Alexander Wilhelm Armin Kellner (Vaduz, 26 September 1961) is a Brazilian paleontologist, a leading expert in the field of the study of pterosaurs.
Alexander Kellner was born in Liechtenstein, in his early childhood moving with his parents to Brazil, where he was naturalized. In Rio de Janeiro he received a primary and secondary education at the bilingual Escola Corcovado. In 1981 he began to study geology at the Universidade Federal do Rio de Janeiro. As a student he soon got involved in the research of fossil vertebrates, especially pterosaur specimens from the Santana Formation, on which he published many papers in the late eighties. He earned a Master of Science degree in geology at UFRJ in 1991, and a M. Phil. in 1994 and the Ph.D. in 1996 from the Columbia University (New York City) in a joint program with the American Museum of Natural History. In 1997 he became professor at the Museu Nacional, the Brazilian National Museum that is part of the UFRJ, the largest university of Brazil and curator of the geological and paleontological department of that institution. From 1998 to 2001, he served as the chairman of the department and from 2008 is heading the zoology graduate program. Kellner is also chief editor of the Annals of the Brazilian Academy of Sciences, the official publication of the Brazilian Academy of Sciences.
Part of his working with fossil reptiles, particularly pterosaurs, entailed organizing the Pterosaur Workshop in Pittsburgh (1995) and the first Pterosaur Symposium ever held at the American Museum of Natural History (1996). Furthermore, he was involved in the organization of several scientific meetings in Brazil such as the 31st International Geological Congress (Rio de Janeiro, 2000) and the 2nd Latin-American Congress of Vertebrate Paleontology (Rio de Janeiro, 2005).