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I was watching a presentation by Dr. Jessica Theodor [1] who discusses (at 38:10), among other things, the skeletal structure of dinosaurs vs. mammals. "Dinosaurs have way lighter skeletons, which means that for the amount of material they can be bigger. If we start to look at sauropods, they have this really interesting set of structures, these big holes in their vertabrae... it allows you to build a lighter, stronger skeleton. Mammals can't do that. It's not how we build our bones."

Why don't mammals do this? Are there fundamental trade-offs which make our (apparently) weaker, heavier bones better, or is it just chance that we haven't matched this development?

(Of course I'm open to the possibility that I misunderstood the talk, or that it was simplified to the point of inaccuracy on this point.)

[1] Jessica Theodor, Being Giant: Why are mammals not as big as dinosaurs? (2015)

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  • $\begingroup$ If one wonder about why mammals in general are so much smaller than dinosaurs, I think the answer lies somewhere in that we simply have not gone down the competitional path of pure size. Just in the same way as we generally don't have evolved to use flight (except for bats) or live an aquatic life (except for whales and dolphins). One could say that we don't have bone structure suited for extreme growth and size just like we don't have bone structure suited for flight. $\endgroup$ – Alex Mar 27 '16 at 7:33
  • $\begingroup$ That is because, they have twenty one percent of body mass than minimum skeletal volume. In Dr.Bill Sellers's journal "Biology Letters", it was said that they laser scanned Brachiosaur as they were estimating it to weigh about 80 tons. But, it actually weighed 23 tons which is relatively light. $\endgroup$ – Komal stavita Mar 27 '16 at 16:15
  • $\begingroup$ @Alex: It's more like "why don't mammals have lighter skeletons, following dinosaur's plans". $\endgroup$ – Charles Mar 27 '16 at 16:44
  • $\begingroup$ @Alex: But also remember that what we know of dinosaurs (and extinct mammals) comes only from fossil remains that have been found. Until relatively recently, big bones sticking out of the ground were a lot more likely to have been discovered than little tiny ones. I suspect, though I don't know for sure, that larger bodies were more likely to have become fossils in the first place. $\endgroup$ – jamesqf Mar 27 '16 at 18:05

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