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RE: New here, General Qs

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Bradley Fischer
> 1. How does this area of the brain compare with other
> Tyrannosaurids and the
> evolutionary forebears?

Extremely good question.
Oh, and you want an answer? :-)  Okay, so do I, and so do a lot of people.
Unfortunately, as of present, complete reconstructions of the brain
(including the olfactory bulbs) of other tyrannosaurids, of basal
coelurosaurs, and of large non-coelurosaur dinosaurs are not published.
There are partial reconstructions for some (like Carcharodontosaurus), but
these lack the olfactory lobes.

So, in fact, this leads to an interesting puzzle.  Yes, the olfactory bulbs
of T. rex are larger, but are they *unexpectedly* large.  That is, are they
unusual in size for a tyrannosaurid?  We don't know.

Furthermore, are they larger than those of other giant theropods?  We don't

Additionally, are large olfactory bulbs like this what one would expect by
allometry (differential growth of different body parts)?  Again, we don't

(Incidentally, good dissertation topic for someone with access to specimens
and a CAT scanner...).

> 2. How does T-Rex brain structure compare with Dromeosaurs and
> other small
> theropods?

Endocasts have been made for ornithomimosaurs, troodontids, and
dromaeosaurids.  All these show higher encephalization quotients than
Tyrannosaurus (which in turn has a higher EQ than basal tetanurans: note
that EQ studies have generally not taken the volume of the olfactory lobes
into account).  Deborah Wharton's SVP presentation a few years ago did show
a reduction in the olfactory lobes in some non-avian maniraptorans.

> 3. Do modern predators have large olfactory lobes? I note that
> Dr. Holtz's
> pursuit and bite theory and he compares T-rex to wolves. Canids
> traditionally have a very keen sense of smell and I am hoping
> that someone
> here can discuss the size the olfactory lobe on canids as well.

Well, that is a body of literature I haven't even opened yet, but even going
to basics one might predict that a large olfactory lobe means a good sense
of smell.  Period.  How that sense of smell gets used is based on the rest
of the animal...

> On a different topic: In a fairly recent issue of Scientific
> American, there
> is an article about the evolution of feathers and their beginnings on
> theropods. The article suggests that even T-rex probably was feathered.
> Only problem I have with this theory is that the subject sample
> is all from
> china and they found no large theropods with feathers. Anyone care to
> comment on this? Am I off on my thinking?

The logic here is that a) the only known integuments for compsognathids,
oviraptorosaur, therizinosauroids, and dromaeosaurids are from these units
in China, and b) all these share either simple "protofeathers" or
honest-to-goodness feathers, than c) given no additional data to the
contrary, the simplest explanation is that their common ancestor shared the
derived trait of "feathers".

Consequently, without evidence to the contrary, the simplest explanation is
that all descendants of that common ancestor also inherited this trait.

This is precisely the same logic used to assert that chalicotheres or
Diprotodon had hair, even though we have never (as far as I know) found
specimens of chalicotheres and Diprotodon showing their integument.

There remains the possibility that large coelurosaurs did indeed lose this
feature, but one would need to find positive evidence to the contrary to
sustain this.

As for why all the feathered Cretaceous dinos found so far have been a)
relatively small (although Beipiaosaurus is still a good sized animal) and
b) from China: this is due to the fact that at present the only known strata
preserving this fine a level of detail from the Cretaceous are lake deposits
in China, and lake deposits typically only preserve small bodied creatures.

An interesting comparison is the Messel locality in Germany, which preserves
exquisite detail of soft tissue in small animals from the Eocene.
Correlative strata in other parts of the world at this time lack the style
of preservation in Messel, and (sadly) no really large Eocene mammals or
birds have been found in Messel (even when their skeletons are known from
other localities).

Hope this helps,

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796