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<<But arboreality does not well explain the large sternal plates seen in 
small advanced theropods. For two reasons. First, climbers do not have 
such large bird-like plates.>>

Juvenile Opisthocomus (hoatzin) individuals have large sternal plates 
and a similiar myology to flying birds.  No mammals have pectoral 
muscles attached to their sternum.  

<<Next, arboreal animals tend to have reduced(!) limb muscles (Grand 
1977), so they do not need large sterna.>>

Again, no birds other than juvenile Opisthocomus climb, and it has a 
typical avian myology.  Mammals do not have large muscles attached to 
their sternum.  I am not sure sure about lepidosaurs, but they (and 
mammals) are different from both birds and dinosaurs in that they are 
quadrapedal so the forces of gravity are equalized in a different 
fashion than bipedal climbers.  And according to Bock and Miller, picine 
hindlimb and pedal musclature is very strong.  

<<Increased attachment area for flight muscles,>>

Or climbing muscles in bipedal animals.  

Again, this whole secondarily flightless theropod issue is not supported 
by the known phylogeny of theropods and the flight characters can be 
explained by arboreality or other processes.

Read Bock and Miller 1959 everybody.

Matt Troutman  

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