If a T-rex were released in New York City, how many humans/day would it need to consume to get its needed calorie intake?
Tony Schmitz
About half of an adult, or one ten-year old child:
Shoot, I forgot to eat one yesterday. Am I allowed to double up?
Tyrannosaurus rex weighed about as much as an elephant.[This always seemed a little off to me; my mental image of elephants is that they're in the same size range as cars or trucks, whereas T-rex, as Jurassic Park showed, is big enough to stomp on cars. But a Google image search for car+elephant shows elephants looming over cars just like the T-rex in Jurassic Park. So, great, now I'm also afraid of elephants.]
Utahraptor will be so jealous.
No one is totally sure what dinosaur metabolism looked like, but the best guesses for how much food T-rex ate seem to cluster around 40,000 calories per day.[Food calories (kcal). Sources: This and this, and this with some notes from this and distraction from this. ]
If we assume dinosaurs had metabolisms similar to today's mammals, they'd eat a lot more than 40,000 calories each day. But the current thinking is that while dinosaurs were more active (loosely speaking, "warm-blooded") than modern snakes and lizards, very large dinosaurs probably had metabolisms that more closely resembled komodo dragons than elephants and tigers.[For big sauropods, we know this must be the case, because otherwise they would overheat. However, there's a lot of uncertainty surrounding T-rex-sized dinosaurs.]
Next, we need to know how many calories are in a human. This number is helpfully provided, by Dinosaur Comics author Ryan North, on this wonderful t-shirt. Ryan's shirt tells us that an 80-kg human contains about 110,000 calories of energy.
Therefore, a T-rex would need to consume a human every two days or so.[Although a T-rex would likely be willing to eat several days to weeks worth of food in one meal, so if it has the option, it might eat a bunch of people at a time, then go for a while without eating.] The city of New York had 239,736 births in 2011, which could support a population of about 1,000 tyrannosaurs. However, this ignores immigration—and, more importantly, emigration, which would probably increase substantially in this scenario.
I wonder if a tyrannosaur could fit into an MTA subway car.
The 33,000 McDonald's restaurants worldwide sell something like 15 billion hamburger patties per year,[They stopped reporting the "x billions served" number on their signs, but this website has some extrapolations.] for an average of 1,245 burgers per restaurant per day. 1,245 burgers is about 600,000 calories, which means that each T-rex only needs about 80 hamburgers per day to survive, and one McDonald's could support over a dozen tyrannosaurs on hamburgers alone.
One of them sleeps in the ball pit. Tell your kids!
Ands if you live in New York, and you see a T-rex, don't worry. You don't have to choose a friend to sacrifice; just order 80 burgers instead.
And then if the T-rex goes for your friend anyway, hey, you have 80 burgers.
More of an acquaintance, really.