Which Came First: Bees or Flowers?

All About Flowers

A revolutionary find of fossils in the state of Arizona has pushed back the possible date for the origin of bees and wasps and caused entomologists and botanists to scratch their heads over the origin of flowering plants and their furry little go-betweens. During the past year, about 40 fossilized bee nests have been found within giant petrified logs at the Petrified Forest National Park in northeastern Arizona. The discovery was made by Dr. Tim Demko, a paleobiologist in the Department of Earth Resources at Colorado State University, Ft. Colins, CO. Dr. Tim Demko located the unique fossils while conducting studies to understand the paleoecology (the study of ancient climates and environments revealed in the fossil record). He and his associates have found many fossil nests they believe to have been constructed by ancient bees, along with scattered cocoons made by wasps from within giant Araucarioxylon-type (the domiant colorful turned-to-stone logs in the park) trees.

What is so amazing and exciting about these new finds from the Petrified Forest? First and foremost, their extreme age. The fossil tree trunks have been dated between 207 and 220 million years before the present! Fossils of adult bees, their larvae, and their burrows including natal cells are extremely rare in the fossil record. Before this discovery, the oldest undisputed fossils of adult bees are 80 million year old specimens prserved enshrined within golden tombs of amber (derived from tree saps and resins) from inland and beach deposits in modern day New Jersey. These little stingless bees belong to the species Trigona prisca Michener & Grimaldi (family Apidae) in New Jersey (Kinkora) amber.

The fossils unearthed by Dr. Demko are much much older. If further studies confirm that they were made by ancient bees (unfortunately, these are ichnofossils or trace fossils showing only nests but no actual bee fossils). The oldest wasp body fossils date to about 116 million years ago, the oldest bee fossils at about 80 million and the oldest described wasp nest at about 75 million. The angiosperms, or flowering plants, are known from fossils from 110 to 120 million years ago although they may have evolved somewhat earlier. Their origin was called an "abominable mystery" by Charles Darwin in the 19th century and modern biologists are still largely in the dark about the exact origin and age of flowering plants. Now we are faced with the fact that bees may have been buzzing around a whopping 140 million years earlier! If there were no angiosperms around then, which seems likely, then the early bees or protobees probably survived on sweet exudates from non-flowering plants and pollen and spores from ferns, cycads and other ancient plants. The complex multi-chambered (individual nest cells) fossil nests found at the Petrified Forest indicate that these bees may have even been social, since the nest architecture seems reminiscent of the type of nests made by modern ground-nesting sweat bees (in the family Halictidae). Each nest consists of clusters of 15 to 30 cells shaped like little flasks or urns and each about one inch long. Most of the nests seem to have gained entry to the tree through open knotholes and were made while the tree was alive, since the team found "reaction wood" to be present. Further, the nests are found high in the top one third of the trees within what would have been the canopy region.

Thus, we have the problem that the origin of flowers dates from only half as long ago. Could it "bee" that bees evolved and lived before flowers appeared to brighten up those ancient landscapes? That very idea was once unthinkable, and still raises the hackles on some botanists and bee biologists. This is so because most biologists still tacitly believe that bees were necessary to spur the explosive adaptive radiation that we see in the Cretaceous fossil record for the flowers. Bees are thought to have played a major role in the early diversification of the flowering plants. Therefore, either the flowering plants evolved much much earlier than anyone has believe (and we haven't located their fossils yet) or the earliest bees did just fine without them dining on pollen from early gymnosperms (including the ferns, cycads, conifers etc.) and related plants before the flowering plants began to show off with eye-catching gaudy colors and abundant floral rewards in the form of sweet energy-richy nectar and protein-rich pollen grains. Therefore, the exciting new discovery by Demko casts doubt on the standard dogmatized theory that flowering plants and the bees co-evolved "hand in hand" and that the spread of flowers across the globe further influenced the spread and diversity of bees, a group with about 25,000 described species, but with perhaps as many as 40,000 extant species worldwide. Demko suggests, in fact, that showy flowers may have evolved to lure bees, as pollen vectors, away from other early plants!
Dr. Demko has been joined in his investigations by his colleague, Mr. Stephen Hasiotis. A longterm Petrified Forest researcher and paleobotanist, Dr. Sid Ash, is also involved in further study of the ancient nests. The team plans to use GIS technology to produce a detailed map of the locations of the nests which occur over a very small area of the forest. Additionally, they will be taking thin sections of some of the fossils to examine the internal structures of the cells and their associated burrows. It is possible that they may even find fossilized pollen grains within the cells. If so, that would put to rest most of the doubts about their origin by excavating female bees since only bees and a few wasps (the Masaridae) are known to collect and provision their nests with pollen as food for their larvae. Amazingly, their team will also conduct studies of the geochemistry of the burrows and cells. It may be possible to identify ancient chemicals (waxes etc.) that are still preserved that may give further clue to the identity of their makers.

Several CHBRC scientists may join Demko and Hasiotis this summer to explore the area looking for more nests and study their contents. If this happens, we will provide you with a report from such a field trip. Stay tuned to GEARS for more information.

Source: USDA/ARS

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