Caperea, Miscontructed

If the occasional Caperea really does have a supernumerary dorsal fin, it would only be a minor anomaly compared to the skeletal madness within:

Caperea (top) from Bisconti (2012).
Fin Whale (below) from Wikipedia Commons.

Caperea has vertebrae counts and proportions that are strikingly different from any other whale. Cetaceans have four types of vertebrae: cervical (neck), thoracic (with ribs), lumbar, and caudal (tail, with chevrons sticking out below); unlike most mammals, there are no sacral vertebrae, which articulate with the hips. Perhaps the most striking difference between Caperea and the Fin Whale (Balaenoptera physalus) is the relative size of the ribcage. Caperea has 17 to 18 thoracic vertebrae, more than any other cetacean, but not much more than Fin Whales, which have 14 to 15 (Buchholtz 2010, True 1904). The extra length of the ribcage is thus mostly due to the elongation of the thoracic vertebrae themselves (Buchholtz 2010) and as a result, the relationship between vertebrae count and length is unlike that of any other cetacean (Buchholtz 2007). Another striking trait of Caperea is the very low number of lumbar vertebrae, with most individuals having one and one individual having none (Buchholtz 2010). In other words, Caperea has a tail coming (almost) straight out of its ribcage. Comparatively, Fin Whales have 14 to 16 lumbars (True 1904) and no other baleen whale has fewer than 10 (Tinker 1988). The River Dolphin Inia reportedly has as few as three lumbars, but it also has 13 thoracic vertebrae (Best & da Silva 1993), which is totally normal. It is likely there are some functional similarities shared between Inia and Caperea, but the proportions of Caperea reminded me more strongly of another aquatic mammal, and it’s not a cetacean.

Caperea (top) from Bisconti (2012)
West Indian Manatee (below) from Wikipedia Commons.

Yes, a manatee, Trichechus manatus. Bear with me here. There are 17 to 18 thoracic vertebrae and 1 to 2 lumbars (Buchholtz et al. 2007), which overlaps with Caperea. The thoracic vertebrae are also elongate (Buchholtz et al. 2007) and judging from the comparison above, it’s roughly to the same degree as Caperea. However, the patterning is not quite the same, since the longest vertebrae in Caperea are near the thoracic/lumbar/caudal region and those of the manatee are about mid-thoracic (Buchholtz et al. 2007; Buchholtz 2010). The ribs of both species are also quite wide, particularly the posterior ones. Unlike Dugongs, Manatees lack sacral vertebrae (Buchholtz et al. 2007). These are some curious parallels, and a purposefully ignorant reconstruction of Caperea as a whale-a-tee was all but inevitable:

Contrary to what hypothetical future (or alternate universe?) palaeontologists may think, Caperea doesn’t look like a manatee at all. It pretty much looks like a Minke with an arched jaw.

Stranded Caperea, from Te Papa’s Blog.

Not only does Caperea look nothing like a manatee in life, it also doesn’t obviously function like one, being oceanic and reportedly a fast swimmer (Kemper 2009). Caperea is reportedly highly flexible (Kemper 2009), as is Inia (Fish 2002), so this makes me wonder if lumbar reduction results in a more flexible body, and that perhaps Caperea and manatees achieved this through a similar mutation. As documented in the three-part series from Tet Zoo (Part 1, Part 2, Part 3) Caperea has other bizarre morphology not shared with other cetaceans or manatees including huge and overlapping transverse processes as well as ribs that appear curiously loosely-connected. As for why it has any of this morphology or would need to be flexible, I have no idea.

Te Papa’s Blog has lots of entries documenting the dissection of a juvenile Caperea, and it is really invaluable for seeing how the soft tissue and skeleton fit together. It’s certainly interesting that soft tissue doesn’t necessarily mean that animals were weirder than their skeletons would indicate, some externally look far more “normal” than they have any reason to.

