Researchers at Oregon State University have discovered the oldest bee ever known, a 100 million year old specimen preserved in almost lifelike form in amber, and an important link to help explain the rapid expansion of flowering plants during that distant period.
The findings and their evolutionary significance are outlined in an article to be published this week in the journal Science.
The specimen, at least 35-45 million years older than any other known bee fossil, has given rise to a newly-named family called Melittosphecidae -- insects that share some of the features of both bees and wasps. It supports the theory that pollen-dependent bees evolved from their meat-eating predecessors, the wasps.
"This is the oldest known bee we've ever been able to identify, and it shares some of the features of wasps," said George Poinar, a professor of zoology at OSU and international expert in the study of life forms preserved in ancient amber. "But overall it's more bee than wasp, and gives us a pretty good idea of when these two types of insects were separating on their evolutionary paths."
Just as important, Poinar said, the discovery points to the mechanism that could have allowed for the rapid expansion and diversity of flowering plants around that time -- the "angiosperms" that depend on some mechanism other than wind to spread their seeds. Prior to that, the world was dominated by "gymnosperms," largely conifer trees, which used wind for pollination and re-seeding.
These changes took place during the Cretaceous Period, which lasted from 65.5 million to 145.5 million years ago. The earliest angiosperms didn't really begin to spread rapidly until a little over 100 millions years ago, a time that appears to correspond with the evolution of bees seen in the new fossil.
"Flowering plants are very important in the evolution of life," Poinar said. "They can reproduce more quickly, develop more genetic diversity, spread more easily and move into new habitats. But prior to the evolution of bees they didn't have any strong mechanism to spread their pollen, only a few flies and beetles that didn't go very far."
The amber specimen Poinar studied, which came from a mine in the Hukawng Valley of northern Myanmar, has certain features that resemble wasps, such as a double spine on the middle tibia and narrow hind legs. But it also has branched hairs all over its body and other key features characteristic of pollen-spreading bees. This species, named Melittosphex burmensis, is long extinct.
"In archaeology, a lot of people look at the species Archaeopteryx, which is believed to be the first bird and was sort of half-bird, half-reptile," Poinar said. "Species such as that can be critically important in helping us to understand when evolution went in different directions. In that sense, this fossil may help us understand when wasps, which were mostly just meat-eating carnivores, turned into bees that could pollinate plants and serve a completely different biological function."
Flowering plants, among other things, account for practically all of the food plants on Earth and much of the food supply for humans and many other animal species. There are now about 20,000 species of bees, which use pollen to feed their young, and over millions of years they have created numerous physical and behavioral adaptations to make them some of Earth's most effective pollinators.
Considering its age, the bee specimen itself is in remarkable condition, showing individual hairs on undamaged portions of its thorax, legs, abdomen and head. The legs and wings are clearly visible. It's a very small bee, consistent with evidence that some of the earliest Cretaceous flowers were also quite small.
Insects trapped in amber, researchers say, often provide some of the most vivid and lifelike glimpses into the distant past. Amber is a semi-precious stone that begins as tree sap, which can ooze down and trap insects or other small things, then ultimately fossilize. It's also a natural embalming agent that can protect and display specimens in nearly perfect, three-dimensional form millions of years later.
This phenomenon has been invaluable in scientific and ecological research, and among other things, formed the scientific premise in the movie Jurassic Park, for the "dinosaur DNA" found in mosquitoes. Poinar, one of the world's experts in the study of amber, also has used it to provide a vivid re-creation of an ancient forest in the book "The Amber Forest: A Reconstruction of a Vanished World."
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