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Re: [dinosaur] Would non-avian dinosaur survive through the whole Cenozoic?

Maybe there is a misunderstanding when I say "not a good proxy for sampling bias". The articles I mentioned suggest that various previously proposed proxies for sampling bias are information-redundant and that it is not clear, whether the proxy is driving diversity counts or vice versa.
Given the current knowledge of both global and local scale studies, the proxies mentioned so far do not seem to do a good job (at least for the terrestrial record).

Regarding a "potential radiation in Africa": If there was evidence for such a radiation it can and should be modelled quantitatively. If there is no such evidence, then it might be an interesting speculation (?), but I don't see how it would be a strong argument against the results of similar studies. I could similarly suggest that birds are direct descendants of temnospondyls and we just have not yet found the respective fossils. I reckon you would agree, that this is a ridiculous suggestion but it appears to me to be the same line of thought (?). A less ridiculous example might be the ancestry of modern turtles, which previously were thought as being closely related to pareiasaurs, but are now considered diapsids, possibly closely related to archosaurs/archosauromorphs considering newly available molecular data (and newly discovered fossil specimens).
We can only work with the available data. Given the available data, these are the results - if new data becomes available (or better quantitative models) results can change.
Again, maybe I just misunderstand your example. Are we talking here about the philosophical underpinnings of empirical research? It is obvious that an (ultimate) proof in such disciplines is impossible (unlike, e.g., in logic).

Regarding the rates: There are other (process-based) methods, that allow for short-term fluctuations in evolutionary rates - but (at least at the moment), they are less flexible than the method used in the paper. But the idea there was not to test for such short-term fluctuations (an interesting topic in itself), but to test, whether overall the capacity of non-avian dinosaurs to speciate had deteriorated over evolutionary time.

On 06/12/2019 16:28, David Marjanovic wrote: 
Gesendet:ÂDonnerstag, 05. Dezember 2019 um 20:46 Uhr
Von:Â"Mailing" <mailinglistinformation@gmail.com>

Outcrop area is not necessarily a good proxy for predicting (terrestrial) diversity, see e.g. Dunhill (2012), Dunhill et al. (2014), Walker et al. (2017), and getting outcrop area/exposure area on a global scale is a non-trivial task (even less so the density of fossils per formation). 
Well, the worst-case scenario is not that we have to use a worse proxy. The 
worst-case scenario is that we simply cannot predict diversity unless we 
perform a non-trivial task.

I am not so sure what you mean with "actually known fossils". The results are obviously based on what is known at the moment - but that is trivial and also holds true for the opposite interpretation of the fossil record. So, I think I misunderstand you here: What do you mean by this? 
As I said: if there was a radiation going on in Africa, we're not likely to 
find out anytime soon.

I'm not trying to argue that I can show there was no decline in origination 
rates; I'm trying to argue nobody has shown a reason to think there was a 
decline.

The shape of the curves is determined by the mathematical properties of the 
involved models. For a model with constant speciation/cladogenetic rates (I will 
stick to speciation since that is the commonly used term) and extinction rates 
(with spec. rates > ext. rates) you expect a linear increase in the number of 
speciation events in log space through time. If speciation rate decreases through 
time and is ultimately surpassed by extinction rate, you expect a quadratic 
relationship (also holds true for the opposite case, where speciation rate 
increases through time + extinction rate remains constant).
You then fit your models to the data and assess which model performs best. That 
will tell you whether non-avian dinosaurs as a whole were in decline or not (in 
terms of speciational capability). You can add various covariates to account 
for other effects involved (e.g., sampling bias, extrinsic controls on 
speciation dynamics, etc.), but it is not necessary for the model per se.
Yes, yes. My problem with this is the long-term view all authors so far appear to have taken. Shouldn't we expect extinction rates, and probably also origination rates, to vary much faster and much more erratically than the smooth curves in the paper? Environments aren't stable, or show stable trends, over tens of millions of years, so why should origination or extinction rates do that?