Hemisyntrachelus is an extinct genus of cetacean.
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 BahÃÂa Inglesa Formation of the Caldera Basin, Chile and in the fossiliferous Pisco Formation of Peru.
The following species have thus far been classified as belonging to this genus:.
The body length of about Hemisyntrachelus was . Its large body size suggests that Hemisyntrachelus was a major predator in the ecosystem of that era.
Hemisyntrachelus cortesii lived about three million years ago (from 3.6 to 2.588 mya). Its fossil skeleton reaches a length of about 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.
Hemisyntrachelus pisanus could reach a length of about . 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.
Hemisyntrachelus likely lived in pods similar to modern orcas. Contemporary predators included Orcinus citoniensis and giant shark otodus megalodon. At that time, large Lamniformes such as Carcharodon hastalis and Parotodus benedenii were also found in Italy. As one of the top large predators of its time, Hemisyntrachelus likely consumed a diverse diet ranging from medium to large bony fish and squid to other small marine mammals. It is estimated to have had a diet similar to that of modern false killer whales and engaged in opportunistic hunting.