Re: Emus a Model for Dinosaurs?

[Michael Skrepnick <palaeopaint@dinosaursinart.com>]

Thanks for referring the previous discussions on this in the archives.

On one hand, Christiansen and Bond are arguing femoral circumference not 
adequate to support knee driven locomotion in Caudipteryx, on the other 
(Holtz commentary on Farlow, Ruben, et al ) comment on both lack of a fourth 
trochanter ( a necessary attachment for caudofemoralis / hindlimb retraction 
in acetabulum driven locomotion in theropods ) and hindlimb segment ratios 
favoring a knee driven performance. Would not the weight of argument 
potentially lean toward a knee driven condition in spite of a more 
"plesiomorphic" femoral condition in Caudipteryx ( perhaps the more robust 
femora in modern birds is related to added evolutionary response of stress / 
loading / compression in avian forms, a result of lift off / landing, etc. . 
.than in 2ndary flightless taxa that might revert to,or may have simply 
maintained a more ancestral condition throughout) wherein locomotion is 
strictly limited to simple terrestrial movement? Lack of a 4th trochanter 
would seem to be a far more overwhelming obstacle to performing traditional 
bipedal theropod locomotion ( where then in fact is the origin for a 
caudofemoral retractor in Caudipteryx? ) than the alternative, a primitive 
knee driven movement supported by slender femora. . . essentially, does a 
missing 4th + "convergent?" knee driven locomotion trump the lack of a 
derived ( if even necessary? ) robust femor ?

I'm actually playing devil's advocate on this, as my painted restoration of 
Caudipteryx a number of years back was based on the more conventional rather 
than derived hindlimb mechanics in birds ( existence of a 4th trochanter or 
lack thereof never came up in discussion between Phil Currie and myself at 
the time I executed the painting. . .  I don't think the first specimen was 
even fully prepared at the time and I was much more focused on the skull, 
forelimb and feathers, than in the balance of the postcrania ).

Mike S.