Tetrapod Zoology

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Welcome to another of those week-long series of themed posts, produced (ostensibly) to save me from spending time on blogging (other jobs require priority). Previous series have been ankylosaur week and sea monster week. This time round we’re looking at seriously frickin’ weird cetacean skulls although, actually, we’re only going to be looking at odontocetes, as these are (1) the ones I want to write about, and (2) the ones I have neat new photos of. This was, of course, all inspired by the comparative work I recently did on the Tursiops skull. All of the skull photos you’re going to be seeing were kindly provided by Colin McHenry and are used with permission. And we begin with a whale that does, indeed, have a frickin’ weird skull: it’s the Pygmy sperm whale Kogia breviceps

There are two currently recognised Kogia species (the other one is the Dwarf sperm whale Kogia sima), but genetic evidence suggests that K. sima might actually be two species (Chivers et al. 2005) [K. sima was known as K. simus until recently]. K. breviceps and K. sima differ in that K. sima has a shorter snout, and a much larger, more anteriorly located dorsal fin. K. breviceps lacks functional upper jaw teeth, but K. sima can sometimes have up to three pairs of small maxillary teeth (though I’ve seen pictures – there’s one in Berta & Sumich (1999) – that show K. breviceps with maxillary teeth too). At 3-4 m long, the Pygmy sperm whale is also bigger than the Dwarf sperm whale, which ranges from 2.1-2.7 m [the skull shown in these images is specimen BMNH 1974-874, images © Natural History Museum, London].

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The rostrum of Kogia is proportionally the shortest of any cetacean, with some of the bones that usually form the skull roof (the nasals and supraoccipital) being either squashed up and fused, or absent. It seems that, as the rostrum shortened, the bones forming the anterolateral margins of the orbits (the lacrimals, the posterolateral parts of the maxillae, and the anterior parts of the frontals) came to overlap the base of the rostrum, thereby closing up the antorbital notches such that they now remain only as long slits (in a fossil kogiid from the Miocene Pisco Formation of Peru, Scaphokogia cochlearis, the antorbital notches form very long slits, with that on the left side being about equivalent in length to the width of the base of the rostrum). The bones of the mandibles are apparently paper-thin and the thin, sharply pointed teeth (which lack enamel) were regarded by Handley (1966) as being ‘strongly reminiscent of the teeth of pythons’.

The most obvious weird thing about the skull, however, is the presence of a large, rounded, supracranial basin on the skull roof. The presence of a wide, rounded supracranial basin, a condition termed scaphidiomorphy, is common to all physeteroids and is a synapomorphy of the clade (Muizon 1991). The basin houses a unique structure called the spermaceti organ, and while I’d like to discuss ideas on its function I’m not going to as that would easily add 1000 words to what was meant to be a short article.

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The supracranial basin of Kogia is strongly asymmetrical and divided along the midline by a septum formed from the asymmetrical premaxillae: the left premaxilla only extends as far as the left naris, while the right premaxilla extends all the way to the vertex, surrounding the right naris entirely and sporting a mid-line crest in the nasal region that then leans over to the left (Schulte 1917, Nagorsen 1985) [you can see these features in the adjacent photo of BMNH 1974-874, here shown in dorsal view]. The right naris is small and sub-rounded while the left one is large and oval. Cranial asymmetry is actually the norm in crown-group odontocetes, only being absent in Pontoporia (the franciscana), though a few other taxa (like Orcinus) are relatively symmetrical compared to their relatives (Ness 1967).

Kogia doesn’t just have a weird skull; it’s one of the weirdest cetaceans all round. Its head is small for the size of the animal, being only 14-16% of total length, and its flippers are proportionally small as well, with unossified phalanges and carpals. Its under-slung mouth has been described by some as shark-like, and it has peculiar ‘false gill’ markings on the side of the head. I have a vague recollection of reading a proposal that it may even try to mimic sharks, but I can’t find this in the literature and wouldn’t take it too seriously anyway. Its neck vertebrae are all fused together and its tail flukes are apparently a lot floppier than those of other cetaceans. I also think it looks pretty scary: the picture below shows the head of a stranded K. sima, reported from Italy by Bortolotto et al. (2003).

