Cranial osteology of a new specimen of Allosaurus Marsh, 1877 (Theropoda: Allosauridae) from the Upper Jurassic of Portugal and a specimen-level phylogenetic analysis of Allosaurus.

This article focuses on the detailed description and phylogenetic analysis of cranial fossil material of Allosaurus from the Upper Jurassic Andrés fossil site in Portugal, and its implications for the taxonomy and palaeobiogeography of the genus. The study confirms that the Portuguese specimens, including those previously assigned to the controversial species Allosaurus europaeus, belong to Allosaurus fragilis, supporting the synonymy of A. europaeus under A. fragilis. Phylogenetic analyses incorporating North American Morrison Formation specimens recognize only two valid Allosaurus species—A. fragilis and A. jimmadseni—with the Portuguese material nested within A. fragilis. This close morphological similarity across the proto-North Atlantic suggests either ongoing faunal interchange or incipient vicariance during the Kimmeridgian–Tithonian, reflecting limited divergence in theropod fauna between the Lusitanian Basin and North America.