Animal Evolution – Glimpses of Ancient Environments

Although amber appears to be a somewhat unusual inorganic mineral, it is actually derived from an organic source – tree resins. Millions of years ago, when this aromatic and sticky substance slowly leached from coniferous trees, insects and other biological materials could get stuck in them. This is why some amber specimens contain fossil specimens, preserved in nearly primitive condition, that provide great snapshots of the flora and fauna of ancient forests. Now, a research team led by LMU animal scientists Viktor Baranov and Joachim Haug has made exciting discoveries in amber samples from the Baltic and Myanmar, which provide new insights into the ecology of two groups of ancient insects.

In the Eocene period – between 56 and 33.9 million years – Baltic amber forests (probably about 38 million years ago) covered large areas of what is now northern Europe, and were the source of most of the amber found in Europe. In one sample, the LMU team identified at least 56 fly larvae, all of which were buried while eating on a single piece of mammalian dung. “This fossil is particularly interesting, because the dung is full of plant debris, which indicates the presence of large herbivores at least in these forests,” Baranov explains. On this basis, he and his colleagues hypothesize that there must be open spaces of nearby grassland, which supports the earlier hypotheses. “The Baltic amber forest is often portrayed as a dense forest with a damp landscape. It’s likely a more open habitat, warm to moderate,” says Baranov.

In other samples, researchers have found insect larvae whose modern descendants reside primarily with plants undergoing chronic stress. “It has always been suspected that forests that produce large amounts of amber have been under environmental pressure,” says Hoge. “That would be completely compatible with having these larvae.” High temperatures and dry conditions are the most likely source of such stress.

The unusual butterfly caterpillar that Hugh identified in amber from Myanmar is much older than specimens from the Baltic Sea. It dates back to the Cretaceous period, more than 100 million years ago, at a time when dinosaurs still dominated Earth. So far, only four Cretaceous larvae have been discovered, and the new discovery is completely different for all of them. “All of the caterpillars previously discovered were relatively naked,” says Haug. “Our caterpillar is the first ‘armored’ sample that has appeared – and it has spines back on some of its parts.” Thus, the new sample supports the idea that butterflies underwent an early stage of diversification and also reveals some aspects of their environment. In modern caterpillars, these thorns act as a deterrent to predators – more specifically, songbirds. “The rapid diversification of birds begins after the demise of the larger dinosaurs, but the smaller birds that may have fed on larvae were already present during the Cretaceous period,” says Haug.


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