T. rex ancestor helps fill fossil record gap

NEW YORK — How did evolution produce a monstrous killer such as the Tyrannosaurus rex? A fossil find in Central Asia is giving scientists a glimpse into the process.

T. rex and other tyrannosaurs were huge, dominant predators, but they evolved from much smaller ancestors. The discovery from Uzbekistan indicates that this supersizing happened quickly and only after the appearance of anatomical features that may have helped the monster tyrannosaurs hunt so effectively.

The finding was reported Monday by Hans-Dieter Sues of the Smithsonian’s National Museum of Natural History in Washington, Stephen Brusatte of the University of Edinburgh in Scotland and others in a paper released by the Proceedings of the National Academy of Sciences.

• THE DISCOVERY. They report finding bones of a previously unknown member of the evolutionary branch that led to the huge tyrannosaurs. The earlier dinosaur lived about 90 million years ago south of what is now the Aral Sea. It looked roughly like a T. rex but was only 10 to 12 feet long and weighed about 600 pounds at most, Sues said. T. rex was about four times as long and weighed more than 20 times as much.

• GOOD TIMING. The discovery helps fill in a gap in the fossil record. Before that gap, which began some 100 million years ago, the ancestral creatures were only about as big as a horse. Right after the gap, at about 80 million years ago, tyrannosaurs were multiton behemoths such as T. rex. The new finding shows the forerunners were still relatively small even just 90 million years ago, so the size boom happened pretty quickly.

• STANDARD EQUIPMENT. The inner ears of the newfound beast already had tyrannosaur features associated with agility and hearing low-pitched sounds, which might have helped it detect prey, but the creature lacked the bone-snapping teeth and large sinuses of T. rex.

• THE NAME. The creature was dubbed Timurlengia euotica, honoring the ancient Central Asian ruler Tamerlane and the large inner ears of the beast. The creature wasn’t a direct ancestor of T. rex, but it indicates what ancestors looked like, Brusatte said.