GEOL 331/BSCI 333 Principles of Paleontology

Fall Semester 2018
Fossil Species and Alpha Taxonomy

Many skulls of the dire wolf Canis dirus discovered at the La Brea Tar Pits, California

Key Points:
•Species delimitation remains problematic. Several different methods have been proposed, but all have some problems in certain situations.
•Nevertheless, the idea of "species" represents a useful concept for describing biodiversity.
•A set of rules, initially established in the 1700s but modified over subsequent centuries, governs the formal taxonomic nomenclature.
•Alpha taxonomy is the core of this work: the description of specimens, identification of the same, and coining of new names if it appears to be a new taxon.

"Of what use are the great number of petrifactions, of different species, shape and form which are dug up by naturalists? Perhaps the collection of such specimens is sheer vanity and inquisitiveness. I do not presume to say; but we find in our mountains the rarest animals, shells, mussels, and corals embalmed in stone, as it were, living specimens of which are now being sought in vain throughout Europe. These stones alone whisper in the midst of general silence." -- Aphorism 132, Philosophia Botanica (1751), Carolus Linnaeus

"I am fully convinced that species are not immutable; but that those belonging to what are called the same genera are lineal descendants of some other and generally extinct species, in the same manner as the acknowledged varieties of any one species are the descendants of that species." -- Introduction, On the Origin of Species by Means of Natural Selection (1859), Charles Darwin

""The usual concept of species can be stated as follows (Mayr 1970): "Species are groups of interbreeding natural populations that are reproductively isolated from other such groups." This concept is grandly called "the biological species concept." But that is an arbitrary appropriation of a term with a more general and earlier meaning. I will instead use the term "reproductive species concept."" -- "Ecological species, multispecies, and oaks" (1991), Leigh Van Valen

"An important aspect of any species definition whether in neontology or palaeontology is that any statement that particular individuals (or fragmentary specimens) belong to a certain species is an hypothesis (not a fact). -- "Cladistic classification as applied to vertebrates" (1977), Niels Bonde.

The Species Problem, Continued

So here are things most people agree with about species:

The previous set of notes includes a look at various proposed species definition concepts (or more precisely, criteria: that is, the means by which species would be delimited). Each of these has two major aspects: some similarity criterion (shared aspects of members of the species) and some difference criterion (features that make the species distinct from other species.) Different species criteria emphasize these to different degrees, but each includes both. For instance, the BSC considers interbreeding (a similarity criterion) within the species, and reproductive isolation (a difference criterion) as the boundary of the species.

The previous notes also indicates some of the problems with each of the distinct species criteria. None entirely encompass the range of biological possibilities, or are either too restrictive or too inclusive compared to the species as actually recognized and used by field naturalist and other working biologists. But just to add to the difficulty, here are some additional problematic issues:

So where does that leave us?

And specifically with regards to fossils: in the end--with the rare exception of fossil genomes--all fossil species are morphospecies, since we really can't see other aspects of them. And since there is the time factor that neontologists don't have to deal with, we see stratigraphic variation which segue into chronospecies. (We'll talk more about this issue and rates of change, later.)

Alpha Taxonomy and Species Grammar

Alpha taxonomy: the discovery, description, and classification of species.

Linnaean taxonomy has its own special set of grammatical rules:

Because there is disagreement about the features used to define a particular species or genus, different biologists and paleontologists will sometimes disagree about which specimens belong in a particular species, and which species belong in a particular genus (and so forth).

For those interested in a website concerning some unusual Linnaean species names, click here.

Types and Type Specimens
Another aspect of Linnaean taxonomy is that each species must have a particular type specimen. This is a particular individual preserved specimen (extant animal) or fossil (extinct animal) that is the "name holder" for that species. A type specimen is specifically referred to in the original description and diagnosis of the species. It need not be the most complete specimen known at the time (although that helps, as the more complete it is, the better the chance a less-complete individual can be compared to it!). The type specimen plus all the additional (referred specimens) are collectively called the hypodigm. Ultimately, if a species is regarded as being "valid" (that is, representing a real species in Nature), the type specimen is the only individual that is absolutely certain to belong that that species.

Similarly, each genus has a particular type species. This is the particular species to which the genus name is linked. If a genus is valid, the type species is the only species that is absolutely guaranteed to be within that genus.

As an example, CM 9380 (in the collections of the Carnegie Museum of Natural History) is the type specimen of Tyrannosaurus rex, and Tyrannosaurus rex is the type species of the genus Tyrannosaurus

There are several types of type specimens:

Objective and Subjective Synonyms

If two synonyms are based on the same type specimen, they are said to be objective synonyms. If they are based on separate type specimens, they are subjective synonyms.

Problematic Names

Difficulties of Paleo-taxonomy
Combining this lecture with the last, there are some inherent difficulties with the taxonomy of fossils that are not (generally) problems with living species:

Parataxonomies: alternative taxonomic systems parallel to the primary one. Ootaxonomy (taxonomic system for vertebrate egg fossils) is one such set. Ichnotaxonomy SHOULD be one, but is considered under the zoological code.

The Peculiarities of Paleobotanical Taxonomy
Different plant organs often have very different taphonomic potentials and so are rarely preserved together. As a consequence, each paleoplant organ system (leaves; trunks; roots; stems; pollen/spores; etc.) has its own taxonomic system. WITHIN each system, the principles of priority apply. But discovery that (for example) leaf A, seed B, and trunk C belonged to the same paleoplant does NOT result in synonomy of A, B & C. This is in gross violation of ANY species concept/criterion, and of the neontological botanical code, but it is ultimately very pragmatic.

To Syllabus.

Last modified: 12 September 2018

Growth series of the Cambrian trilobite Elrathia kingii