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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 ).