Alexander Wilhelm Armin Kellner (born September 26, 1961) is a Brazilian geologist and paleontologist who is a leading expert in the field of studying pterosaurs.

[1] Kellner is also chief editor of the Anais da Academia Brasileira de Ciências, the official publication of the Brazilian Academy of Sciences.

[1] Kellner has organized or taken part in several paleontological expeditions to many locations around the globe, including Brazil—Mato Grosso, Rio Grande do Sul and Ceará;[5] the deserts of Atacama, Chile and Kerman, Iran; Montana in the United States; Patagonia in Argentina;[1] the famous deposits of Liaoning, China,[5][6] and James Ross Island in Antarctica.

He has published more than 160 primary studies[4] and two science books: Pterossauros - os senhores do céu do Brasil ("Pterosaurs — Lords of the Brazilian Sky")[9] and the novel Na terra dos titãs ("In the Land of the Titans").

He organised the 1999 exposition No Tempo dos Dinossauros ("In the Time of the Dinosaurs") at the Museum of Earth Sciences, which has been regarded as a landmark for the establishment of paleontology in Brazil, attracting the attention of the people of Brazilian to the studies of fossils.

[1] In 2006 he organized the mounting of the first large-scale dinosaur skeleton in Brazil, that of the sauropod Maxakalisaurus topai, for which he received recognition from the Brazilian Congress.

[5][11] Since 2004 he has written a monthly column in Caçadores de Fósseis (Fossil Hunters), on the website Ciência Hoje On Line, a project of the Brazilian Society for Scientific Progress.