Re: Cretaceous taeniodont -- long, combined answer

["David Marjanovic" <david.marjanovic@gmx.at>]

> > There is
> > 1. a fossil bias against finding _anything_. That's a BIG bias.
> > [...]
>
> Still, all other things being equal, one would expect to find bigger
> things (i.e., teeth of larger mammals) more easily than small.

Yes -- if we find enough of any that such statistical considerations apply.
In many strata, we don't.

> > In other words: We are _not_ going to be able to make statistically
> > meaningful statements about the abundance of big mammals over time.
>
> I wonder why we keep looking, then?

:-) Because we're foremost interested in phylogeny, in description, and only
later in quantitative ecology.

> >... fossils are not equally but
> > _randomly_ distributed between the strata.
>
> That's the same thing--

No. "Equally distributed" means the distances between neighboring ones are
all equal -- which they aren't.

> if you sprinkle a thousand salt crystals over a
> meter square pan at random, you can sample a couple of areas, multiply
> by area, and come up with a thousand.

But to get a metaphor for the fossil record of terrestrial vertebrates, you
have then to take big buckets of water and smash them against random parts
of that pan.

> I mean, in statistics, we make
> solid assumptions based upon randomly distributed data all the time.

When the samples are large enough to tell us anything. Here we have Student
distributions, not Gauß ones.

> > We do not know if we have a parallel size increase, a parallel size
> > _decrease_, or _any_ trend _at all_ here. The sample is _too small_.
>
> So, back to my original qustion: at what point can we say anything at all?

When the sample will have multiplied in size.

> Another way of saying it, what statistical test did you use to conclude
> the data cannot reject the null hypothesis of no trend?

I can turn this back... what statistical test did you use to conclude it can
reject it? :-)

> As I understand it, birds have by far the worst fossil record--so, back at
> ya with your not enough data argument.

Oh, correct. But, given the... probable... position of Falconiformes in the
phylogeny of Neoaves, and the phylogenetic positions of the known K
Neornithes, there is so far no evidence for or against the presence of
Falconiformes in the K. The presence of Avisauridae, however, is certain.

> I frankly like my argument better,
> viz., old birds replaced by new birds for reasons having nothing to do
> with asteroid, but, rather, adaptations.

The oldest known neornithine is the ?anseriform *Apatornis* from the
Campanian, ~ 80 Ma ago. Means, Neornithes is at least 80 -- 85 Ma old. If
Neornithes was so much better than Enantiornithes and Ichthyornithidae and
*Apsaravis* and whatnot, then why did it take it over 15 Ma to outcompete
them? And how should it have happened in the first place -- what could the
adaptations that you mention be?

> > Pterosaur decline? First show me that there _was_ a pterosaur decline.
The
> > fossil record of LK pterosaurs is simply too bad to judge _this_ at the
> > moment. In other words: There may not be anything for you to explain!
>
> Pterosaurs were plentiful and gradually declined over the Cretaceous with
> only a few species appearing in the record of the latest K. Are you
> suggesting they enjoyed a last minute rebound at the latest K only to be
> KOd by asteroid?

Nope. I suggest that they may _not_ have gradually declined over the K.
Throughout the LK, there is no Solnhofen-Eichstätt, no Liaoning, no Santana
Fm, no Niobrara Fm even -- and over the latter part of the LK there's not
even a Cambridge Greensand! This means that, in strata from that time, we
_can_ only find big terrestrial pterosaurs if we aren't _very_ lucky -- no
matter how large the true pterosaur diversity was at that time.
http://www.cmnh.org/dinoarch/2003Jul/msg00405.html

> > > you can sustain more predation because
> > > your reproductive success is better.
>
> > Your reproductive rate is _worse_ when you're bigger.
>
> Size alone is not the determining factor, e.g., sauropods had bigger
> clutch than elephants.

All other things being equal, which they aren't when we compare sauropods
(or hadrosaurs) and elephants, bigger animals have a lower reproductive
rate. -- I don't know if more sauropods could hope to survive to maturity
than is the case with elephants. I doubt it, though.

> > At the K-T boundary, it seems... Enantiornithes and Ichthyornithidae, at
> > least, survived to the end.
>
> And became extinct due to as yet unknown forces.

Correct -- but the most parsimonious assumption about what that force was is
that they, too, were victims of the K-T impact. To postulate an extra cause
for their extinction means making one additional assumption.