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Dilkes, D.W. 2001. An ontogenetic perspective on locomotion in the Late 
Cretaceous dinosaur
*Maiasaura peeblesorum* (Ornithischia: Hadrosauridae). _Canadian Journal of 
Earth Sciences | Revue
canadienne des sciences de la Terre_ 38: 1205-1227.


  "Ontogenetic growth in the forelimb and hindlimb of the dinosaur Maiasaura 
(Ornithischia: Hadrosauridae) from the Upper Cretaceous 
(Campanian-Maastrichtian) Two Medicine
Formation of Montana is investigated by multivariate and bivariate 
morphometrics and the
biomechanics of beam theory. Results support a hypothesis of an age-dependent 
selection of stance.
Juveniles walked primarily as bipeds. As an individual matured, its predominant 
stance shifted to
quadrupedality. Within the forelimb, morphometric results show a probable 
allometric enlargement
of postural muscles, an allometric increase in the lever arms of protractor 
muscles, and an
increased robustness of the humerus to enhance its resistance to bending 
stresses. In contrast,
the hindlimb is characterized by a relative decrease in the resistance of the 
femur and tibia to
bending stresses. In addition, there is an allometric enlargement of the 
femoral fourth trochanter
and positive allometry of the lengths of metatarsals III and IV. The most 
likely explanation for
the different growth patterns is that the hindlimb was sufficiently robust at a 
young age to
accommodate increased postural and locomotory stresses through largely 
isometric growth, whereas a
behavioral shift to quadrupedality in older individuals necessitated an 
allometric response in the
forelimb. Osteological adaptations for weight-bearing in the manus include 
metacarpals that are
united firmly with a resultant cross-sectional shape that is resistant to 
bending and
hyperextendable joints between the metacarpals and first phalanges. It is 
probable that flexor
muscles that attached to the caudal surface of the metacarpals reinforced the 
reduced carpus and
lessened the likelihood of collapse during quadrupedality."

Jaime A. Headden

  Where the Wind Comes Sweeping Down the Pampas!!!!

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