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Re: Do not misunderestimate the king was Re: Evolution of tyrannosauroid



(Reposted in plain text for Ken.)
 
Thanks, David. There is much new data in Lipkin and Carpenter's paper in  the 
T rex book due out soon. The evidence includes various pathologies (stress  
fractures, fractures, muscle avulsions of the humerus) that it it clear that 
the  forelimbs are placed under a great deal of stress. Remarkably, the 
incidence (as  %) of these pathologies of JUST the forelimb bones (including 
scapula, 
coracoid,  and furcula) is highest of any theropod. Although Farkes' caution 
is a good one,  it is important to look at what the entire "system" says, 
rather than one  feature. Thus, while the enlarged peroneal process (single 
feature) may not  correspond to the grasping power of the peroneus longus in 
some 
lemurs,the  entire hindlimb (a "system") clearly does show an adaptation for 
grasp while  climbing. Thus, the new evidences from the entire forelimb system 
of 
T rex show  the forelimb was used actively.

Ken

Kenneth Carpenter,  Ph.D.
Curator of Lower Vertebrate Paleontology
and Chief  Preparator
Department of Earth Sciences
Denver Museum of Nature &  Science
2001 Colorado Blvd.
Denver, CO 80205 USA

ph: 303-370-6392/  or 6403
fx: 303-331-6492

for PDFs of my reprints, info about the Cedar  Mtn. Project, etc.  see:
https://scientists.dmns.org/sites/kencarpenter/default.aspx
for fun,  see  also:
http://dino.lm.com/artists/display.php?name=Kcarpenter

-----Original  Message-----
From: owner-DINOSAUR@usc.edu on behalf of David  Marjanovic
Sent: Sun 12/30/2007 6:27 PM
To: DML
Subject: Do not  misundreshtmate the king was Re: Evolution of tyrannosauroid 
bite  power

> "Strong" is a relative term. Carpenter and Smith (2001)  estimated the 
> maximum force capable of being generated by the M. biceps  in T. rex to be 
> about 1955 N, or about 199 kg (440 pounds) per  arm.

As you mention, this is just the biceps alone.

Furthermore,  the shapes and the cortex thicknesses of the arm bones are 
stupefying, and  the scapulocoracoid is large, even though the arm is not.

Here are a few  lines from Table 9.1 of Carpenter & Smith (2001); I recommend 
to compare  the measurements (all in cm) to your  own:

MOR 555  (gracile)            FMNH  PR 2081 (robust)
humerus  length                 37.7                             37.3
humerus distal width         8.4                                 8.9
ulna  length                         >  19.5                         21.9
ulna prox. anteropost. length  6.7                         7.1
ulna width  prox.                 6.4                             4.4
radius  length                     >  15.1                         17.3
radius prox. anteropost. length  4.2                     5.2
radius prox.  width                 2.9                         3.7
metacarpal II  length             9.4                         10.9
metacarpal II prox. anteropost. length  -             4.1
metacarpal II prox. width         -                         4.9
metacarpal II distal width         -                         3.9

"Finally, the least amount of forearm motion is that of *T. rex*  (fig. 
9.13), which has short arms and the very low MA [mechanical advantage]  of an 
FBS [force-based system]. The limited ROM [range of motion] and short  lever 
arm of the forelimb provided a very stable platform for the very  powerful M. 
biceps. This indicates to us that the forelimbs were used to  hold a [sic] 
struggling prey. In support of this interpretation, we note the  pathology 
along the medial side of the humerus in FMNH PR 2081. The [huge]  site of 
damage corresponds to the medial head of the M. triceps humeralis,  which 
serves to adduct and extend the lower arm. As noted above, the  pathology is 
characteristic of partial avulsion caused by abnormally high  stress loads. 
Such loads might occur while clutching a large, struggling  animal, such as 
an adult hadrosaur (see Carpenter in press)[.] Indeed, the  straight shaft of 
the humerus, as compared with that of *Allosaurus* (see  Gilmore 1920), is 
precisely what is expected for maximum strength per unit  mass (Bertram and 
Biewener, 1988). Such conditions occur where the bone must  resist axial 
compression, as it would do in this case with the powerful M.  biceps (see 
fig. 9.12). Furthermore, the very low K [ratio of marrow cavity  radius to 
bone radius] and R/t [bone radius to cortical thickness] values  for the 
humerus, ulna, and radius indicate bones selected for ultimate  strength or 
impact loading. Finally, to ensure that the struggling prey not  escape while 
the mouth is attempting to kill it, the two ungual claws point  somewhat 
inward (fig. 9.13C) so that they do not slip out of the prey  easily." 
(Carpenter & Smith 2001:112sq.)

Clearly, there was  _strong_ selection _for_ power, even though the arms 
(except the hands) are  short (not small -- just short). Carpenter & Smith 
even suggest that the  arms are short in order to bring the distal ends of 
the bones closer to the  muscle attachment sites on the same bones, 
decreasing speed and increasing  force. And the force was with *T. rex*, even 
though not enough of it to  prevent the abovementioned partial tendon  
avulsion.



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