Scientists care because
phylogeny is the
fundamental product of evolution. Therefore, a phylogenetic hypothesis
is essential if you want to understand biological phenomena, most of which
have an evolutionary explanation.
Since many scientists would like to know how animal diversity and
animal body plans came to be, presently there is a great deal of work
on resolving the
among the major groups of animals. Much of this research has
relied upon morphological characters, especially those expressed in early
development (e.g. embryological characters). More recently, a
significant advance in our
understanding of animal phylogeny has been brought about by the
study of molecules (in particular genes and their protein
products) contained within animal cells.
The phylogeny presented here is a relatively conservative guess
based upon various published studies of
18S ribosomal RNA sequence data. As you can see, there are quite a
few unresolved branches, and therefore a great deal
of work to be done in this area.
Note that the phylum Porifera
(the sponges) is
A few lines of independent evidence suggest that one group of sponges
is actually more closely related to non-sponge animals than it is
to the other sponges. This is an important finding for it implies that
the lineage leading to all other animals (including ourseleves!) was
directly descended from an animal with a sponge body and a sponge
Visit the Tree of Life
for more information concerning the
systematics of animals.
For some classic images of invertebrate animals and protists, created
in the 19th century by the great zoologist Rudolph Leuckart, click here
to visit the
Marine Biological Laboratory at Woods Hole, Massachusetts.
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