If there were placental mammals in the Early Cretaceous of Australia, Krause says, it would "push back the record of placentals farther than we expected on any southern land mass and in many ways revolutionize our concept of early mammalian biogeography."

DIGGERS

Still, explaining how they could have gotten there remains a tall order. "Almost undoubtedly you would need some intermediate land masses to show the presence of placental mammals and right now we don't have those records," he admits. But Krause thinks his explanation of gondwanathere dispersal may be of help. "Finding gondwanatheres in Madagascar and India forced us to rethink how that distribution could make sense, and we made sense of it by suggesting that Antarctica, not Africa, served as the biogeographic link...The same kind of scenario could hold for this Early Cretaceous mammal."

Considering A. nyktos along with a contemporaneous placental from Mongolia called Prokennalestes, Rich guesses that placentals may have had a wider distribution around the world during the Early Cretaceous than previously thought. Perhaps placentals arose earlier that expected--say, while the continents were still lumped together into the single supercontinent, Pangaea. Even if terrestrial placentals were present in Australia 115 million years ago, however, Rich is quite certain that they went extinct, perhaps displaced by marsupials, and only reentered the continent 5 million years ago.

It would seem that the only way to resolve these many differing views is to find more fossils. And that's exactly what Rich and his team hope to do. They have extensive plans to continue working at the site where A. nyktos was discovered. In the meantime, the debate will surely continue. "This is the fun part," Archibald says, "discussing what it might be."

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