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How many Tyrannosaurus rex have walked the earth?
_Tyrannosaurus rex_ stretched across ancient North America, and about 20,000 lived simultaneously. 1Ado123 / Wikimedia Commons, CC BY-SAT The Research Brief is a brief overview of interesting academic work. The Big Idea During 2.4 million years of existence on earth, a total of 2.5 billion Tyrannosaurus rex have ever lived and 20,000 individual animals would have lived at any one time, according to a new calculation method we used in an article on Published April 15, describes 2021 in the journal Science. To estimate the population, our team of paleontologists and scientists had to combine the extraordinarily comprehensive existing research on T. rex with an ecological principle that links population density and body size. From microscopic growth patterns in bones, researchers concluded that T. rex was first mated at 15 years old. With growth records, scientists can also generate survival curves – an estimate of a T. rex’s chance of living to a given age. Using these two numbers, our team estimated that T. rex generations took 19 years. Eventually, T. rex existed 1.2 to 3.6 million years as a species. With all this information, we calculate that T. rex existed 66,000 to 188,000 generations. From the fossil record alone, we generated a T. rex conversion rate. If our team could estimate the number of individuals in each generation, we would know how many T. rex have ever lived. Damouth’s law links body mass with population density. Sara Volz, CC BY-ND In ecology, there is an established link between body mass and population density called Damuth’s law. Larger animals need more space to survive – one square kilometer of grassland can carry many more rabbits than elephants. This ratio is also dependent on metabolism – animals that burn more energy require more space. Paleontologists have made a series of good estimates of T. rex’s body mass and also its metabolism – slower than mammals, but somewhat faster than a large modern lizard, the Komodo dragon. With Damuth’s law, we then estimated that the ancient world owned about one T. rex every 109.4 square miles (109.4 square kilometers). It’s about two individuals in the entire Washington, DC area. Now we had all the pieces we needed. The multiplication of the population density with the area in which T. rex lived gives us an estimate of 20,000 individuals per generation. Knowing the total number of T. rex that have ever lived unlocks other pieces of knowledge – such as the fraction that was turned into fossils and found. Franz Anthony, CC BY-ND Why It Matters After determining the average population size, we were able to calculate the rate of fossilization for T. rex – the chance that a single skeleton would survive to be discovered 66 million years later by humans. The answer: about 1 in 80 million. That is, for every 80 million adult T. rex, there is only one clearly identifiable specimen in a museum. This number shows how incomplete the fossil record is and makes researchers ask how rare a species can be without disappearing completely from the fossil record. In addition to calculating the T. rex fossilization rate, our new method can be used to calculate the population size for other extinct species. What is not yet known Estimates of extinct animals always contain some uncertainty. Our estimate of T. rex population density varies from one individual for every 7 square kilometers (7 square kilometers) to one for every 665.7 square kilometers (1,724 square kilometers). But surprisingly, the biggest source of this uncertainty comes from Damuth’s law. There is a lot of variation in modern animals. North foxes and Tasmanian devils, for example, have a similar body mass, but demons have six times the population density. Further study of live animals may sharpen our estimates on T. rex. We also do not know the fossilization rate of other long-extinct dinosaurs. If we have many fossils of one species, does that mean they were more abundant than T. rex, or do we simply recycle their fossils more often? The large amount of research done on T. rex has played an important role in the calculation of this calculation. Evolutionnumber9 / Wikimedia Commons, CC BY-SA What’s next? This study may lead to other hidden facts about T. rex biology and ecology. For example, we can learn whether T. rex populations alternated up and down with Triceratops – similar to the predatory and prey ratios between wolves and elk. However, most other dinosaurs do not yet have the incredible wealth of decades of meticulous fieldwork that has enabled our team to gather T. rex. If scientists want to apply this powerful technique to other extinct animals, we need to dig even deeper. This article was published from The Conversation, a non-profit news site dedicated to sharing ideas from academic experts. It was written by: Ashley Poust, University of California, Berkeley and Daniel Varajão de Latorre, University of California, Berkeley. Read more: Dinosaurs: how do we change our understanding of what they look like there, other than dinosaurs, what will we need to create a Jurassic world? The authors do not work, consult, own shares in or receive funding from any company or organization that would benefit from this article, and have not disclosed any applicable commitments outside of their academic appointment.