I’m always deeply concerned when I see someone using a coordinate system with double logarithmic axes, drawing nice straight lines (sometimes even with correlation coefficients) through data points and then claiming a realationship of some kind.
The actual errors in the graph at the outer points are much higher than nearer to 0/0. But the human eye (and simple linear regression as well) does not recognize this easily and it thus easily fooled to “see” a correlation which might be there or not.

CU

@Sven, the more active an animal is, the more bone rebuilding is necessary. This is particularly critical once animals are running, because of the higher impact forces associated with it. Surprisingly, bone does cost a significant amount, metabolically, to maintain, with regular building and breaking down of the structure, and hard use results in quite a bit of turnover in bone structure. It’s nowhere near the metabolic cost of muscle or neural tissue, but even highly-active neurons only take around 40 times more energy per unit weight than bone.

I, also, would love to see some data on ratites here. This seems like a paper of its own, though; quite a bit of work, since fossil species would be needed to give any statistical power to the group data.

Seymour estimates that mammal bones receive around 54 times more oxygen than reptiles ones do. This all makes sense. When they’re doing exercise, mammals have higher metabolic rates than reptiles and they need more oxygen to fuel their activities

To fuel the activities of their femurs?
It doesn’t make that much sense.
Or is this supposed to be an index of bloodflow rates more generally?

Obviously missing but crucially important comparator group: birds.