The feather pattern of its leaves also indicates that the plant lived in the water, Dilcher says, an observation that is further supported by the fossils of fish found in the same slab. It probably lived in a shallow lake populated by dinosaurs, crocodiles, turtles, and numerous types of fish.
Archaefructaceae's seeds are enclosed inside fruits, a characteristic that separates flowering plants from more primitive seed-producing plants.
Interestingly, however, petalstypical of many flowering plantsare absent. Given the quality of the fossil's preservation, they were not apparently lost during the process of fossilization. Instead, it seems, this plant never had petals.
"It's a really incredible fossil," says Michael J. Donoghue of Yale University. "It's spectacular that they've got a specimen that shows pretty much the entire plant," he says.
The researchers analyzed the fossil to determine where it fits into the evolutionary tree of the plants. By comparing the physical forms of related ancient and modern organisms, scientists can make educated guesses about which are most closely related and in what order various innovative features evolved.
Based on their analysis, Dilcher and his colleagues conclude in the May 3rd issue of the journal Science, Archaefructaceae was a sister family to all living flowering plants.
That means that Archaefructaceae diverged from the flowering plants before the ancestor of all modern members of the group arose, making it as close to the original flowering plant as any fossil yet found.
That raises the possibility, says Dilcher, that flowering plants actually evolved in aquatic environments, a scenario that runs counter to conventional wisdom.
Other scientists, however, say it's difficult to evaluate exactly where the new fossil fits in among flowers. Several suggest that the fossil may have been an early, petalless variation on the waterlilyanother aquatic, flowering plantthat ultimately went extinct.
"It would be fascinating if there were several separate lineages [of early flowering plants] that were exploring life in the water," says Donoghue. But from the limited data the researchers presented in the paper, he says, "it's not clear to me why they reached this conclusion."
Even if there were two lineages of early flowering plants that were aquatic, says James A. Doyle of the University of California, Davis, "it would still be a pretty wild hypothesis to say flowers evolved in the water."
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