The evolution and systematics of the iguanid genus Uma and its relation to the evolution of other North American desert reptiles. Bulletin of the AMNH ; v. 114, article 3

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New York : [American Museum of Natural History]
"The genus Uma occurs on the Mojave and Sonoran deserts and on the Chihuahuan Desert of Mexico. 2. The genus is totally restricted to aeolian sand deposits, most of which are of recent origin. 3. Migration of present-day forms of Uma seems entirely limited by movements of occupied sand accumulations. 4. Dominant plant associates of the genus are quite uniform over its entire range. 5. Uma occurs on the most arid portions of the deserts. The genus endures habitat temperature extremes from about 0° F. to over 189° F. (black bulb, within the surface layer of the microclimate). By virtue of morphological and behavioral temperature-control adaptations, a small portion of this thermal range is selected (26° C. to 41° C. approximately) for activity. 6. Surface activity of Uma is often restricted to a small portion of the available daylight hours because of a narrow range of temperature tolerance. 7. The genus is found from 244 feet below sea level to about 3700 feet above sea level. 8. A study of variation within the genus shows: A. Three major levels of differentiation are present. The most aberrant and primitive form is exsul, scoparia is intermediate, and the three subspecies notata notata, notata rufopunctata, and notata inornata form a homogeneous group which is closely related to scoparia. B. Uma n. rufopunctata has been redefined on the basis of measurements, counts, and a distinctive breeding coloration. Its known range has been extended to include the Arizona populations, formerly thought to be part of the range of Uma n. notata. C. The known ranges of all forms have been extended by the discovery of isolated populations. D. Color variations in Uma are numerous. The individuals of nearly every population closely match the sand color of their habitat. E. Intraspecific variation in pattern and scale configuration has been noted within scoparia. 9. The white ventral coloration of many diurnal desert lizards, including Uma, may possibly have been produced by selection towards shadow reduction, background color matching, and temperature control (by reflection of radiated heat from the substratum). 10. Because a fossil record is lacking, any proposed evolutionary history of Uma must be based on environmental, history. The conclusions drawn from this evidence are hypothetical and subject to considerable possible error. 11. The development of most North American desert reptiles appears to be correlated with the development of the Madro-Tertiary Flora. This flora originated in the Oligocene and Miocene in northern Mexico and southwestern United States in genetic response to increasing aridity. 12. Increasing aridity, reaching a climax in middle Pliocene, caused segregation of this flora into a number of vegetative types occupying separate ecological situations. Present desert vegetation has developed from the most xeric of these segregates. 13. Uma apparently arose as an offshoot of an early Callisaurus-Holbrookia-Uma stock as arid habitats developed, possibly in thorn forest or arid, subtropical, scrub associations. 14. It is postulated that the precursor of Uma was split into western and central Mexican populations by extensive volcanism along the axis of the Sierra Madre Occidentál in middle or late Miocene time. 15. Since this separation, parallel evolution due to similar environmental stresses has kept the two groups closely allied morphologically. Middle Pliocene aridity most probably enhanced the development of widespread sand habitats. The pre-Uma of the two regions adapted to aeolian sand and, for the first time, developed the distinctive dune-adapted morphology associated today with the genus Uma. 16. Semi-desert vegetation underwent a widespread development in early and middle Pliocene times. Pre-Uma was probably associated with this vegetation as it developed. Many other desert reptile genera have probably followed a similar path of evolution. 17. Late Pliocene and Pleistocene climactic extremes were such that Uma was restricted from part of its northern range as were other mesic desert reptiles. During the Pleistocene glacial advances, the Great Basin and most of the Mojave Desert were most likely uninhabitable to Uma. 18. Uma scoparia has differentiated in the north, probably as a result of isolation incurred during a pluvial period. 19. Uma notata notata and Uma notata rufopunctata have resulted from division of the Sonoran Desert populations by the rejuvenated Colorado River of Pleistocene time. Gene exchange between the two subspecies may occur intermittently because of shifts in the course of the lower Colorado River. 20. Uma n. inornata has resulted from differentiation north of ancient Lake LeConte which has occupied the lower portions of the Cahuilla Basin during portions of the Ice Age. 21. Uma scoparia has reinvaded a considerable portion of the Mojave Desert since the last Pluvial age. The routes can be followed along stream courses and over low divides by a study of the present distribution of the species and the paths of Pluvial drainage"--P. 318-319.
p. 251-326, [4] p. of plates : ill., maps ; 27 cm.
Includes bibliographical references (p. 320-326).