Eigil Hans Aage Nielsen (16 August 1910 – 8 December 1968) was a Danish paleontologist, who specialized in fossil vertebrate anatomy, particularly of Triassic bony fish.
[1] Nielsen is mostly known for his in-depth monographs on Triassic ray-finned fishes from East Greenland (Australosomus, Birgeria, Boreosomus, Pteronisculus), which were colleced from the Wordie Creek Formation during several expeditions.
He took part in Lauge Koch's 1931 expedition to Greenland and worked on the recovered Devonian vertebrate material (early amphibians, fish).
This time he collected ammonoids and fish fossils from layers dating back to the Permian and Triassic periods.
In 1950, Nielsen did field research in the Himalayas (Spiti region), where he collected Permo-Carboniferous and Triassic fish fossils.