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Kogia does some weird behavioural stuff. K. sima has been reported to release a reddish anal fluid (presumably faeces) which then spreads out in the water to form a cloud of about 100 m sq, and to then hide in the middle of the cloud (Scott & Cordaro 1987). This is of course irresistibly comparable to what cephalopods do, which is all the more ironic given that kogiids are cephalopod predators. They’ve also been reported to be surprisingly aggressive, ramming boats and leaping towards them when trapped in seine nets. This is somewhat reminiscent of what Physeter – the big sperm whale – does, though its size of course means that its boat-ramming activities are better documented. Incidentally, it may not be a coincidence that sperm whales big and small have a spermaceti organ, and indulge in head-ramming. More on this another time. As for feeding, Kogia species use rapid jaw-opening, powerful retraction of the tongue and expansion of the throat to generate negative pressures when suction-feeding (Bloodworth & Marshall 2005). I’ve been mentioning suction-feeding on and off at Tet Zoo for ages now and, again, will elaborate on it at some other time.

Incidentally, I personally quite like the name Kogia. It seems that our predecessors did not share this opinion however. Writing in 1854, W. S. Wall ‘regretted that a barbarous and unmeaning name like Kogia should have been admitted into the nomenclature of so classical a group as the cetacea’. Richard Owen agreed with Wall and used the name that Wall proposed, Euphysetes Wall, 1851, over Kogia Gray, 1846, writing of Kogia in 1870 that ‘I have that confidence in the common-sense and good judgment of my fellow countrymen and labourers in philosophical zoology which leads me to anticipate a tacit burial and oblivion of the barbarous and undefined generic names with which the fair edifice begun by Linnaeus has been defined’. This was all recounted by Gill (1871) who, while using the name Kogia because of its nomenclatural priority, recognised ‘the justness of the criticisms upon it’ (p. 740). Oh, come on, the name ‘Kogia‘ is really not that bad.

More tomorrow…

Refs – –

Berta, A. & Sumich, J. L. 1999. Marine Mammals: Evolutionary Biology. Academic Press, San Diego.

Bloodworth, B. & Marshall, C. D. 2005. Feeding kinematics of Kogia and Tursiops (Odontoceti: Cetacea): characterization of suction and ram feeding. The Journal of Experimental Biology 208, 3721-3730.

Bortolotto, A., Papini, L., Insacco, G., Gili, C., Tumino, G., Mazzariol, S., Pavan, G. & Cozzi, B. 2003. First record of a dwarf sperm whale, Kogia sima (Owen, 1866) stranded alive along the coasts [sic] of Italy. In 31st Symposium of the European Association for Aquatic Mammals. Tenerife.

Chivers, S. J., LeDuc, R. G., Robertson, K. M., Barros, N. B. & Dizon, A. E. 2005. Genetic variation of Kogia spp. with preliminary evidence for two species of Kogia sima. Marine Mammal Science 21, 619-634.

Gill, T. 1871. The sperm whales, giant and pygmy. The American Naturalist 4, 725-743.

Handley, C. O. 1966. A synopsis of the genus Kogia (pygmy sperm whales). In Norris, K. S. (ed) Whales, Dolphins and Porpoises. University of California Press (Berkeley & Los Angeles), pp. 62-69.

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.

Nagorsen, D. 1985. Kogia simus. Mammalian Species 239, 1-6.

Ness, A. R. 1967. A measure of asymmetry of the skulls of odontocete whales. Journal of Zoology 153, 209-221.

Schulte, H. von W. 1917. The skull of Kogia breviceps Blainv. Bulletin of the American Museum of Natural History 37, 361-404.

Scott, M. D. & Cordaro, J. G. 1987. Behavioral observations of the dwarf sperm whale, Kogia simus. Marine Mammal Science 3, 353-354.

