{"id":25110,"date":"2021-04-16T23:13:00","date_gmt":"2021-04-16T23:13:00","guid":{"rendered":"https:\/\/www.lifeandnews.com\/articles\/?p=25110"},"modified":"2021-04-18T01:29:06","modified_gmt":"2021-04-18T01:29:06","slug":"how-many-_tyrannosaurus-rex_-walked-the-earth","status":"publish","type":"post","link":"https:\/\/www.lifeandnews.com\/articles\/how-many-_tyrannosaurus-rex_-walked-the-earth\/","title":{"rendered":"How many Tyrannosaurus Rex walked the Earth?"},"content":{"rendered":"\n

Ashley Poust<\/a>, University of California, Berkeley<\/a><\/em> and Daniel Varaj\u00e3o de Latorre<\/a>, University of California, Berkeley<\/a><\/em><\/p>\n\n\n\n

The Research Brief<\/a> is a short take about interesting academic work.<\/em><\/p>\n\n\n\n

The big idea<\/h2>\n\n\n\n

During 2.4 million years of existence on Earth, a total of 2.5 billion Tyrannosaurus rex<\/em> ever lived<\/a>, and 20,000 individual animals would have been alive at any moment, according to a new calculation method we described in a paper published on April 15, 2021<\/a> in the journal Science.<\/p>\n\n\n\n

To estimate population, our team of paleontologists<\/a> and scientists<\/a> had to combine the extraordinarily comprehensive existing research on T. rex<\/em> with an ecological principle that connects population density to body size<\/a>.<\/p>\n\n\n\n

From microscopic growth patterns in bones, researchers inferred that T. rex<\/em> first mated at around 15 years old<\/a>. With growth records, scientists can also generate survivorship curves \u2013 an estimate of a T. rex<\/em>\u2018s chances of living to a given age<\/a>. Using these two numbers, our team estimated that T. rex<\/em> generations took 19 years. Finally, T. rex<\/em> existed as a species for 1.2 to 3.6 million years<\/a>. With all of this information, we calculate that T. rex<\/em> existed for 66,000 to 188,000 generations.<\/p>\n\n\n\n

From the fossil record alone, we had generated a T. rex<\/em> turnover rate. If our team could estimate the number of individuals in each generation, we would know how many T. rex<\/em> ever lived.<\/p>\n\n\n\n

\"A<\/a>
Damouth\u2019s law connects body mass to population density. Sara Volz, CC BY-ND<\/a><\/figcaption><\/figure>\n\n\n\n

In ecology, there is a well-established relationship between body mass and population density called Damuth\u2019s law<\/a>. Larger animals need more space to survive \u2013 one square mile of grassland can support a lot more bunnies than elephants. This relationship is also dependent on metabolism \u2013 animals that burn more energy require more space.<\/p>\n\n\n\n

Paleontologists have come up with a range of good estimates of T. rex<\/em>\u2019s body mass<\/a> and have also estimated its metabolism<\/a> \u2013 slower than mammals but somewhat faster than a large modern lizard, the Komodo dragon. With Damuth\u2019s law, we then estimated that the ancient world held about one T. rex<\/em> every 42.4 square miles (109.9 square km). That\u2019s about two individuals in the entire area of Washington, D.C.<\/p>\n\n\n\n

Now we had all the pieces we needed. Multiplying the population density by the area in which T. rex<\/em> lived gives us an estimate of 20,000 individuals per generation.<\/p>\n\n\n\n

\"Thousands<\/a>
Knowing the total number of T. rex<\/em> that ever lived unlocks other pieces of knowledge \u2013 like the fraction that turn into fossils and were found. Franz Anthony, CC BY-ND<\/a><\/figcaption><\/figure>\n\n\n\n

Why it matters<\/h2>\n\n\n\n

Once we figured out the average population size, we were able to calculate the fossilization rate for T. rex<\/em> \u2013 the chance that a single skeleton would survive to be discovered by humans 66 million years later. The answer: about 1 in 80 million. That is, for every 80 million adult T. rex<\/em>, there is only one clearly identifiable specimen in a museum.<\/p>\n\n\n\n

