One of the specimens found in the amber from the late Oligocene Pomahaka Formation of the South Island of New Zealand. Photo: Viktor Baranov

An international scientific team led by the Doñana Biological Station - CSIC has identified the first amber-preserved fossils of  Chironomidae (non-biting midges) in New Zealand. These fossils date back to the late Oligocene, approximately 26 million years ago. During this period, the ancient continent of Zealandia was mostly submerged under the ocean, resulting in very few amber fossil records. The study, published in  PeerJ, hprovides new insights into the biogeography and past ecosystems of this region.

The analysis of thirteen Chironomidae specimens found in amber from the Oligocene Pomahaka Formation has revealed the presence of insects from the subfamily Orthocladiinae Kieffer. Among the most significant findings is the identification of Bryophaenocladius zealandiae, the first Southern Hemisphere fossil species of the genus Bryophaenocladius Thienemann, which is absent from the current fauna of New Zealand but may still be present in the isolated subantarctic Auckland Islands. A second species, Pterosis extinctus, the first fossil record of the extant genus Pterosis Sublette & Wirth, which today is represented by a single endemic species in the subantarctic Auckland and Campbell Islands.

“Since New Zealand has few terrestrial and aquatic fossils from the Oligocene, this amber is very important for understanding the history of the New Zealand land mass and as a unique biogeographical region”, explains Viktor Baranov, a researcher at the Doñana Biological Station and lead author of the study. 

Additionally, researchers have found other specimens include incomplete individuals corresponding to the morphotypes of Bryophaenocladius and Metriocnemini.

These new fossils belong to animals requiring terrestrial or semi-aquatic habitats for larval development. This supports the theory of the existence 26 million years ago of a humid forest swamp paleoenvironment in southern New Zealand.

Extinction and vulnerability of freshwater fauna

Beyond its scientific significance, these findings have important environmental implications. The regional extinction of entire genera of aquatic insects—despite their widespread global distribution—highlights the vulnerability of freshwater fauna to environmental changes.

"Curiously, while both genera of midges discovered in the Pomahaka amber are absent from the New Zealand mainland today, both of them still survive in the Auckland Islands", says Baranov. "This opens new lines of investigation in dispersal and extinction of freshwater animals in Southern Hemisphere”

Understanding the mechanisms of extinction in these organisms is crucial, as freshwater species are among the most threatened by the current biodiversity crisis. "Given the great economic, recreational, and intrinsic value of animals living in freshwater, understanding and halting their extinction is of large social importance," concludes the researcher.

The study was conducted in collaboration with the Doñana Biological Station - CSIC (Spain), the Institute of Materials Research at the Helmholtz Centre (Germany), the University of Otago (New Zealand), and the University of Göttingen (Germany).

Reference

Viktor Baranov, Joerg U. Hammel, Daphne E Lee, Alexander R Schmidt, Uwe Kaulfuss Extending the fossil record of late Oligocene non-biting midges (Chironomidae, Diptera) of New Zealand, PeerJ. https:// doi.org/10.7717/peerj.18893 

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