Porto Geologists Identify a 298-Million-Year-Old Insect Nymph at the Pejão Coalfield, Unlike Any Known From Its Period
Found in shale at the Paraduça mine, the 10-millimetre juvenile resembles a dragonfly nymph and may have lived in water. Its closest match is an extinct order of winged insects, the Paoliida.
Researchers at the Faculdade de Ciências da Universidade do Porto (FCUP, the University of Porto's Faculty of Sciences) have described the fossil of a young insect, about 298 million years old, that does not match any nymph known from its period. It was found in the Pejão coalfield, in the Aveiro district, and resembles the nymph of a modern dragonfly.
Where it was found
The specimen was found by Sara Silva, who holds a doctorate in geosciences, in Upper Carboniferous shale at the Paraduça mine, an open-cast coal working in the Pejão area, the FCUP said in a statement sent to Lusa on Wednesday. Pejão lies in the Douro Carboniferous Basin, which the faculty describes as one of Portugal's main continental records of that time. The Upper Carboniferous ran from roughly 323 to 298 million years ago, long before the first dinosaurs.
The fossil is small: a body of about 10 millimetres, with fragments of legs, eight visible segments and short cerci (the paired appendages at the tip of an insect's abdomen).
Why it matters
"Insect nymphs from the Carboniferous are quite rare," said Helena Couto, a retired FCUP professor and a researcher at the Instituto de Ciências da Terra (Institute of Earth Sciences), who helped identify the specimen. They are hard to place in groups with a common ancestor, she explained, because those groups are usually defined from fossils of adult insects.
The team says the specimen "does not correspond to any of the known Palaeozoic nymphs" and is "clearly a species never before found in the Carboniferous". Its short cerci, long and sturdy hind thigh bones and elongated abdomen without side appendages bring it closest to nymphs assigned to the Paoliida, an extinct order of winged insects, which the authors consider the most likely hypothesis. Its bulky abdomen and large hind legs suggest that it may have lived in water.
The study, "A new enigmatic insect nymph from the Pennsylvanian Douro Basin, Paraduça Mine, Portugal", was published on 15 September in Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen, a German palaeontology journal (volume 318, issue 1, pages 9 to 15). Its authors are Torsten Wappler, a palaeontologist and entomologist at the University of Bonn; Helena Couto; Sara Silva; and André Nel, an entomologist at the Muséum national d'Histoire naturelle (National Museum of Natural History) in Paris. "Pennsylvanian" is the name used internationally for the Upper Carboniferous.
What comes next
The researchers now hope to find a better preserved specimen, in which they could see the structures of the head and the beginnings of the wings, which are not yet developed in juveniles of this kind. That, they say, could allow a more precise identification.
