Yep the most endangered elephant is the Asian elephant and there are about 50,000 left in the wild right now, in total there are half a million elephants in the world of all species having only up to 20K at any given time for a species that was pretty much on top of the food chain is quite surprisingly low.
T. Rex was a predator, however, and an apex predator at that. Elephants are herbivores. That changes the expected numbers quite a bit. Prey populations typically outnumber their predators by two to three orders of magnitude.
Google says there are about 50,000 killer whales right now. They are apex predators and similar in mass. Of course sea creature versus land animal, but also I believe we are at a low point for killer whale population.
I would put dolphins up there too and their numbers are dwindling due to humans directly fishing them for centuries and now destroying their habitats by over fishing.
1. Water covers ~70% of the Earth's surface. Whales migrate of course but can exist from the poles to the equator;
2. Of the 30% land, for pretty much any species, some portion of that is uninhabitable. Dinosaurs being reptiles likely require hot and wet environments. As predators, T. Rex would be limited by where their food could live too.
The dinosaur era was largely one of a super-continent (Pangaea). A good portion of that was likely too cold or too dry to support such a large predator.
Note that Pangaea had already started breaking apart a hundred million years before Tyrannosaurus rex, which lived right at the end of era of non-avian dinosaurs. Indeed T. Rex is much closer to our time than Pangaea was to T. Rex's time!
They lived in what is now Western North America, but was then an island continent called Laramidia [1] so yes, they were geographically quite limited.
Many dinosaurs were warm-blooded; fossils of dinosaurs have been found in Antarctica (granted, that’s from a time when the global climate was warmer and Antarctica was ice-free, but still...).
Looking at the paper, it looks like the authors didn't correct for the fact that CO2 levels during the late Cretaceous period were around 1000pm, so at the time there would have been significantly more available calories per square mile. If each individual really did require 40 square miles, it's hard to understand how they would successfully reproduce.
There are plenty of animals with less density, that reproduce successfully.
T-Rex was probably a solitary animal, and perhaps akin to a modern Tiger in its matting patterns.
The spatial distribution and population density of tigers in mountainous terrain of Bhutan
"Based on our top model, the estimated tiger population size (N) was 91 individual tigers with 60 adult females and a density of 0.24 tigers/100 km2 "
Another interesting comparison between T Rex and tigers: the diameter and crushing force of a T Rex's jaws are pretty closely matched by the killing triangle of a tiger's front paws and fangs. Citation: John Vaillant's amazing book "The Tiger: a True Story of Vengeance and Survival". (Highly recommended)
Only 2.5B over 2 and a half million years that seems astonishingly low. I wonder if we have any idea about their reproductive lifecycle and lifespan.
There are about 1 billion cows on the planet today mostly because we breed them and there are nearly half a million elephants living currently while being hunted by pesky humans.
T. rex were apex predators, which tend to have fairly low populations compared to herbivores. They're also megafauna, which tend to have fairly low populations compared to smaller animals. So comparisons with cattle aren't really adequate. While I'm sure the error in the population estimate is greater than the estimated value, it does seems to make sense that their population would be quite small.
On the other hand, T. rex probably had a significantly larger range than we've found evidence of.
Someone already mentioned this but there are far more killer whales right now and dolphins both who are apex predators and we don’t make it easy for them to survive.
There are 25-20,000 lions left after we’ve hunted them to nearly extinction.
2.5 billion Tyrannosaurus rex lived and died during the roughly 2.4 million years
I'm in a meeting so I'm not totally paying attenion to this comment as I write it (sorry) but I believe that works out to just a little over 1000 per year. That's not a huge number for an entire species across an entire planet.
20k seems unlikely low, even as a median. A population that small would be difficult to sustain for that long through variations in climate, resources, ecosystem, and evolutionary competition.
Not sure what your comment has to do with mine. That doesn't mean the total available biomass to predators in aggregate was larger or smaller, just because some big dinosaurs existed.
It doesn't even mean T-rex hunted brontosaurus frequently or at all (given the somewhat different eras), much like the modern lions don't really hunt adult elephants.
It's worth pointing out to anyone in the comments before they read the article:
They arrived at the ~20k number living at any one time number first; ~1k per year * 19yr lifespans. They extrapolated it out to that 2.5B based on how long they were around.
It seems extremely unlikely that there was a flat population for millions of years (considering e.g. the human population has doubled in the last 50 years), and this wouldn't be my starting assumption.
A small, flat population is even more unlikely - any disruption would wipe out the population more quickly than millions of years down the line.
Populations reach equilibrium very quickly on a geologic timescale. Humans had a relatively flat population graph until the past 10kya or so as well (and realistically long after that point as well).
