[HN Gopher] 2.5B T. rex inhabited the planet, researchers say
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2.5B T. rex inhabited the planet, researchers say
Author : jimmy2020
Score : 46 points
Date : 2021-04-15 20:05 UTC (2 hours ago)
(HTM) web link (www.axios.com)
(TXT) w3m dump (www.axios.com)
| kingsuper20 wrote:
| 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.
| felixfurtak wrote:
| Humans are currently up to 105 Billion Total (since 50,000 BC)
|
| https://en.wikipedia.org/wiki/Estimates_of_historical_world_....
| oever wrote:
| So 7.5% of all humans born in 52.000 years are still alive.
|
| Ergo, humans have an average lifespan of 4.000 years.
| pixl97 wrote:
| Or there has been a massive increase in human survival in the
| last 100 years.
| space_ghost wrote:
| 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?
| thejohnconway wrote:
| 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).
| ardit33 wrote:
| bones can tell a lot...
|
| same way you can tell the age of a tree when it was cut, but
| just looking a the cut trunk.
| vmception wrote:
| > the researchers were able to approximate that about 20,000 T.
| rex were alive at any given time
|
| low
| Alex3917 wrote:
| 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.
| enkid wrote:
| 40 Square Miles is only 6.3 miles to a side. That's not that
| far to travel for mating.
| ardit33 wrote:
| 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 "
| chrisweekly wrote:
| 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)
| dogma1138 wrote:
| 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.
| rightbyte wrote:
| Maybe the other dinosaurs were quite dangerous for the king?
| I mean the ones with spike tails etc.
| Sharlin wrote:
| _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.
| dogma1138 wrote:
| The elephant might be a herbivore but it is prey only for
| humans.
| Sharlin wrote:
| Yes, but the point is we should expect elephant
| population to be larger than that of an apex predator.
| ALittleLight wrote:
| 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.
| cletus wrote:
| Two issues:
|
| 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.
| dogma1138 wrote:
| 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.
| aquadrop wrote:
| Their method of estimation is not far from guessing and they
| even say themselves, that accuracy is "low".
| dogma1138 wrote:
| 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.
| klyrs wrote:
| 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.
| dogma1138 wrote:
| 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.
| twistedpair wrote:
| Data point: 100B humans have inhabited the planet.
| tessierashpool wrote:
| It's not 2.5B T. Rex at the same time.
|
| _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.
| [deleted]
| sanj wrote:
| Deeper in the article, there's an estimate of a 19 year
| lifespan.
|
| So ~20k alive at any point in time, assuming a flat
| distribution during that 2.5B year window.
| chrisco255 wrote:
| 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.
| dharmab wrote:
| There is a supported theory that at one point there were
| 10,000 or fewer humans on the planet: https://en.wikipedia.
| org/wiki/Toba_catastrophe_theory#Geneti...
| antisthenes wrote:
| On the contrary, for apex predators, smaller populations
| are easier to sustain than large populations.
|
| Especially apex predators of that size.
| kelnos wrote:
| They need not have been spread across the entire planet,
| though. 20k in a smaller area might have been fine.
| maldeh wrote:
| I'm frankly astonished that the species lasted for two and a
| half million years all while being highly endangered the whole
| time.
|
| Like, nevermind a comet, a poorly timed burp from a volcano
| could have sufficiently reduced diaspora enough to make them
| disappear.
| midasuni wrote:
| T Rex lifespan of what, 10-20 years? That's a tiny number -
| about 3 TRexes in the entire country of Belgium
| rightbyte wrote:
| Imagine how much land you need to support one T rex though
| given how big they were.
| ksaj wrote:
| Agreed. It's the one thing we know for sure about the ocean
| and its rather large predators.
| [deleted]
| creamynebula wrote:
| One of the threads that make me wish we had downvotes here...
| Very deceiving clickbaity title!
| jimmy2020 wrote:
| sounds a boring meeting.
| kjeetgill wrote:
| 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.
|
| Parent reverse engineered it in reverse!
| teachingassist wrote:
| 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.
| AlotOfReading wrote:
| 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).
| Impossible wrote:
| When I first saw the headline I imagined flocks for T-Rexes
| devouring everything. 2.5B for all of history is more
| reasonable
| Sharlin wrote:
| 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].
|
| [1] https://en.wikipedia.org/wiki/Laramidia
| pbreit wrote:
| In that case then "2.4m years" is the unbelievable number.
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