Why Medium-Sized Dinosaurs are Missing From the Fossil Record

Juveniles from species of massive carnivorous dinosaurs, such as Tyrannosaurus rex, may have out-competed species that would have otherwise succeeded as medium-sized adults, according to new research. (UNM Biology)

Why Medium-Sized Dinosaurs Are Often Missing From the Fossil Record

by Alex Fox/Smithsonianmag.com

In the age of the dinosaurs, it took a hatchling Tyrannosaurus rex about 20 years to reach its full adult size of between 12,000 and 18,000 pounds. Now, new research suggests that as they grew up, these massive meat-eating dinosaurs exerted tyrannical influence over their prehistoric ecosystems by out-competing medium-sized predators, reports Laura Geggel for Live Science.

The paper, published last week in the journal Science, seeks to explain the conspicuous absence of predators weighing between 220 pounds and 2,200 pounds as adults from the fossil record.

The study surveyed more than 550 species from 43 dinosaur communities across 136 million years. Broadly, the researchers found lots of species that weighed under 220 pounds and over 2,200 pounds as adults, but very few in between.

Speaking with Live Science, Katlin Schroeder, a paleontologist at the University of New Mexico and lead author of the study, proposes that juvenile T. rex and other immature big predators “may have outcompeted other medium-sized dinosaurs, resulting in deflated global dinosaur diversity.”

Schroeder tells Riley Black for New Scientist, that “the implication is that we’re not missing medium-sized dinosaurs from the fossil record because they didn’t fossilize well or haven’t been collected,…read more:


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