Tyrannosaurus rex, as the name implies, was a kingly creature of the late Cretaceous period. Thought to be one of the largest carnivores to ever walk on land, T. rex owes much of its status in popular culture to the hard work of its forefathers. Scientists long thought that dinosaurs achieved world domination through superiority: their evolutionary trajectory suggested they simply adapted better than those with which they were competing. But a new finding may take some of the shine off the origins of their 100-million-year reign.
Though the exact cause of the Cretaceous-Tertiary extinction event is still debated, it is no secret that the dinosaurs met their demise 65 million years ago. What come as a surprise to some is how they rose to prominence. A new study of dino bones published Thursday in Science is challenging the long held belief that dinosaurs possessed some evolutionary advantage over their crocodilian kin. Instead, it argues that won the evolutionary race simply by surviving not one, but two extinction events in the Triassic period. Sheer luck, it would seem, propelled the dinosaurs ahead of their competitors.
An assortment of crurotarsan skulls.
Image: Stephen Brusatte, Columbia University.
Experts thought dinosaurs were the benefactors of "competitive adaptive radiation," a scientific way of saying the dinosaurs’ ancestors were out-and-out better than their competition. Scientists who accept this hypothesis have posited that dinosaurs possessed one of two advantages: a highly mobile, upright stature or an endothermic physiology—warm-bloodedness. Yet, as the new study notes, dinosaurs' close relatives gave the "terrible lizards" a run for their money in the 28-million-year period between the Carnian-Norian extinction and the Triassic-Jurassic extinction.
The paper’s authors reached this conclusion by studying a staggering number of skeletal characteristics—437 in total—across 64 relevant vertebrates. With measurements in hand, the scientists calculated two numbers—disparity and evolutionary rate—and assigned the results to their respective place on a Triassic family tree. The first, disparity, helps scientists quantify the physical differences between one species’ skeleton and another's. Evolutionary rate, on the other hand, estimates the amount of evolution required to realize those physical differences.
The early competitors to the dinosaurs, called crurotarsans, were close relatives of modern crocodiles. Yet unlike modern crocodiles, crurotarsans were incredibly diverse. In fact, the new study claims they were evolving just as quickly as dinosaurs were. By the end of the Triassic period, crurotarsans were more abundant in some places than dinosaurs and, according to the new findings, were "experimenting" with a wider range of body types than their terrible lizard relatives.
"If we were standing in the Late Triassic, 210 million years ago or so, and had to bet on which group would eventually dominate ecosystems, all reasonable gamblers would go with the crurotarsans," Stephen Brusatte, a doctoral student at Columbia University and the paper’s main author, said ina statement. "There was no sign that dinosaurs were eventually going to succeed."
Science, 2008. DOI: 10.1126/science.1161833Posted on