This number highlights how incomplete the fossil record is<\/a> and allows researchers to ask how rare a species could be without disappearing entirely from the fossil record.<\/p>\n\n\n\n

Beyond calculating the T. rex<\/em> fossilization rate, our new method could be used to calculate population size for other extinct species.<\/p>\n\n\n\n

What still isn\u2019t known<\/h2>\n\n\n\n

Estimates about extinct animals always include some amount of uncertainty. Our estimate of T. rex<\/em> population density ranges from one individual for every 2.7 square miles (7 square km) to one for every 665.7 square miles (1,724 square km). But surprisingly, the largest source of this uncertainty comes from Damuth\u2019s law. There is a lot of variation in modern animals. For example, Arctic foxes and Tasmanian devils have similar body mass, but devils have six times the population density.<\/p>\n\n\n\n

Further study of living animals could tighten up our estimates on T. rex<\/em>.<\/p>\n\n\n\n

We also don\u2019t know fossilization rates of other long extinct dinosaurs. If we have many fossils of one species, does that mean they were more common than T. rex<\/em>, or do we simply recover their fossils more often?<\/p>\n\n\n\n

\"A<\/a>
The huge amount of research that has been done on T. rex<\/em> played an important role in making this calculation. Evolutionnumber9\/Wikimedia Commons<\/a>, CC BY-SA<\/a><\/figcaption><\/figure>\n\n\n\n

What\u2019s next<\/h2>\n\n\n\n

This study might lead to other hidden facts about T. rex<\/em> biology and ecology.<\/p>\n\n\n\n

For instance, we might be able to learn whether T. rex<\/em> populations fluctuated up and down with Triceratops<\/em> \u2013 similar to wolf and moose predator and prey relationships today<\/a>. However, most other dinosaurs do not yet have the incredibly rich data<\/a> from decades of careful fieldwork that allowed our team to tally up T. rex<\/em>.<\/p>\n\n\n\n

If scientists want to apply this powerful technique to other extinct animals, we\u2019ve got some more digging to do.<\/p>\n\n\n\n

Ashley Poust<\/a>, Research Associate in Paleontology, University of California, Berkeley<\/a><\/em> and Daniel Varaj\u00e3o de Latorre<\/a>, Ph.D. Student in Paleontology, University of California, Berkeley<\/a><\/em><\/p>\n\n\n\n

This article is republished from The Conversation<\/a> under a Creative Commons license. Read the original article<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"

Ashley Poust, University of California, Berkeley and Daniel Varaj\u00e3o de Latorre, University of California, Berkeley The Research Brief is a short take about interesting academic work. The big idea During 2.4 million years of existence on Earth, a total of 2.5 billion Tyrannosaurus rex ever lived, and 20,000 individual animals would have been alive at […]<\/p>\n","protected":false},"author":44,"featured_media":25111,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[3410],"tags":[7783,1207,584,248,1206,9779,2197,7727,9674,9780,9778],"_links":{"self":[{"href":"https:\/\/www.lifeandnews.com\/articles\/wp-json\/wp\/v2\/posts\/25110"}],"collection":[{"href":"https:\/\/www.lifeandnews.com\/articles\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.lifeandnews.com\/articles\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.lifeandnews.com\/articles\/wp-json\/wp\/v2\/users\/44"}],"replies":[{"embeddable":true,"href":"https:\/\/www.lifeandnews.com\/articles\/wp-json\/wp\/v2\/comments?post=25110"}],"version-history":[{"count":2,"href":"https:\/\/www.lifeandnews.com\/articles\/wp-json\/wp\/v2\/posts\/25110\/revisions"}],"predecessor-version":[{"id":25126,"href":"https:\/\/www.lifeandnews.com\/articles\/wp-json\/wp\/v2\/posts\/25110\/revisions\/25126"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.lifeandnews.com\/articles\/wp-json\/wp\/v2\/media\/25111"}],"wp:attachment":[{"href":"https:\/\/www.lifeandnews.com\/articles\/wp-json\/wp\/v2\/media?parent=25110"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.lifeandnews.com\/articles\/wp-json\/wp\/v2\/categories?post=25110"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.lifeandnews.com\/articles\/wp-json\/wp\/v2\/tags?post=25110"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}