The Twilight World

Amazing Adventures# 3 (Aug 1961), Kirby/Ayers cover and the splash page from the first story “We Were Trapped in the Twilight World,” also penciled by Kirby and inked by Dick Ayers.

A Tyrannosaurus Rex from Steven Spielberg’s Jurassic Park (1993) series.

Showing humans interacting with dinosaurs has been a common theme that pops up a lot in science-fiction. Here’s an excerpt from an interesting article published by the AP today on the great dinosaur die-off.

Dinosaur die-off cleared way for gigantic mammals

By Lauran Neergaard
Associated Press / November 26, 2010

This undated diagram image provided by the journal Science shows the largest land mammals that ever lived, from left, Indricotherium and Deinotherium, that would have towered over the living African Elephant. Indricotherium

WASHINGTON—They just needed some leg room: New research shows the great dinosaur die-off made way for mammals to explode in size — some more massive than several elephants put together.

The largest land mammal ever: A rhinoceros-like creature, minus the horn, that stood 18 feet tall, weighed roughly 17 tons and grazed in forests in what is now Eurasia. It makes the better known woolly mammoth seem a bit puny.

Tracking such prehistoric giants is more than a curiosity: It sheds new light on the evolution of mammals as they diversified to fill habitats left vacant by the dinosaurs.

Within 25 million years of the dinosaurs’ extinction — fast, in geologic terms — overall land mammals had reached a maximum size and then leveled off, an international team of scientists reports Friday in the journal Science. And while different species on different continents reached their peaks at different points in time, that pattern of evolution was remarkably similar worldwide.

“Evolution can happen very quickly when ecology permits,” said paleoecologist Felisa Smith of the University of New Mexico, who led the research. “This is really coming down to ecology allowing this to happen.”

Anyone who frequents natural history museums knows that the end of the dinosaurs 65 million years ago ushered in the age of mammals, and that some of them were gigantic. But the new study is the first comprehensive mapping of these giants in a way that helps explain how and why their size evolved.

“We didn’t have a clear idea of how the story went after the extinction of the dinosaurs,” explained Nick Pyenson, a curator at the Smithsonian Institution’s National Museum of Natural History, who wasn’t involved with the new research.

Previous theories suggested that species diversity drove increases in size, but the new study didn’t find that connection.

“It suggests there’s a deeper explanation of how large body size evolves in mammals,” he said.

Mammals did coexist with dinosaurs, but small ones, ranging from about the size of a mouse to a maximum of a small dog.

“We were pretty much the varmints scurrying around the feet of the dinosaurs,” is how New Mexico’s Smith puts it.