By JOHN NOBLE WILFORD
Published: May 23, 1995 in The New York Times
BEFORE time turned them to stone at least 220 million years ago, the fossilized logs of the Petrified Forest in eastern Arizona stood as tall trees in a tropical environment. Many of them, scientists have now discovered, still bear traces of insect nests the trees once harbored. The logs are riddled with holes containing little chambers strung together in lines or clusters, nearly everything about them resembling the nests of modern bees.
The problem is that flowers date from only half as long ago. Could bees have lived before flowers? The very idea, once unthinkable, is upsetting traditional theory about the early history of bees and their supposed co-evolution with flowering plants, or angiosperms.
If confirmed by further research, the new findings at the Petrified Forest mean that bees were buzzing around some 140 million years earlier than previously thought. The oldest known fossil of a bee is an 80-million-year-old specimen trapped in amber from present-day New Jersey. Scientists now must be on the lookout for fossil bees to fill that huge time gap.
And then they must figure out what those bees were doing before the emergence of angiosperms, the earliest evidence for which is dated at 110 million to 120 million years ago. Either flowers actually appeared much earlier than anyone can conceive, or the first bees did without flowers for a long time, feeding on and pollinating cone-bearing, woody plants known as gymnosperms, a group that includes conifers, cycads and ferns.
In the latter and more likely case, scientists said, the discovery casts serious doubt on the standard theory that flowering plants and social insects like bees more or less evolved together, with the spread of flowers presumably influencing the development and proliferation of the bees.
“This new evidence suggests it was probably the other way around, and that insects like bees and wasps may have facilitated the evolution and diversification of angiosperms,” said Stephen T. Hasiotis, a paleobiologist at the United States Geological Survey in Denver and a doctoral student in geology at the University of Colorado at Boulder.
Mr. Hasiotis came upon the fossil bee nests while conducting studies aimed at reconstructing the ancient ecosystem and climate at the Petrified Forest, particularly as it applied to invertebrate life. He and other researchers found the remains of several hundred nests and cocoons, and tests put their ages at 207 million to 220 million years. Although no bee or wasp body parts were found with the fossil nests, they said, the only creatures that make similar structures today are bees and wasps.
The discovery was announced last week by Mr. Hasiotis at a regional meeting of the Geological Society of America, held at Montana State University in Bozeman. His collaborators were Dr. Russell Dubiel of the Geological Survey in Denver and Dr. Tim Demko of Colorado State University.
Despite the discovery’s stunning implications, other scientists tended to react favorably, in part because the evidence seemed compelling and it supported recent revisionist thinking about insect evolution. This stems from a growing recognition that the greatest expansion and diversification of insects occurred many millions of years before the appearance of flowering plants.
“We’re all very impressed,” said Dr. Charles D. Michener, an entomologist at Kansas University in Lawrence who is the author of “The Social Behavior of the Bees,” published by Harvard University Press in 1974. Mr. Hasiotis visited the Kansas campus earlier this year and showed the evidence to Dr. Michener and his colleagues.
Dr. Michener agreed that the fossil nests looked like the clusters of chambers, or cells, that make up the nests of modern bees. But like other scientists, he cautioned that more research would be needed to confirm the findings. It is always possible that some insect no longer extant made bee-like nests back then. The best evidence, of course, would be to find some fossil bees associated with the nests, he said.
“It’s exactly what we would have expected,” was the reaction of Dr. J. John Sepkoski Jr., a paleontologist at the University of Chicago. It was he and Dr. Conrad C. Labandeira, a specialist in fossil insects at the Smithsonian Institution’s National Museum of Natural History in Washington, who reported two years ago the results of a comprehensive study of insect evolution. Their conclusions challenged orthodoxy by pointing out that the appearance of flowering plants did not prompt the great diversification of insects because they had been flourishing at least 120 million years before that.
Mr. Hasiotis found the ancient nests over the last four years of field work among the fossil logs. They were usually in shallow hollows inside the trunks, reached through knot holes. Each nest consisted of 15 to 30 cells shaped like little flasks, each less than an inch long. Each shell had a narrow entrance that led to a wider chamber. The walls were probably constructed out of sap and resin from the tree.
In shape and size, Mr. Hasiotis said, each cell was “virtually identical” to similar enclosures in the nests of modern bees. Their practice is to deposit an egg in each cell, along with a store of pollen and resin as food for the larva that emerges from the egg.
The researchers also found the remains of other nests underground and clusters of cocoons in the logs. They closely resemble cocoons of present-day wasps. The evidence could push back the known origin of wasps by as much as 100 million years.
“The nest construction of these insects is fairly complex, indicating a highly developed behavior,” Mr. Hasiotis said.
The nest builders would not have been the same species as modern honeybees, he said, but probably primitive insects related to a smaller species today commonly known as the sweat bee. The appearance of the nest suggests the builders would have had an anatomy similar to that of today’s bees and wasps. That is, they would have needed a flexible and jointed head, thorax and abdomen with strong legs and the ability to fold the wings behind and flat against the back in order to maneuver around individual nest cells.
Because it is difficult to imagine bees without flowers, the new findings could have enormous implications for botany.
As it stands now, a tiny fossilized plant that lived 120 million years ago is considered the oldest known flower. Identified by Yale University botanists in 1990, it was apparently an herb, barely one inch tall and resembling the black pepper plant. Only later, it is assumed, did angiosperms evolve more dazzling flowers and nectar to lure insects, birds and bats to act as agents, transferring the pollen of one plant to the seed of another.
But recent research has led some botanists to suspect that the first angiosperms probably originated much earlier — perhaps as far back as 200 million years ago in the Triassic period, when dinosaurs were getting started. If it could be established that bees already existed then, theories of an earlier history for angiosperms would receive a big boost.
But the earlier bees would not necessarily have required angiosperms, said Dr. Thom Taylor, a paleobotanist at Ohio State University in Columbus. Although he has not studied the evidence for fossil bee nests, he could conceive of bees existing in a green world of ferns, conifers and cycads and other ancient gymnosperms, the dominant vegetation in the Triassic.
The pollen of these plants is normally scattered by wind, not by insects and birds. But Dr. Taylor said, “It would not surprise me to learn that bees and fern plants developed a relationship that involved pollination.”
In that case, as Mr. Hasiotis speculated, flowering plants did not so much open up new ecological niches for insects, including bees and wasps. Instead, they may have evolved to compete for the attention of insects that were already flourishing.
“Primitive angiosperms probably took advantage of this bee and wasp behavior by developing various colors of flowers as a pollination strategy to compete with gymnosperms,” the researcher said. “Over time, most of the insects actually shifted from gymnosperms to the flowering plants.”
Angiosperms may well be late bloomers as far as bees are concerned, but with the help of a lot of busy bees they have certainly flourished. Now there are 250,000 species of angiosperms, compared with fewer than 15,000 remaining varieties of gymnosperms.