| Cladistic analysis of the
relationships of the giant and lesser pands. Note: time has been added
onthe horizontal scale after the cladistic analysis was done. Image from
Purves et al., Life: The Science of Biology, 4th Edition, by
Sinauer Associates (www.sinauer.com)
and WH Freeman (www.whfreeman.com),
used with permission.
One of the more interesting applications of
cladistics is to the question of the pandas. The giant panda was once
thought to be a bear, but later its racoon-like characters caused it to be
placed closer to racoons. The red (lesser) panda lives in the same areas
of China as the giant panda, but has a far greater similarity with racoons.
DNA hybridization studies suggest the giant panda is in the bear clade,
while the red panda is in the racoon clade. Both share a common ancestry,
as indicated by shared derived characters, followed by convergent
evolution of other characters. The diagram above indicates this divergence
from common ancestry, and even attempts to show the time of that
divergence.
Phenetics
Phenetics is a process by which taxa are
clustered together based on the number of their similarities (or
differences, depending on the numerical coefficient employed). Traits are
measured and either converted into integers or input directly as numerical
data. Theses data are then mathematically processed using an algorithm
that generates a similarity (or distance as the case may be) matrix.
Various graphical representations of this matrix include a phenogram, and
principal coordinate plot. Phenetic classifications are plagued by
problems of convergence and parallelism, but are useful in their attempt
to objectify the classification process. My previous work on triprojectate
pollen employed phenetics to deal with a wide array of subjective ratios
or other classification methods. Convergence was a given with this group
of fossil pollen produced by one or more groups of unknown extinct plants.
Since monophylesis could not be established for the entire group,
phenetics was use to help delineate possible monophyletic groups for
eventual cladistic study.
Nomenclature
The naming of species and other taxa
follows a set of rules, the International Code of Botanical Nomenclature (ICBN,
click here
for an online version) for plants, the International Code of Zoological
Nomenclature (ICZN) for animals.
Some general rules for nomenclature:
- All taxa must belong to a higher
taxonomic group. Often a newly discovered organism is the sole species
in a single genus, within a single family...etc.
- The first name to be validly and
effectively published has priority. This rule has caused numerous name
changes, especially with fossil organisms: Brontosaurus is
invalid, and the correct name for the big sauropod dinosaur is Apatosaurus,
Eohippus (the tiny "dawn horse") is invalid and
should be referred to as Hyracotherium. Sometime, however,
names can be conserved if a group of systematists agrees.
- All taxa must have an author. When you
see a scientific name such as Homo sapiens L, the L stands for
Linneus, who first described and named that organism. Most scientists
must have their names spelled out, for example Libopollis jarzenii
Farabee et al. (an interesting fossil pollen type I stumbled across a
very long time ago!).
The Kingdoms of
Life
Monera
Monera are the only kingdom composed of
prokaryotic organisms, they have a cell wall, and lack both membrane-bound
organelles and multicellular forms. The Archaebacteria, the most ancient
of this kingdom, are so different that they may belong to a separate
kingdom. Other groups of Monera include the cyanobacteria (autotrophic)
and eubacteria (heterotrophic).
Protista
The most ancient eukaryotic kingdom,
protists include a variety of eukaryotic body (single-celled-colonial-multicellular?)
and nutritional heterotrophic, autotrophic, and both) forms. Perhaps they
are best defined as eukaryotes that are NOT fungi, animals, or plants.
Fungi
Fungi are a eukaryotic, heterotrophic,
usually multicellular group having multinucleated cells enclosed in cells
with cell walls. They obtain their energy by decomposing dead and dying
organisms and absorbing their nutrients from those organisms. Some fungi
also cause disease (yeast infections, rusts, and smuts), while others are
useful in baking, brewing, as foods, drugs and sources for antibiotics.
Plantae
Plants are immobile, multicellular
eukaryotes that produce their food by photosynthesis and have cells
encased in cellulose cell walls. Plants are important sources of oxygen,
food, and clothing/construction materials, as well as pigments, spices,
dyes, and drugs.
Animalia
Animals are multicellular, heterotrophic
eukaryotes that are capable of mobility at some stage during their lives,
and that have cells lacking cell walls. Animals provide food, clothing,
fats, scents, companionship, and labor. |
..Biological
Diversity and Classification 
