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He made numerous contributions in the fields of paleontology and biological evolution. He studied at the Universidad de La Plata, but did not complete his studies. Later he worked at the University of Buenos Aires in the Department of Biological Sciences working with the biological evolution of mammals. In 1966 he began work at the Museum of Comparative Zoology at Harvard University. He worked for almost fifteen years at the Central University of Venezuela and the Simón Bolívar University. In 1973 he received his PhD in Zoology and Paleontology from the University of London. Among the important papers he authored was the description of Herrerasaurus, one of the earliest dinosaurs known.
In 1955, Reig was a founding member of the Asociación Paleontológica Argentina alongside Mathilde Dolgopol de Sáez.
Reig died in 1992.