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Introduction to Horned Lizards of North America

Introduction to Horned Lizards of North America

Wade C. Sherbrooke
Copyright Date: 2003
Edition: 1
Pages: 191
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  • Book Info
    Introduction to Horned Lizards of North America
    Book Description:

    * Features detailed species accounts; gives information on horned lizard biology, ecology, and evolution; and describes the role of these fascinating reptiles in mythology, culture, and art * Covers the United States, Mexico, and Canada, and includes all species of horned lizards

    eISBN: 978-0-520-92675-2
    Subjects: Biological Sciences

Table of Contents

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  1. Front Matter
    (pp. i-vi)
  2. Table of Contents
    (pp. vii-viii)
    (pp. ix-x)
    (pp. xi-xiii)

    • [Introduction]
      (pp. 1-3)

      So-called horny toads are actually horned lizards. The confusion evident in these conflicting common names has arisen because these lizards bear a superficial resemblance to toads, a fact clearly recognized by the zoologist who gave the scientific namePhrynosomato the genus of horned lizards in 1828. He named them the “toad-bodied” lizards; in Greek,phrynosmeans toad, andsomameans body.

      Like many toads, horned lizards have a broad body‚ rough skin‚ and a rather awkward gait (although they do not hop). Also‚ in toadlike fashion‚ they flick out their tongues to pick up insect food and‚ when molested‚...

      (pp. 4-8)

      Through their genetic heritage, horned lizards, like humans, are linked to the first Paleozoic land vertebrates and their evolutionary advances. Much more recently, the evolution of their closest reptilian predecessors, and of horned lizards themselves, has been molded by Cenozoic geologic and climatic events throughout North America. Today, 13 currently recognized species of horned lizards live within, and are adapted to, the contemporary diversity of ecological settings on this continent. The lives of these lizards, like ours, are edges of the living past cutting into the ever-arriving future.

      Five hundred million years ago, all the backboned ancestors of horned lizards...

      (pp. 9-17)

      All horned lizard species are immediately distinguishable from other North American lizards by their horns and flattened bodies. Their ancestors evolved this body form and appropriate behaviors, a mode of life distinct among lizards. Horned lizards have diversified into a number of closely related species of similar form, an evolutionary process known as adaptive radiation. The distinctive life and unique design of horned lizards have been a successful evolutionary development that gives us a window into understanding the processes of life on earth, of which we are a part.

      The unusual appearance of all horned lizards is due to their...

      (pp. 18-25)

      (pp. 28-51)

      IDENTIFYING CHARACTERISTICS: White midback stripe; two rows of lateral fringe scales; dark lines going up face and over top of head; sharp spines over eyes; two occipital horns pointing upward; ventral scales weakly keeled.

      The scientific name of the Texas Horned Lizard isPhrynosoma cornutum(from the Latincornutus,meaning horned). It is a large, robust species. The adult generally measures 2.7 to 4.5 inches in snout-to-vent length. Its horns are prominent; the median pair is the longest and these horns are nearly conical in cross-sectional form. The back is very spiny, and there are two rows of enlarged fringe...

      (pp. 52-66)

      IDENTIFYING CHARACTERISTICS: Large in size; with two rows of back spines, one down each side; middle pair of horns (occipitals) usually erect; usually only two temporal horns on each side of head; strong spines above eyes; ventral scales keeled; two rows of lateral fringe scales.

      The scientific name of the Giant Horned Lizard isPhrynosomaasio(the Latinasiomeaning horned owl). This may be the largest species of horned lizard in total size and weight, reaching 4.9 inches in snout-to-vent length, with an elongated tail, deep and forward-protruding head, and extremely spiny appearance. In overall body form, this species is...

      (pp. 67-71)

      Sometimes in the course of evolution, unrelated animals independently acquire convergent adaptations that result in remarkably similar structures or forms. The horned lizard, of the New World family Iguanidae, and the Australian Thorny Devil(Moloch horridus),of the Old World lizard family Agamidae, are a striking example of convergent evolution. Of similar size, horned lizards and the Thorny Devil are all stocky and spiny (pls. 33, 34). The horned lizards of North America resemble one another because of their close genetic heritage. Horned lizards resemble the Thorny Devil, in spite of their different genetic lineages, because both have independently evolved...


      (pp. 74-108)

      In a lifetime, not every individual completes a full cycle of growth, survival, and reproduction. The reproductive successes and failures of genetically distinct individuals over generations continually adapt a species to changing environments. Thus, each species of horned lizard has been genetically molded by its environment, and each individual inherits a genetic frame work for a complex way of life.

      The rotation of the earth and its revolutions around the sun influence the activities of all horned lizards. Sun rays warm their otherwise cold and immobile bodies, permitting activity.

      Horned lizards, along with other reptiles, fishes, and amphibians, are sometimes...

      (pp. 109-129)

      Since horned lizards are potential meals for many animals, they need good defenses to ensure their long survival. Those lizards that survive longest usually leave the largest number of young; they are the parents of tomorrow’s horned lizards. Here, in the mathematics of individual differences in lifetime reproductive success, is the means by which natural selection becomes the driving force of evolution.

      Young horned lizards are the most vulnerable to predators. Being smaller than adults and less well armored, they are more easily captured, killed, and swallowed. Inevitably,many hatchlings and newborns are eaten before they can enter their first hibernation....

      (pp. 130-146)

      With each new generation, the lines of life are extended another step into the future. In reproduction, the genetic inheritance of the past is united, through natural selection, with change for survival today. Life would never have continued over the more than three billion years it has evolved on earth without the repeated replacement of generations.

      Almost all lizards reproduce sexually. Each is able to distinguish between the sexes and among species, often through social behavior. The function of social behavior is to ensure order in relations among individuals of a species and to allow for the proper selection of...

      (pp. 147-162)

      When men and women ventured across the Bering land bridge between Asia and America, perhaps 15,000 to 25,000 years ago, our species entered the New World for the first time. As these Ice Age hunters and their descendants penetrated the American continents, they encountered a truly new world, of which horned lizards were a small but distinctive part.

      What were the reactions and thoughts of these earliest immigrants when they encountered lizards with horns and spines? Are they dangerous? Can we eat them? Do their spirits demand respect? Those hunters struggled long ago with their desires, fears, intellect, and emotions,...

    (pp. 163-169)
    (pp. 170-171)
  10. INDEX
    (pp. 172-176)
  11. Back Matter
    (pp. 177-178)