RE: Climate Changes Mid-late Dinosaur era.

["Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>]

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> His Dark Lordship
>
> Twas 01-Jul-01, whence Daniel Bensen didst dost proclaimeth to me...
>
> >>> The reason being is that, as I understand it, we notice a significant
> >>> drop
> > in the Sauropod and gigantic plant eaters and a larger rise in the lower
> > to the ground plant eaters, such as Hadrosaurs, Anklyosaurids
> and others,
> > whilst the Carnivore side of the spectrum appears to be
> somewhat similiar
> > (although there is a shift from the classic Carnosaur to the Tyrannosaur
> > in the northern hemesphere.)<<
>
> > I don't know about that. Titanosaur sauropods were still hearty and hale
> > in South America and Africa during the Cretaceous. I have the feeling
> that
> > the changes in herbivore diversity during the time were due to the rise
> of
> > angiosperm plants (didn't HP Bakker say something of the kind). Anyway,
> > what is "global climate"? You can't say much for Earth's climate, at the
> > moment, except that temperature tends to hover between the freezing and
> > boiling points of water.
>
> Okay, well, maybe I'm just ill informed (most of my infomation comes from
> Discovery Channel and the Newspaper.)

Actually, Dan is a bit misinformed (or overstates his point).  In fact, a
heckuva lotta work has been done on paleoclimate work, particular in the
marine record.  Note that during the Late Jurassic and the Cretaceous we
begin to pick up some really good, essentially continuous, deep sea sediment
records.  This aids us in reconstructing oxygen, carbon, strontium, etc.
isotopic profiles, which are proxies for various aspects of climate.

For those interested in paleoclimate, there is a HUGE database available.
(In fact, there are far more paleoclimatologists then there are dinosaur
paleontologists, and they have lots of journals in which to publish).  Two
books that are relevent to the point here are:
Huber, B.T., K.G. MacLeod & S.L. Wing (eds.) 2000. Warm Climates in Earth
History.  Cambridge Univ. Press.

Barrera, E. and C.C. Johnson (eds.). 1999. Evolution of the Cretaceous
Ocean-Climate System.  GSA Special Paper 332.

There's plenty more out there, if you look.

> Anyway, I'll lay it out;
>
> What possibilities would there be of an "Ice Age" (or several of them)
> during the course of the Jurassic and Cretacious?

Almost none.  Ice Ages leave a very strong geological and geochemical
signal.  These have been well-studied way back to the Paleoproterozoic.
There are no proxies for Ice Ages within the mid-to-late Mesozoic.

> It just strikes
> me as odd
> that landbound creatures would develope feathers for the purpose of
> handling their body temperatures (since they probably weren't
> using them to
> fly) when scales would suffice (assuming it was continually warm.)

True.  However, there are some other possibilities:
        *Maybe feathers gave just a tiny bit advantage over scales (because 
even a
tiny advantage can be selected for)?
        *Maybe coelurosaurs developed these structures in the cooler uplands?
        *Maybe coelurosaurs were the first (only?) dinosaurs with a metabolism
elevated enough to require insulation?
        *Maybe insulation wasn't the primary selective factor in developing
feathers?
        *Maybe only coelurosaurs among reptiles developed the mutation that led 
to
the development of feathers?

> The other thing that bothers me is this Bering Strait. In more
> recent times,
> the only time North America and Asia have been connected was during an ice
> age;

[Head, wall, bang... ;-)]

See some relatively recent comments by myself and others in the dinosaur
list archives about the very problematic nature of the paleogeography of the
Mesozoic Bering region.  It is not that useful to compare the situation of
the late Cenozoic with these earlier connections.

Furthermore, there are earlier Tertiary Asian-North American (and also
European-North American) connections that existed in non-Ice Age intervals.

> now, while it's equally likely that there was a large rock formation
> between the two continents, that would basically mean that there was a
> constant flow of migrations between the two continents (which we
> don't seem
> to see that frequently either.)

Actually, there could have been only intermittent connections, for a number
of reasons:
        *Tectonic conditions may have been such that the connections were only
exposed occasionally
        *Tectonic conditions may have been such that there was NEVER a 
continuous
connection, but instead a series of islands which were periodically in
contact with some of the other islands, so that the migrants moved in a
step-wise fashion
        *Eustatic sea level changes are known throughout this interval: perhaps 
the
connection was tectonically continuous, but was of low topographic relief,
and thus periodically flooded and exposed.

> Some other things I was thinking was an Ice Age could explain the rise of
> the gigantic sauropods. Think about it; if you're going to have large
> quantities of creatures ranging from 30-90 ft in length, you are going to
> need a HUGE expanse of land, and imagine a 20 ton Sauropod trying to cool
> off on a hot day?

Interesting poings.  However, it is interesting that some of the largest
known sauropods (most notably _Paralititan_) occur in relatively equatorial
regions in times of high global temperature (as determined by other
proxies).

> The last thing that bothers me is the migration patterns of the
> Hadrosaurs.
> It seems they were migrating (or spread out, at least) between Australia,
> Antartica, North and South America, and probably Asia (I'm not sure if any
> have been found in Asia.) Now, it would make more sense that these intense
> migrations were possible due to the land bridges that would be above sea
> level due to expanding ice caps.

Land bridges (and other land connections) can form under various conditions,
and not just due to exposure due to glaciers.  Furthermore, remember that at
least some of the distribution of dinosaurs is due to the fact that some
groups evolved PRIOR to the break up of various supercontinents, so the
populations in different regions just went along for the ride. (And yes,
hadrosaurs are known in Asia).

> And of course, how would the dinosaurs exist in these conditions? Well, if
> they're warm blooded, they most likely could survice in cool temperate
> areas with little trouble, and if they had feathers, well...
>


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