Re: Triassic radiation

[John Alroy <jack@homebrew.uchicago.edu>]

I think we went around on this already, so to summarize:

1) It's not clear how many "remarkable" originations really took  
place in the Triassic. Birds originate in the late Jurassic (figuring  
the Protoavis theory to be not much more likely as the Flat Earth  
theory); mammals have not-so-dissimilar ancestors in the Permian, and  
there is nothing "sudden" about their origination; turtles are part  
of a lineage that goes back to the Carboniferous, even if they  
themselves don't show up until the Triassic; squamates show up in the  
Jurassic. Crocodylians are hard to pin down because it depends once  
again on where you want to draw the line; arguably, true crocodylians  
aren't around until the Jurassic. I won't argue about pterosaurs,  
frogs, and dinosaurs; salamanders must have been around in the  
Triassic despite the lack of fossils because their sister group is  
the frogs.

2) Even if we could agree on definitions, we would still have to show  
STATISTICALLY that something unusual happened in terms of the rate of  
origination of "remarkable" groups. This is tough going; take my word  
for it, this is the kind of problem I do my research on.

3) Even if we could show there were a lot of "remarkable"  
originations, we would still have to show that the PROPORTION of  
"remarkable" originations was unusual. Because there was a huge  
number of originations in the Triassic because of a "rebound" after  
the P-T mass extinction (a global, 95% species-level event, easily  
the worst in history), we expect in the first place that a lot of  
major groups would have originated just at random. You'll see my  
point if you take a look at a diversity curve for the Permian and  
Triassic.