Tag Archives: Cetaceans

Cutting off the Trunk to Spite the Whale

A new look for Makaracetus bidens

In Trunks, Proboscides & Makaracetus, I argued the extinct whale Makaracetus bidens probably didn’t have a “trunk” or “proboscis”, contra Gingerich et al. (2005). For one thing, an overhaul of terminology resulted in ‘trunk’ no longer referring to a nasal appendage, ‘proboscis’ being restricted to tubular nasal/lip structures capable of grasping food, and all other elongate nasal structures being termed ‘prorhiscis’ (Milewski & Dierenfeld 2013). Makaracetus certainly had over-developed facial features compared to its cetaceous relatives, but it didn’t appear any more likely to have a “trunk” than, say, a camel.

Boar skull, courtesy of Markus Bühler.

One feature of Makaracetus I didn’t discuss in the last round were its maxillary fossae, which Gingerich et al. noted were also present in pigs. This feature is plainly visible on the boar skull above — it’s the virtual trench running from the orbits down the snout. These fossae provide attachment for the maxillolabialis superior and inferior, which are responsible for moving the protruding snout (Gregory 1920).

PiggyNoses

Pig snout musculature. From Gregory (1920)

What’s interesting is that pigs almost fit the definition of having a proboscis. Pigs can apparently grasp food items with both their nose and lip musculature, but fall short of the definition since only the disc is mobile (Milewski & Dierenfeld 2013). Does this mean Makaracetus may have had some sort of proboscis after all? Probably not. It’s notable that one trait shared by proboscides owners is directional olfaction (Milewski & Dierenfeld 2013), which seems like an unlikely trait for a cetacean to evolve, considering they lack the ability to smell underwater. Furthermore, pigs don’t have exclusive rights to maxillary fossae.

Top: Makaracetus from Gingerich et al. (2005)
Middle: Potamochoerus sp. from Gregory (1920)
Bottom: Macropus sp. from Gregory (1920)

Kangaroo maxillary fossae bear a surprising resemblance to those of Makaracetus — they’re similar in extent, only present anterior of the antorbital foramen, and are on the lower half of the rostrum. Unlike pigs, the maxillary fossae of kangaroos provide an origin for part of the buccinator muscle (Gregory 1920). The fossae are also present in baboons, where I suspect they have something to do with this display. Maxillary fossae also appear to be present in llamas but apparently not camels, for some reason. Considering the apparently variable functions of maxillary fossae and the additional premaxillary fossae of even more mysterious purpose, I’d agree with Gingerich et al.’s interpretation of “hypertrophied facial muscles” for Makaracetus and hesitate to speculate much further.

So if the nose of Makaracetus didn’t bear a proboscis or prorhiscis, what did it do? Perhaps the expanded nasal vestibule was merely a side effect of the snout warping into a down-turned shape. Another parallel could be found in Gray Seals, which have nasals retracted to a similar degree as Makaracetus and enlarged noses which function as displays (Miller & Boness 1979); however more specimens will be required to conclude that the trait was sexually dimorphic. Milewski & Dierenfeld (2013) hypothesized that the enlarged nose of Moose may act as a buoy to counterbalance to forelimbs when foraging underwater, a trait which could be beneficial to the apparently benthic-feeding Makaracetus. However, Makaracetus appears to have a much smaller nasal chamber than Moose, so the potential benefits could have been minimal.

I reconstructed Makaracetus as a Hippo/Manatee/Walrus-thing up top, but I suspect my endeavors were far too conservative. Makaracetus was a beast without obvious parallels and its true appearance can probably never be known. Still, there’s no reason to go slapping a “trunk” on strange-looking skulls, and I hope Milewski & Dierenfeld (2013) will get the attention it deserves and open minds to the myriad other possibilities of big, weird noses.

References:

Gingerich, P. et al. (2005) Makaracetus bidens, a New Protocetid Archaeocete (Mammalia, Cetacea) from the Early Middle Eocene of Balochistan (Pakistan). Contributions from the Museum of Paleontology 31(9) 197—210. Available

Gregory, W. (1920) Studies in comparative myology and osteology, No. V. — On the anatomy of the pre-orbital fossæ of Equidæ and other ungulates. Bulletin of the American Museum of Natural History 42 265—283. Available

Milewski, A. & Dierenfeld, E. (2013) A structural and functional comparison of the proboscis between tapirs and other extant and extinct vertebrates. Integrative Zoology doi: 10.1111/j.1749-4877.2012.00315.x

Miller, E. & Boness, D. (1979) Remarks on display functions of the snout of the grey seal, Halichoerus grypus (Fab.), with comparative notes. Canadian Journal of Zoology 57 140—148. Available

Trunks, Proboscides & Makaracetus

The terms ‘trunk’ and ‘proboscis’ have been applied to a heterogeneous array of bits danging off vertebrate faces such as the bulbous nose of male Proboscis Monkeys, the pendulous resonating chamber of male Elephant Seals, the hydrostatic facial tentacle of proper elephants, and even the chins of Elephantnose Fish. Milewski & Dierenfeld (2013) argue the terminology has become “dysfunctionally vague” and in need of a massive overhaul. The authors trash the term ‘trunk’ as it is vague and redundant (being a synonym for ‘torso’) and lacks precedence over ‘proboscis’, which was originally applied to elephants and roughly translates as ‘forager’. Due to this etymology and the extreme morphology exhibited by elephants, the term ‘proboscis’ was redefined to be a tubular extension of nasal and lip musculature capable of grasping food (Milewski & Dierenfeld 2013). The only extant non-Proboscideans to fit this definition are tapirs, and while numerous extinct mammals have been interpreted with proboscides (Palorchestes, Cadurcodon, Brachycrus, Macrauchenia, Pyrotherium) only Astrapotherium has a good case for having a proboscis under this new definition, since it doesn’t appear to have been capable of feeding itself otherwise.

