Evrim Yazgin
Cosmos science journalist
A newly discovered fossil site in the northeast US provides a glimpse into an ancient ecosystem nearly 100 million years older than the first dinosaurs.
The exceptionally well-preserved find is described in Nature Communications.
The site is about 50km southwest of Boston, Massachusetts in the Wamsutta Formation. It dates to about 320–318 million years ago, during the Carboniferous period.
Carboniferous fossils include the largest ever arthropods – the group which includes spiders and insects. Among them were millipedes the size of cars, spiders the size of cats and dragonflies the size of eagles.
Today’s coal deposits are the remnants of Carboniferous forests.
The Carboniferous is split into the Mississippian (359–323 million years ago) and the Pennsylvanian (323–299 million years ago) periods.
Much of what is known about the Carboniferous era comes from fossils dating to the Middle Pennsylvanian, starting about 315 million years ago. Earlier fossils – including those which mark critical stages in the evolution of insects, arachnids, seed plants and tetrapods (the first vertebrates to walk on land) – are sparse.
Many of the newly found Wamsutta fossils are among the oldest representatives of their groups.
Not only have palaeontologists found body fossils of animals and plants. They also uncovered trace fossils including footprints and burrows.
Among the fossils is some of the earliest evidence of insect behaviour including egg-laying and irritation of plants called “galling”. Plant galling can arise from feeding or insect egg-laying and leads to abnormal growths on the plants.
Researchers identified more than 130 different species from the fossils.
The ancient ecosystem is a drier, higher elevation environment than the coal swamps typically associated with the Carboniferous.
“This site gives us an unprecedented look at a terrestrial ecosystem from a crucial time in the evolution of life on land,” says lead author Richard Knecht, from Harvard University. “We’re seeing evidence of complex plant-insect interactions and some of the earliest appearances of major animal groups that went on to dominate terrestrial habitats.”
“The exceptional preservation of delicate impressions and traces allows us to reconstruct behaviours and ecology in ways not usually possible with body fossils alone,” says co-author Jacob Benner of the University of Tennessee. “We can see how these early terrestrial communities functioned as integrated ecosystems.”
Wamsutta would have been a seasonally wet, forested area close to the equator. The formation is the result of deposition of silt and sediment in a triangular shape called an alluvial fan.
