Over 290 million years ago, a thriving forest ecosystem was brought to a sudden end. A volcanic eruption nearby produced a pyroclastic flow, in which a current of fast-moving hot gas and rock instantaneously buried the ancient forest and all its inhabitants. Now researchers have uncovered the site of the disaster, which has become the best and most well-preserved Permian forest ecosystem ever discovered. Within the tangle of roots and beneath the leaf litter, researchers have also unearthed the first complete fossil scorpions from this period, some still in the burrows in which they died. The research is published in BMC Evolutionary Biology.
The astonishing site in Chemnitz, Germany, gives a unique look into an ancient ecosystem at a time when the world’s continents were still joined together as Pangea. The vegetation shifted to become dominated by seed ferns and conifers, as flowering trees were yet to evolve, while it also saw the development of the first fully terrestrial vertebrates, including large herbivores and carnivores. But insects still dominated, with cockroaches and their ancestors commanding the ground, while dragonflies ruled the air.
Researchers have found a preserved section of forest with trees and roots still lying in situ, including one patch containing 53 trunk bases still standing upright where they originally grew 291 million years earlier. Among these remains, palaeontologists have found whip scorpions, centipedes, amphibians, and even parts of the giant centipede Arthropleura, which could reach up to 2.3 meters (7.5 feet) in length. Found among the network of wooden roots, less than 2 meters (6.5 feet) apart, the researchers found the fossils of two potentially undescribed species of scorpions.
While earlier than 300 million years ago in the Carboniferous the arachnids are incredibly well represented in the fossil record, when we enter the Permian the number of scorpion fossils suddenly drop off. That is why the finding of not one, but two entirely preserved specimens is such an important discovery. Not only that, but the level of preservation, and the fact that they were buried in situ as they would have been in real life, can tell the researchers an extraordinary amount about the way these creatures lived.
A reconstruction of the fossil bed, showing the locations of the two scorpion fossils in relation to the roots and other creatures found preserved nearby. Volker Annacker
By studying the appearance of the fossils, the researchers are able to work out their sexes. Scorpions have what are known as “pectines,” or comb-like teeth that they use as sense organs. Normally, males have longer pectines than females, allowing the palaeontologists to determine that the two fossil creatures were of opposite sexes. Not only that, but it appears that they were buried in the burrows in which they lived and not washed in at a later date. This has allowed them to speculate about the behavior of the scorpions, with the close proximity of both a male and female raising some interesting questions, such as was the male mate guarding the female, as sometimes happens with modern scorpions?
The researchers hope that the fossils will help fill a gap in the evolution of scorpions, and with more fossils from the preserved forest still to examine, it is hoped that these scorpions will add to the knowledge of the food chains of the early Permian, as well as how they slotted into the ecosystem as a whole.
Image in text (top): The two scorpion fossils found within 2 meters (6.5 feet) of each other, seemingly still in their burrows. Dunlopet al. 2016