Figure 1
From: The bone microstructure of polar “hypsilophodontid” dinosaurs from Victoria, Australia
Medullary drift comparison between a hypsilophodontid femur (NMV P221151) and tibia (NMV P186334). (a) In hypsilophodontid femora, there was pronounced ontogenetic change in transverse diaphyseal shape, as indicated here by the green rings which trace the outlines of annual CGMs and the periosteal surface. The border of the medullary cavity is traced in pink to illustrate directional medullary drift, which partially obliterated the first three CGMs of NMV P22151. (b) Compared to the transverse diaphyseal shape of the femur NMV P22151, the tibia NMV P186334 underwent less annual ontogenetic shape change. The green rings trace the outlines of annual CGMs and the periosteal surface, while the outline of the medullary cavity is traced in pink. Medullary cavity enlargement is less directional compared to that of the femur, and only partially obliterates a single CGM in this case.
