RE: Bakker's Brontosaurus and Late Cretaceous populations

[Denver Fowler <df9465@yahoo.co.uk>]

> 3) There is no evidence from the Javelina Formation
> that tyrannosaurids 
> fed on sauropods.


>  Considering the small size of the specimen compared
>to T. rex, that isn't surprising. Alamosaurus was too
>big to overcome, except for juveniles. Maybe that was
>why Alamosaurus was so common in the Javelina but not
>in the units where T. rex apparently is known, the
>McRae and North Horn.

You can't really state this because there is not a
enough published material from the North Horn and
McRae to look at percentages. Anyway, I think
taphonomic bias is more an influence in preservation
percentages than actual life abundance, at least in
large-bodied animals.

Toothmarked dino bone is not particularly common in
the fossil record, and when it is found, is more
likely indicative of carcass processing, which doesn't
necessarily indicate active predation. I've not seen
any rehealed injuries for Alamosaurus material, but
then, I don't recall that many for the whole sauropod
record. There are certainly a few tail pathologies
I've seen, but nothing on the scale that we see for,
say, Iguanodon.

That said, bone surface preservation in the
Naashoibito at least, is not generally good enough to
preserve fine tooth scratches, although it might
preserve deeper punctures, if they were present.


> 
> >So there's a very
> > strong argument for declining diversity before the
> > K-T
> > boundary... at some point in the Edmontonian,
> 
> 
>  Maybe at the boundary between the Edmontonian and
> Lancian. AFAIK, Hypacrosaurus is still abundant in
> unit 4.
> 

What's the ref for this? 

By my understanding, there is no decent evidence of
Lambeosaurines in North American Lancian strata. The
only possiblity is Boyd & Ott 2002.


> 
> 
> > very
> > probably associated with onset of the final
> > regression
> > of the WIS.
> 
> 
>    Why?  There had been transgression and regression
> prior to that, in the Campanian, when diversity
> seems
> to have peaked. Logically, a regression should have
> favored the more inland types like lambeosaurs and
> saurolophines but there appear to have been few if
> any
> left in the Lancian.
> 

Assuming the 'inland' preferences of particular taxa
are real and not just a form of preservation or
temporal bias. 

It's just a hypothetical point but something happens
pre-Lance/Alamosaurus that shakes up the latest
Maastrichtian faunas. You can hypothesise what that
is, but the last major (mid-late
Maastrichtian)regression cycles are pretty severe and
greater in extent than the previous cycles. It
wouldn't be unreasonable to postulate a corresponding
greater influence on the fauna.

 > 
> >(until the boundary of course).
> > Historically, you could argue that we see a small
> > diversification amongst Chasmosaurines; instead of
> > just one species (as was the status quo throughout
> > the
> > N. Am Late K), there are two. But this is false
> > since
> > both Torosaurus and Triceratops are present in the
> > Alamosaurus fauna,
> 
> 
> Triceratops was present in the Alamosaurus fauna? It
> may have been coeval with one or more Alamosaurus
> bearing units which yield T. rex but AFAIK not
> itself
> in that environment.
> 

yeah, well... from new material it would seem there
are two ceratopsians. Type I is most similar to
Torosaurus, and is probably, but unconfirmable as, T.
utahensis (my preference), or T. latus depending on
whether you lump or split (and the stratigraphic
implications of doing so; my main objection). Type II
initially at least, seems most similar to Triceratops.
This isn't really unexpected, but TBC.

Denver.



                
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