References:

Best, R. & da Silva, V. (1993) Inia geoffrensis. Mammalian Species 426, 1—8. Available

Bisconti, M. (2012) Comparative osteology and phylogenetic relationships of Miocaperea pulchra, the first fossil pygmy right whale genus and species (Cetacea, Mysticeti, Neobalaenidae). Zoological Journal of the Linnean Society 166(4) 876—911. Supplement available

Buchholtz, E. (2010) Vertebral and rib anatomy in Caperea marginata: Implications for evolutionary patterning of the mammalian vertebral column. Marine Mammal Science. Available

Buchholtz, E. et al. (2007) Vertebral anatomy in the Florida manatee, Trichechus manatus latirostris: a developmental and evolutionary analysis. Anatomical Record 290(6) 624—637.

Buchholtz, E. (2007) Modular evolution of the Cetacean vertebral column. Evolution & Development 9(3) 278—289. Available

Fish, F. (2002) Balancing Requirements for Stability and Maneuverability in Cetaceans. Integrative and Comparative Biology 42(1) 85—93. Available.

Kemper, C. (2009) Pygmy Right Whale IN: Perrin, W. et al. (eds.) Encyclopedia of Marine Mammals.

Tinker, S. (1988) Whales of the World. Partially Available

True, F. (1904) The whalebone whales of the western North Atlantic.  Smithsonian Contributions to Knowledge 33 1—332. Available

Will New Whales Be Discovered?

Compared with terrestrial predators, the ~90 species of cetaceans (WoRMS 2012) ranging from wolf-sized to the largest animals ever, are a mind-boggling array. They’re the Pleistocene megafauna that, until recently, survived mostly intact (Anderson 2001) and no place on land, even Recent sub-Saharan Africa, can really compare with our oceans. It’s shocking that on top of this vast menagerie, one author claimed as many as 15 species remain to be discovered, including exotic beasts such as an 18 meter baleen whale with two dorsal fins (Raynal 2001). In a previous article I argued that particular hypothetical species, Amphiptera pacifica, was far more likely to be an early observation of (an anomalous?) Caperea than anything new and began to wonder if the discovery of unmistakable new species is at all probable. It isn’t.

Giglioli’s Whale

After his lunch on 4 September 1867, the young naturalist Enrico Hillyer Giglioli observed a remarkable baleen whale with two dorsal fins far off the coast of Chile. Due to the unusual fins and an apparent lack of ventral pleats, Giglioli felt the whale was sufficiently distinct to name Amphiptera pacifica and hoped other, luckier naturalists would shortly acquire a specimen*. This never happened. The hypothetical whale is now almost forgotten, aside from being listed as a nomen dubium in databases, but there are still believers. Raynal & Sylvestre (1991) argued that Amphiptera is a valid entity, has been observed on multiple occasions and may be distinct enough to warrant its own ‘family’ (Amphipteridae). While some cetaceans can be surprisingly cryptic, the notion that one of the world’s largest and most unmistakable animals has almost entirely avoided human detection is a tough sell. Additionally, anecdotal evidence – even from experts – is notoriously problematic and cannot be used to describe new species. I’m just not satisfied with leaving Giglioli’s Whale as a nomen dubium, and I suspect the animal he saw was a remarkable representative of a rare, but known, species.

* Which has precedent with Lagenorhynchus cruciger, Cephalorhynchus commersonii & Sousa chinensis. See Dubois & Nemésio (2007) for why hypothetical descriptions are unacceptable today.

The critical information for identifying Giglioli’s whale comes from an illustration included in his 1870, which unfortunately is missing from the Google Books edition. The only copy I can find is from Raynal’s website, and while I can’t vouch for how well it represents the original, all the important details are reasonably visible.

Giglioli’s Whale bears an uncanny resemblance to Caperea marginata – which I refuse to call ‘Pygmy Right Whale’ because that name is the worst – specifically, a stranded 3 meter individual whose dissection was documented at Te Papa’s blog. Caperea was first described in 1846, however knowledge of its external appearance appeared to be quite rudimentary as of Beddard (1901). Giglioli was also only 22 when he observed the whale – having inherited the position of ship’s naturalist after the death of Filippo de Filippi (Croce 2002) – and didn’t appear to have a specialized interest in cetaceans. So not only is it unlikely for Giglioli to have ever heard of Caperea, even if he did the species probably would have been known only from baleen plates and ear bones at the time.