Prehistoric heavyweights such as the Tyrannosaurus rex may have outcompeted their smaller rivals whilst in their teens, leaving medium-sized dinosaurs missing from the fossil record, researchers from The University of New Mexico and at the University of Nebraska-Lincoln have found.


Palaeontologists have long been puzzled why the number of different dinosaurs types known around the globe is so low, particularly among small and medium-sized species. Now, a new study published in the journal Science suggests this may be because they were outcompeted by adolescent megatherapods that were not yet fully grown.

Despite growing to the size of double decker buses, colossal dinosaurs such as the T. rex started life relatively small - roughly the size of a Chihuahua - on account of being born from eggs. This means that they would likely have been in competition with smaller dinosaurs as they grew, the researchers say.

“We wanted to test the idea that dinosaurs might be taking on the role of multiple species as they grew, limiting the number of actual species that could co-exist in a community,” said Kat Schroeder, a graduate student in the UNM Department of Biology who led the study.

“Dinosaur communities were like shopping malls on a Saturday afternoon - jam-packed with teenagers. They made up a significant portion of the individuals in a species and would have had a very real impact on the resources available in communities.”

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To investigate the question of decreased dinosaur diversity, the team gathered data from multiple well-known fossil locations scattered across the globe, comprising fossils from more than 550 dinosaur species. They then organised the dinosaurs by mass, diet, size, and location.

They then built up a picture of what the dinosaur communities would have looked like by combining data from growth rates taken from lines found in cross-sections of bones and the number of infant dinosaurs surviving each year based on the fossil record. This enabled them to calculate what proportion of a megatheropod species would have been juveniles.

“There is a gap - very few carnivorous dinosaurs between 100-1000kg exist in communities that have megatheropods,” said Schroeder. “And the juveniles of those megatheropods fit right into that space.”

They also found that the gap was much smaller in Jurassic communities, which ran from 200 to 145 million years ago, than Cretaceous communities, which ran from 145-65 million years ago – the period when the T. rex was king.


“Jurassic megatheropods don't change as much -- the teenagers are more like the adults, which leaves more room in the community for multiple families of megatheropods as well as some smaller carnivores,” said Schroeder. “The Cretaceous, on the other hand, is completely dominated by Tyrannosaurs and Abelisaurs, which change a lot as they grow.”

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Reader Q&A: What would dinosaurs have tasted like?

Asked by: Peter Makepeace, Northamptonshire

Dinosaurs probably would have tasted like chicken. Okay, so everybody always says that everything tastes like chicken. But I’m not being facetious. Birds evolved from dinosaurs, which means that they’re essentially modern-day dinosaurs.

Of course, not all birds taste like chicken, though. So maybe some dinosaurs would have tasted like duck or turkey or game birds, depending on the dinosaur’s diet and fat content. Plant-eating dinosaurs such as Triceratops and Diplodocus probably would have been tastiest.

The animal fat in the diet of carnivorous dinosaurs such as Tyrannosaurus rex and Velociraptor would have given them an overly ‘gamey’ flavour (one of the reasons we eat cows but not wolves).

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Jason Goodyer
Jason GoodyerCommissioning editor, BBC Science Focus

Jason is the commissioning editor for BBC Science Focus. He holds an MSc in physics and was named Section Editor of the Year by the British Society of Magazine Editors in 2019. He has been reporting on science and technology for more than a decade. During this time, he's walked the tunnels of the Large Hadron Collider, watched Stephen Hawking deliver his Reith Lecture on Black Holes and reported on everything from simulation universes to dancing cockatoos. He looks after the magazine’s and website’s news sections and makes regular appearances on the Instant Genius Podcast.