Hemisyntrachelus

This genus is known in the fossil records from the latest Miocene to the Quaternary (age range: from 5.332 to 1.806 million years ago). Fossils are found in the marine strata of Italy, the Netherlands, the Bahía Inglesa Formation of the Caldera Basin, Chile and in the fossiliferous Pisco Formation of Peru.[2][3]

The following species have thus far been classified as belonging to this genus:.[2][3]

• Hemisyntrachelus cortesii Fischer 1829
• Hemisyntrachelus oligodon Pilleri and Siber 1989
• Hemisyntrachelus pisanus Biannuci 1996

Hemisyntrachelus cortesii lived about three million years ago (from 3.6 to 2.588 mya).[3] Its fossil skeleton reaches a length of about 3 metres (9.8 ft) and it has been found only in La Torrazza, Italy. This species shows intermediate characters between the bottlenose dolphin and the killer whale. It fed on large fishes and squids.

Hemisyntrachelus oligodon lived from 7.246 to 5.332 million years ago. Fossils have been found only in the Pisco Formation of Peru.[3]

Hemisyntrachelus pisanus could reach a length of about 5 metres (16 ft). It was widespread in the Mediterranea Sea during the Miocene. Fossils have been found only in Orciano, which is in a Piacenzian coastal claystone in Italy.

• 
  Skull cast of Hemisyntrachelus cortesii
• 
  Skull cast of Hemisyntrachelus pisanus

• G. Bianucci, S. Sorbi, M. E. Suarez and W. Landini. 2006. The southernmost sirenian record in the eastern Pacific Ocean, from the Late Miocene of Chile. Systematic Palaeontology 5:945-952