Comments

  1. #1 Carpworld
    July 28, 2008

    Please, Darren, do a post on the function of the spermaceti organ! I’ve spent so long talking to people like Hal Whitehead etc about what the hell they’re for, i’d love to hear your ideas. On a side note, when there was that big discussion on Loren Coleman’s blog about the sea monster postcard photo you featured the other week i commented that i thought it might be kogia – i still think it looks very similar.

  2. #2 Ian Tindale
    July 28, 2008

    (top picture) – Yay, it’s duckrabbit!

  3. #3 Mo Hassan
    July 28, 2008

    True, while I prefer descriptive names rather than those named after someone, Kogia is a cool name, and not many Turks are honoured in scientific names! The ICZN says you can’t rename it anyway, so it has to stick, whether we like it or not!

  4. #4 Someone
    July 28, 2008

    Dang, but those whales look like sharks on the outside and inside!

  5. #5 JW Tan
    July 28, 2008

    Thank you Darren. I, for one, really enjoy the week-long series format.

  6. #6 Sordes
    July 28, 2008

    The Kogia-species are really among the most unsual whales, it is really sad that they are often overlooked in literature. I read some time ago an old paper with a comparison of the skull of the archaic whale Aulophyseter with those of a young Physeter and a young Kogia. Interestingly the Kogia skull seemed to be much higher specialized than those of Physeter, although its general proportions looks much lesser weird than those of the monster-headed sperm whales.
    The cranial respiration tracts differs also very much between Kogia and Physeter, and again it looks much higher specialized in Kogia.

  7. #7 Tengu
    July 28, 2008

    I thought you would start with a ziphid but you started with something else!

    but the little brothers of the mighty Catchalot are certainly strange creatures. Which one has the big dorsal fin? The pygmy or the dwarf?

    Mo, your right about naming things after people being boring. (though I will say that is what I find so attractive about the ziphids…they almost all belong to someone) But what do you call the beast? `Yet-another-beaked-whale-known-only-from-beached-carcase`?

    And pygmy and dwarf sperm whale…seems so lame.

    Perhaps this is where the latin should become the common name, eh?

    Im off to Pembroke next week, I may go on a wildlife trip…Ill tell you what I do see

  8. #8 Zach Miller
    July 28, 2008

    Freaky. I wasn’t aware this whale existed.

  9. #9 Bee
    July 28, 2008

    Likewise, I didn’t know this animal existed. In fact, every time I confidently think I probably at least know a little bit about all the BIG animals, someone like Darren comes along to set me straight. Yay, Darren!

  10. #10 Allen Hazen
    July 28, 2008

    “in a fossil kogiid from the Miocene Pisco Formation of Peru, Scaphokogia cochlearis”
    … kogiID? Does that mean that the Kogias now have their own family, “Kogiidae,” separate from the Physeteridae? Are they still thought of as closely related to (non-dwarf, non-pygmy) Sperm whales?

    …Assuming they ARE related to sperm whales… Reduced facial elements (i.e. short rostrum), un-ossified appendages, all with a comparatively small body size: this sounds like achondroplastic dwarfism! Has anyone tried to look at Kogia from a developmental point of view?

  11. #11 Darren Naish
    July 28, 2008

    Allen: kogiids have been regarded as distinct from physeterids since the 1980s at least (actually, Miller 1923 was first to regard them as a ‘family'; Kogiinae had been named by Gill in the 1871 citation given above). So far as I know everyone working on cetacean phylogeny and evolution follows this. Kogiids and physeterids share lots of weird characters not seen in other odontocetes, as well as molecular and behavioural characters, so physeteroid monophyly is pretty sound. As for developmental work, I don’t know of any, but I don’t keep up with that kind of stuff. I doubt that kogiids are that well studied however.

  12. #12 Nathan Myers
    July 28, 2008

    Yay, indeed.

    Likewise, I had no idea hyraxes existed, only to find out Spain was named after them even though what lived there was rabbits. King James’s biblical translators labored under the same ignorance, perhaps more forgivably. We might suppose that they had some experience of Spain, and if what they saw there were “sephanim”, then the ones they were translating must be rabbits too.

