Post on 11-May-2015
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The Species Problem
How it Affects Paleontology
““The boundaries of the species, whereby men sort them, are
made by men.”- John Locke
What is a Species?
• A species is “the fundamental taxonomic unit in nature” (39.)
• Species “recognize each other.”
• Proof of this “recognition” is displayed in reproductive habits, or the potential for interbreeding.
Species of Lilies
Variation in a Single Butterfly Species
SpeciesAgrias
Kingdom - Animalia Phylum - ArthropodaClass - InsectaOrder – LepidopteraFamily- NymphalidaeGenus-Agrias
What is phylogeny?
Loosely (according to the dictionary) phylogeny is the
evolutionary history of a group of organisms as
depicted in their family tree or “cladogram.”
A Basic Cladogram
Two Concepts of Species (p 39)
• Morphological SpeciesDiagnosible
clusterPattern of
ancestrySelf contained
group“beyond
which there is not” (Eldredge and Cracraft)
• Biological Species Population
array Actual
interbreeding
OR Potential
interbreeding
Reproductive isolation
These opposing ideas break into two camps:
Phyletic Gradualism
• Often favored by biologists and life scientists
• Speciation is slow, uniform and gradual
Punctuated Equilibrium
• Makes more sense in the context of paleontological studies
• Most species exhibit little net evolutionary change
A paleontological study of speciation in favor of phyletic gradualism.
Scientists Today…
-Tend to adhere to a biological concept of species.
-This can pose a problem for Paelontologists.
There are at least 24 different species concepts and none of them can be applied to all organisms that have ever lived. (Hey, J. 2001 qtd in Techne)
How do Paleontologists Know?• Fossils cannot demonstrate interbreeding or the lack thereof.
• Therefore, typological (morphological) species divisions make the most sense.
Potential Problems
Sexual Dimorphs
Recent reconstruction of Pterodactyls
Ontogeny (developmental
stages)
Modern Sexual Dimorphs
Modern Insect Ontongeny
Is Time on our Side?
Paleontologists have a different perspective
than biologists.
TIME
Key Word
anagenesis-gradually changing from one
form to another
Determining a “Cut Off”
GAPS IN RECORD VS
• Artificial• Convenient
CONTINUOUS SERIES
First Specimen? Halfway
through?
New Problem: Pseudoextinction
What is “Pseudoextinction?”
• Parent species go extinct as new species evolve in succession
• Not the same as extinction.
• Part of the evolutionary species concept.
Trilobite Family Tree
Take your Pick!
• Biostratigraphers make use of many fine species divisions to date layers of stratigraphy.
• General paleontologists will find the evolutionary species concept (a lineage that evolves separately with separate lineages and tendencies) more practical
A Solution to the Mayhem
Punctuated Equilibrium to the Rescue!
• Phyletic gradualism(gradual transformation among species) is actually not that common in the fossil record.
• Actually, fossil records appear to remain static and relatively unchanged throughout paleo reconstructions for the most part.
Punctuated Equilibrium• Most large species
populations do not evolve in any direction.
• Fossil populations remain in stable equilibrium for long periods,
• Punctuated by the introduction of a new species formed in an isolated area (and then migrated back to main group.)
Eldredge and Gould
Stephen J. Gould Niles Eldredge
There is very little proof of anagenetic transformations
taking place.
Exception:Biostratigraphy
Exception:George Simpson of Columbia University says,
“The state of rest is the exception and it seems that some restraint or force must be required to maintain it."
Main Idea
Anagenetic continua are rare, and thus species division is not as complicated as it seems.
Nietzche says, “Out of chaos comes order.”
Punctuated Equilibrium simplified the species problem significantly.
Sources:
"Biostratigraphy." Harvard University Museum of Comparative Zoology. Harvard University, 2004. Web. 7 Sep 2011. <http://www.mcz.harvard.edu/Departments/InvertPaleo/Tren ton/Intro/GeologyPage/Sedimentary%20Geology/biostrat.htm
Crampton, , James. Gale, A. "A plastic boomerang: speciation and intraspecific evolution in the Cretaceous bivalve Actinoceramus." Paleobiology 31.4 (2005): 559-577. BioOne. Web. 7 Sep 2011. <http://www.bioone.org/doi/abs/10.1666/04003.1>.
Phylogeny. (2012, April 14). Retrieved from www.dictonary.com
Prothero, Donald. Bringing Fossils to Life. 2nd ed. NY: McGraw-Hill, 2004. 39-45. Print.
Punctuated Equilibrium." Wikipedia. Online. 2011. Print. <www.wikipedia.com>.
Unknown. (Image Creator). (2012). Phylogenetic tree of life. [Print Photo]. Retrieved from http://en.wikipedia.org/wiki/Phylogenetic_tree