Tusks Exhibit

I officially took last week off, although I spent most of it working from home. The Florida Museum of Natural History put together a traveling exhibit called “Tusks”, which is currently at VMNH. This Thursday I’m giving a lecture at VMNH as part of the promotion for the exhibit, so I spent my holiday working on slides.

My lecture is on the evolutionary history of proboscideans, so that gives me a chance to talk about one of the coolest fossil mammal groups, the shovel-tuskers. These were specialized gomphotheres which are known from Africa, Asia, Europe, and North America. A couple of species of Amebelodon are known from Florida, and the exhibit includes a beautiful lower jaw of A. britti, shown above.

Shovel-tuskers had elongate lower jaws with huge flattened incisors (the specimen of A. britti below is from FLMNH; a cast of this specimen is included in the Tusks exhibit):

This feature is also well-shown in the old world genus Platybelodon, such as this specimen at the American Museum of Natural History:

Shovel-tuskers used to be considered specialist feeders of aquatic plants (which seems to be the default lifestyle for any extinct herbivore that doesn’t have a direct modern analog). The current interpretation, based on wear patterns on the lower tusks, is that the tusks may have been used to scrape bark from trees.

Unfortunately, shovel-tuskers have never been found in Virginia, and we don’t have any in the VMNH collection, but I can always hope!

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8 Responses to Tusks Exhibit

  1. Doug says:

    I think any fossil elephant is cool. I have only seen skeletons of Platybelodon and Gomphotherium, so I have trouble imagining what the skeleton of Amebelodon looks like (all I’ve seen is it’s jaw). I have heard the water plant idea, and it stuck for a while. After all, it couldn’t be a coincidence that the last Nebraska shovel-tusker died out at the same time as the last Nebraska alligator. The wear marks are certainly convincing that they were doing something heavy duty with them, but I have trouble seeing how these jaws could be for scraping bark off trees. I mean, that’s what i always heard for Deinotherium, ad that made some sense because conceivably the animal could have knocked a tree over, straddled the trunk, and dragged it’s fang-like tusks down the tree trunk. And what is interesting is that Megabelodon had no lower tusks but instead a round knobby ball of bone, which may have supported a grisly pad. Also, why did gomphotheres eventually lose their long jaws and lower tusks, since trees may have been reduced but never wiped out in most areas.

  2. Alton Dooley says:

    In this scenario, the trees aren’t necessarily being pushed over; the bark would be scraped off a standing tree. I’ve also heard bark feeding suggested for deinotheres, but I don’t know how strong the evidence is; if they were feeding on bark it certainly would seem to be in a different fashion than Platybelodon (assuming it was).

    It seems that the different gomphotheres may have been doing different things with their lower tusks. Things like Gomphotherium and Rynchotherium had rather pointy lower tusks, rather than spatulate ones like Platybelodon. I’m not sure what they were used for, but I think it was something different.

    I also find it very interesting that the mastodonts, elephantids, and gomphotheres all eventually converged on the loss of the lower tusks. The last surviving gomphotheres (Cuvieronius, Stegomastodon) lacked lower tusks, a condition that elephants (Mammuthus, Stegodon, modern elephants) and mastodonts (Mammut) had already independently achieved (although some specimens of Mammut retained very reduced, relict lower tusks). This is an interesting 3-way convergence, considering that all three groups had ancestors with lower tusks (Eritreum) and apparently retained the lower tusks after they diverged. Moreover, gomphotheres retained (and hyper-developed) the lower tusks for at least 20 million years before finally losing them. There’s an interesting evolutionary story here, but I don’t know what it is.

  3. Paul says:

    Very cool – sounds like a nice exhibit!

    I know that it sure would be exciting to find a Gomp along the Calvert Cliffs or at the Carmel Church site. Seems that all that turns up along the cliffs so far is just tooth and tusk fragments. With less than 5% of the CC site quarried (and even less prepared) I’m hoping one (or a decent amount of one) will turn up there at some point. If you have horse and croc already Gomps can’t be too far away!

  4. Doug says:

    Perhaps they did have different functions. Like I said, the tusks of deinotherium seem like the only design to take bark of even a standing tree (even though I presented a scenario where it knocks the tree over). I would need to see diagrams and illustrations to understand how a gomp could do it. And it is interesting to note that most early elephants had long lower jaws and bottom tusk, which, as you say, hyper-developed and then disappeared.

