Now follow me closely.
If the pressure is higher than a certain level the bones will break.
Therefore, for an animal not to break its bones when the mass goes up by a certain factor let's say a factor of four in order for the bones not to break d squared must also go up by a factor of four.
That's a key argument in the scaling here.
You really have to think that through carefully.
Therefore, I would argue that the mass must be proportional to d squared.
This is the breaking argument.
Now compare these two.