is inherently hierarchical, as is the great "Tree of Life".
Its boughs are analogous to the higher Linnean rankings, i.e., the
domains, kingdoms, phyla, classes, etc. Smaller branches correspond
to middle rankings, i.e., the orders, families and genera. At the
end of the many branches are the twigs, the uncountable species,
some 99% of which are extinct. The great Tree of Life is real. It
is a phylogenetic tree representing the unique ancestral history
of each and every creature. Darwin believed that all creatures on
Earth might have originated from a single common ancestor so that
each species through geological history fit somewhere in an overarching
the first dawn of life, all organic beings are found to resemble
each other in descending degrees, so they can be classed in
groups under groups."
too does modern biology believe all life began with a common ancestor.
further believed that the classification of living creatures, extinct
and extant, should be based on phylogeny:
believe that the arrangement of the groups within the class,
in due subordination and relation to the other groups, must
be strictly genealogical in order to be natural."
aside the supernatural, so too does modern biology and zoology.
the dream of placing all the boughs, branches and twigs in their
rightful place is a formidable task, and doing it accurately is
intractable. Even with the ability to fully sequence the genomes
of related creatures, accurately unfolding the lineage of related
creatures might only be done to a limited statistical certainty.
If we consider the beloved trilobite, extinct for hundreds of million
of years, where we will never have DNA, the uncertainties in classification
rise enormously. Despite rigorous if not painful descriptive protocols
used by invertebrate paleotologists for trilobites, the precepts
of decent with modification allow morphological change without evolution
and evolution without morphological change, such trilobite classification
will forever be highly confounded. Decent with modification also
allows multiple evolutionary paths to a common morphological end.
With all confounders considered, the metaphorical tree for subphylum
trilobita will forever be shrouded with great mystery. Recently,
the concept of a single unifying, hierarchical tree has been challenged
by sequence studies that suggest lateral transfer of genes may
further confound lineage among species.
Museum presents one structure for the Tree of Life, but since the
museum is devoted to collectable fossils, we will not venture far
down some boughs of the tree, will not venture at all down many
branches, and in the end, will not cover many twigs of life. The
data presented will concentrate on the areas where the fossil record
is most rich, where the collector can hope to obtain specimens,
and where we can provide photographs.
number of known living species on earth sets somewhere below 2,000,000.
A review of the literature shows that in the 1970's, estimates of
the actual number of extant species ranged from 10,000,000 to 100,000,000,
with 30,000,000 being a reasonable average. In this post-genomic
era, with bacterium included, and extrapolating back 3.5 billion
years knowing what we now know about the ratio of extinct to extant
species in some families, an astonishing 4 trillion species of life
can be conjectured to have existed over geologic time.