RE: dino-lice

[Jason Brougham <jaseb@amnh.org>]

I've been trying to understand alvarezsaurid arms from an evo-devo perspective.

I looked into anchondropalsia and dwarf breeds of dogs to see what happens to 
pectoral morphology when genetic changes shorten the limbs.

Guess what I found? The long bones tend to retain their ancestral diameter, but 
they get much shorter, making them proportionately more robust. Much more 
importantly, the processes appear to hypertrophy, because they also stay large 
while the overall size of the bone reduces. . Below I have photographs of a 
bulldog skeleton and a coyote skeleton for comparison. I am not an expert on 
mammal osteology, but please tell me if you see what I see. The humeri have 
expanded proximal tuberosities, a hypertrophied deltoid tuberosity that has 
moved proximally, and enlarged epicondyles. 

The olecranon also looks longer and more rugose to me, do you agree? This is 
also true in the achondroplastic human skeleton I've linked to on the bottom 
there.

These details are strikingly similar to alvarezaurs.  This seems, to me, to 
suggest that the characteristic morphology of alvarezsaur pectoral anatomy may 
be a consequence of the genetic process that reduced it.

Now, it may appear that the processes for muscular attachment have enlarged 
from the ancestral state but they haven't. Not at all. They have only become 
RELATIVELY larger as the rest of the bone became smaller at a faster rate. I 
think that this has confused many workers, who may say that the limbs have 
become MORE robust when, in fact, they have only become wider relative to 
length  as, overall, they reduced to a tenth of their ancestral length.

I also read the Linhenykus paper this morning and checked the measurements on 
the forelimb. Linhenykus weighed the same as a large pigeon (C. livia), 450 
grams. It's hand was 17mm long, the same as your thumbnail, and the rest of the 
arm was about equal in length, so the whole pectoral limb was the same length 
as the last segment of your thumb. Wouldn't it take several kilograms of force 
to break the concrete - hard matrix of a termite mound? If so, if those tiny 
arms could somehow produce that much force, wouldn't the arm of Linhenykus push 
it strongly away from the termite mound before the mound cracked? The little 
fellow would be doing pushups!

Bulldog:
http://www.skullsunlimited.com/record_variant.php?id=5199

http://www.flickr.com/photos/57537109@N07/5362863697/

http://www.google.com/imgres?imgurl=http://3.bp.blogspot.com/_PGvSoaafXiI/S-2j3P43PII/AAAAAAAAIJ8/gRZlx0bAS6w/s1600/english-bulldog-skeleton.jpg&imgrefurl=http://terriermandotcom.blogspot.com/2010/05/complete-english-bulldog-skeleton-in.html&usg=__N1vR6SAuPKgT2JyzaXCkdDcNnEw=&h=758&w=900&sz=166&hl=en&start=0&zoom=1&tbnid=A505LOkHTaCfFM:&tbnh=133&tbnw=158&ei=wa6xTaDjMZGUtwfZ9KXlCw&prev=/search%3Fq%3Dbulldog%2Bskeleton%26um%3D1%26hl%3Den%26safe%3Dactive%26client%3Dsafari%26sa%3DN%26rls%3Den%26biw%3D1277%26bih%3D903%26tbm%3Disch&um=1&itbs=1&iact=rc&dur=380&page=1&ndsp=30&ved=1t:429,r:6,s:0&tx=116&ty=42

Coyote:
http://www.skullsunlimited.com/userfiles/image/variants_large_6748.jpg
http://www.skullsunlimited.com/record_variant.php?id=6748

Human achondroplastic olecranon:
http://www.boneclones.com/images/sc-279-a-lg.jpg

Dachshund humerus with enlarged proximal tuberosities:
http://www.google.com/imgres?imgurl=http://cal.vet.upenn.edu/projects/saortho/chapter_22/22F1.jpg&imgrefurl=http://cal.vet.upenn.edu/projects/saortho/chapter_22/22mast.htm&usg=__k3NO9fcKT910SIpghYpVD-DBe74=&h=350&w=640&sz=96&hl=en&start=0&zoom=1&tbnid=f94UlNhlQSrzBM:&tbnh=110&tbnw=202&ei=9K-xTd-yFJGjtgfa6YXpCw&prev=/search%3Fq%3Ddachshund%2Bhumerus%26um%3D1%26hl%3Den%26safe%3Dactive%26client%3Dsafari%26sa%3DN%26rls%3Den%26biw%3D1277%26bih%3D903%26tbm%3Disch&um=1&itbs=1&iact=rc&dur=450&page=1&ndsp=30&ved=1t:429,r:0,s:0&tx=92&ty=28

Comparison of human humeri and femora with and without achnondroplasia:
http://books.google.com/books?id=ctMRLv6oA8wC&pg=PA324&lpg=PA324&dq=Figure+17.11+achondroplasia&source=bl&ots=QeFMwvGMM1&sig=Zyabj9mLYi0C3M26XHJ2L5qv04Q&hl=en&ei=j7CxTZGdBYOEtgfN0-n5Cw&sa=X&oi=book_result&ct=result&resnum=1&ved=0CBsQ6AEwAA#v=onepage&q=Figure%2017.11%20achondroplasia&f=false

Jason Brougham
Senior Principal Preparator
American Museum of Natural History
jaseb@amnh.org
(212) 496 3544