The recent discussion of Caperea‘s skeletal morphology (Caperea = Pygmy right whale) inspired Joy Reidenberg to send these photos of a Caperea skeleton, taken in New Zealand and used here with her permission.
In this view of the whale’s thoracic region (we’re standing beneath the whale, looking up into its ribcage), you can see that the transverse processes (the wing-shaped structures that project from both sides of each vertebra) are proportionally huge: so big that many of them overlap. The dorsal ends of the ribs – the parts of the ribs that contact the transverse processes – look strangely small and narrow by comparison, and also seem to have really loose connections with the transverse processes. Compare this with the ribcage of a North Atlantic right whale Eubalaena glacialis…
Here, you can see that the transverse processes are, proportionally, much smaller and don’t come close to overlapping. The rib heads also look much larger in comparison with the transverse processes, and there are obvious big facets on the transverse processes for the rib heads. And, sorry that the ribcage isn’t the main focus of the photo: when I took it I was more interested in the hyoid apparatus and sternum. The photo was taken in the NHM, London. The next photo takes us back to Caperea: now we’re looking at the posterior part of the ribcage and the proximal part of the tail. Again, the enormous size of the transverse processes and their overlapping nature should be striking. You can also see the relictual pelvis and the more proximal of the haemal arches, or chevron bones. As we saw last time, the ribs have a peculiar flattened shape.
Again, compare this with the more normal condition present in the balaenid Eubalaena glacialis…
As is normal for a whale – and indeed for a tetrapod – the ribs here are sub-cylindrical, with shafts that are either rounded or oval in cross-section. The flattened ribs of Caperea are really, really weird: as I said last time, it’s been suggested that these ribs might somehow function as armour, that they might stiffen the body*, or that they might be something to do with the enlarged laryngeal sac. More study is needed – very little is known of this whale (a real shame given its peculiar anatomy). As it happens, I learnt yesterday that Emily Buchholtz has just published a paper in which she discusses the peculiar rib shape and transverse process anatomy of this whale (Buchholtz 2010). However, her paper is mostly concerned with the reduction in tail length and increase in thorax length, and also in the fact that Caperea‘s first rib seems to be a ‘composite ontogenetic fusion product’ representing both the first and second thoracic ribs (weird fused first ribs – located somewhere round about the cervico-thoracic junction – are present in various baleen whales and sometimes incorporate a supernumery cervical rib).
* The idea that Caperea might be particularly stiff-bodied seems paradoxically inconsistent with the fact that extensive flexing of the whole body during swimming has been reported (Ross et al. 1975).
Finally, here’s a close-up of Caperea‘s proximal caudal region. Note again the relictual pelvis and haemal arches. I don’t know whether they’re correctly positioned…
While I’m here, it’s worth saying a few other things about Caperea. Textbooks always used to include Caperea in the right whale family Balaenidae, but its distinctive anatomy has led some authors to give it its own ‘family’, Neobalaenidae Gray, 1874. While some phylogenetic studies find Neobalaenidae and Balaenidae to be sister-taxa (e.g., Deméré et al. 2005, Steeman 2007) (in which case, the name Balaenidae might still be used for the Caperea + (Balaena + Eubalaena) clade*, as per Bouetel & Muizon (2006)), others find Neobalaenidae to be closer to Balaenopteridae (the rorquals and humpbacks) (e.g., Saski et al. 2005).
* Most authors have used Balaenoidea for this clade.
Unlike balaenids proper, Caperea has a dorsal fin, is proportionally slender and has a small head (‘only’ 25% of total length, compared to c. 40% in Balaena) [the adjacent image is a famous photo, taken in 1967 in Plattenberg Bay, South Africa. Until fairly recently it was the only photo showing a live Pygmy right whale]. The first specimens recognised by science were collected between 1839 and 1843 when HMS Erebus and Terror toured the world; three baleen plates collected in Western Australia by Mr J. Warwick were studied by J. E. Gray. Recognising them as unusual because of their small size and near-white colour, Gray based the new species Balaena marginata Gray, 1846 on these remains. A complete skull from New Zealand, possessing the same kind of baleen and obviously belonging to the same species, was described by Gray in 1870 and he now regarded this animal as special enough for its own genus: Neobalaena (proof that lack of originality is nothing new in devising new generic names). However, Gray had earlier given the name Caperea antipodarum Gray, 1864 to an isolated tympanic bone from New Zealand, and this proved to belong to the same animal. Accordingly, the animal is properly known as Caperea marginata today. This brief potted history is based on Hershkovitz (1966) and Watson (1981). The animal seems to be a Southern Hemisphere specialist, with all sightings and strandings coming from Argentina, Namibia, South Africa, Australia and New Zealand.
Many people know that, among the living whales of the world, a few beaked whale species were named for isolated skulls and other such remains; the fact that one of the baleen whales was also originally named for fragments is less widely recognised.
Many thanks to Joy Reidenberg for supplying the Caperea photos, and to Bobby Boessenecker for alerting me to Buchholtz (2010). For previous Tet Zoo articles on baleen whales, see…
- A 6 ton model, and a baby that puts on 90 kg a day: rorquals part I
- From cigar to elongated, bloated tadpole: rorquals part II
- Lunging is expensive, jaws can be noisy, and what’s with the asymmetry? Rorquals part III
- The newest whales
- Inside Nature’s Giants part II: whale guts and hindlimbs ahoy
- When GREY WHALES – you know, from the PACIFIC OCEAN – crossed the Atlantic
- Pouches, pockets and sacs in the heads, necks and chests of mammals, part III: baleen whales
Refs – –
Bouetel, V. & Muizon, C. de 2006. The anatomy and relationships of Piscobalaena nana (Cetacea, Mysticeti), a Cetotheriidae s.s. from the early Pliocene of Peru. Geodiversitas 28, 319-395.
Buchholtz, E. 2010. Vertebral and rib anatomy in Caperea marginata: implications for evolutionary patterning of the mammalian vertebral column. Marine Mammal Science 10.1111/j.1748-7692.2010.00411.x
Deméré, T. A., Berta, A. & McGowen, M. R. 2005. The taxonomic and evolutionary history of fossil and modern balaenopterid mysticetes. Journal of Mammalian Evolution 12, 99-143.
Hershkovitz, P. 1966. Catalog of living whales. Smithsonian Insitution United States National Museum, Bulletin 246, 1-259.
Ross, G. J. B., Best, P. B. & Donnelly, B. G. 1975. New records of the pygmy right whale (Caperea marginata) from South Africa, with comments on distribution, migration, appearance and behavior. Journal of the Fisheries Research Board of Canada 32, 1005-1017.
Sasaki, T., Nikaido, M., Hamilton, H., Goto, M., Kato, H., Kanda, N., Pastene, L. A., Cao, Y., Fordyce, R. E., Hasegawa, M. & Okada, N. 2005. Mitochondrial phylogenetics and
evolution of mysticete whales. Systematic Biology 54, 77-90.
STEEMAN, M. (2007). Cladistic analysis and a revised classification of fossil and recent mysticetes Zoological Journal of the Linnean Society, 150 (4), 875-894 DOI: 10.1111/j.1096-3642.2007.00313.x
Watson, L. 1981. Whales of the World. Hutchinson, London.