Re: Cretaceous taeniodont

[John Bois <jbois@umd5.umd.edu>]

On Sun, 11 Apr 2004, Michael Habib wrote:

> Quick question:  You mention mammalian pressure on egg-layers, as well as
> mammalian size increase as an indicator of dinosaur decline.  Are you
> proposing the mammalian size increase as a response to dinosaur faunal
> changes, or a cause of those faunal turnover events? (you may have mentioned
> this already, and I apologize if you have)

My ideal _scenario_ would be this: new birds outdo pterosaurs, old
birds, and challenge small non-avian dinosaurs.  Mammals are under less
predatory pressure because these birds are not as efficient at rooting
them out as small non-avians were.  So, their initial size increase up to,
say, racoon/cat/small dog size was a response to small dino decline.  Once
they were above this threshhold, mammals were able to consume the eggs and
hatchlings of larger dinosaurs (remember that the larger the dinosaur the
smaller the baby is relative to the parent).

Apart from the whole asteroid thing, evidence in support of this is:
- decrease in pterosaur diversity (prime suspects being birds)
- eradication of old bird clade by new birds (unless one accepts
Feduccia's lucky survivor of shorebirds theory)
- decrease in dino diversity before the K/T
- increase in mammal size just before the K/T (if this is demonstrated)
- susceptibility of large egg layers to small racoon-size
mammalian predators in extant communities
- susceptibility of young of large egg layers to bird predation.