Re: Cretaceous taeniodont

[Michael Habib <mbh3q@virginia.edu>]

Some interesting ideas, but I am a bit skeptical of some of the evidence you
laid out...


> Apart from the whole asteroid thing, evidence in support of this is:
> - decrease in pterosaur diversity (prime suspects being birds)
This only supports your case if indeed birds somehow directly (and by this I
mean predation, nest site sequestering, etc) impacted pterosaur diversity.
Hardly conclusive at this point that this was the case.

> - eradication of old bird clade by new birds (unless one accepts
> Feduccia's lucky survivor of shorebirds theory)
I am in agreement with Tim; this is a hypothesis, not yet evidence.

> - decrease in dino diversity before the K/T
This supports any hypothesis holding that a pre-K/T impact was involved in
the extinction event.  I will grant that it supports your hypothesis, but
only in the most general sense.

> - increase in mammal size just before the K/T (if this is demonstrated)
Assuming it is demonstrated, yes.  Assuming this is true, you will still
need the next point (see below) to link the size with nest predation.

> - susceptibility of large egg layers to small racoon-size
> mammalian predators in extant communities
To really back this one up, it would be useful to have data on nest
mortality in various oviparous species; specifically what proportion of
mortality can be attributed to mammalian predators.  I suspect the data are
available for threatened turtles or other species of conservation interest.

Sounds like what you are looking to show is that 1) nest predation is a
primary source of nest mortality for large-bodied oviparous species and 2)
that this predation is mostly from mid-sized mammalian predators.

I should also mention that I think you have a sample size problem, of sorts.
You seem to be arguing that the prevalence of mammals (eg. Viviparous
species) in the large terrestrial zone today (and the corresponding rarity
of large oviparous species) is not a product of chance clade
diversification.  Rather, you seem to prefer the idea that there is strong
advantage for large species in being viviparous.

This is not a bad idea, however, the Cenozoic marks the only time to date
that this has been the case (as best we can tell).  This means that anything
proposed to link to the radiation of viviparity (such as more nest
predators) could simply have lined up by chance alone; it only has to line
up once, so the likelihood is high.  This stacks some dice against you, and
thus you're going to need some very strong data from extant communities,
etc.


> - susceptibility of young of large egg layers to bird predation.
Same as above.  I am honestly still not terribly clear on how this would be
more potent in the latest Cretaceous...


I am not hugely convinced of predation as major element in mass extinction,
including your argument here for the K/T.  However, overall you have some
neat ideas regarding extinction and paleoecology, and the lack of data to
support them at this point simply means you have some interesting research
ahead of you.

--Mike Habib