This Mountain Tapir demonstrates that if narial tubes are wrapping around food, it’s a proboscis. From Wikipedia Commons.

As for other nasal structures that are incapable of grasping food, those have now been termed ‘prorhiscis’. These, uh, ‘prorhiscides’ (?) have disparate functions ranging from a directional sense of smell in Elephant-Shrews, dust filtration in Saiga, thermoregulation and water conservation in Dik-Diks, amplification of roars in Elephant Seals, and possibly acting as a buoy for diving Moose (Milewski & Dierenfeld 2012). There are other weird structures formerly labeled ‘proboscis’ in fish, but that’s really a story for a different time.

The snout of a Saiga rivals that of Tapirs in length, but does not incorporate the lips or grasp food, and is thus a prorhiscis and not proboscis. From Wikipedia Commons.

Gingerich et al. (2005) interpreted the extinct whale Makaracetus as having a “trunk” or “short, muscular proboscis” but confusingly referenced tapirs, manatees and walruses as “imperfect models”. Were they proposing an elephantine proboscis, prehensile lips, or something in between? This is a great example of how the now-archaic terminology was “dysfunctionally vague” and in light of Milewski and Dierenfeld’s efforts, it’s time for a reassessment.

Dorsal and lateral views of: Makaracetus (top) from Gingerich et al. (2005); Artiocetus (bottom) from Gingerich et al. (2001)

Makaracetus is classified as a protocetid and appears fairly similar to species such as Artiocetus (above), although with four pronounced differences: a nasal vestibule extending to the end of the snout, a downward-deflected rostrum with two rather than three pairs of incisors, “extraordinary” fossae (labeled LFM, LFP above) suggesting massive facial muscles, and enlarged antorbital canals (labeled AF above) indicating increased blood supply to the end of the snout (Gingerich et al. 2005). Clearly something odd was growing on the face of Makaracetus, but without living protocetids, it’s a bit hard to tell just what. I’m not even certain if a Tapir-style proboscis can be distinguished from a prorhiscis without live specimens, so, unfortunately, it appears there’s just no way of knowing things for certain. That won’t stop me from rampantly speculating.

Top: Makaracetus
Second: Brazilian Tapir from Witmer et al. (1999)
Third: West Indian Manatee from Husar (1994)
Last: Walrus from Wikipedia Commons

Imperfect models indeed. Gingerich et al. (2005) compared Makaracetus and Tapirs on the basis of expanded nasal vestibules, however, the nasals of Makaracetus are only around half as retracted. Makaracetus and Manatees were compared on the basis of being aquatic and having down-turned rostrums, which Gingerich et al. suggested to be an indicator of benthic feeding. Walruses were suggested as an ecological model, namely as a species that uses facial muscles to prey on bivalves, despite having some very different anatomy. The proposed ecology seems reasonable — although it requires better-known teeth to confirm — but as for what was happening with the nose of Makaracetus, there are some more interesting models.

Makaracetus-Camel

Dromedary from Harvard Museum of Natural History.

Superficially, Makaracetus looks kinda camel-y. The rostra of the two species, while differing considerably in depth, appear to be deflected downward at a similar relative place and to a similar degree. Camels have one less pair of incisors than Makaracetus and, oddly, the placements of the remaining incisor pair, canine, and first premolar are comparable. The antorbital foramen (“AF”) of the camel appears to be larger than that of Makaracetus. There are of course several pronounced differences between the two, namely, the fossae in Makaracetus (LFM, LFP) do not appear to have equivalents in camels and, perhaps as a result of these structures, Makaracetus has a rostrum that looks spoon-like when viewed above and camels don’t. Makaracetus and camels undoubtedly had enlarged noses for very different reasons, but this comparison makes a proboscis or even prorhiscis seem unlikely in the whale.

But I’m not quite done with Makaracetus yet, I haven’t even talked about pigs and moose! That will have to wait for a followup to this increasingly out-of-control article.

References:

Gingerich, P. et al. (2005) Makaracetus bidens, a New Protocetid Archaeocete (Mammalia, Cetacea) from the Early Middle Eocene of Balochistan (Pakistan). Contributions from the Museum of Paleontology 31(9) 197—210. Available

Gingerich, P. et al. (2001) Origin of Whales from Early Artiodactyls: Hands and Feet of Eocene Protocetidae from Pakistan. Science 293 2239—2242. Available

Husar, S. (1978) Trichechus manatus. Mammalian Species 93 1-5. Available

Milewski, A. & Dierenfeld, E. (2013) A structural and functional comparison of the proboscis between tapirs and other extant and extinct vertebrates. Integrative Zoology doi: 10.1111/j.1749-4877.2012.00315.x

Witmer, L. (1999) The proboscis of tapirs (Mammalia: Perissodactyla): a case study in novel narial anatomy. Journal of Zoology 249 249—267. Available

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:

Whale-A-Tee

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.

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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 crucigerCephalorhynchus commersonii & Sousa chinensisSee 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.

Amphiptera-Caperea

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