[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

RE: Tyrannosaurus was not a fat boy or girl



  I thought the point of all this was some sort of dependable mass estimation?

  Now, it is good to note that among mass estimations, some estimates work 
better than others, with volumetric immersion not being high on the list, but 
long-bone circumference not as well. Sander et al. note, with help from a few 
other sources, that spline and segment scaling is likely the best method, but 
this requires computer technology. They write:

    "Mass estimates are generally either based on some measure of volume that 
is then converted into body mass or on a biomechanical approach, e.g. using 
long bone circumference (Anderson, Hall-Martin & Russell, 1985; corrected by 
Alexander, 1989; see also Packard, Boardman & Birchard, 2009; Cawley & Janacek, 
2010). Each method has different sources of error, and the main advantages and 
disadvantages of some of these methods have been intensively discussed in the 
literature (Colbert, 1962; Lambert, 1980; Schmidt-Nielsen, 1984, 1997; Anderson 
et al., 1985; Haubold, 1990; Gunga et al., 1999; Paul, 1997b, Henderson, 1999; 
Seebacher, 2001; Motani, 2001; Christiansen & Fariña, 2004; Mazzetta et al., 
2004; Foster, 2007; Packard et al., 2009).
  "One method for estimating body mass based on reconstructed body volume 
involves three-dimensional photogrammetry of actual skeletons using a laser 
scanner (Gunga et al., 1999; 2007, 2008; Bates et al., 2009; Stoinski et al., 
in press). Advantages of this approach include that geometrical calculations 
can be made easily based on the respective body parts, and that different 
hypothetical body shapes, resulting in different body masses, can be tested 
(Gunga et al., 2007, 2008; Bates et al., 2009; Stoinski et al., in press). 
Segment masses can also easily be obtained. Finally, with photogrammetrical 
methods, measurement errors are
also partitioned and do not affect the entire estimate. In
mass estimated based on long bone circumference, on the other hand, whenever a 
local measurement error occurs (e.g. due to deformation during fossilization), 
the direct result is that the total mass of the animal is calculated 
incorrectly. A similarmethod is based on creating 3D skeletal mounts from 
digitized bones, and using these instead of laserscanned mounts (Mallison, 
2007, in press b). This allows easy correction of errors in mounts and thus 
revisions.
  "Recent work by Wedel (2005) suggests that volume-based estimates are 
generally too high because they are based on a specific density in a living 
sauropod of 0.9–1 kg L−1, as in modern crocodilians. However, it is becoming 
generally accepted that because of their extensively pneumatized axial skeleton 
(Perry, 2001; Henderson, 2004; Wedel, 2003a, b, 2005, 2009; Schwarz & Fritsch, 
2006) living sauropods probably had a specific density of about 0.8 kg L−1 
(Wedel, 2005), which is more like that of birds (0.73 kg L−1, Hazlehurst & 
Rayner, 1992). Wedel (2005) accordingly suggested that volume-based mass 
estimates published before the modern consensus on pneumatized skeletons should 
be reduced by about 10%."
[Sander et al., 2011, pg.120]

  Based on some of Paul's writings, a bivariate immersion-circumference method 
is implied and used, but I do not know if this has been an acceptable 
methodology for mass estimation. Nonetheless, it should be known (as I point 
out here: http://qilong.wordpress.com/2011/10/19/walking-sledgehammers/ ) that 
many other immersion or volumetric mass estimation models are based on what are 
essentially ultra-slim bodies, and the recent work by Hutchinson et al., 
Mallison, and Persons and Currie shows that these estimates may be way off. As 
they also involve the issues of segment estimation, simply cutting the models 
up and beefing up or slimming down other elements as needed may create a more 
synthetic and realistic range of measurement without having to do things like 
reduction by percept by _estimating_ segment volume. You get the volume 
straight off, simply by pulling the models apart and correctly estimating the 
mass by volume.

  Note that in even the most recent work by Paul, top-down view of the 
skeletals with fleshed outlines still show slimmed caudofemoralis musculature, 
and as should be apparent by now, these are heavy muscles that modify weight 
distribution and the center of mass. These influence the posture and walk-step 
cycle, and should be taken into account. This is why I, while I don't need to 
_agree_ with Hutchinson et al's specific conclusions when present, I would take 
the modeling over that of Paul's. It is even more apparent when taking living 
animals more seriously, such as the flexed knee, the non-vertical femoral, 
etc., of virtually all reptiles, mammals and birds.

  The hardest part will, I think, be making one's reconstructions without 
vertical femoral as a norm. I wonder if Paul should spend his influence on the 
artists who follow his work so avidly for its skill and actually modify the 
work to show more reasonable or realistic trends. In this way, art may have to 
give way to science _just a tad_.

Cheers,

  Jaime A. Headden
  The Bite Stuff (site v2)
  http://qilong.wordpress.com/

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


"Ever since man first left his cave and met a stranger with a
different language and a new way of looking at things, the human race
has had a dream: to kill him, so we don't have to learn his language or
his new way of looking at things." --- Zapp Brannigan (Beast With a Billion 
Backs)


----------------------------------------
> Date: Sat, 22 Oct 2011 19:42:08 -0400
> From: GSP1954@aol.com
> To: dinosaur@usc.edu
> Subject: Re: Tyrannosaurus was not a fat boy or girl
>
>
> In a message dated 10/22/11 6:19:07 PM, archosauromorph2@hotmail.com writes:
>
> << What happened to the evidence for a ~12-tonne T. rex discussed on page
> 345 of Predatory Dinosaurs of the World?  >>
>
> Oh, who pays attention to that silly old book nowadays?
>
> I know I don't.
>
> At least the parts that have since proven errant.
>
> As far as I currently know no Tyrannosaurus postcrania dramatically exceeds
> the size of Sue. If someone knows this is not correct please let us know.
>
> Greg
>
>
>
> </HTML>