Massive Extinction Event – Evidence for Bee Diversity Decline at the End of the Cretaceous

The Cretaceous mass extinction event that saw the demise of the Dinosauria, is perhaps the best known to the general public, of all the great extinctions recorded in the fossil record.  Something like 60% of all, large terrestrial life forms became extinct some sixty-six million  years ago. Although, the causes of the extinction are still debated, we often come across members of the public who can be very knowledgeable about asteroid impacts and such like but seem to have missed some of the important implications of this particular event that occurred back in deep time.

Cretaceous Mass Extinction

It was not just those scary, non-avian dinosaurs  that failed to make it through to what was later termed the Palaeogene.   Whole groups of other organisms died out near to or around the time that the K-T boundary was laid down.

Marine reptiles, ammonites and the pterosaurs become extinct.  Other classes of organism suffered dramatic losses and a rapid reduction in their diversity, groups such as marine plankton, brachiopods, echinoderms and bivalves.  Plants were not immune to effects either.  Although the fossil record for the angiosperms at the end of the Cretaceous is far from complete, scientists have shown that flowering plants, including hardwood trees also suffered, especially those genera associated with the Northern Hemisphere.

Flowering Plants Affected

If flowering plants were affected by the mass extinction event, then it is logical to assume that those organisms that have a close association with these plants would also have declined too.  We are not just talking about the plant-eaters, what about the pollinators?

An international team of researchers have identified a dramatic decline in bee numbers at around the same time the dinosaurs became extinct.  The research team, including Dr Sandra Rehan of the department of Biological Sciences (University of New Hampshire) and her collaborators from the South Australia Museum, the University of Adelaide and Flinders University (South Australia) used a series of molecular phylogenetic analyses to demonstrate that one particular type of bee suffered a significant decline.

Given the implied dramatic changes to ecosystems that occurred at this time, the events recorded in the fossil record at or near the K-T boundary would have significantly disrupted many plant-insect relationships.  Such disruption would have had major consequences for the subsequent evolution of those flowering plants that depend on the likes of bees to pollinate them and vice versa.

Studying Bee Populations

The researchers chose to study bees within the subfamily known as Xylocopinae, the long-tongued bees which included the carpenter bees.  These bees may have evolved more than ninety million years ago, a time when it could be argued that the dinosaurs were in their heyday with the flowering plants also doing extremely well and beginning to dominate the flora in a number of habitats.  It had been assumed by scientists that insect pollinators would have been severely affected by the Cretaceous mass extinction event, but as the paper’s (the paper having just been published in the online journal PLoS One), lead author, Dr Sandra Rehan stated:

“There is a relatively poor fossil record of bees.  This has made the confirmation of such an extinction difficult.”

However, the researchers were able to use an extinct clade from the  Xylocopinae Subfamily as a calibration point for timing the diversification and the radiation of these bees.  The team also studied the fossils of angiosperms that had evolved traits that allowed them to be pollinated by these long-tongued forms.

Dr Rehan commented:

“The data told us something major was happening in four different groups of bees at the same time and it happened to be the same time as the dinosaurs went extinct.”

This research could have important implications for bee conservation today, as environmentalists, governments and scientists express concern over the loss of important bee pollinator species today.

Dr Rehan added:

“Understanding extinctions and the effects of declines in the past can help us understand the pollinator decline and the global crisis in pollinators today.”

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