Pycnonemosaurus (meaning ‘thick forest lizard’) is a genus of carnivorous theropod dinosaur that belonged to the family Abelisauridae. It was found in the Upper Cretaceous Bauru-type red conglomerate sandstone, Mato Grosso, Brazil, and it lived about 70 million years ago during the Late Cretaceous (Maastrichtian stage). Initial size estimations put this animal at 7 metres (23 ft) in length, but later analyses have found that it was likely larger, being about 8.9 metres (29.2 ft) long. This new size estimate currently makes Pycnonemosaurus the largest formally described member of the Abelisauridae thus far.
Thus far, the remains of Pycnonemosaurus have been fragmentary: five incomplete teeth, parts of seven caudal vertebrae, the distal part of a right pubis, a right tibia, and the distal articulation of the right fibula. The small pubic foot and hatchet-shaped cnemial crest of the tibia distinguish this species within the abelisaurs. The type species, Pycnonemosaurus nevesi, was formally described by Kellner and Campos in 2002.