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



See the "early" in the URL? If you have access, go to the non-early site https://www.pnas.org/content/113/18/5036 and scroll down to the "Materials and Methods" section. There it says at the end:

Extrinsic Factors.

Because the fossil record has long been known to be incomplete (50, 51), it is possible that the observed slowdown and downturn are byproducts of undersampling. This assumption would imply that there is a systematic downward bias in the phylogeny toward recent times, which would be counter to the usual expectation for poor sampling (50, 51). Here, to test the effect of such biases, we fitted additional models with appropriate covariates, including stage-level formation counts (because formation count is widely reported to be associated with sampling bias) (9, 10, 12, 35, 44, 52, 53), taxon-specific formation counts (the number of formations in which a taxon is found), taxon-specific collection count (the number of fossil collections in which a taxon is represented), cladewise valid taxa counts (the known underrepresentation in the phylogeny) (54), fossil quality scores (state of preservation) (55), and body size (smaller taxa are less likely to be preserved) (56).

As an indirect measure of the influence of geography on speciation dynamics, such as segregation by geographic barriers (30), we used Mesozoic eustatic sea-level reconstructions (34) as an additional covariate in our models (mean sea-level value along each terminal branch). We also tested the ecological limit on clade diversification or the possible effects of niche saturation by adding a measure of intraclade diversity taken as the number of contemporary branches (including internal branches) for each taxon (the number of tips in time-sliced trees) (48). All data files are available in Datasets S1–S13.

As far as I can tell, all this assumes that if the quality of preservation is the same in two formations, then they will produce the same number of specimens if all else is equal; not all else is equal, and the corrections for this are listed. What is not listed, as far as I understand, are the area on which each formation is exposed now (as opposed to the area over which it was deposited; that's what the sea level correction is for), and the density of fossils in each formation (apparently higher in the Dinosaur Park than in the Hell Creek, AFAIK).
 
On top of all that, the emphasis on actually known fossils (spelled out at the start of the "Materials and Methods" section) means that all conclusions are heavily biased toward North America. If there was a decline there but an increase in Africa, we're simply not going to find out anytime soon.
 
Finally, the curves in the figures are awfully smooth for spanning so much time. Why would they be? How would that work?
 
(...Also, may I request that people stop saying "speciation" when they mean cladogenesis? There's only one of 150 species concepts under which those are reliably the same thing, and it's never used.)
 
Gesendet: Mittwoch, 04. Dezember 2019 um 20:59 Uhr
Von: "Mailing" <mailinglistinformation@gmail.com>
An: dinosaur-l@mymaillists.usc.edu
Betreff: Re: [dinosaur] Would non-avian dinosaur survive through the whole Cenozoic?

There was a slow-down in speciation rates prior to the K-Pg, see:

Sakamoto, M.; Benton, M. J. & Venditti, C.
Dinosaurs in decline tens of millions of years before their final extinction
Proceedings of the National Academy of Sciences, 2016, 113, 5036-5040
https://www.pnas.org/content/early/2016/04/13/1521478113.abstract