[Paleopsych] SW: Dinosaurs and Grass

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Paleontology: Dinosaurs and Grass

[And God said, Let the earth bring forth grass, the herb yielding seed, 
and the fruit tree yielding fruit after his kind, whose seed is in itself, 
upon the earth: and it was so. And the earth brought forth grass, and herb 
yielding seed after his kind, and the three yielding fruit, whose seed was 
in itself, after his kind: and God saw that it was good. And the evening 
and the morning were the third day. --Genesis 1:11-13

[And God created great whales, and every living creature that moveth, 
which the waters brought forth abundantly, after their kind, and every 
winged fowl after his kind: and saw that it was good. And God blessed 
them, saying, Be fruitful and multiply, and fill the waters in the seas, 
and let fowl multiply in the earth. And the evening and morning were the 
second day. --Genesis 1:21-23

[Paleontologists, however, hold that there were sea animals long before 
there was grasss. In either case, the role of grass is generally 

    The following points are made by D.R. Piperno and H-D. Sues (Science
    2005 310:1126):
    1) Grasses (family Poaceae or Gramineae), with about 10,000 extant
    species, are among the largest and most ecologically dominant families
    of flowering plants, and today provide staple foods for much of
    humankind. Dinosaurs, the dominant mega-herbivores during most of the
    Mesozoic Era (65 to 251 million years ago), are similarly one of the
    largest and best known groups of organisms. However, the possible
    coevolution of grasses and dinosaurs has never been studied. New
    work[1] reports analysis of phytoliths -- microscopic pieces of silica
    formed in plant cells -- in coprolites that the authors attribute to
    titanosaurid sauropods that lived in central India about 65 to 71
    million years ago. Their data indicate that those dinosaurs ate
    2) Part of the difficulty in studying the question of dinosaur-grass
    coevolution results from the poor quality of the fossil record for
    early grasses. The earliest unequivocal grass fossils date to the
    Paleocene-Eocene boundary, about 56 million years ago [2,3], well
    after the demise of nonavian dinosaurs at the end of the Cretaceous
    Period. Pollen and macrofossils of Poaceae are uncommon in sedimentary
    strata until the middle Miocene, about 11 to 16 million years ago,
    when the family is thought to have undergone considerable evolutionary
    diversification and ecological expansion [2]. Thus, dioramas in
    museums have long depicted dinosaurs as grazing on conifers, cycads,
    and ferns in landscapes without grasses. The work of Prasad et al [1]
    is the first unambiguous evidence that the Poaceae originated and had
    already diversified during the Cretaceous. The research shows that
    phytoliths, which have become a major topic of study in Quaternary
    research over the last 20 years [4,5], can provide a formidable means
    for reconstructing vegetation and animal diets for much earlier time
    periods when early angiosperms were diversifying. These results will
    force reconsideration of many long-standing assumptions about grass
    evolution, dinosaurian ecology, and early plant-herbivore
    3) Researchers have long known that grasses make distinctive kinds of
    phytoliths in the epidermis of their leaves and leaflike coverings
    that surround their flowers. More recent work has examined in greater
    detail phytolith characteristics from a large set of grasses
    comprising taxa representing the entire range of diversification
    within the family, showing that discriminations at the subfamily,
    tribe, and genus levels are often possible [1,4,5]. In addition,
    publication of a well-resolved consensus phylogeny of the Poaceae by
    the Grass Phylogeny Working Group (GPWG) considerably advances our
    overall understanding of the evolutionary history of grasses and leads
    to improved interpretations of the early grass fossil record. For
    example, by mapping the phytolith characters that discriminate clades
    and subfamilies of extant taxa onto this phylogenetic tree, we can
    infer how phytolith morphology changed at the origin of major clades
    and lineages.
    References (abridged):
    1. V. Prasad, C. A. E. Strömberg, H. Alimohammadian, A. Sahni, Science
    310, 1177 (2005)
    2. B. F. Jacobs, J. D. Kingston, L. L. Jacobs, Ann. Mo. Bot. Gard. 86,
    590 (1999)
    3. E. A. Kellogg, Plant Physiol. 125, 1198 (2001)
    4. D. R. Piperno, Phytolith Analysis: An Archaeological and Geological
    Perspective (Academic Press, San Diego, CA, 1988)
    5. G. G. Fredlund, L. T. Tieszen, J. Biogeogr. 21, 321 (1994)
    Science http://www.sciencemag.org
    Related Material:
    The following points are made by G.P. Burness et al (Proc. Nat. Acad.
    Sci. 2001 98:14518):
    1) The size and taxonomic affiliation of the largest locally present
    species ("top species") of terrestrial vertebrate vary greatly among
    faunas, raising many unsolved questions. Why are the top species on
    continents bigger than those on even the largest islands, bigger in
    turn than those on small islands? Why are the top mammals marsupials
    on Australia but placentals on the other continents? Why is the
    world's largest extant lizard (the Komodo dragon) native to a
    modest-sized Indonesian island, of all unlikely places? Why is the top
    herbivore larger than the top carnivore at most sites? Why were the
    largest dinosaurs bigger than any modern terrestrial species?
    2) A useful starting point is the observation of Marquet and Taper
    (1998), based on three data sets (Great Basin mountaintops, Sea of
    Cortez islands, and the continents), that the size of a landmass's top
    mammal increases with the landmass's area. To explain this pattern,
    they noted that populations numbering less than some minimum number of
    individuals are at high risk of extinction, but larger individuals
    require more food and hence larger home ranges, thus only large
