Pharyngula

Darwin had problems with the fossil record that he explained as a result of imperfections. Modern paleo has corrected some of that with the discovery of many intermediates. Jablonski is going to talk about the fossil record as a laboratory for testing evolutionary hypotheses. Marine bivalves are model systems with both modern forms and good fossil preservation for developing analysis techniques.

The fossil record gives access to raw rates of development, unique events, and long intervals, spatial dynamics, and morphological transitions in form.

Extinction in the fossil record is a problem. Huge variation in extinction intensity over time; there is also differential extinction of mollusc clades. There is no contant rate of extinction over time and across phylogenies.

Compared bivalve living clades with total clades over time.

Tropics are a cradle of new taxa that trickle up into the higher latitutdes; lineages preferentially arise in the tropics. Tropical origins seen despite poor fossil record in tropics, and occurs in spite of increasing harshness of higher latitudes over the same period.

Evolution of form: there is a pattern seen in fossils, (type 1) a rapid increase in morphological disparity early leading to taxonomic diversity, or (type 2) disparity and diversity rise together, or (type 3) morphological disparity is low, but diversity rises rapidly.

Echinoderms fit type 1; Aporrhaidae follow type 2 model; Trilobites are type 3, where stable body plan is accompanied by huge species diversity.He catalogs many lineages and characterizes which type they fall into. I’m a bit lost as to what point he’s trying to make here. OK, so there are different patterns of disparity and diversity in different lineages, but why is this interesting? I seem to be lacking some important background to follow this talk.

We get a question: Ecological opportunity is a key factor in diversity. Is it enough to generate the type 1 pattern of diversification? Alas, I don’t seem to get an answer.

For understanding long term patterns of change, we need both evolution and paleontology. Extinction varies temporally and among clades. Clades are spatioally dynamic and geographic histories are often surprising, and there are multiple pathways to prolific diversification.

This talk actually generated a fair number of questions, so I confess that I’m missing something here. It looks like I’m going to have to dig into a few Jablonski papers. Either that or I need more sleep/coffee.