cost in the tail-a specialization not found in most lizard of moving the entire lizard, and the rate of success- families. Most large carnivorous lizards probably feed ful captures is high; it is thus feasible for a large primarily on smaller lizards. Mammalian predators chameleon to be carnivorous. compete with large lizards for small lizards and in 844 F. HARVEY POUGH Ecology, Vol. 54, No. 4 addition can prey on birds and other mammals. Mam- Hamilton, W. J. III, and C. G. Coetzee. 1969. Thermo- mals furthermore have the advantages of nocturnal regulatory behavior of the vegetarian lizard Angolo- saurus activity and the use of scent to locate concealed prey. skoogi on the vegetationless northern Namib Desert dunes. Sci. Pap. Namib Desert Res. Stn., no. A lizard has no compensatory advantage that makes 47: 95-103. it more efficient than a mammal at catching other Harris, V. A. 1963. The anatomy of the rainbow lizard. lizards. Evolution of a large carnivorous lizard in- Hutchison and Co., Ltd. London. 104 p. volves direct competition with mammals, and in most Hirth, H. F. 1963a. Food of Basiliscus plumifrons on a tropical strand. cases the lizard has been unsuccessful in this compe- Herpetologica 18: 276-277. 1963b. Some aspects of the natural history of tition. Thus, evolution of a large lizard both requires Iguana iguana on a tropical strand. Ecology 44: 613- and permits a switch from carnivory to herbivory. 615. Kitchell, J. F., and J. T. Windell. 1972. Energy budget ACKNOWLEDGMENTS for the lizard, Anolis carolinensis. Physiol. Zool. 45: 178-188. I am grateful to Drs. George Bartholomew, Carl Gans, Licht, P., and R. E. Jones. 1967. Effects of exogenous Jack Hudson, Robert Whittaker, and especially Albert prolactin on reproduction and growth in adult males Bennett, who offered helpful suggestions. Edward Fran- of the lizard Anolis carolinensis. Gen. Comp. Endo- colini did most of the literature search. George Angehr, crinol. 8: 228-244. Jeff Daniels, Lynda Majors, and Lynn Terrell assisted Mayhew, W. W. 1963. Some food preference of captive with the measurement of Iguana guts. Drs. Ernest Wil- Sauromalus obesus. Herpetologica 19: 10-16. liams (Museum of Comparative Zoology, Harvard) and Mertens, R. 1960. The world of amphibians and rep- Richard Zweifel (American Museum of Natural History) tiles. McGraw-Hill, New York. 207 p. kindly allowed me to examine and dissect specimens in Minnich, J. E. 1971. Seasonal variation in weight-length their care. This study was supported by NSF Grant GB relationships and fat body size in the desert iguana, 18,985. Dipsosaurus dorsalis. Copeia 1971: 359-362. Minton, S. A., Jr. 1966. A contribution to the herpetology LITERATURE CITED of West Pakistan. Bull. Am. Mus. Nat. Hist. 134(2): 27-184. Anderson, J. 1898. Zoology of Egypt. Vol. I. Reptilia Moberly, W. R. 1968. The metabolic responses of the and batrachia. Bernard Quaritch, London. lxi + 371 p. common iguana, Iguana iguana, to activity under re- Asplund, K. K. 1970. Metabolic scope and body tem- straint. Comp. Biochem. Physiol. 27: 1-20. peratures of whiptail lizards (Cnemidophorus). Herpe- Mueller, C. F. 1970. Energy utilization in the lizards tologica 26: 403-410. Sceloporus gracious and S. occidentalis. J. Herpetol. Avery, R. A. 1971. Estimates of food consumption by 4: 131-134. the lizard Lacerta vivipara Jaquin. J. Anim. Ecol. 40: Nagy, K. A. 1971. Seasonal metabolism of water, energy 351-365. and electrolytes in a field population of desert lizards, Bartholomew, G. A., and V. A. Tucker. 1964. Size, body Sauromalus obesus. Ph.D. Dissertation. Univ. of Cal- temperature, thermal conductance, oxygen consump- ifornia, Riverside. 126 p. tion, and heart rate in Australian varanid lizards. Phys- Ostrom, J. H. 1963. Further comments on herbivorous iol. Zool. 37: 341-354. lizards. Evolution 17: 368-369. Beattie, J. 1926. The ileo-caecal region in reptiles: I. The Parker, W. S. 1972. Notes on Dipsosaurus dorsalis in ileo-caecal region of Tupinambis teguixin. Proc. Zool. Arizona. Herpetologica 28: 226-229. Soc. Lond. 28: 931-939. Pough, F. H. 1971. Bioenergetic aspects of lizard her- Carey, W. M. 1966. Observations on the ground iguana, bivory. Herpetol. Rev. 3: 107. Cyclura macleayi caymanensis, on Cayman Brac, Brit- Sokol, 0. M. 1967. Herbivory in lizards. Evolution 21: ish West Indies. Herpetologica 22: 265-268. 192-194. Dubuis, A., L. Faurel, C. Grenot, and R. Vernet. 1971. . 1971. Lithophagy and geophagy in reptiles. J. Sur le regime alimentaire du lezard saharien Uromas- Herpetol. 5: 69-71. tix acanthinurus Bell. C. R. Acad. Sci. (Paris) Ser. D. Swanson, P. L. 1950. The iguana, Iguana iguana iguana 273: 500-503. (L). Herpetologica 6: 187-193. El-Toubi, M. R., and H. M. Bishai. 1959. On the anatomy Szarski, H. 1962. Some remarks on herbivorous lizards. and histology of the alimentary tract of the lizard Evolution 16: 529. Uromastyx aegyptia [sic] (Forskal). Bull. Fac. Sci. Throckmorton, G. S. 1971. Digestive efficiency in the Cairo Univ. 34: 13-50. herbivorous lizard Ctenosaura pectinate. Herpetol. Gibbons, J. W. 1967. Variation in growth rates in three Rev. 3(6): 108. (abstr.) populations of the painted turtle, Chrysemys picta. Tucker, V. A. 1966. Oxygen transport by the circulatory Herpetologica 23: 292-303. system of the green iguana (Iguana iguana) at different Golley, F. B. 1961. Energy values of ecological materials. body temperatures.J. Exp. Biol. 44: 77-92. Ecology 42: 581-584. Wilhoft, D. C. 1958. Observations on preferred body . 1969. Caloric value of wet tropical forest vege- temperaturesand feeding habits of some selected trop- tation. Ecology 50: 517-519. ical iguanas. Herpetologica 14: 161-164.