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Highlights
from 2008
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Latino
Initiatives Fund
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NMNH Home | What's New ? | Calendar of Events | Information Desk | Search |
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Research
Abstracts |
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Paleotemperature
Estimates and Carbon Isotope Stratigraphy
Across the Cretaceous Supergreenhouse Interval in Tanzania |
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Kristin
Adams Brian Huber, Ph.D.
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Paleotemperatures
and paleooceanographic characteristics from the geologic past can be derived
by stable isotope mass spectrometry on foraminifera. Multiple foraminifera
species, both benthic and planktic, were picked from the Tanzania Drilling
Project (TDP) Site 22 and sent to be analyzed with a mass spectrometer.
The 133 m sequence of clay-rich siltstone drilled at Site 22 spans ~2
million years within the Turonian Stage, Cretaceous Period (~93-91 million
years ago). Oxygen isotope paleotemperatures estimated from high latitudes
and mid-bathyal paleodepths have shown this time period to be extremely
warm; however, reliable low latitude data have been almost nonexistent
before this point. The reason behind this lack of data is the inherent
lack of pristinely preserved (glassy) samples in the low latitudes, but
clay-rich marine sediments found in southeast Tanzania provide rich foraminiferal
assemblages that are perfectly preserved. Oxygen isotopic data show a
temperature range of 29°C-34°C for planktic foraminifera (surface-dwelling),
approximately 3°C-5°C higher than the average sea surface temperature
today. The data also show variation throughout the 2 m.y. time period,
with a temperature decrease at the beginning of the time period (deeper
depth), peak in temperatures at a sample depth of 60 to 80 meters, and
a temperature increase near the end of the time period (shallow depth).
The vertical profile of planktic species show the biserial and unkeeled
species as being the most shallow inhabitants, double-keel species being
in the middle, and the single-keel species as being the deepest dwellers.
The benthic (or bottom-dwelling) profile shows interspecies oxygen and
carbon isotope offsets among Lenticulina, Hoeglundina, and
Gavelinella species due to different vital effects. Carbon isotopic
data show the expected distinction between the planktic and benthic foraminifera,
with the surface-dwelling, planktic species being present in an area of
more primary productivity. Results from this study support the hypothesis
that significantly elevated levels of carbon dioxide caused warming at
low and high latitudes during the Turonain “Supergreenhouse Event”.
The understanding of this global warming event may provide insights to
computer models representing past and future climatic trends. This research was supported by grants and donations to the Research Training Program. |
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An
Evaluation of DNA Barcoding as a Method for Species Identification
in the Ant Genus Pheidole |
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Phillip
Barden Ted Schultz, Ph.D.
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The ant
genus Pheidole is a hyper-diverse group found across six continents,
with potentially over 1,000 species. Many of these ants exhibit worker
dimorphism, that is, two morphologically different worker types (called
major and minor workers) within single colonies. This, along with a wide
assortment of morphotypes, makes identifying known, as well as unknown
species, very difficult. The effectiveness of a relatively new method
for species identification called DNA barcoding was evaluated both for
associating worker morphotypes and identifying species in general. Leaf
litter-dwelling Pheidole specimens from Guyana were collected and
identified to species from morphology and then sequenced for the mtCOI
barcode region. From these genetic data, it was found that DNA barcoding
is a valuable tool for associating worker castes, as well as identifying
new species. A major and minor worker from the species P. allarmata
were successfully sequenced and were shown to be related not only from
initial morphological identification, but from the genetic analysis as
well, illustrating the value of DNA barcoding in associating worker castes.
A total of 21 species were identified through morphology and 26 putative
species were produced by the sequence data, showing a clear advantage
to using DNA barcoding species identification along with morphological
methods. This research was supported by grants and donations to the Research Training Program. |
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Comparative
ontogeny of compound leaves: deciphering the enigmatic
3-parted leaf of the bishopwood tree (Bischofia; Phyllanthaceae) |
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Ana
Marcela Florez Kenneth Wurdack, Ph.D.
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This research was supported by grants and donations to the Research Training Program. |
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Geological
Significance of Blue Quartz in the U.S.
