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RE: More about Erickson et al. 2004 and RE: Delayed "growth spurt" in T. rex



> From: Jaime A. Headden [mailto:qilongia@yahoo.com]
>
> Tom Holtz (tholtz@geol.umd.edu) wrote:
>
> <So, perhaps, Tyrannosaurus was functionally a different animal
> ecologically (one might dare say a "Nanotyrannus"... :-) as a youngster
> than as an adult.>
>
>   Speaking of, was the type of *Nanotyrannus* tested? Perhaps the final
> nail in so-called adult Nano?
>
Neither the Nanotype, nor "Jane", were part of the database in Erickson et
al. As this requires destructive study of the specimen (i.e., slicing and
dicing), I'm not certain if the Cleveland Museum would be too keen on the
Nanotyrannus specimen being so disturbed. ("Jane" is a different story,
since there are lots of postcranial elements available).

But yes, this method has great potential for resolving the adult status of
problematic specimens in this and other dinosaurian taxa (such as some of
the hadrosaurs and ceratopsians, for instance).

The database does show a new RTMP specimen of Albertosaurus which was only
about 2 years old and estimated mass of 31.6 kg (one of the specimens from
the reopened Barnum Brown quarry).

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Phil Bigelow
>
> Anyone care to speculate on why the "growth spurt" phase in the _T. rex_
> young occured 10 years AFTER the animal's birth?  Logically, such a
> growth spurt would have taken place from birth through adolescence.
>
> Are there any modern analogs to this developmental style?

Ummm... humans?

Erickson et al. (2001. Nature 412:429-433) previously mention that many
vertebrates have a sigmoidal growth curve. However, as you point out,
tyrants seem to start later than most critters, even other dinosaurs: the
Psittacosaurus, Maiasaura, and Apatosaurus curves in Erickson et al. (2001)
has the "growth spurt" beginning around 5 years old.

Mere speculation here, but if there were some selective factor favoring some
attribute of the animal when it was a relatively small-bodied animal (e.g.,
Currie's hypothesis of different jobs for different ages within a tyrant
population) that might favor delay of the onset of growth.

I am given to understand that the growth curve of elephants (except for
their long adult lives) is similar to the T. rex curve, excepting of course
that elephants start as MUCH bigger animals, but I've not actually seen
those curves plotted out.

                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