    Rhynchotherium had a short jaw but long pointy tusks, so what he was doing is up for debate. Also, I once read that “spoon-bill” mastodonts like Gnathobelodon may have used their spatulate tuskless lower jaws to dig in mud while shovel-tuskers like Amebelodon may have dug in firmer soil. And then yeah, Platybelodon, with it’s spatulate tusks and a jaw that Roy Chapman Andrews once described as “…resembling a great coal shovel”. Perhaps some actually did dredge water plants with their jaws and tusks. As I noted above, the last Nebraska shovel-tusker disappeared around the same time as the last Nebraska alligator, yet abundant remains of gopher tortoises shows that the climate was still warm. The fossil record in Nebraska (which arguably has the best proboscidian fossil record on the planet) seems to indicate that they relied on wet climates and environments. Just an observation.

    There does seem to be an interesting convergence there. More interestingly, the late Miocene gomphotheres like Eubelodon and Megabelodon had no lower tusks, but still had long lower jaws, but by the start of the Pliocene, you had Anancus, who had a short, tuskless lower jaw like mammut.

    And as a side note, I once heard a creationist posit that the American mastodon specimens with atavistic lower tusks are actually a separate species who used those little tusks and more mobile neck vertebra to scoop up water plants like the shovel-tuskers of old. Of coarse, being a creationist, you can never trust what those guys say.

    Paul,
    I wouldn’t expect a whole lot. Sharktooth Hill here in California has a richness (though very different taphonomic history) comparable to Calvert Formation/Carmel Church, and yet the most complete remains are a lower leg bone and an ankle. But then again, Alton did find camel or rhino teeth (how is that going, Alton?) at Carmel Church (and in the jaws of a baleen whale, no less!) so maybe it is just a matter of time before something is found.

  5. Alton Dooley says:

    I think the Calvert has a richer land mammal assemblage than Sharktooth Hill, considering the size and logistic differences in the localities. That’s not terribly surprising, as STH probably represents deeper water. The Calvert land mammal fauna is surprisingly rich (especially if the Smyrna DE site is included), and probably includes around 100+ known specimens.

    Reading my post from last night, I think I inadvertently implied that shovel-tuskers lost their lower tusks; that’s not the case. Ancestral gomphotheres had lower tusks, shovel-tuskers hyper-developed them while other gomphothere lines lost them.

    One thing to keep in mind with elephants with respect to feeding is that modern elephants are very intelligent and highly adaptable, and will routinely eat things that they aren’t “supposed” to be adapted for. (Dolphins present the same problem; they pretty much eat what they want.) I wouldn’t be surprised to find that ancient elephants were locally modifying their feeding habits, and may have been using their tusks in several different ways.

    The “Tusks” exhibit includes a nice painting depicting Amebelodon scraping bark from a tree; essentially the tree is held between the upper tusks and with the trunk, while the lower teeth scrape against it.

    I’ve also seen suggestions that the lower tusks may have been used to excavate water holes during dry season. This makes more sense for the African Platybelodon than for Amebelodon in Florida (or the Nebraska species, for that matter), so I have doubts about that as a primary function. Even so, I don’t doubt that they were doing things like that if the need presented itself. A somewhat analogous function has been suggested for the huge crossing mammoth tusks, which might have been used to remove snow cover from vegetation (caribou use their antlers for this; caribou are, I think, the only deer with antlered females, as the only species in which antlers serve a feeding function).

  6. Brian Beatty says:

    First, I have to say that I’m glad that Tusks is at the VMNH. As someone that was an undergraduate working at the FLMNH when this exhibit was first put together in 1999 and thereabouts, many of these specimens are dear to me and I am glad to see others learning from them. In particular, the Amebelodon tusk pictured here is one I spent many an hour scanning for wear marks. I have been focused on sirenia and desmostylia, but hope to finish up some tusk wear projects on Proboscidea sometime in the near future, and this is a pleasant reminder.

    And regarding tusk wear, it is interesting to note that even those gomphotheres that reduce their chin tusks have wear on them. It is hard to argue that wear is anything else besides evidence of use, and some Rhynchotherium specimens have wear on their chin tusks that suggests they were repeatedly running something abrasive along their sides, wearing a deep groove on one side. The only scenarios that come to mind immediately is one of stripping leaves off of vines, or pulling up roots/rhizomes. It needs further work, but I anticipate it will help illuminate that tusks are not only the multi-purpose tools that modern elephants make them into, but have served many other purposes for other animals as well, some we may not see in modern animals.
    One good example may be from fossil dugongs, such as Corystosiren and Rytiodus. For more on that, you might check out this paper from The Anatomical Record:
    http://www3.interscience.wiley.com/journal/114265135/abstract

    Cheers,
    Brian

  7. Alton Dooley says:

    I had been wondering if you had worked on any of these specimens, Brian. FMNH did a great job with this exhibit.

  8. Alton Dooley says:

    Darren Naish has a post up right now about Elephas (the Asian elephant) over at Tetrapod Zoology:

    (http://scienceblogs.com/tetrapodzoology/2008/12/the_domes_of_wisdom.php#more)

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