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Background
A.
Primary Research Interests: Comparative and Biomedical Studies of Bone Structure and
Biology
I am a physical anthropologist by training.
My current work focuses on primate cancellous bone using broad,
comparative studies to gain a better understanding of fundamental
principles of bone structure and biology.
I use the microCT imaging modality to capture high-resolution
images of cancellous bone for quantification.
The initial focus of my work has been to investigate whether structural
correlates of locomotor behavior could be discerned in anthropoid
primates. The work
naturally expanded to investigations of intraspecific variation,
sex-based variation, the allometry of cancellous bone, and structural
constraints (if they exist). My
work to date has used the anthropoid species Macaca fascicularis
(macaque), Alouatta seniculus (howler monkey), Ateles
geoffroyi (spider monkey), Colobus guereza (Colobus monkey), Symphalangus
syndactylus (siamang, closest relative to man in my work), and Papio
cynocephalus (baboon). These
investigations have revealed the following:
- Trabecular
thickness is the only parameter investigated so far that shows a
relationship to body size. Trabecular
thickness scales with strong negative allometry (increases in
thickness very slightly with body size), a result similar to that
obtained by Swartz et al. (1998) for mammals in general.
Results indicate that this relationship is much stronger in
male anthropoids, especially male cercopithecoids, than in female
anthropoids.
- Structural
constraints at the intraspecific level are not similarly expressed
at the interspecific level. Intraspecifically,
the only structural parameter that consistently correlates with bone
volume fraction from species to species is the structural model
index (SMI). However,
the SMI does not correlate with the bone volume fraction at the
interspecific level. In
contrast, the degree of anisotropy does correlate with the volume
fraction at the interspecific level but this does not obtain
intraspecifically. This
suggests flexibility in the construction of trabecular architecture
across species, at least among anthropoid primates.
- In
the proximal femoral neck, trabecular bone architecture does not
correlate with locomotor mode.
- Macaca
fascicularis
males and female express sex-based differences in femoral neck
trabecular architecture. No
other anthropoid species so far studied express sex-based
differences. Moreover, M.
fascicularis females show a clear pattern of higher trabecular
number and connectivity density in the femoral neck than other
anthropoid primates studied so far.
Since
arriving to the OBL, I have worked on, and gained experience in, a
number of other projects involving microCT.
These projects include investigations of bone tissue engineering
using different scaffold types and bio-reactors, viral delivery of BMP-2
in a rat femur critical defect model, and the creation of a murine model
of resorption to better understand the role of osteocalcin in this
process.
B.
Other Research Interests: Paleontological and Evolutionary Studies
By academic interests
also extend to patterns and processes in mammalian evolution.
Colleagues and I are investigating macroevolutionary patterns in
primate body size. We are
using a variety of methods to map out patterns in body size evolution
and test the extent to which Cope’s Rule holds for primates.
We use lower M1 crown area as a surrogate for body size and use
general primate and clade specific regressions to estimate body sizes in
fossil primates. To test
Cope’s rule, we are employing McShea’s subclade test and Wang’s
analysis of skewness.
A project I am excited about but have trouble finding time to advance
lately concerns sloth evolution. This two-part study examines the
craniofacial size and shape of Hapalops, a Miocene xenarthran
from the Santacrucian land mammal age. Numerous remains of putative Hapalops
fossils have been recovered since the late 1800’s with no real
agreement on how many of the putative Hapalops fossils actually
belong to this taxon (see F. Ameghino and Scott’s quarrels in the
early part of this century) nor of the systematic position of this
genus. The first part of my study, in collaboration with Mike Lague,
showed that there are two distinct morphs in the material currently
referred to Hapalops and that these shape differences are greater
in magnitude than those seen between Choloepus (middle image in
pic) and Bradypus (top image in pic). This is rather surprising
considering that the two genera of living sloths are members of
different sloth families. The second part of this study, which is
currently underway, examines the internal structure of the craniofacial
skeleton using high-energy CT scans in the hopes of discovering features
that can be integrated into a systematic analysis (bottom image, Hapalops
in frontal section).
C.
Civic Responsibility: Great American Paleontologic Interchange Website
I created a website that attempts to help South American
paleontologists, especially graduate students, quickly locate
information on paleontological collections in the United States, funding
opportunities for short term research visits; funding opportunities for
graduate work in the U.S., names of volunteer researchers who are
willing to edit English manuscripts for South American researchers and a
few other things. The idea
for such a site came about after a conference in Bolivia in which South
American professors and graduate students voiced some need for help in
making paleontology in South American prosper.
The success of paleontological programs in South America is a
vital first step in ensuring that museum collections in these countries
do not fall too far into a state of disorganization and disrepair.
The long history of North American and European involvement in
South America, in all realms of possible interactions, has been replete
with exploitation. Interactions
are not one-sided these days for a variety of reasons and North American
and European researchers now do what they can to help their South
American colleagues. In
spite of this, our southern colleagues still need our help.
The website I set up, “Great American Paleontologic
Interchange” (http://www.sinc.sunysb.edu/Stu/rfajardo/PaleoSAm/PaleoSAm.htm),
is my small way of helping out for the time being.
This site is currently up but will soon be under renovation and
eventual move to a local server. The
much needed updating will begin 12/03. |
