Just to pop in briefly..before going on the last leg of my travels..What are the creationist "answers" or suggestions to approach the subject of sloth diversity. One often hears the concept of "kinds" brought up as a supposed valid alternative to systematics and taxonomy. How could creationism further this particular science? Is there a "special divine creation" testable hypothesis that could be proposed to answer the question of the origin of arboreality in specific sloth groups?
Note: As an apology to all, not all of the references are accessible for free. The abstracts can be accessed without a subscription but except for PNAS, all charge for the articles. However, most of the journals should be availabe in most university libraries.
Hi Mr.H, Glad that you are also still around. I should be a bit more active this coming week...though I fear the pile of work i.e. lab disasters that await me I also see the stunning creationist response to my article...they must be thinking hard or testing their "hypothesis" in the lab
Cheers, weak from French cheese, sunshine, and strange Gaudi art Mam
However, mtDNA may not yield an accurate picture either because the length of time separating some of the lineages is so great that you get multiple substitutions occuring at many sites which totally obscure the phylogenetic signal. In the Greenwood, Castresana et al. article, they did an analysis to compare the "saturation" levels of mutations for 12S rDNA and cytb...and both show that mutliple substitutions are more apparent for 12S though a problem for both.For extremely long branches, morphology may in fact be a better indicator of phylogeny than DNA. It will be interesting to see what the nuclear genes say when Mylodon is added in eventually, but then one may run into the problem of too slow evolution of the sequences leading to no phylogenetic resolution....as you mentioned..a muddled situtation...
so, any creationists out there going to help unmuddle the poor scientists?
Hi Percy, Given the initial rather limited response to the first column, I can only suggest that columnists perhaps try to be less technical than I was and keep the references down to a minimum. While I tried to distill the issues down to a more generally understandable level, I doubt very many people are familiar with sloths or their evolution. I also introduced way to many separate topics from ancient DNA, to phylogenetics, to a bunch of really strangely named animals. It also does not help that most of the references are not open access and require either purchase of the articles or an institute registration.
I will be glad to contribute monthly or semi-monthly columns and I do have ideas for more...I will try to make them a bit more controversial and accessible in the future.
And I hope Andya becomes a columnist as well! cheers, M
Re: Mammuthus, no genius...but I can drink a lot of beer
Hi Ediacaran, Though I am one of the authors on three of the cited papers (will try to preserve some anonymity by not saying which one), I am not Svante
While I will probably disappoint you as I am a molecular biologist and certainly no expert morphologist, what I can say is that because of convergent evolution, sloth (and all Xenarthran) phylogenetics based on morphology is a mess. It is not really clear what they are. This is not really unique problem as it is still not entirely clear what the primates are most closely related to either. Another problem with sloths is that they appear to have diversified rapidly over a relatively short time period while filling similar ecological niches in different places i.e. Antillian sloths, South American sloths etc. which makes finding phylogenetically informative characters difficult ...this is also a problem for DNA based analysis.
For two morphology based analyses of sloth phylogeny there are McKenna, M.C. and Bell, S.K. (1997) "Classification of Mammals above the Species Level", Columbia University Press, New York
and Gaudin, T.J. (1995) The ear region of edentates and the pyhlogeny of the tardigrada (mammalia, xenarthra). J. Vertebr. Peleo. 15: 672-705.
One more general reference is
Engelmann, G.F. (1985) The phylogeny of Xenarthra. in "The Evolution and Ecology of Armadillos, Sloths, and Vermilinguas" (G.G. Montgomery, Ed.) pp. 51-64, Smithsonian Institution, Washington, D.C.
Influence of Tertiary paleoenvironmental changes on the diversification of South American mammals: a relaxed molecular clock study within xenarthrans Frédéric Delsuc1, 2 , Sergio F Vizcaíno3 and Emmanuel JP Douzery1