The first amber fossils from the African continent have been discovered, revealing a snapshot of life 95 million years ago and giving clues to the evolution of animals and plants, scientists report in journal PNAS this month.
An international team, including scientists at the Natural History Museum, studied the amber fossils, which are some of hundreds of specimens uncovered from the Debre Libanos Sandstone Unit in the northwestern plateau in Ethiopia.
Preserved inside the amber pieces are an amazing variety of animals, plants and fungi. The team identified ancestors of modern spiders, wasps, and ants and these finds are among the earliest African records of these groups of insects.
'This new discovery closes a major gap in our knowledge on the distribution of biodiversity of various lineages of organisms including plants, insects, and fungi around 100 million years ago,' says Dr Harald Schneider, botanist and expert in land plant biodiversity, at the Natural History Museum.
The amber was dated to 93-95 million years ago, during the middle of the Cretaceous. This was an important time in the evolution of life on Earth when flowering plants (angiosperms), and then ants, mammals and birds, began to dominate most terrestrial environments. These changes coincided with major changes in the biodiversity (the diversity of plants and animals and their habitats) of land environments.
As well as being treasured for its attractiveness, amber is very important scientifically. Amber is fossilised tree resin. The soft and sticky resin oozes from tree bark and can trap small insects, preserving them incredibly well when fossilised. Insects are rarely preserved in the rock fossil record, making amber even more important for studying these creatures.
Afircan amber specimen showing a well-preserved ancient ant from around 95 million years ago © PNAS and Alexander Schmidt
The species uncovered in the African amber allow scientists to put together a snapshot of the ecology in Cretaceous woodlands. They are able to get a picture of the diversity of animals and plants that lived together in their environment at that time.
‘The unique diversity of the discovered amber provides a window to study the environment of Cretaceous African woodlands at the beginning of the revolution of terrestrial environments that coincide with the rise of the angiosperms,' says Dr Schneider.
Many of the species identified by the team shed new light on the origin of some arthropods (the group that includes insects, crustaceans, spiders, millipedes and centipedes).
One insect specimen is a wingless female ant. It is one of the oldest records of an ant found anywhere and so gives important clues to ant evolution.
Linyphiid spider preserved in amber. This is the only the third fossil spider to be described from Africa. © PNAS and Alexander Schmidt
Until now, the oldest ant specimen came from the northern continents, which would have been part of the supercontinent Laurasia during the middle of the Cretaceous. Many scientists thought ants originated there.
Africa and the southern continents, such as Antarctica, Australia, Madagascar and South America, would have been part the supercontinent Gondwana, so this ancient ant discovery challenges these ideas.
Most of the world’s amber has been uncovered in Laurasia. Very few amber specimens have been found in areas that were formerly Gondwana because, until now, no amber fossil deposits (sites) had been found.
Another well-preserved specimen identified in this research is a male spider. The team says it probably belonged to the family of spiders called Linyphiidae that weave sheet-webs.
Magnified view of a fossilised stellate hair from an ancient fern preserved in African amber. It resembles those found on modern ferns. © PNAS and Alexander Schmidt
This specimen is the second oldest linyphiid discovered, and only the third fossil spider species to be described from the African continent.
Also identified were some of the earliest fossil ancestors of parasitoid wasps, and tiny plant structures called stellate hairs that resemble those of modern tree ferns (stellate hairs are hairs on leaves and plant stems with branches radiating from a centre that are sometimes star-shaped, shown in the image to the right).
Dr Schneider concludes that these new discoveries expand our knowledge on the origin of the groups that make up most of the Earth’s biodiversity living today, the plants and insects.
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