Page 151 - Introduction to Paleobiology and The Fossil Record
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138  INTRODUCTION TO PALEOBIOLOGY AND THE FOSSIL RECORD


                      Charles Darwin gave us phylogenetic trees       joints and cannot run very fast. In the early
                      (see p. 117) and he gave us biodiversity (see   years of bipedalism on the African plains 5
                      p. 535); he also gave us an evolutionary view   million years ago, perhaps speed was not
                      of form. He was astonished by the variety of    always essential. A human could never outrun
                      external appearances of plants and animals,     a lion or a cheetah, but could perhaps climb
                      and by their wonderful adaptations to life. He   a tree or hide in a cave, or act with other
                      discovered many remarkable examples of          humans to distract the predator.
                      extraordinary bodily appearance and func-         Paleontologists have always been fascinated
                      tion in insects, birds and plants. He was       by the form and function of fossils. Not only
                      intrigued by the specialized beaks and tongues   are fossil forms often startlingly beautiful,
                      some birds and moths have for feeding on        they may be puzzling. So many fossils belong
                      nectar from particular plants. He was fasci-    to groups without modern analogs that it
                      nated by species where the males and females    becomes an intriguing exercise to determine
                      look utterly different because of the rigors    why they had the forms they had, and what
                      of pre-mating displays. He tried to under-      their functions may have been. The form of
                      stand how such remarkable adaptations           fossils is important for paleontologists for
                      could be honed and sustained through the        three reasons:
                      generations.
                        The form, or external appearance, of any      1  Form is the only evidence we have in
                      microbe, plant or animal is shaped by evolu-       fossils for identifying species and wider
                      tion. The wings of birds are adapted for fl ight;   relationships to reconstruct the tree of life
                      the long beak and tongue of the hummingbird        (see below and p. 128).
                      is adapted for feeding on nectar deep in a      2  Form can tell us about behavior and

                      flower. The amazing tail of the male peacock        ecology (see p. 80).
                      is adapted through sexual selection to attract   3  Variations in form are commonplace
                      a mate.  Sexual selection is the set of evolu-     within a species, and the study of changes
                      tionary processes that depend on interactions      in form through time informs us about
                      between the sexes. The most familiar exam-         evolution (see p. 121).
                      ples are the astonishing tails and colors of
                      male birds, the antlers and horns of male deer
                      and antelope, the mane of the male lion, and    GROWTH AND FORM
                      other structures that are there to impress
                      females. These structures generally have little   Recognizing ancient species
                      to contribute in protecting the animal from     Paleontologists must interpret fossil species,
                      predators or in helping it to fi nd  food:  in   and their ranges of variation, solely from the
                      many cases they are a considerable handicap.    morphology, or external shape, of the speci-
                      So sexual selection can act counter to natural   mens. There are problems in deciding where

                      selection; but the benefit for a male peacock    one species ends and another begins. When

                      in finding a willing female, or females, and in   there are close living relatives, it may be pos-
                      mating (sexual selection) is clearly greater    sible to compare the modern species with
                      than the disadvantage of carrying such a huge   the fossils. But how are paleontologists to
                      tail when trying to avoid a predator (natural   decide just what is a species of dinosaur or
                      selection).                                     trilobite?
                        Plants and animals have  adaptations that       For modern plants and animals, system-
                      function in the context of both natural and     atists ideally apply the biological species
                      sexual selection. An adaptation is an aspect    concept (see p. 121). Clearly paleontologists
                      of form that performs a physical or behav-      cannot test whether fossil species can or
                      ioral function. It may not perform that func-   cannot interbreed. So, paleontologists use the
                      tion terribly well, merely well enough. So,     morphological species concept, judging the
                      human beings are adapted to walking upright,    bounds of a species entirely on form. The
                      and this has changed many aspects of our        assumption is that all members of a species
                      body shape. But we are not enormously good      should look similar, and that a few simple

                      at it, and we betray some of our quadrupedal    statistical observations should define the mean
                      ancestry: humans still get bad backs, arthritic   or average characteristics of members of a
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