    Do all the cetaceans mentioned here swim, still?

  13. #13 Boesse
    July 28, 2008

    I thought I would mention that extant phocoenids (true porpoises) also have symmetrical crania, although extinct basal phocoenids have asymmetrical crania.

  14. #14 Darren Naish
    July 28, 2008

    I thought I would mention that extant phocoenids (true porpoises) also have symmetrical crania, although extinct basal phocoenids have asymmetrical crania.

    Hi. I recall you mentioning this before: I have phocoenid skull photos with me now, and while the asymmetry is minor it’s present in some of them (e.g., Phocoena and Neophocaena), being most obvious in the nasals. I checked Ness (1967), and minor cranial skew was reported here in several phocoenid genera. I can’t see any asymmetry in Phocoenoides however.

  15. #15 John Scanlon FCD
    July 28, 2008

    Those mandibular teeth are indeed quite python-like, though the posterior teeth in pythons usually point more medially than posteriorly (useful for tucking the prey in at the corner of the mouth), and the lack of enamel is not a point of similarity. What do we know about mandibular kinesis in kogiids? – e.g. how freely mobile are the symphysial tips, does the mandible (‘paper-thin’ as you say) flex much during suction-feeding, do the mandibles rotate on their long axes (check dentary-squamosal joint surfaces) to turn the tooth row outward/inward?
    The most ‘shark-like’ undershot mouths in snakes occur in scolecophidians, which (like physeteroids) usually have teeth either only in the upper, or only the lower jaws. Might be interesting to compare with Leptotyphlops, with edentulous maxilla and highly kinetic toothed mandibles (e.g. Kley 2001).

    I’m fascinated and appalled, though not especially surprised, that folks such as Owen didn’t like J.E. Gray’s generic names. I’ve long been a fan of Gray’s onomatopoeic creativity, because of the beautiful names he came up with for some of my favourite animals, names like Demansia, Liasis, Lialis, Gehyra, Tiliqua, Oedura and so on. Richard Owen reminds me a lot of Isaac Newton (I’m re-reading Neal Stephenson‘s Baroque Cycle at the moment) and it makes perfect sense to me that Owen would try to bury Gray’s legacy in much the same way as Newton buried Hooke’s.

    Kley, N.J. 2001. Prey transport mechanisms in blindsnakes and the evolution of unilateral feeding systems in snakes. American Zoologist 41: 1321-1337.

  16. #16 DDeden
    July 29, 2008

    The head shape looks rat-like, in the bottom photo. Strange cetacean.

    OT: The sea monster-like fish, the ‘long nose chimera’ alomst reminds me a swimming platypus. It’s related to sharks and rays, but reminds me of tetrapod vertebrates, ancestrally perhaps rootstock for them.

    “This strange cartilaginous fish uses its long snout to scan over the sea floor for the electrical impulses of its prey that bury in the muddy sea floor, just like a metal detector”. I think platypuses do that as well.

    http://www.who-sucks.com/animals/real-life-sea-monsters-24-bizarre-creatures-of-the-deep

  17. #18 DDeden
    July 30, 2008

    http://scienceblogs.com/tetrapodzoology/2008/04/functional_anatomy_part_ii.php
    this post
    I was referring to ‘this post’ above, which somehow vanished, sorry.

  18. #19 Dr. Nick
    July 30, 2008

    What is the etymology of Kogia, anyway?

  19. #20 John Scanlon FCD
    August 1, 2008

    Dr Nick, I think Gray’s names are often just made up to sound beautiful; he would sometimes start with a personal or place-name, or a pre-existing nomen, and roll it around in a virtual Latin-evolver until he liked the sound of it. Some names are obtained by swapping a single letter, or transposing syllables of an earlier one (e.g. Pelamis and Lapemis, Liasis and Lialis and Lisalia…). Elseya may be named after a wife or girlfriend known as Elsie, for all I know. Demansia was widely assumed in the later C19 to be derived from ‘[Van] Diemen’s [Land]’ and hence emended to Diemansia, Diemennia etc. by others, but they may have been completely wrong about that (no member of the genus was ever reported from Tasmania). Does Morelia (a python) have anything to do with morel mushrooms? I don’t know, and since Gray didn’t state etymologies when he coined the names it may be impossible to be sure.

