Tetrapod Zoology

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Another article on babirusas – yaay! Like many (but not all) pigs, babirusas are omnivorous, and are said to eat invertebrates whenever they find them. They have also been reported to eat fish on occasion, to catch small mammals, and even to catch and eat the juveniles of other babirusas (Leus & Morgan 1995). They eat all kinds of plant material, including fruits, leaves, flowers, berries, nuts, bark and tubers, and they not only browse and dig to obtain such items, they are also surprisingly good at standing bipedally (without support) to feed on leaves. This again is a curious parallel with deer, in particular Sambar.

So… what’s with the bizarre curving tusks? Present only in males (females lack canines entirely), they grow continuously throughout life, and their growth, anatomy and function are all odd. The lower canine is normal in position and anatomy, it’s just that it becomes particularly long during growth, overlapping the outside edge of the snout as it grows. The upper canine is another story. Initially growing downwards – like any normal mammalian upper canine – it is then rotated as the alveolus itself turns to force the tooth upwards, and it eventually emerges from the dorsal surface of the snout. The most anterior part of the spiral parallels the long lower canines. As mentioned earlier, we’re mostly familiar with those babirusas where the upper canines curl in a circle as they grow, forming a spiral over the animal’s forehead. As we’ll see later, spiralling upper canines of this sort are not present in all kinds of babirusas.

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Regardless, in those babirusas with spiralling tusks, some authors say that, if the animal lives long enough, the tusks grow fatally into the face (Irven 1996). However, in the old male skulls that I’ve seen (see accompanying images: the woodcut is from Alfred Russel Wallace’s 1869 The Malay Archipelago), the tips of the upper canines begin the anterodorsal part of their curvature a short distance dorsal to the upper surface of the skull, so if they were to continue to grow they would harmlessly curl upwards. Furthermore, so far as I can tell from the literature, no-one has ever found a babirusa skull in which the upper canines have bored into the bone [though a colleague told me that he once saw a specimen where exactly this had happened... ].

A Balinese demon with curling tusks that emerge from its cheeks – the Raksasa – might have been inspired by stories or sightings of babirusas (Groves 1980) (Raksasa rendition below from here].

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Famously, people on Celebes once supposed that babirusas hung from trees with their tusks, and then stayed there in wait for passing females. This seems to be the one ‘fact’ about babirusas that everyone knows, as it’s mentioned in just about every article, paper and book that discusses them. It’s often stated that the tusks might be used in display or fighting, but there’s also the old idea that the tusks allow males to push their way through dense stands of ratten cane, thereby allowing tusk-less females and juveniles to follow in single file behind. Well, maybe the tusks can be used in this way, but this can’t of course have been the main selection pressure driving the evolution of the teeth, given that the intermediate stages leading up to this ‘end’ condition wouldn’t have been at all useful. More on tusks in the next post.

Perhaps surprisingly in view of their sensitivity to cold, babirusas have fared quite well in zoological collections, having first been kept in Europe at ‘la Ménagerie du Roi’ in Paris during the 1840s, and having bred at London Zoological Garden as early as 1884. In 1995, 29 zoos worldwide held babirusas. Several individuals have survived in captivity for more than 20 years, with the record holder being an animal kept at Chicago which, on its death in 1920, was 21 years and 4 months old. Paul Irven (1996) wrote that captive babirusas are ‘sensitive and responsive … with an endearing character’. They are also said to exhibit excitement and enthusiasm on greeting familiar people, engaging in tail wagging, head shaking and jumping and running about. This friendly disposition makes them quite different from many other non-domesticated suids.

For previous babirusa articles see…

For other Tet Zoo articles on artiodactyls see…

Refs – -

Groves, C. P. 1980. Notes on the systematics of Babyrousa (Artiodactyla, Suidae). Zoologische Mededelingen 55, 29-46.

Irven, P. 1996. The Babirusa. Mainly About Animals 29, 5-7.

Leus, K. & Morgan, C. A. 1995. Analyses of diets fed to babirusa (Babyrousa babyrussa) in captivity with respect to their nutritional requirements. Ibex J.M.E. 3, 41-44.

Comments

#1 Sordes
February 17, 2010

I´v seen some really strange tusks of domestic pigs from Polynesia at the ethnological Museum of Berlin. I wrote a longer blog-post about them, but for unknown reasons my blog doesn´t work at the moment, so I have to wait untill I can make a link.
One of the skulls had lower tusks which were so much curved, that they grew into the mandible. This caused serious damage to the bone, and some teeth were lost as a result of this inflammation of the bone tissue. There were some other skulls of pigs which had surely suffered from similar problems if they had grown older. One especially interesting item was the isolated lower boar canine which formed a perfect circle and nearly grow into its own Foramen apicale. Of course this is pathological, and would not happen via natural selection, but only by selective pressure by humans who probably found such extremely curved tusks nice to make jewelry of it.
#2 Andreas Johansson
February 17, 2010

Initially growing downwards – like any normal mammalian upper canine – it is then rotated as the alveolus itself turns to force the tooth upwards, and it eventually emerges from the dorsal surface of the snout.

