Biospecies vs. Morphospecies

     Based on genetic information scientists can group living organisms into biospecies,  groups of organisms separated by genetic differences.  Being unable to sample the DNA of organisms that lived millions of years ago,  paleontologists identify species of  fossilized organisms on the basis of quantifiable morphological characteristics, hence the term morphospecies.   

dog evolutionBiospecies:  The evolution of Modern dogs as observed by quantified changes in DNA over the last 12,000 years
trilobite evolutionMorphospecies:  The evolution of rilobites as observed in the fossil record over the last 500 million years
                                  

        Breaking fossil organisms up in to morphospecies is an effective tool to study evolution, however it requires the researcher to quantitatively separate changes that come about due to evolution from those that may be a result of "environmental plasticity", or the potential that most organisms have to vary their morphology as a response to environmental change.  Examples of this behavior can be observed in some tropical corals, for example Porites spp. which are able to adapt their colony shape to environmental stress, such as sedimentation rate. However, if the stressor is removed, colony shape will revert. This raises the question,  "how do scientists delineate between morphological change associated environmental plasticity and evolutionary change?"  Paleontologists need to examine environmental factors recorded in the rocks, and compare these to how morphology changes over time.  Environmental stressors such as sedimentation rate are short lived, and often are cyclic, whereas morphological change due to evolution is ongoing and unidirectional. 

Photographs courtesy of the University of California Museum of Paleontology: (http://evolution.berkeley.edu/)


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