9/12/02 Taxonomy
The Linnean (or taxonomic) hierarchy
Kingdom, Phylum, Class, Order, Family, Genus, species
Species definitions and working concepts
Biological species definition
Morphological species definition
The unfinished job of cataloging
Formal description of species: why?
New discovery - new name needed
Re-evaluation #1: “splitting” new name(s) needed; old name kept
Re-evaluation #2: “lumping” one old name kept; one (or more) other old names
Discarded.
The rules and regulations – The International Code of Zoological Nomenclature (ICZN)
A recipe for a
species description:
The principal topic for this lecture is Taxonomy - the
science of classification.
Classification of living things is according to a system known as the Linnean system or the Linnean Hierarchy, named after the 18th century Swedish naturalist Carl von Linne, or Linnaeus, who, in fact, established it. It has proven to be a logical and remarkably convenient system and is universally adopted in the scientific world.
It consists of a series of hierarchical categories
-each category is known as a taxon - plural = taxa.
-It's hierarchical in that a category includes categories with it. (contrast with non-hierarchical classification =>
Easier with examples: (overhead)
Kingdom Plantae Animalia Animalia
Phylum Angiospermophyta Chordata Chordata
(plural=phyla)
Subphylum Subphylum
Vertebrata Vertebrata
Class Monocotyledonae Mammalia Mammalia
Order Liliales Primates Proboscidae
Family Lilaceae Hominidae Elephantidae
Genus Allium Homo Loxodonta
plural=Genera
Species sativum sapiens africana
Some rules and guidelines
1. Intermediate taxonomic levels can be created by adding super, infra or sub to any of these categories. (note that Vertebrata is a subphylum in the example)
2. Species names are never written alone, the genus name (or an unambiguous abbreviation) must precede it.
3. Genus and species names must always be italicized or underlined.
4. The species name is not capitalized. All other formal names are capitalized.
5. The species is the fundamental unit. All other taxa are groups of species.
6. A species is:
a. biological definition -groups of populations whose individuals interbreed to produce fertile offspring. (difficult to apply in paleontology)
b. morphological definition - groups of populations whose individuals are mophologically similar to each other (so similar that their individuals probably interbred). The most commonly used definition in practice.
7. A classification is said to reflect evolution when closely related species (or other taxa) are grouped together in the next higher taxon.
Consider now how species are named and formally described.
If you think that all of this has been done already, think again. The number of species of living things is estimated at about 30 million. Approx 2 million have been described.
-Number of preserved marine animal species has been estimated at 4 to 10 million. About 200,000 fossil species have been named and described.
So..., the bulk of paleontological work that has been done in the approx 200 year history of the field has been naming and describing. This is essential work, because until a lot of cataloging is done, it's difficult to extract much meaning out of the record.
Much of the paleontological literature consists of the naming and describing of species.
Consider three circumstances under which a species should
be formally described:
1. New discovery. A form is found that has not been named and described before.
2. Re-evaluation: splitting. A species already named and described is newly judged to be, in fact, two or more species.
3. Re-evaluation: lumping. Two or more species already described and named are judged to be, in fact, only one species.
In situation # 1 or # 2, a new name is given. In situation #3, one of the old names is declared invalid.
The rules and regulations for naming a new species are contained within the ICZN. (International Code of Zoological Nomenclature) A similar rule book exists for botanists.
A recipe for a species description:
1. Name. Binomial in format (Genus plus species)
Properly latinized (tense, gender, etc.)
Name (the combination) must not be already “occupied” (not already in use for some other species.) If already occupied, the older name is said to "have priority".
Name must be "in good taste" - is often descriptive (e.g. "ruber" = pink; "edulis" = edible; "ponderosa" or "gigas" refers to big size; "rex" = king. Honors collector or benefactor; Considered bad form to name species after one's self.
2. Synonomy. If a description of a previously named species, a synonomy - a list of all the names previously given to this species. e.g. those names designated as synonyms.
3. Description.
a. Basic description of the morphology, other characteristics that may be observable (song, behavior, etc.).
b. Diagnosis. Special mention of those characters (=features) especially useful in distinguishing this species from some closely related species. Such features are often said to be taxonomic characters.
c. Illustration. Though not formally required, it's unthinkable in practice to describe a species without some sort of illustration - photo, drawing, SEM, what have you.
4. Occurrence. Information on where the species is found - geographic, stratigraphic, geologic time.
5. Discussion (optional) comments about ecology, growth, evolutionary relationships.
6. Designation of reference specimens. Types and repository
a. The specimens used in the description of the species
holotype - single specimen (the "Type specimen")
paratypes - other specimens used together with a holotype
syntypes - specimens used without designating a holotype
b. Repository - where the specimens are kept and are available for study. Usually museum or university collections
7. Publication. The name and description must be published in the scientific literature so that it's known. Theses, dissertations, self-publications, newspapers, talks, don't count.
-Why is the correct name Apatosaurus or Brontosaurus?
-Should plenary powers be invoked?
-Should paleontologists be so fussy about such a well-established name?
1877 O.C. Marsh Apatosaurus
1879 O.C. Marsh Brontosaurus
1903 Elmer Riggs - studied specimens, judged that they belonged to the same species; applied the Law of Priority, noted that Brontosaurus was a synonym
Plenary Powers allows exceptions to Law of Priority, but no appeal has been made