You would be forgiven that doubting that this awesome object – displayed in the Santa Barbara Museum of Natural History – is a fossil odontocete skull, but it is. Discovered in Lompoc, California, and as yet unreported in the scientific literature (so far as I can tell), it is the skull of a large predatory sperm whale purportedly closely related to the Japanese Miocene physeterid Brygmophyseter shigensis (but read on).
The extant sperm whale Physeter lacks functional teeth in the upper jaw and in fact even possesses special sockets in the maxillae that house the lower jaw teeth when the mouth is closed (it may actually have as many as eight teeth in each maxilla, but when it does they are unerupted and remain buried in their alveoli). However, this was not true of all extinct physeteroids, many of which possessed fully erupted premaxillary and maxillary teeth (Kellogg 1928, Kazár 2002). In some of these sperm whales, large upper and lower jaw teeth, combined with a robust skull morphology and large body size (6-7 m long), indicate that the animals were macropredators, probably attacking other cetaceans (Bianucci & Landini 2006, Hampe 2006)…
The best known of these ‘killer sperm whales’, Zygophyseter varaloi from the Late Miocene of Italy, had an extremely long zygomatic process on the squamosal that provided an attachment surface for hypertrophied jaw musculature, and helped stabilise the lower jaw when it was opened wide. This character is clearly present in the Lompoc sperm whale, suggested that it might be a close relative of Zygophyseter. If this is correct, the Lompoc animal might have been outside of the kogiid-physeterid clade within Physeteroidea, as Bianucci & Landini (2006) found Zygophyseter to be a stem-group physeteroid. Other macropredatory sperm whales, the hoplocetines (the monophyly of this group is controversial), were crown-group physeteroids and are probably members of Physeteridae (Muizon 1991, Hampe 2006). If the Lompoc animal is close to Zygophyseter it can’t also be close to Brygmophyseter, for Brygmophyseter is a crown-group physeteroid and probably a hoplocetine [image below shows Zygophyseter, from Bianucci & Landini (2006)].
What makes the Lompoc skull look particularly incredible is its deep, massive rostrum. It almost looks like the skull of Andrewsarchus. In fact this makes it look decidedly different from all other sperm whales, as even the macropredatory ones have a low, dorsally flattened rostrum that, in the nasal region, exhibits scaphidiomorphy due to the possession of the spermaceti organ. Alas, this massive rostrum seems to have been reconstructed without reference to sperm whale anatomy. Dammit! The photo is from Doug Shore’s flickr site (here) and is used with permission.
Another one tomorrow!
Refs – –
Bianucci, G. & Landini, W. 2006. Killer sperm whale: a new basal physeteroid (Mammalia, Cetacea) from the Late Miocene of Italy. Zoological Journal of the Linnean Society 148, 103-131.
Hampe, O. 2006. Middle/late Miocene hoplocetine sperm whale remains (Odontoceti: Physeteridae) of North Germany with an emended classification of the Hoplocetinae. Fossil Record – Mitteilungen aus dem Museum für Naturkunde in Berlin 9, 61-86.
Kazár, E. 2002. Revised phylogeny of the Physteridae (Mammalia: Cetacea) in the light of Placoziphius Van Beneden, 1869 and Aulophyseter Kellogg, 1927. Bulletin de l’Institut Royal des Sciences Naturelles de Belgique. Sciences de la Terre 72, 151-170.
Kellogg, R. 1928. The history of whales – their adaptation to life in the water (concluded). Quarterly Review of Biology 3, 174-208.
Kimura, T., Hasegawa, Y. & Barnes, L. 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, 1-23.
Muizon, C. de 1991. A new Ziphiidae (Cetacea) from the Early Miocene of Washington State (USA) and phylogenetic analysis of the major groups of odontocetes. Bulletin du Muséum national d’Histoire naturelle (4e sér.) 12, 279-326.