Insects in amber reveal ecosystem when dinosaurs roamed the Earth

By Stephen Beech

Insects trapped in amber have provided a unique window to ecosystems that died out millions of years ago.

Ants and other species who lived alongside dinosaurs but preserved in fossilized tree resin reveal a great deal about their roles as pollinators, parasites, predators, and prey, say scientists.

Researchers in Spain scrutinised six key samples which preserve now-extinct insects unusually well, to try to learn more about the ancient ants.

Study lead author Dr. Jose de la Fuente of the Institute for Game and Wildlife Research, Ciudad Real, said: “Amber inclusions are representative of possible interactions between different organisms shaping the environment.

“The identification and morphological characterisation of fossil ants in amber with other inclusions of insects provides a snapshot of life on Earth millions of years ago.”

The scientists looked at six different pieces of amber which include several different organisms of different species, a rare phenomenon called syninclusion.

They chose the pieces of amber because they include ants, which are considered particularly important to ecosystems.

The earliest ants, which were first found in the Upper Cretaceous period 66 to 100 million years ago, are known as Stem ants and didn’t leave modern descendants. All ants alive today evolved from Crown ants.

Both species are found in the six pieces of amber studied by the scientists, as well as Hell ants, which evolved from Stem ants.

The study, published in the journal Frontiers in Ecology and Evolution, included four pieces of Cretaceous amber around 99 million years old, one piece of Eocene amber from around 34 to 56 million years ago, and one piece of Oligocene amber from around 23 to 34 million years ago.

The scientists used powerful microscopes to examine the amber, identify the different species found inside, and measure the distance between ants and other species.

In three of the six pieces of amber, the scientists found ants in close proximity to mites.

In one piece of amber the scientists found a Crown ant, wasp, and two mites so close to the ant that they may have been travelling on it.

Another, known as Case 4, contained a Stem ant and a mite, about four millimeters apart.

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A further piece also contained three different species of ant close to a mite and some termites, as well as poorly-preserved mosquitoes and a winged insect.

In another piece of amber, known as Case 6, the research team found a Stem ant alongside a probable parasitic wasp and a spider.

Dr. de la Fuente said the ant seems to have been feeding on something.

It is resting against another insect inclusion, which could be a worm or a larva, but as there’s no indication that the two were interacting, the scientists think it was a coincidence.

Another piece contains a Stem ant and a spider, while the other contained a Hell ant, a snail, a millipede, and some unidentifiable insects.

Dr. de la Fuente said: “The closest ant syninclusions are more likely to reflect behavior and interactions between these organisms.

“The proposed ant-mite interactions in Case 4 may reflect two possible scenarios.

"First, a commensal specialised temporal relationship where mites attach to ants for free ride dispersal to new habitats.

"Second, a parasitism when mites feed on the ant host during transport.”

He said that although pieces of amber that contain ants are rare, and pieces of amber that contain multiple species are rarer, there is some published evidence that points to interactions between mites and ants, sometimes mutually beneficial.

Dr. de la Fuente says future research could help clarify that by using micro-CT scanning to look for attachment structures on mites which would have allowed them to clamber onboard ants to travel.

He said the spider in Case 6 is a species which could camouflage itself as an ant and might have benefited from proximity to real ants.

The scientists say that smaller distances between insects in amber are more likely to reflect interactions during life, such as those between ants and mites.

But they cautioned that insects that aren’t in contact could just be insects that got stuck in the same resin.

Dr. de la Fuente added: “To improve the analysis of interactions between different organisms in fossil amber inclusions, future research should use advanced imaging techniques.

“Nevertheless, these results provide evidence of insect behavior and ecological habits.”