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RE: More about Erickson et al. 2004



> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Mickey Mortimer
>
> A few things.
>
> I thought AMNH 5428, AMNH 5432 and USNM 12814 were Gorgosaurus, not
> Albertosaurus.

Good catch (although AMNH 5428 and USNM 12814 are the same specimen:
transferred from the AMNH to the USNM in (I believe) the Barosaurus deal).
The AMNH retains some of the gastralia, and maybe some other elements; most
of the body is on display on the wall at the USNM.

The net result is the transfer of two points to the Gorgo curve from the
nearly identical Alberto curve, making the former more secure but the latter
less so.

As for why neither the authors nor any of the reviewers didn't catch this,
the simple explanation is... um... hey, look at that over there!!!  What's
that behind you? [hoping to distract people]

> I also thought LAG's were unreliable for absolute age
> measurements, as they
> could be caused by trauma and seasons of unusually low nutrition
> too.  But I
> don't really follow the histological lit...

LAGs are used as the best possible marker for age, but it is true that one
can generate LAGs in the broad sense by other causes.  Best port in a storm,
really.

> Could the aberrant growth trajectory of Tyrannosaurus be due to a few
> species of different sizes being grouped together accidentally, ala
> Olshevsky's hypothesis for Tarbosaurus?

"Aberrant"? No.  Different, yes.  In dinosaurs, maximal growth rate scales
with adult body size (as shown by Erickson et al.'s 2001 paper).
Tyrannosaurus, as a much larger critter than its relatives, has a higher
maximal growth rate. In fact, doing a quick look at the 2001 paper, a 5 t T.
rex should have something like a 2 kg/day maximal growth rate.

If the selection of specimens used here actually represented a variety of
adults and subadults of tyrannosaurines of different sizes, it is remarkable
that they fall on a single nice logistic curve rather than (as would be
predicted) a series of curves of different slopes during the exponential
growth phase.

To put things in perspective:
*The slope of the maximal growth part of the curve isn't surprising for T.
rex, although the other tyrannosaurids are slightly lower than expected
based on the previous work on dinosaurian growth.
        -However, all these slopes are weird if you cling to a crocodilian-style
biology for dinosaurian growth...
        -Also, these help reinforce the idea of determinate growth in at least 
many
dinosaur clades.

*The maximal life span of tyrants is also not wholly unexpected based on
recent work, but is unexpected if one were expecting either an elephant-like
or crocodile-like life history.

*What *IS* weird for tyrants compared to other dinos, and perhaps for T. rex
compared to other tyrants, is the longer childhood, delaying the exponential
growth phase until their teens (rather than starting around 5 or earlier).
        -Now, granted, the non-avian dinosaurian record for this is sparse:
Shuvuuia, Psittacosaurus, Megapno... *cough* *choke*, er, Syntarsus,
Massospondylus, Maiasaura, and Apatosaurus for Erickson et al. 2001, the
four tyrants here.  More data is need to secure this. Folks looking for a
Masters Thesis might consder doing this for one or two species; for a Ph.D.,
perhaps a much larger survey.  And pterosaurs might be useful, too. And
non-mammalian therapsids.  And... well, obviously this technique opens a lot
of opportunity for further study.

So, the "live fast and die young" idea applies to all non-avian dinosaurs,
so far as has been determined. The tyrant way is "live like a kid for a long
time, then grow fast, than die young".

Incidentally, the idea that Neanderthal's (and H. erectus, etc.) "lived fast
and die young" is actually only in light of our own species truly bizarre
life style of living for an exceptionally long time as a kid (i.e., a
delayed adolescence) and a very prolonged life span for a mammal of our
mass.  Homo erectus et al. by and large simply kept with the typical primate
profile: it is us who are the weird ones.

                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