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Gigantic sauropod dinosaurs had relatively small heads (and consequently small mouths) in comparison to their overall body mass.

In the book "Dinosaur Odyssey: Fossil Threads in the Web of Life" (by Scott D. Sampson) the author says (on pp. 218-219) that

The sheer size of the biggest sauropods has long shrouded them in mystery. How could such gigantic animals with such small heads (at least compared to their body sizes) manage to consume enough food to sustain themselves? The mystery deepens when we look inside the mouths of sauropods. Cows are typical of big mammalian herbivores (e.g. elephants, deer, antelope, and the like) in possessing oversized teeth well suited for processing large amounts of fodder. Chewing serves not only to break food-items into bite-size chunks' it also grinds up the plant matter and begins the process of digestion by making the bits of vegetation more susceptible to chemical attack. By comparison, sauropods have puny teeth well suited to tearing or, at best, slicing, but not for grinding.

(emphasis added)

I don't remember Dr. Scott providing an explicit answer to the question "How could such gigantic animals with such small heads (at least compared to their body sizes) manage to consume enough food to sustain themselves?" but somewhere in the book he did mention that the earth's ecosystem may have been rather different back then.

However, since the book came out nearly a decade ago, I was curious on whether any other findings have been made since then.

How did sauropods manage to consume enough food to sustain themselves? Was it because of some differences in the ecosystem that are now lost?

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Unlike mammals, saurischian dinosaurs don't have to chew their food. Like birds they have a gizzard to do that instead.

Look at a modern ostriches: they have a very small head because the head is only used to gather food not process it. Mammals process food in the head (chewing) so the head has to be large to support the muscles, teeth, and other apparatus for this. On the other hand, birds and sauropods use stones in the gizzard to grind up their food, so all that space is taken up in the torso instead of the head. Ornithischian dinosaurs, which do chew, have large heads just like mammals.

Additionally since the mouth is not occupied chewing the time that would be lost chewing can be spent feeding instead. This can be a lot of time a cow spends 8 hours a day just chewing.

Source

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Note several things:

  1. Their long neck allow them access to a lot of food enabling to broswe with minimal movement and energy consumption.
  2. The sauropods had very big and long digestive system, and they probably also used gastroliths. These allowed them to process the food without chewing it in their mouths.
  3. I didn't relate to the question rather they were "cold blooded" or "warm blooded". If they were partially cold blooded (mesothermic) then they would need less food than a warm blooded critter of their size.
  4. I guess the vast majority of their diurnal activity was eating... a lot.

Hope it helps.

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    $\begingroup$ What you say about high O2 is true for the Carboniferous. Actually through at least the Triassic and Jurassic, pO2 was below present levels. annualreviews.org/doi/10.1146/annurev.earth.31.100901.141329 $\endgroup$ – kmm May 22 '18 at 14:57
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    $\begingroup$ Point 1 here is wrong, as @kmm says. Point 2 is speculation, based on an incorrect fact that doesn't lead to the conclusion anyway. Remove those and the remaining points would make a decent answer if any references were given; there are many references to support those points so it shouldn't be hard $\endgroup$ – iayork Jun 21 '18 at 12:12
  • $\begingroup$ I removed them. $\endgroup$ – Dr. Evenor Jun 24 '18 at 17:17

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