Perucetus is an extinct genus of an early whale from Peru that lived during the Bartonian age of the middle Eocene.

It was initially claimed to have rivaled or exceeded the modern blue whale in weight, partly due to the incredibly thick and dense bones this animal possessed, coupled with its already great size, but subsequent studies argued that it was significantly lighter.

Its diet can only be speculated, but one suggestion proposes that it may have fed on benthic animals like crustaceans and molluscs living on the ocean floor.

[1] The remains of the Perucetus are currently under protection and on display at the Natural History Museum of Lima, which belongs to the National University of San Marcos, the main institution of the team of Peruvian paleontologists involved in the discovery.

[3] The name Perucetus derives from the whale's country of origin, Peru, while the species name references the enormous size of the animal.

[1] The innominate bone of Perucetus is highly reduced but still features a well-developed acetabulum, a condition considered ancestral among whales.

The innominate, however, differs in shape from that of Basilosaurus, and the proximal end of the ilium is notably more robust than in other early Pelagiceti.

The centra of the lumbar vertebrae are greatly elongated like in basilosaurines and pachycetines but do not quite reach the proportions of the most extreme members of said groups.

Ultimately, extreme values were used in the calculations, leading to the wide range for the weight estimate present in the type description.

Within Pelagiceti, the well-defined acetabulum suggests closer affinities with basilosaurids (like Basilosaurus, Pachycetus, Cynthiacetus and Chrysocetus) and llanocetids (Mystacodon).

[1] The immense size and bone density both make it impossible for Perucetus to have gone on land, which is in line with its classification as a basilosaurid.

Given its size and weight, Perucetus could have resisted crashing waves in more turbulent waters, something inferred for the similarly buoyant Steller's sea cow.

The strong ventral flexion in particular may have been of great importance for the animal when pushing itself off the ocean floor in order to breathe at the surface.

The precise function of this combination of pachyosteosclerosis and gigantism is not fully understood, but may be linked to the energetic cost of undulating movements or the ability to dive for longer periods of time.