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Thushara
Gunda Michael Wise, Ph.D.
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This research was supported by grants and donations to the Research Training Program. |
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Instrumental
studies of phonemic contrasts and sentence intonation in Unami
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Maureen
Hoffmann Ives Goddard, Ph.D.
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This research examined phonological properties of the Algonquian language Unami, whose last speaker died in 2000. The purpose was to provide technical analysis of recordings using computer software that was not readily available at the time of the original field research (1966-1970). A freeware program (Praat) was used to analyze sound clips from digitized sound files of texts and word lists. Contrasts between phonemic short and phonemic long (geminate) consonants, specifically t, s, x, and š, were examined. (Phonemes are the minimal units of sound that contrast in a particular language and can therefore distinguish words.) For this research, the duration of the consonant (for the fricatives) and the duration of the stop closure (for t) were measured. It was discovered that there was no direct correlation between measurable duration and phonemic length. While most of the instances patterned such that the phonemic long consonants had longer durations than the phonemic short consonants, there was overlap in the mid-range values and there were several outliers. Patterns in sentence intonation (prosody) were also identified and described. In comparing the pitch contours of a variety of sentences, it was seen that these patterns did not always correlate with syntactic boundaries. This is evidence that it is possible for prosodic features to function at least partially independently from the grammar, which suggests the hypothesis that prosody can in part play a role in integrating discourse structures involving more than one sentence. Both the consonant length and sentence intonation data provide evidence for the complex relationship between linguistic structures and the phonetic features that express them. Further investigation of these features is required to fully understand how they function. This research was supported by grants and donations to the Research Training Program. |
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Hybrid
or Species: Unraveling the Taxonomic Status of Murdannia discreta
(Commelinaceae), A Rare Plant from Thailand
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Irene
Liao Robert B. Faden, Ph.D.
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This research was supported by grants and donations to the Research Training Program. |
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Analysis
of a Late Jurassic, Eggshell-rich Microsite
from the Big Horn Basin of Wyoming |
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Jonathan
Mitchell Matthew Carrano, Ph.D.
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The Fox
Mesa locality is an unusual microvertebrate site in the Morrison Formation
(Late Jurassic) of Wyoming because it includes embryonic dinosaur bone
and hundreds of thousands of eggshell fragments, but a paucity of aquatic
taxa. Fossil embryos with eggshell are rare and poorly understood, especially
in the Morrison, making this site a unique opportunity to study the reproductive
biology of a specific taxon, and thus learn more of this long gone world.
The Fox Mesa site was mapped and bulk sampled in blocks (in 1999, 2001,
2003, and 2006). Body fossils and eggshell fragments were sorted by block.
The site was buried in a floodplain mudstone typical of the Morrison Formation,
and the eggshell and bones are very poorly sorted and well preserved.
Analysis of the embryonic body fossils reveals a large number of elements
assignable to Theropoda. Specifically, some of the jaws preserve minute
(< 1 mm) coelurosaur-like teeth, and cervical vertebrae exhibit characteristic
evidence of pneumaticity. It is not yet clear whether this represents
a known Morrison coelurosaur, or a new taxon. Diagenic calcite is present
on the eggshell surfaces, and are all of a low, uniform curvature with
some being "inside out". Surface morphology is therefore uninformative.
In order to identify potentially informative microstructural features,
and to test whether all the eggshells were from the same taxon, fragments
from different blocks were embedded in epoxy and thin-sectioned. These
thin-sections were analyzed under transmission, polarized light, and cathodoluminescent
light microscopes. Fractured radial sections and acetic-acid-etched, polished
sections of shells were imaged under an environmental scanning electron
microscope. The ultrastructure of the eggshells preserves the following
theropod synapomorphies: 1) both oblique and vertical tubular pore canals,
2) an unevenly upward-grading mammillary layer of acicular cystals, 3)
a single, continuous second layer, and 4) a possible third, external layer.