I suppose that means the answer to my question in the previous thread is that they gradually rotated, and that ontogeny is recapitulating phylogeny in this case.

In which plane do they rotate?
#3 Raymond Ho
February 17, 2010

I think they are fascinating too. There’s a few babirusa in The Bronx Zoo here in NYC.
#4 Sordes
February 17, 2010

So my blog works again, here are the pathological boar-tusks:

http://bestiarium.kryptozoologie.net/artikel/massive-zahnanomalien-bei-ozeanischen-schweinen/
#5 Andreas Johansson
February 17, 2010

The possessor of the circular tooth must have looked pretty trippy in in life!
#6 Christopher Taylor
February 17, 2010

Which pigs aren’t omnivorous?
#7 Jerzy
February 17, 2010

I think there is one record of abnormal growth which bored into b. skull to death.
#8 Jerzy
February 17, 2010

I remember old paper that tusk wear suggests that males of one subspecies lock tusks and pull, but another – butt frontally.

Another paper suggested that upper tusks mostly block fatal stabs by lower, sharp tusks.

The second explanation seems more likely. This is more in line of how ruminant horns and antlers work. Even the most elaborate antlers – like forked ones by deer – actually have pointed ends which are fatal if aimed at soft body. What differs is elaborate design which blocks these blows acccording to animals favorite mode of combat. Thats why display and size of antlers is so important. Longer horns/antlers have crucial advantage. They block rival’s weapons – plus have one extra inch which would penetrate to the rival’s body. So even elaborate ornaments and ritualized combats have very obvious killing component.

Because babirusas can be now even observed by tourists in Sulawesi, I would think the matter is long solved?
#9 wolfwalker
February 17, 2010

Magnificently weird animals. Thanks for such an interesting and fun-to-read set of posts, Darren.
#10 Owlmirror
February 18, 2010

It’s all very well to show the skulls and the upper tusks curving away from the cranium, but some of the pictures of the live animals certainly look like the tusks are “aimed” right at the forehead.

I wonder if it’s possible that the animals have physical behaviors that actually change the direction of tusk growth, perhaps shoving them against a solid tree or rock.
#11 Darren Naish
February 18, 2010

Which pigs aren’t omnivorous? (comment 6). When I wrote the text (2006), I recall hearing that Desert warthogs Phacochoerus aethiopicus were strict herbivores in which omnivory was unknown (sorry, cannot remember where I heard this). I now think that this is unlikely to be correct, given that Common warthogs P. africanus have often been seen eating carrion and small animals.

Fighting style (comment 8): see next article. As for when and where the tusks curl (comment 10), while they do often look like they’re heading straight for the brain, they typically curl sharply forwards and upwards on making contact with the forehead. So many people say, however, that they recall seeing or hearing about at least one specimen that was gored to death by its own tusk that such a creature must have been recorded – however, I still have yet to see any picture of such an individual. Lots more on babirusas to come…
#12 Anthea Fleming
February 18, 2010

In Polynesia, maybe in New Guinea as well, domestic boars sometimes have the upper tusks deliberately knocked out by their owners. This causes the lower tusk to grow eventually in a complete circle, or even two or more, and makes the boar immensely valuable in the local economy. Presumably this originated from seeing the results of accidental injury.
#13 David Marjanović
February 18, 2010

they typically curl sharply forwards and upwards on making contact with the forehead.

But how does that work? Teeth grow from the tip of the root, not the tip of the crown.
#14 Darren Naish
February 18, 2010

Good point, I feel dumb for not realising this and have no clue how any of this works.
#15 Sordes
February 18, 2010

I once read that giant forest hogs are mainly (completely?) herbivorous, but I don´t know to which degree this is actually true.
#16 Alan
February 18, 2010

I have just checked the ISIS website and the current status of the captive babirusa population is as follows:

Buru babirusa Babyrousa babyrousa – 67 worldwide, with only 3 in the US.

North Sulawesi babirusa B.celebensis 47, all in the US

between them there have been 15 births in the last 12 months
#17 John Scanlon FCD
February 18, 2010

Commiserations, Darren. I remember the embarrassment I felt on having it pointed out that hair grows from the base, not the tip. I was 10, and had thought I knew a lot more about animals than my classmates.

For the rotation of the alveolus you’d need an ontogenetic series of skulls, but each tusk should preserve a nearly complete record of its own growth (subject to wear). It’s unlikely that the tusks bend significantly, i.e. the curvature should be a fixed property at any particular point along their length. So it should be simple enough to measure, and find out if that’s a smooth logarithmic spiral (so the tooth can be modelled like a regular snail shell or ram’s horn) or if distinct inflections are present.
#18 Dartian
February 21, 2010

Darren:

Several individuals have survived in captivity for more than 20 years, with the record holder being an animal kept at Chicago which, on its death in 1920, was 21 years and 4 months old.

Nitpick: Mohr (1960) claims that a female babirusa kept at Hamburg Zoo (which, coincidentally, also died in 1920) reached an age of 24 years.

Reference:

Mohr, E. 1960. Wilde Schweine. Die Neue Brehm-Bücherei 247, A. Ziemsen Verlag.