I study a wide variety
of topics on cranial development,
function and evolution in
vertebrates. In recent years
I have focused on comparative
studies of craniofacial development
in marsupial and placental
mammals. This work has demonstrated
that the most fundamental
difference between the two
taxa is a delay in marsupials
of the development of the
central nervous system (CNS)
and cranial sense organs
and an advancement of certain
cranialskeletal-muscular
tissues. Specifically, in
marsupials the central nervous
system and particularly the
forebrain is delayed relative
to the development of the
bones around the oral apparatus,
the chondrocranium and the
differentiation of cranial
muscles. This observation
is important because in many
fundamental ways the central
nervous system is responsible
for patterning the skeletal
tissues of the head. In particular,
the CNS, through the differentiation
of the neural crest, provides
the material for the cranial
skeleton, and the CNS provides
signals thought to be important
in the induction and patterning
of the chondrocranium.
I am continuing this study
using a variety of morphological
and molecular-genetic markers
that indicate early differentiation
and patterning in the central
nervous system and skeletal
tissues of the head. In particular,
I am examining the timing
and pattern of early neural
crest migration in marsupials.
In addition, I am looking
at the phylogenetic context
of these heterochronies.
Three sets of taxa are included:
Monotremes will help elucidate
the primitive mammalian condition;
selected eutherian and metatherians
will confirm that the patterns
in Mus and Monodelphis are
general for these clades;
and, finally, comparisons
with non-mammalian amniotes
will further allow identification
of the primitive developmental
condition for mammals.
See a
picture
of Dr.
Smith's
research
in our Gallery.
