In 1964, Miguel Telles Antunes described "Mosasaurus iembeensis" from a partial skull excavated from the Itombe Formation near the town of Iembe, Angola. As the deposit was of the Turonian age, this discovery represented one of the oldest derived mosasaurs. In 1992, Lingham-Soliar argued that the features of the skull disagreed with those of "Mosasaurus" and were instead characteristic of "Tylosaurus". He subsequently moved the species into the genus, becoming "Tylosaurus iembeensis". However, Lingham-Soliar did not figure the holotype skull, which he identified as residing in the collections of NOVA University Lisbon without a catalog number, and it was later reported in 2006 that the specimen may have been lost during a fire. In a 2012 multi-author study led by Octávio Mateus, it was reported that an additional "T. iembeensis" fossil consisting of fragmentary skull elements was recovered during an expedition to the lost holotype's locality, although the specimen was not figured or formally described.