Week 4: Macroecology before Macroecology
Paper for Tuesday, Feb. 7: Community
Evolution and the Origin of Mammals (1966)
Commentary/blurb
authors: Mark D. Uhen and Jessica Theodor
Mark
D. Uhen received his PhD from the University of Michigan in 1996. Uhen’s
interests lie in the evolution of cetaceans. More generally, he is interested
in diversification theory and the use of stratigraphy to studying phylogenetics.
Uhen is currently a professor at George Mason University.
Jessica Theodor received her PhD in
Paleontology from Berkeley in 1996. Theodor now works at the University of
Calgary, studying ungulate diversity patterns. Specifically, Theodor is working
to track down the causes of diversity patterns – climate plays a big role, but these
causes could also include factors due to phylogenetic history.
Paper author: Everett C. “Ole” Olson
Olson received his PhD from the
University of Chicago in Geology in 1935, after which he was appointed as the
new vertebrate paleontologist. He is known by the National Academy of Science
as one of the most important vertebrate paleontologists of the 20th
century for his pioneering work on the origin and evolution of early
vertebrates and their ecosystems. The idea of morphological integration is attributed
in part to Olson, as well as the popularization of the idea of taphonomy in the
U.S. Ole coined the term “chronofauna,” an idea that sets the groundwork for
his 1966 paper “Community
Evolution and the Origin of Mammals.”
Cliffnotes:
Olson is attempting to study origin of
taxa through the evolution of their communities. Specifically, he hopes to map
out the evolution from primitive reptiles to mammals. Ole defines a community
in this paper as the consistent flow of energy and environmental interactions
of varying taxa in the community; with this definition, it’s possible (if you
squint) to see communities as evolving entities, just like their taxa.
Three types of vertebrate-containing
communities from the Permian are found: Type I, Type II, and Type III. Olson
comes up with these three based on stratigraphic information from the U.S.,
USSR, and a little in South Africa; he makes a big point of the horrors of
taphonomy (i.e., everything that can possibly go wrong during fossilization),
and the bias of fossil assemblages.
Based on his stratigraphic data, Olson
finds that pre-mammals (therapsids) stemmed from Type I (energy originally
flows from aquatic plants) while reptiles (diapsids) stemmed from Type III
(energy flows from terrestrial plants to terrestrial invertebrates). These two
communities eventually developed into Type II independently and diapsids and
therapsids, finding themselves in the same communities, began to compete.
Olson points out that these
conclusions weren’t based on a whole lot of evidence. Despite this, his paper pushed
the ideas trophic analysis and taphonomy in paleontological research. Subsequent
papers have been published using this same idea, including studies on marine
invertebrate communities.
Some
questions:
1. Are
chronofauna and Olson’s definition of a community for this paper similar
concepts? Or could we have this definition of community without the idea of
chronofauna?
2. Why
do you suppose this paper is considered macroecology?
3. Are
chronospecies and chronofauna the same thing?
Olson says a few times that mammal evolution required
an initial environment with ties to the water, while reptile evolution needed
an environment that had been separated from
My last question seems to be cut off, so I'll paste the whole thing here: "Olson says a few times that mammal evolution required an initial environment with ties to the water, while reptile evolution needed an environment that had been separated from water longer. Why is this?"
ReplyDelete(∪∩∪) - I am sick. Bleh. Anyways, I found Olson's analysis of a "type 1" Permian community (Fig 2) very odd. For example, he puts a tentative question-marked line between Diadectes and terrestrial plants while at the same time connecting Diadectes with a solid unquestioned line to mollusks. Whut? Maybe their understanding of the diet of Diadectes was incomplete at the time, as I understand it all modern paleontologists believe Diadectes exclusively consumed terrestrial plants - it had molars and a secondary palate which allowed it to chew and breath at the same time. Not much point in being able to breath while you chew simultaneously if you're underwater. Furthermore, Diadectes' extremely thick leg bones suggest it spent a lot of time on the land. Similar problems arise for many of the other so-called pseudoamniotes listed in the diagram - particularly for Seymouria, which I have heard called an insectivore. Finally, perhaps most importantly, there are only two synapsids(Edaphosaurus and Dimetrodon) in the entire diagram, yet this 'Type 1' mode is meant to represent pre-mammal organisms? I question the likelihood that Dimetrodon preyed heavily on any amphibians or that Edaphosaurus ate anything other than terrestrial plants. Beyond this, other edaphosaurids like Ianthasaurus, a smaller cousin of Edaphosaurus, almost certainly ate insects - insects that likely ate terrestrial plants in their turn. Olson's claims majorly conflict with what I understand to be the modern view on early synapsid diets. From what I understand, synapsid life modes from the early to the late Permian should be classified as a mixture of what Olson calls type II and type III - all the way. Of course, Olson admits that this is all "based on less than sufficient evidence." I hate to think how the conclusions I draw will be utterly overturned in the subsequent century. Anyway, I hope to see you all tomorrow, but if I'm sick I'll probably stay home. Wish me well!
ReplyDeleteIn reference to Agathe’s first question, chronofauna and community are similar concepts but I wouldn’t consider them synonyms. Chronofauna refers to a basic structure affected by time. Olson in 1951 defines it as a “geographically restricted, natural assemblage of interacting animal populations that has maintained its basic structure over a geologically significant period of time”. On the other hand, the concept community used by Olson in this paper refers to the interactions of this taxon groups. The author also differentiates between the concepts complex and community, where complex is used in paleontology to “give a taxonomic designation to an assemblage of animals that is encountered repeatedly in the record”. Maybe in this context I would consider chronofauna and complex to be more similar concepts.
ReplyDeleteAlso, I personally see the macroecological point of view used in this paper. The paleocommunity approach that Olson uses is a new “big picture” approach to hypothesize about the different communities that existed during the Permian but, as the author points out (and Agathe also commented) all this theory is based on “less-than-sufficient evidence”. I feel like maybe there isn’t enough evidence to build all the community types theory?
I kind of agree with Olson's concept that there had to have been a transition away from the water in order to enable the evolution of mammals. This would make sense as amniotes needed to evolve different types of skin and eggs to prevent desiccation. However, I also agree with Lucius and Laura that the assertion could be better supported. The record of these communities is really only isolated to two regions: Russia and the Karoo Basin in South Africa. It would be nice if some other region in the world from this time was found so we could really see if the change is as explicit as Olson makes it out to be.
ReplyDelete