    landmasses can support at least the necessary minimum number of
    individuals of larger-bodied species. If this reasoning were correct,
    one might expect body size of the top species also to depend on other
    correlates of food requirements and population densities, such as
    trophic level and metabolic rate. Hence the authors assembled a data
    set consisting of the top terrestrial herbivores and carnivores on 25
    oceanic islands and the 5 continents to test 3 quantitative
    a) Within a trophic level, body mass of the top species will increase
    with land area, with a slope predictable from the slope of the
    relation between body mass and home range area.
    b) For a given land area, the top herbivore will be larger than the
    top carnivore by a factor predictable from the greater amounts of food
    available to herbivores than to carnivores.
    c) Within a trophic level and for a given area of landmass, top
    species that are ectotherms will be larger than ones that are
    endotherms, by a factor predictable from ectotherms' lower food
    3) The authors point out that on reflection, one can think of other
    factors likely to perturb these predictions, such as environmental
    productivity, over-water dispersal, evolutionary times required for
    body size changes, and changing landmass area with geological time.
    Indeed, the database of the authors does suggest effects of these
    other factors. The authors point out they propose their three
    predictions not because they expect them always to be correct, but
    because they expect them to describe broad patterns that must be
    understood in order to be able to detect and interpret deviations from
    those patterns.
    Proc. Nat. Acad. Sci. http://www.pnas.org
    Related Material:
    The following points are made by A.R. Ives and B.J. Cardinale (Nature
    2004 429:174):
    1) Growing concern about how loss of biodiversity will affect
    ecosystems has stimulated numerous studies(1-5). Although most studies
    have assumed that species go extinct randomly, species often go
    extinct in order of their sensitivity to a stress that intensifies
    through time (such as climate change).
    2) For two reasons, interactions among species make it difficult to
    predict how ecological communities will respond to environmental
    degradation. First, the sensitivity of an individual species to
    environmental degradation depends not only on the direct impact of
    degradation on that species, but also on the indirect effects on that
    species caused by changes in densities of other species. For example,
    environmental degradation may decrease the density of competitors
    and/or predators of a species, thereby causing a compensatory increase
    in the density of that species. Second, as species go extinct, links
    within the food web are severed, changing the pathways through which
    indirect effects operate. Changes in food-web structure depend on the
    order in which species go extinct, making it difficult to extrapolate
    from studies that assume extinctions are random to real communities
    facing progressively intensifying stress from environmental
    3) To disentangle the effects of species interactions on the ability
    of communities to tolerate environmental degradation, the authors used
    mathematical simulations to compare how communities resist changes in
    abundance as species go extinct randomly versus going extinct in order
    of their sensitivity to an environmental stress. The authors
    considered communities with three trophic topologies that span a range
    of community types: tritrophic communities with plants, herbivores,
    and predators; monotrophic communities comprising just competitors;
    and communities with arbitrary topology containing prey and predators,
    competitors, and mutualists. For each topology, the authors
    constructed 1000 communities in which interaction strengths were
    chosen from random distributions under the constraints of the
    specified topology. The direct effects of the stressor on each species
    were also selected at random, but constrained so that the stressor had
    a negative effect on all species by decreasing their population growth
    4) The authors demonstrate that the consequences of random and ordered
    extinctions differ. Both depend on food-web interactions that create
    compensation; that is, the increase of some species when their
    competitors and/or predators decrease in density due to environmental
    stress. Compensation makes communities as a whole more resistant to
    stress by reducing changes in combined species densities. As
    extinctions progress, the potential for compensation is depleted, and
    communities become progressively less resistant. For ordered
    extinctions, however, this depletion is offset and communities retain
    their resistance, because the surviving species have greater average
    resistance to the stress. Despite extinctions being ordered, changes
    in the food web with successive extinctions make it difficult to
    predict which species will show compensation in the future. This
    unpredictability argues for "whole-ecosystem" approaches to
    biodiversity conservation, as seemingly insignificant species may
    become important after other species go extinct.
    References (abridged):
    1. Sala, O. E. et al. Global biodiversity scenarios for the year 2100.
    Science 287, 1170-1174 (2000)
    2. Chapin, F. S. I. et al. Consequences of changing biodiversity.
    Nature 405, 234-242 (2000)
    3. Ehrlich, P. & Ehrlich, A. Extinction (Random House, New York, 1981)
    4. Terborgh, J. et al. Ecological meltdown in predator-free forest
    fragments. Science 294, 1923-1926 (2001)
    5. Naeem, S., Thompson, L. J., Lawler, S. P., Lawton, J. H. & Woodfin,
    R. M. Declining biodiversity can alter the performance of ecosystems.
    Nature 368, 734-737 (1994)
    Nature http://www.nature.com/nature

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