Brygmophyseter Shigensis

***Brygmophyseter***, known as the **biting sperm whale**, is an extinct genus of toothed whale in the sperm whale family with one species, ***B. shigensis***. When it was first described in 1994, the species was placed in the genus *Scaldicetus* based on tooth morphology, but this was later revised in 1995. In 2006, it was classified into the genus ***Naganocetus***, which is considered to be a junior synonym. The only known specimen, a nearly complete skeleton, was dated to be around 14–15 million years old. *Brygmophyseter* is thought to have been 6.5–7 meters (21–23 ft) long, and it probably had 11 or 12 teeth in the upper and lower jaws. *Brygmophyseter* is part of a group of macroraptorial sperm whales (often shortened to "raptorial") which tended to be apex predators using their large teeth to catch struggling prey such as whales. It had a spermaceti organ which was probably used for biosonar like in the modern sperm whale. The whale has made an appearance on The History Channel's TV series *Jurassic Fight Club*.

Like other raptorials, *Brygmophyseter* had enamel-coated teeth in both jaws, unlike the modern sperm whale (*Physeter macrocephalus*). It probably had 11 or 12 teeth in each jaw, though no upper teeth were preserved in the holotype. The skull of the holotype measured around 1.5 meters (4.9 ft), and it had an elongated snout. The brow ridge was broad and flat-topped, and the zygomatic process of the squamosal bone on the cheeks was large and robust. The temporal fossa on the sides of the skull were elongated, which may have been plesiomorphic features from archaeocetes, that is, it is an ancestral characteristic of the whale. The right nasal passage was small and was asymmetrical with the left nasal passage, like in the modern sperm whale. Characteristic of sperm whales, it had a deep basin on the top of its skull, known as the supracranial basin. Like in the modern sperm whale, this basin probably held the spermaceti organ, and so the whale had biosonar capabilities. The nuchal crest which is the part of the whale skull which projects upwards on the back end of the skull, behind the supracranial basin, was low and broad. Similar to modern-day toothed whales, but unlike in the modern sperm whale, the shoulder blades were thicker than they were tall.

*Brygmophyseter* is estimated to have been around 6.5–7 meters (21–23 ft) long. The holotype had preserved zero neck vertebrae, ten thoracic vertebrae, ten lumbar vertebrae, and fifteen tail vertebrae. In comparison, the modern sperm whale has eleven thoracic, eight lumbar, and twenty-two tail vertebrae, and the smaller tail in *Brygmophyseter* is probably a primitive characteristic. The vertebra segments increase in height until the seventh lumbar vertebra, then they begin to decrease. In the thoracic vertebrae, with the exception of the tenth one, the width of the segments is larger than the height. The lumbar and tail vertebrae are circular in shape.

The head of the humerus arm bone of *Brygmophyseter* was positioned perpendicular to the shaft. The elbow joint on the humerus was not distinct from the ulna, typical in cetaceans. The ulna was more primitive than that of the modern sperm whale, in that the shaft was longer and more slender, and the head of the bone was smaller.