Teeth taken to the extreme! From mammoths to warthogs to walruses to whales, in this episode we discuss the selective pressures, functions, diversity, and mysteries in the evolution of Tusks.
In the news
Newly-discovered mosasaur had a unique set of razor-like teeth.
New method for understanding how dinosaurs might have moved.
Sidewinding snakes have specially-adapted skin.
One of the oldest known Megatherium ground sloths found in Argentina.
My What Big Teeth You Have
What comes to mind when you think of a tusk? Elephants? Warthogs? Whales? This feature – huge teeth repurposed as tools for various uses – seems to be pretty popular, as it’s popped up several times in mammal evolution.
There isn’t really a standard definition for what makes something a “tusk” as opposed to a “fang” or just a “pretty big tooth.” But there are some features that are generally shared across the various things we call tusks: they’re usually large anterior teeth (incisors or canines); they often grow continuously; they tend to stick out of the mouth when it’s closed; and they’re generally used as tools beyond just biting things, such as displaying or digging. Of course there are exceptions: hippo teeth are often called tusks despite not sharing all of these features, and naked mole rat teeth are not called tusks even though they’re basically tusks.
The uses of tusks are many and varied. It’s very common for tusks to be sexually dimorphic, being smaller or absent in females, and as you might expect, they’re often used in male combat or display. We see this in hogs, elephants, “fanged deer,” and more. Elephants also commonly use their tusks to modify their environment, clearing vegetation or mining for minerals; walrus tusks are employed, among other uses, to help them break holes in ice or to pull themselves up out of the water; and then there are some truly strange tusks that have inspired lots of discussion, such as those of babirusas and narwhals.
Tusks Through Time
Unsurprisingly, given how much paleontologists love teeth, tusks are well-known in the fossil record, mostly from ancient relatives of living tusked animals. Examples include the enormous tusks of mammoths, the shovel-shaped tusks of gomphotheres, and the varied tusks of ancient walruses. There are also the dicynodonts, extinct mammal cousins whose tusks sat on either side of their beaks, plus the enormous rodent Josephoartigasia, which may have used its teeth like tusks. Some have even argued that certain large teeth in other animals such as fish and even theropod dinosaurs like Herrerrasaurus could possibly count as tusks.
When it comes to research, tusks can be very handy. Since they grow throughout the life of an animal, they can serve as a record of that animal’s life, retaining chemical and physical signatures of the animal’s diet and migratory habits. Tusks can also be useful in identifying the sex of an ancient animal, and there’s even some evidence that tusk shape might relate to an animal’s environment.
And of course, humans have a long history with tusks. Not only have we collected them for years for practical and artistic purposes, but we’ve also taken tusk-collection to the extreme in the form of poaching; such an extreme, in fact, that our habits seem to be driving the evolution of tusk reduction in elephants.
Tusks, the extra-oral teeth (technical, paywalled)
How Animals Got Their Horns, Tusks, and Antlers (non-technical)
Explore more about tusks and tusk evolution in walruses, babirusas, fanged deer, beaked whales, and narwhals.
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