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Hey, it's out a little early!! Here's the news on the new T. rex growth paper!!



Okay, it turns out that Nature launched its website a tad earlier than I
thought they would, so now I can speak about it.

First, the paper itself:
GREGORY M. ERICKSON, PETER J. MAKOVICKY, PHILIP J. CURRIE, MARK A. NORELL,
SCOTT A. YERBY & CHRISTOPHER A. BROCHU. 2004. Gigantism and comparative
life-history parameters of tyrannosaurid dinosaurs. Nature 430, 772-775.

The Method:
Erickson et al. measured LAGs (lines of arrested growth) from
non-loadbearing bones of a number of tyrannosaurid specimens of T. rex, A.
sarcophagus, G. libratus, and D. torosus (& sp. 2?), in order to estimate
age at time of death.  (They chose sections that showed little sign of
reworking).
They ALSO estimated the mass of the same individuals by various allometric
equations, primarily derived from Currie's recent Canadian Journal of Earth
Sciences paper. (Incidentally, their range for T. rex is 29.9 kg for the 2
year old Jordan theropod specimen to 5654 kg for the 28 year old Sue).
They then plotted the age and mass estimates for the individuals, and
derived ontogenetic curves for each species.

The Results:
All the tyrannosaurids plotted on the same type of curve, with a juvenile
stage, a period of rapid growth, and a levelling off (adulthood).  The
latter is represented histologically by extremely closely spaced growth
lines, showing the essential cessation of growth. Sue is the only fully
grown T. rex in their sample, and it apparently stopped growing about 9
years before death.
In the case of T. rex, juvenilehood (and a mass less than 1000 kg) lasted
about 12 years; "adolescence" (or at least the period of rapid growth: we
can't say for the moment when fertility begins) from ~12 to ~18-20, and then
adulthood.  In this aspect, it is very human-like.
The other tyrannosaurids have fewer data points, so the onset of adolescence
is less certain.  The big mounted FMNH Daspletosaurus (FMNH PR308, mass
estimate 1791 kg) was fully grown, as was the Albertosaurus specimen RTMP
81.10.1 (mass estimate 1142 kg).
What really stands out about Tyrannosaurus is its rate of growth during
"adolescence": about 2 kg/day, or about 4 times what the other tyrants had.
So it achieved its tremendous size by growing faster, not by growing for a
longer period of time.

So Lancian herbivores must have been dying at a substantially higher rate to
supply all those scavenging T. rex... :-)

The Future:
I have been informed that Erickson et al. want to do the complementary study
on Tarbosaurus, which seems natural.  It might also be interesting to see
the same study for ceratopsids and hadrosaurids with similar abundant
material.

The DML Exclusive:
Yesterday, Greg Erickson phoned me to let you (the DML) know about a mistake
that you, and not many others, would catch: the cover.  Check it out here:
http://www.nature.com/cgi-taf/dynapage.taf?file=/nature/journal/v430/n7001/i
ndex.html

There is a mistake in it.  The artist, attempting to use photoshop or
something similar to correct the deformation of the skull of Sue, wound up
creating a single midline premaxillary tooth!!  Now THAT'S an autapomorphy!!
:-)  Erickson did catch it, and had a new image made, but somehow the
original (incorrect) version was used.  He wanted to say to you that he
feels sorry about that, and to let you know that he's not crazy...

There's a lot of interesting implications for this study: in fact, expect to
see some at SVP...

More later,

                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