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Re: Emus a Model for Dinosaurs?



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.