You have to have a flat population over long timescales. If you started with two tyrannosaurs and had a population growth rate of just 0.02% (population doubles every 6600 years), there would be approximately 500 billion tyrannosaurs on the planet at the same time by the point they went extinct.
It's likely the population fluctuated up and down slightly on short timescales, but the average would have been constant. They were spread out over a continent so any disruption would need to be very widespread to take them all out - which eventually of course is exactly what happened.
Humans are unique in that we can develop technology to exceed our carrying capacity.
This graph is smoothed out first by the logarithmic nature, and second by the fact that "estimates for the 1st century suggest uncertainty of the order of 50%" (and that's only 2000 years ago).
The graph does not show us that anybody thinks the human population was flat before a certain point.
They were not spread across the entire planet, though, far from it. They lived in what is now Western North America and used to be an island continent called Laramidia[1].
> I'm in a meeting so I'm not totally paying attention to this comment
I'm in a meeting too and your comment made me chuckle. I love the idea of HN-goers going through the motions of professional life, when in reality they just want to talk about dinosaurs and the nuance behind dinosaur research.
I'm dubious. What do we know about the actual lifespan of the T. Rex? At what age did they reproduce, and how often? What was the survival rate? Mating practices? Territorial behaviors?
The age estimate is one of the more solid variables. The wildly uncertain variable is population density (which is why the error bars in the paper are orders of magnitude).
That doesn't seem like a crazy-high number. If there used to be 100k tigers at any one time, mostly before the problem of too-damn-many-humans, 20k T-Rexes doesn't seem like a stretch. I wonder how broad their range was.
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1. Water covers ~70% of the Earth's surface. Whales migrate of course but can exist from the poles to the equator;
2. Of the 30% land, for pretty much any species, some portion of that is uninhabitable. Dinosaurs being reptiles likely require hot and wet environments. As predators, T. Rex would be limited by where their food could live too.
The dinosaur era was largely one of a super-continent (Pangaea). A good portion of that was likely too cold or too dry to support such a large predator.
They lived in what is now Western North America, but was then an island continent called Laramidia [1] so yes, they were geographically quite limited.
[1] https://en.wikipedia.org/wiki/Laramidia
The spatial distribution and population density of tigers in mountainous terrain of Bhutan "Based on our top model, the estimated tiger population size (N) was 91 individual tigers with 60 adult females and a density of 0.24 tigers/100 km2 "
There are about 1 billion cows on the planet today mostly because we breed them and there are nearly half a million elephants living currently while being hunted by pesky humans.
On the other hand, T. rex probably had a significantly larger range than we've found evidence of.
There are 25-20,000 lions left after we’ve hunted them to nearly extinction.
2.5 billion Tyrannosaurus rex lived and died during the roughly 2.4 million years
I'm in a meeting so I'm not totally paying attenion to this comment as I write it (sorry) but I believe that works out to just a little over 1000 per year. That's not a huge number for an entire species across an entire planet.
So ~20k alive at any point in time, assuming a flat distribution during that 2.5B year window.
Humans ended up surviving that disaster, and then went on to populate the whole earth. Also side note, supervolcanoes are scary as hell.
Especially apex predators of that size.
It doesn't even mean T-rex hunted brontosaurus frequently or at all (given the somewhat different eras), much like the modern lions don't really hunt adult elephants.
They arrived at the ~20k number living at any one time number first; ~1k per year * 19yr lifespans. They extrapolated it out to that 2.5B based on how long they were around.
Parent reverse engineered it in reverse!
A small, flat population is even more unlikely - any disruption would wipe out the population more quickly than millions of years down the line.
It's likely the population fluctuated up and down slightly on short timescales, but the average would have been constant. They were spread out over a continent so any disruption would need to be very widespread to take them all out - which eventually of course is exactly what happened.
Humans are unique in that we can develop technology to exceed our carrying capacity.
The graph does not show us that anybody thinks the human population was flat before a certain point.
[1] https://en.wikipedia.org/wiki/Laramidia
Like, nevermind a comet, a poorly timed burp from a volcano could have sufficiently reduced diaspora enough to make them disappear.
I'm in a meeting too and your comment made me chuckle. I love the idea of HN-goers going through the motions of professional life, when in reality they just want to talk about dinosaurs and the nuance behind dinosaur research.
https://en.wikipedia.org/wiki/Estimates_of_historical_world_....
Ergo, humans have an average lifespan of 4.000 years.
same way you can tell the age of a tree when it was cut, but just looking a the cut trunk.
There were other Tyrannosaur species in other places and times.