Some 65 million years ago, a mass extinction of global proportions stamped out much of the earths flora and fauna, perhaps most notably the dinosaurs. The fossil record indicates that worldwide species diversity did not recover from this catastrophic event for another 10 million years. It came as a surprise, then, when researchers recently discovered near Denver, Colo., remnants of an incredibly plant-rich rain forest dating to just 1.4 million years after the devastation.

Writing in the current issue of the journal Science, Kirk Johnson and Beth Ellis of the Denver Museum of Nature and Science report that fossilized leaf remains collected from five different sites in the area reveal an assortment of vegetation very similar in form and quantity to that of lush modern-day tropical forests (see artist's reconstruction above). Large leaves with elongated "drip tips," palmlike fronds and the large numbers of new species evidenced by these specimens contrast sharply with what is known from other sites dated to the same period, most of which are species-poor. Johnson and Ellis posit that a so-called rain shadow from nearby mountains may have enabled frequent dousing of the area with water, perhaps from monsoons originating in the Gulf of Mexico or a large sea that once sat in present-day North Dakota. Such nourishing conditions, they propose, would have allowed this forest to flourish while others recovered more slowly.