  20. #21 Darren Naish
    August 1, 2008

    John: in absolute agreement with what you’ve written, no-one really knows the etymology behind Kogia and all people have been able to do is guess at it. The most popular suggestion seems to be that it’s based on ‘codger’ (as in, a miserable old sod). If true, this might provide a guide as to intended pronunciation (say it ‘Codgia‘ instead of ‘Kogia‘). Richard Ellis noted that Japanese names for these whales include Komakko and Uki-kujira, but neither are similar enough to serve as an obvious inspiration.

    DDeden: nope, Kogia does not do any bottom-walking, and is a pelagic deep-diver, capturing prey in the water column. Its ribs and skull are no denser-boned that those of other odontocetes so far as I can tell.

    Incidentally, I finally found a reference alluding to the alleged shark-mimicry of Kogia

    Fordyce, R. E. 2002. Cetacean evolution. In Perrin, W. F. et al. (eds) Encyclopedia of Marine Mammals. Academic Press (San Diego), pp. 214-220.

  21. #22 Graham King
    August 2, 2008

    That’s a very uncetacean face. Looks more like a seal or dog!

    More amazing novelty! (Darren, your blog is a prime place I come to satisfy my regular hunger for novelty… thanks.)

    Please DO write on spermaceti organ function (spermaceti AND junk). I have seen ‘buoyancy regulation’ and ‘sonic focussing’ given as reasons. I think there is likely lots to say on this; maybe more than one post. I wonder what squid think of it?

  22. #23 David Marjanovi?
    August 11, 2008

    “This strange cartilaginous fish uses its long snout to scan over the sea floor for the electrical impulses of its prey that bury in the muddy sea floor, just like a metal detector”. I think platypuses do that as well.

    Yes, but with a completely different set of sense organs. No homology here. Obvious convergence.

    the stiff neck (as if suctioning up from below)

    Huh?

    And whale necks are already practically immobile because the vertebrae are so extremely short.

    Do Kogia have noticeably denser rib or skull bones than more pelagic cetaceans or surface cetaceans like right whales?

    Would really surprise me, because, being whales, they have collapsible lungs and don’t need any ballast to stay down! Not to mention the sheer awesomeness of the spermaceti organ! Pachyostosis/osteosclerosis is for animals that need to carry filled lungs down.

  23. #24 DDeden
    August 18, 2008

    Thanks Darren & David M.

    Re. the Kogia ballast, I thought the large amounts of oils in sperm whales and their small kin might be complemented by denser-than-normal whale bones. (I wasn’t thinking of large amounts of air to ballast.)

  24. #25 Allen Hazen
    August 19, 2008

    As for the etymology of the name…
    Mo Hassan suggested something about Turkey (did you have a particular Turk in mind, Mo?). And the shape of the head might just, to someone with an odd imagination, suggest a man wearing a fez. And the H in the name of the Turkish (and, I think, general Middle Eastern) folklore figure Nasser din Hodja is, in some languages at least, a stronger sound than the English H. So maybe…

  25. #26 David Marjanovi?
    August 19, 2008

    It isn’t simply oil. It’s a fat that changes its density with temperature — and this temperature is something the whale can regulate very precisely, by regulating the blood flow to the spermaceti organ. If a sperm whale wants, it drops like a stone or jumps up like a cork.

  26. #27 Eugenie
    August 21, 2008

    Kogia!! Two of my favorite cetaceans…

    I think there may be a paper on cardiomyopathy in a stranded Kogia? I think I might have seen that somewhere.

    by the way, I enjoy your blog, and I’m adding it to my blog roll!

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