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2.5B T. rex inhabited the planet, researchers say
- vmception 6y ago> the researchers were able to approximate that about 20,000 T. rex were alive at any given time low
- dogma1138 6y agoYep 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 6y agoMaybe the other dinosaurs were quite dangerous for the king? I mean the ones with spike tails etc.
- Sharlin 6y agoT. 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.
- ALittleLight 6y agoGoogle 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.
- dogma1138 6y agoI 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.
- cletus 6y agoTwo 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.
- Sharlin 6y agoNote 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. [1] https://en.wikipedia.org/wiki/Laramidia https://en.wikipedia.org/wiki/Laramidia
- Keysh 6y agoMany 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...).
- dogma1138 6y agoThe elephant might be a herbivore but it is prey only for humans.
- Sharlin 6y agoYes, but the point is we should expect elephant population to be larger than that of an apex predator.
- aquadrop 6y agoTheir method of estimation is not far from guessing and they even say themselves, that accuracy is "low".
- Alex3917 6y agoLooking 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 6y ago40 Square Miles is only 6.3 miles to a side. That's not that far to travel for mating.
- ardit33 6y agoThere 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 6y agoAnother 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 6y agoOnly 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 6y agoT. 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 6y agoSomeone 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.
- tessierashpool 6y agoIt'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 6y ago[deleted]
- sanj 6y agoDeeper 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 6y ago20k 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.
- kelnos 6y agoThey need not have been spread across the entire planet, though. 20k in a smaller area might have been fine.
- dharmab 6y agoThere 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#Genetic_bottleneck_in_humans https://en.wikipedia.org/wiki/Toba_catastrophe_theory#Geneti...
- chrisco255 6y agoThis claim is not that there was 20K T-rexes at one dire point in history but an average over millions of years. Humans ended up surviving that disaster, and then went on to populate the whole earth. Also side note, supervolcanoes are scary as hell.
- felixfurtak 6y agoHumans are currently up to 105 Billion Total (since 50,000 BC) https://en.wikipedia.org/wiki/Estimates_of_historical_world_population#:~:text=An%20estimate%20on%20the%20%22total,rate%20throughout%20pre%2Dmodern%20history https://en.wikipedia.org/wiki/Estimates_of_historical_world_....
- oever 6y agoSo 7.5% of all humans born in 52.000 years are still alive. Ergo, humans have an average lifespan of 4.000 years.
- space_ghost 6y agoI'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?
- ardit33 6y agobones 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.
- thejohnconway 6y agoThe 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).
- Tagbert 6y agoAlso, remember that T-Rex only lived in the western US and it was a large island. 20,000 individuals is not unreasonable for a predator population. There were other Tyrannosaur species in other places and times.
- kingsuper20 6y agoThat 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.
- twistedpair 6y agoData point: 100B humans have inhabited the planet.
- toomuchredbull 6y agoMy son will be pleased.
- windex 6y agoWouldnt they have evolved in that amount of time? Wouldnt that be visible in fossil records? What did they evolve into?
- iamgopal 6y agoThere was a calculation on what if Xkcd that every water droplet at one point in history was inside a dinosaur