A Brygmophyseter-based Livyatan

Life reconstruction of this giant Miocene sperm whale, based on the related stem-physeteroid Brygmophyseter.
With proportions as restored here, the total length of the holotype is estimated at about 15.4 m. The accompanying volumetric model gives an estimated mass of ~51 t.

Similar to extant orcas, these basal physeteroids were likely macrophagous predators of large vertebrate prey (e.g. other whales), and probably among the apex predators of their time.
This is supported by the presence of large, enamel-bearing teeth in both the mandible and the upper jaw, a robust cranial morphology and large temporal fossa, features on which they converge with extant macrophagous delphinids. The presence of exostoses adjacent to the teeth of the related Acrophyseter deinodon is a sign of activity-related bone remodeling as a consequence of stresses induced by habitual powerful biting (Lambert et al. 2014).

Methods:
Modified skeletal and silhouette multiview restoration
I estimated postcranial axial length of the holotype of Brygmophyseter shigensis based on the table of vertebral measurements and the lateral-view photograph of the skeletal cast (p. 23, Plate 8) in Kimura et al. (2006).
The lengths of incomplete vertebrae were estimated based on the adjacent ones, or missing epiphyses were added based on the size of those in more complete vertebrae from adjacent positions. Intervertebral cartilage was measured as restored in the tail and lumbar region of the cast (where it was not obscured by ribs), and this percentage was applied to the entire post-cervical vertebral collumn in order to get an estimate of the in-vivo length that corresponds to the figured skeleton. Based on the above methodology, postcranial length (including the neck, also based on photo measurements) is about 4.2m.

Thanks to for providing valuable imput during this and later stages!
The ribs of the reconstruction were rotated for a more streamlined, life-like thorax, but space for the sternal complex (not figured) was left beneath the ventral end of the dorsal ribs.

The relative size of Livyatan, to which the postcrania of Brygmophyseter were fitted, bases on their relative bizygomatic skull widths. My measurements from fig. 5a and fig. 7a in Hirota & Barnes 1994 were within less than 1.5% of each other, at 70-71cm,consistent enough to suggest accuracy of the scalebars. Using the mean of those, Livyatan has a skull 2.79 times as wide (197cm, Lambert et al. 2010), and it is herein assumed that the postcranium scales isometrically with bizygomatic width. The entire skeleton was scaled based on its digitally-measured axial length, and the skull replaced with that of Livyatan.

Soft tissue bases primarily on the extant Physeter macrocephalus, but with the addition of a larger fin and flippers, in a semblance of other active, macrophagous cetaceans (note that these were not included in the 3D model since their size and thickness would have been con. Their impact on the animal’s overall mass is unlikely to be significant).

Based on this reconstruction, and again incorporating data from extant sperm whales, I produced a 3D model in blender to estimate its body volume:
Blender model, multiview
The result being a volume of about 50.8m³, which, given a density of 1000 kg/m³ (as would be expected in aquatic animals) corresponds to the same number of tons (proper tons, i.e. 1t=10³kg).
A very bulky bodied animal, with a mass[kg]/length[m]³-ratio of 14.01, it compares favourably to the largest macroraptorial animal alive today, Orcinus, where it averages ~14.35 (source), and to the related pygmy and dwarf sperm whales Kogia spp., whose published records (Long 1991, McAlpine et al. 1997, Scott et al. 2001, Stamper et al. 2006, link) indicate an average of ~14.63.

I will of course continue to update this reconstruction and seek for ways to improve it. Any constructive advice or discussions that help me do so will definitely be appreciated!

UPDATE: 14/10/2015: Adapted the dorsal view of the silhouette and 3D-model to match the proportions of Physeter. Drawing of dorsal view will also need an update based on that.

UPDATE: 11/12/2015: Finally came round to scanning my new reconstruction taking the aforementioned revisions into account, and also experimenting with an altered colour-scheme.

References:
Hirota, Kiyoharu; Barnes, Lawrence G. (1994): A new species of Middle Miocene sperm whale of the genus Scaldicetus (Cetacea; Physeteridae) from Shiga-mura, Japan. The island Arc, 3 (4), pp. 453-472.
Kimura, Toshiyuki; Hasegawa, Yoshikazu; Barnes, Lawrence G. (2006): Fossil sperm whales (Cetacea, Physeteridae) from Gunma and Ibaraki prefectures, Japan; with observations on the Miocene fossil sperm whale Scaldicetus shigensis Hirota and Barnes, 1995. Bulletin of the Gunma Museum of Natural History, 10 pp. 1-23.
Lambert, Olivier; Bianucci, Giovanni; Beatty, Brian L. (2014): Bony outgrowths on the jaws of an extinct sperm whale support macroraptorial feeding in several stem physeteroids. Naturwissenschaften, 101 (6), pp. 517-521.
Lambert, Olivier; Bianucci, Giovanni; Post, Klaas; Muizon, Christian de; Salas-Gismondi, Rodolfo; Urbina, Mario; Reumer, Jelle (2010): The giant bite of a new raptorial sperm whale from the Miocene epoch of Peru. Nature, 466 (7302), pp. 105-108.
Long, Douglas J. (1991): Apparent predation by a white shark Carcharodon carcharias on a pygmy sperm whale Kogia breviceps. Fishery Bulletin, 89 (23) pp. 538-540.
Mcalpine, Donald F.; Murison, Laurie D.; Hoberg, Eric P. (1997): New Records for the Pygmy Sperm Whale, Kogia Breviceps (physeteridae) from Atlantic Canada with Notes on Diet and Parasites. Marine Mammal Science, 13 (4) pp. 701-704.
Scott, M. D.; Hohn, A. A.; Westgate, A. J.; Nicolas, J. R.; Whitaker, B. R.; Campbell, W. B. (2001): A note on the release and tracking of a rehabilitated pygmy sperm whale (Kogia breviceps). Journal of Cetacean Research and Management 3 (1) pp. 87-94.
Stamper, M. Andrew; Whitaker, Brent R.; Schofield, T. David (2006): Case Study: Morbidity in a Pygmy Sperm Whale Kogia breviceps due to ocean-bourne Plastic. Marine Mammal Science 22 (3) pp. 719-722.