Posted by Nima On Tuesday, March 21, 2017 1 comments
This is a question we hear a lot, especially from dino-fans in awe of the size and scale of some of these creatures, which can only go up after seeing one in a museum.
|However huge you think they are, they always look bigger in person.|
We've all heard they needed outrageous amounts of food just to stay alive (and that they shook the earth with each step...) but how much time did these giants really need to spend eating each day?
The answer is, a lot less than you might think, even with being warm-blooded... but it depends on the species. A lot of people imagine that sauropods were so big that they had to spend all their time eating, or that a warm-blooded metabolism would demand more food than they could ever possibly take in. But this simply isn't true! Now of course sauropods didn't all have the same energy requirements, but most would have been in a similar nutrient/tissue conversion range, and in general the worst-case formula goes like this:
A big warm-blooded herbivore needs to eat about 2% of its mass in food per day to keep going. (A 5 ton elephant = 5,000kg, needs minimum 200 pounds or 100kg of food per day, that's 2% or 0.02 of the elephant's mass). Now this is a very high estimate of the minimum intake - it assumes sauropod digestion was as bad as that of elephants or horses, but it was likely much more efficient, this is just a worst case scenario to show how much easier feeding was for sauropods than we often imagine.
Going by a similar measure for sauropods, we get the following:
We'll use the Berlin Giraffatitan HMN SII (subadult) as a test case, since we actually have a complete mouth and most of the skeleton: Since we have the basic 2% formula already, we just need to know (1) the animal's mass, (2) the volume of its bite, (3) the time it took to swallow each bite.
So how heavy was it?
Now if you look at the subadult Giraffatitan, as restored by Paleo-King, it's ~33 tons (lean mass). We could use another skeletal restoration that estimates it lighter or heavier, but since this one is the best, most detailed, most beautiful, most thoroughly researched and lifelike, and likely will not be surpassed for another Cosmological Decade or so, this restoration is the gold standard to use.
So, 33 tons or 33,000 kg x 0.02 = 660kg of food = 1320 lbs of food required per day, or around 6/10 of a ton, minimum.
So how big was each bite?
The mouth of HMN SII (skull HMN S116) is big. Very big. Here's where most paleontologists get lost - they assume based on modern mammal rates of feeding that sauropods needed many hours to feed - not true, since despite having proportionally small heads, sauropods had much bigger mouths than modern mammals. The skull of SII/S116 (left column, second skull down) was at least 0.8m long, that's pushing 3 feet - with the toothy portion of the mouth being about 0.4m long, and just as wide, and about a foot deep. So its volume is about 1.47 cubic feet, bigger than a laundry basket = Big enough to bite off 70 pounds of conifer leaves/needles. Though lets be conservative and say it was on average 50 pounds per bite because not every bite was on full branches.
Heck, even the smaller HMN t1 skull looks like it could gobble up close to 50 pounds without much effort!
So how long did feeding take?
Each ~50lb bite takes 30 seconds max to hack off and gulp down, probably it was much faster, since these animals didn't chew, but we don't know if their brain stem could coordinate breathing independently of swallowing (most reptiles and birds can pull it off, some mammals can't) so worst case we'll give him 30 seconds per bite for a breather. So that's 2 bites or 100 pounds of food per minute. 1320 pounds daily requirement, divided by 100 pounds per minute, = 13.2 minutes to eat the minimum food to stay alive, assuming elephant-like digestion (which is, again, far less efficient than we'd expect for any sort of archosaurs).
Of course they probably ate a lot more than the minimum. But even if they took in twice as much on average, that's 2,640 pounds or 1,320 kg... which translates into 27 minutes of feeding. But lets be REALLY conservative and say that most of the trees in the area have already been depleted of branches up to the Giraffatitan's feeding height... so our friend SII has to spend half of the time moving around and looking for fresh trees that have not been fed on. This doubles the feeding time to just under an hour. If the area is totally depleted and SII has to walk around another 5 miles to find enough food, that's another hour (5mph is easy for a big brachiosaur, with that huge stride length, it's next to no effort). So even in a worst case scenario with competing herds eating everything, you travel 5 miles from where you were yesterday, foraging and feeding time is under 2 hours, eating twice the minimum needed. And as for bigger sauropods, like an adult Giraffatitan (HMN XV2?) or even the really huge titanosaurs like Argentinosaurus or Puertasaurus? They were larger but also likely had bigger mouths to match. The width of the neck in many advanced titanosaurs indicates there was probably a big-mouthed head at the top. So realistically I don't see feeding taking much more than 2 hours for these species either.
|Giraffatitan by Brian Franczak - an example of a "worst case" feeding scenario|
So we're talking around 2 hours max, but usually much less time than that. And that's assuming both a warm-blooded metabolism and a fast, inefficient digestive system like that of elephants. In reality sauropods probably had much more efficient digestion like ostriches, and so may have needed less food and feeding time even with a fast metabolism (Foster, 2007 says that even the heavier Brachiosaurus altithorax needed only 400kg a day, not 660kg - so my minimum is likely on the high end anyway). So 2 hours is really a worst case. I know, shocking - especially if you grew up with all those awful, horrible outdated books that claimed sauropods needed to eat all day long or spend their whole lives barely moving in a lake surrounded by water plants lest they burn one calorie too many.
Mark Hallett's and Dougal Dixon's Giraffatitans - less accurate anatomy, but more likely feeding scenarios.
We can forget about all the crazy stories of sauropods needing to eat nonstop 24 hours a day without resting, it simply isn't true, not even close. 2 hours per day is more than enough. In fact if you added in the minutes needed to drink water, the total would still be unlikely to top 2 hours. The rest of the day is sleep and play, and whatever else sauropods liked to do. Shocking, I know. Life actually seems "normal" for them. The facts really are stranger than the fiction.
Posted by Nima at 3:14 PM