RE: body size and teeth

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

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> r.diesel@t-online.de
>
> Sorry, this was only part of the email.
> You are right! I have to admit. I am not a dinosaurier specialist. WE are
> interested in the question what limits body size in animals. So it should
> read dinosaurs instead sauropods.
>
> Rudolf Diesel
>

Many hypotheses have been suggested for the larger total body size of
dinosaurs than terrestrial mammals.  Some include:
1) Lower metabolic rate of adult dinosaurs vs. adult mammals, so that a 3
tonne ceratopsian required only about the same amount of food as a .5 tonne
bison; possible, but the metabolic rates of dinosaurs are rather hard to pin
down, and the evidence shows that Mesozoic dinosaurs growth rates during the
juvenile years were in the marsupial - precocious bird ranges.
2) Mammalian limits are due to mammalian reproduction modes. In placental
mammals gestation period scales against body size, so rhinos have about 1
year gestations, elephants have 2 years, and giant mammoths and
indricotheres would have 3. And at the end of that stressful time, only one
or two offspring are produced.  On the other hand, Mesozoic dinosaurs of all
sizes had clutches of 12 or more (and an even higher rate if more than one
clutch was possible per breeding season). This means that larger body size
would not put the same reproductive stress on dinosaurs as on mammals.
3) Higher productivity in the Mesozoic. Highly speculative, but O2 and CO2
levels were elevated in the Mesozoic with respect to Cenozoic atmospheres,
possibly supporting greater productivity in plants, possibly providing more
food per unit time available for herbivores.

Hope this helps.  (Personally, I think that #2 is the most important of
these).

                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