The Lost Tribe of the Mammals

Abstract

nyone who believes that the reign A of the dinosaurs ended long ago has not visited the gift shops at the American Museum of Natural History in New York. Walk into the Dinostore and it becomes clear that Tyrannosaurus rex and its kin still rule, at least over the world of consumer merchandise. The extinct reptiles stare back from racks of T-shirts, ties, hats, necklaces, earrings, and bracelets. Their images adorn stickers, shoelaces, and stuffed animals. You can even buy trays that produce dinoshaped ice cubes. Completely missing from this blitz of products is any hint of the museumgoers' early relatives-the mammals that lived alongside the dinosaurs during Earth's Mesozoic era. The reason seems obvious: Mammals from that span were little, shrewlike creatures, not the sort of animal that prompts children to call instinctively, Mommy, I want that. Yet in evolutionary terms, Mesozoic mammals underwent remarkable adaptations that in some ways dwarf those of their larger, reptilian neighbors. Though mammals of this time remained small, they developed the specialized teeth, highly sensitive hearing, and enlarged brains that would later drive their rise to power. Chief among these early mammals was an order called the multituberculates, a tongue-twisting name that paleontologists often shorten to multis. Multituberculates are probably the most interesting group of mammals that ever lived, says Guillermo W Rougier, a paleontologist at the American Museum. They appeared in the upper Triassic period, 210 million years ago, and they became extinct in the Eocene epoch, a little more than 30 million years ago. So they survived for a huge span of time. Despite their evolutionary endurance record and their wide diversity of species, multituberculates have remained an enigma, even after a century of study. So little is known about these creatures that paleontologists are still debating what multituberculates looked like, how they originated, and, most important, how they relate to the mammals living today. One potential reason for their obscurity is that no one has been able to figure them out, says David W Krause of the State University of New York at Stony Brook. A bevy of new fossil discoveries from Mongolia, Madagascar, and Greenland is now helping paleontologists draw a more complete picture of this pivotal group of early mammals. Researchers unveiled some of their most recent finds at a symposium on multituberculates held at the American Museum in October as part of the annual meeting of the Society of Vertebrate Paleontology.