Temporal range: Tortonian
Bianucci & Landini, 2006
Zygophyseter varolai is an extinct cetacean, similar to the sperm whale. The common name of killer sperm whale refers both to its relation to modern day sperm whales, and to its similarity in size to and its "probable similar feeding adaptation to the extant delphinid killer whale (Orcinus orca)".
The genus name Zygophyseter emphasizes the elongation of the zygomatic process of the only known species Z. varolai, while the term physeter refers to the type genus of the family Physeteridae. The Latin species name honors the discoverer, Angelo Varola. 
The genus Zygophyseter is known in the fossil records on the basis of an almost complete skeleton of Z. varolai, discovered in Southern Italy in the marine lime mudstone of the Pietra Leccese Formation and described in 2006 by G. Bianucci and W. Landini. This species dates back to the Tortonian Age of the Late Miocene Epoch (age range from 11.608 to 7.246 millions years ago). 
Z. varolai had a large body, reaching an estimated length of 6.5–7 m (21–23 ft). The large teeth are present in both jaws, making it capable of feeding on large prey. It had a very long zygomatic process, probably for housing the spermaceti organ. Like in all modern sperm whales, this species had a very large basin above the braincase which housed the spermaceti organ and melon, indicating it was able to echolocate.
- Bianucci, Giovanni; Landini, Walter (2006). "Killer sperm whale: a new basal physeteroid (Mammalia, Cetacea) from the Late Miocene of Italy". Zoological Journal of the Linnean Society. 148: 103–131. doi:10.1111/j.1096-3642.2006.00228.x. Retrieved 10 February 2017.
- Karen's Komments - A New Killer Sperm Whale from Italy – Zygophyseter
- Paleobiology Database
- Boessenecker, Robert. "Zygophyseter varolai". NYIT. Retrieved 10 February 2017.
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