The thousands of eggshell fragments and hundreds of embryonic bones suggest
an original life association. The concentration of fragments implies that
this was either a continual nesting ground for these theropods, or that
a large group of theropods all nested together. Either situation represents
a unique window into this Jurassic ecosystem. Study of the Fox Mesa eggshell
fragments has shown possible evidence for a new early coelurosaur, and
opened up the study of reproductive strategies in Morrison theropods by
assigning this eggshell type to a coelurosaur. Also, either explanation
for the vast quantities of egg at the site—group nesting behavior
or perennially occupied nests—is a rare phenomenon in non-avian theropod
dinosaurs, previously discussed at only one other site in Portugal. This research was supported by grants and donations to the Research Training Program. |
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Modeling
Sustainability and Severe Weather Events in Mongolia
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Teresa
Nichols J. Daniel Rogers,
Ph.D.
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Sustainability
has always been a central factor in the long tradition of a nomadic pastoralist
lifestyle in the Mongolian steppes. To understand how social complexity
has developed in the region since the Bronze Age, it is necessary to examine
the dynamics of the human-environment relationship. We used an agent-based
simulation model called HouseholdWorld, developed by scientists at George
Mason University in conjunction with archaeological research conducted
by the National Museum of Natural History, to explore the interplay between
ecology, herds, and humans in Mongolia. To better understand the human-environment
dynamic, extreme weather events were researched and recreated in our model
as a means of exploring adaptive capacity. Results indicate the importance
of mobility and the delicate balance between the social and genetic benefits
inherent in forming culture groups as opposed to problematic population
clusters and competition for forage. This research was supported by grants and donations to the Research Training Program. |
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Diversification
of Wellerellinae brachiopods during the West Texan
Permian: A combined phylogenetic and morphometric approach |
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Andrew
Rominger Peter Wagner, Ph.D.
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The diversity
of life has long fascinated scientists. The theory of natural selection
provides a unifying framework in which to consider the evolution of diversity
through time; however, consensus is still lacking in our understanding
of how organisms have explored their potential morphospaces in such a
way to produce the plethora of species on Earth. The idea of a theoretical
morphospace, and adaptive landscapes therein, provides quantitative rigor
in addressing questions of how morphologic diversity evolves. But here
again little consensus exists, even on model predictions of evolution
given assumed adaptive scenarios. In the current project we seek to bring
a phylogenetic perspective to the question of diversification within a
theoretical morphospace, namely a generalized morphospace for pseudo-logarithmically
expanding shells, in order to test hypotheses about how diversity evolves,
whether it is similar to random diffusion, driven by adaptive "basins
of attraction," or the result of genetic and developmental constraints
on organism structure. Here we present preliminary results achieved towards
this goal. Specifically, a phylogenetic tree based on 35 discrete morphologic
multistate characters and stratigraphic occurrence was recreated for 46
species in the subfamily Wellerellinae (Brachiopoda: Wellerellidae). These
species largely originated and went extinct in the Permian of West Texas.
Change in whorl expansion rate was also calculated. The generalized morphospace
will be forthcoming, as will an analysis of support for three different
models of evolution: (1) evolution is the result of random diffusion,
(2) evolution is driven by basins of attraction within the morphospace
(i.e. adaptive peaks), and (3) genetic and developmental constraints determine
extent and direction of diversification. This research was supported by grants and donations to the Research Training Program. |
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Geographic
variation in Cinclodes fuscus,
an ovenbird of the high Andes and Patagonia |
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Camilo
Sanin R. Terry Chesser,
Ph.D.
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Cinclodes fuscus is a widespread and common species of ovenbird (Furnariidae) that breeds from Tierra del Fuego to the northern Andes. Traditionally, C. fuscus has been considered a single species composed of nine subspecies, and its long and narrow range suggests the possibility of considerable genetic variation among populations. We used two mitochondrial genes to reveal discrete and geographically coherent groups of Cinclodes fuscus; surprisingly these groups were more closely related to other species of Cinclodes than to each other. We also found evidence for incomplete lineage sorting or hybridization between C. oustaleti and one group of C. fuscus. This research was supported by grants and donations to the Research Training Program. | |||||
