[Taxacom] Hedges /Kumar (eds) The Timetree of Life

[Jason Mate]

Dear John,

All data can be "problematic" in its interpretation. There are undertainties in the timing, the method, etc. I fail to see why you specify fossils. It could also be argued, correctly, that tectonic data can be problematic.

As regards to extant taxa morphology resulting in the wrong assignment of fossil taxa, who ever said it was error free? This is a source of error in timing, like any other and open to reinterpretation by researchers armed with better data or methods. All these points notwithstanding, the right fossil at the right location can destroy an argument, even if this argument was the most parsimonious explanation for the previously available data. It doesn´t matter who or how a hypothesis was developed, if it doesn´t fit the facts (fossils, geology) then it is wrong. 

"Phylogeny gives biological relationships. It cannot give spatial relationships. Tracks identify spatial relationships. However, tracks are not constructed in isolation of phylogeny, but with reference to given taxa (i.e. one has a phylogeny) and it is very clearly stated that one can draw tracks first for the lowest taxonomic units (e.g. species, and then sequentially between the higher taxonomic levels. I have called this technique 'vicariance analysis' and given examples in the Brazil chapter."
 
The phylogeny provides the structure on to which organise the distributional data. Also saying that one starts from the lowest level (i.e. genus) hardly matters if your genus is something more speciose than hominids (Onthophagus for example?).

"True, one does not correlate tracks with geological events since the latter are historical theories. One must first correlate tracks with tectonics and from that one has a basis for suggesting the track is linked to the history of those tectonics. A simple example is where a taxon is found either side of a transform fault, but disjunct from each other at distances that match past fault movement. This correlation would suggest the ancestor originated at a time when the fault positions the disjuncts together. When this is found for many taxa of various ecologies the conclusion of a historical relationship becomes even more apparent. One could deny it of course. .... The point is that they can lead to the prediction of geological features or events that were not already apparent to geologists."

Maybe you didn´t mean to say it this way, but what I am reading here suggests that if you have lots and lots (how many?) of tracks joining two areas then you can somehow justify that a geological event occurred. If so, is vicariance disproved if we look and not find any features or events? Or better, if the actual phylogenies of the organisms, under closer scrutiny, do not match the tracks? To make it clearer, lets have a taxon (tribe P) with 2 genera, one in South America (Genus Sam, 3 species) and one in Africa (Genus Afri, also 3 species). If I ignored the phylogeny to the extent that you seem to suggest then I would have two groups linked by a minimum spanning tree which fits other such patterns ((Sam1,Sam2,Sam3)(Afri1,Afri2,Afri3)) thus suggesting that the tribe P shows a typical vicariant distribution. However if I were to look at the phylogeny of the group and find the relationships to be ((Sam1,Sam2)Afri3)(Sam3(Afri2,Afri1)) would your story be so neat? I´d guess you would need to time the divergences to know which (or if any) of the 2 splits is the result of vicariance.

Finally, in regards to my silly comments. They are an extension of your system, i.e., panbiogeography can lead to silly situations. If you look at the distribution of organisms armed with just the basic knowledge of their relations (i.e. monophyletic tribes, genera, etc) then you can, at best say that either the lineage broke apart (vicariance) or they somehow got to the other side. If you want to know which you need to know how the taxa relate to each other precisely  and time their divergences as best as possible. 

Good night


Jason