Yay: day 3 of seriously frickin’ weird cetacean skull week. While we’ve previously been looking at the skulls of extant species, this time we have a fossil (or, actually, a diagram of one: from Muizon 1988). It’s Scaphokogia cochlearis from the Miocene Pisco Formation of Peru, described by Muizon (1988). Exhibiting an incredible amount of cranial asymmetry and a wide, round supracranial basin, it’s clearly a physeteroid (sperm whale), and the presence of slit-like antorbital notches, absence of nasals and other characters indicate that it’s a kogiid (Muizon 1991) (if you need help with the terminology go see the Tursiops and Kogia articles)…
Scaphokogia had a much longer rostrum than the only surviving kogiid, Kogia, and it also differed from both Kogia and Physeter in having a blunted, rectangular bony rostrum, rather than a pointed one. Exactly how this affected the shape of its head in life is a good question: Physeter has a broad-based, triangular bony rostrum, yet its massive head is deep and rectangular and wider dorsally than at the jaws. As mentioned previously, Scaphokogia is weird in having very long antorbital slits. What appear to be remnants of alveoli remain in two grooves that run along the ventral surfaces of the maxillae: teeth are unknown from the only known specimen, but Muizon (1988) suggested that non-functional teeth may have been present, but unerupted.
There are several fossil kogiids: Muizon (1988, 1991) proposed that Scaphokogia was the sister-taxon to Kogiinae, the clade that includes Kogia and its fossil relatives. Bianucci & Landini (2006) confirmed the kogiid affinities of Scaphokogia, but we await testing of the hypothesis that Scaphokogia is outside of a Kogiinae clade.
So by now you’re thinking of that huge, inescapable question that arises whenever you look at fossil whales: why the hell isn’t there a good, comprehensive volume that reviews the cetacean fossil record? And I don’t mean yet another book that looks at whale origins and archaeocete diversity, but one that covers all the fossil odontocetes and mysticetes (the Neoceti). I get asked this question quite a lot, and the best I can do is direct people to Kellogg (1928a, b). Needless to say, it’s a tad out of date now and we really need a good, modern volume on fossil whales. I’ll do it, get me the money.
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.
Kellogg, R. 1928a. The history of whales – their adaptation to life in the water. Quarterly Review of Biology 3, 29-76.
– . 1928b. The history of whales – their adaptation to life in the water (concluded). Quarterly Review of Biology 3, 174-208.
Muizon, C. de 1988. Les vertébrés de la Formation Pisco (Pérou). Troisième partie: des Odontocètes (Cetacea, Mammalia) du Miocène. Travaux de l’Institut Francais d’Études Andines 17, 1-244.
– 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.