EARTH'S ORGANISMS
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No Teeth, Long Tongue, No Problem - Adaptations for Ant-eating

A strict ant diet plus convergent evolution leads to cool adaptations.

When different organisms have a similar trait, one possible explanation is that they inherited the trait from a shared ancestor. For example, cats and lizards both have four limbs because the last common ancestor of cats and lizards had four limbs. However, some traits arise by convergent evolution, meaning that a similar trait evolved independently in two groups whose last common ancestor did not share that trait. An example of this is flight in birds and bats—it’s been over 300 million years since the reptile lineage leading to birds split from the mammal branch leading to bats, and that ancient, heavy-set lizard-ish ancestor definitely didn’t fly. Therefore, bird and bat wings are the result of convergent evolution, meaning each group has evolved wings independently.

Finding examples of convergent evolution is of interest to many biologists because it helps us uncover patterns in how structures evolve. Although they both have wings, birds and bats construct those wings very differently and use them in different ways. Studying these kinds of convergent traits lets us explore the realm of what’s possible (both feathers and skin-flaps supported by the arms can be used for flight) and what’s probably not (for example, we haven’t found any animals that fly by modifying their tails into propellers).

As an evolution nerd, my all-time favorite kind of convergence involves mammals that are highly specialized ant- and termite-eaters. Ants and termites are an interesting food source for large mammals because they’re so tiny that an animal has to eat thousands to get any nutrition at all. Luckily, both ants and termites are closely-related social insects that live in huge colonies/lunch buffets! Species that prey on these insects have evolved many times throughout the mammal family tree, and they share some bizarre adaptations that let them thrive on their specialized diet. Here are a few of my favorites:

Giant anteater

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Fig. 1 A giant anteater (Myrmecophaga tridactyla) displaying its specialized tongue. Image source: Wikimedia Commons.

Giant anteaters are amazing creatures found in Central and South American forests and savannahs. (Even though they are called “anteaters”, they also consume termites!) Their ant-based diet differs from that of their closest relatives, the sloths, who are dedicated plant-eaters. Since they don’t need to chew their prey, giant anteaters have long narrow skulls, extremely thin jaws, and no teeth. They feed by using their enormous front claws to rip open termite mounds and tear bark off of tree trunks, then deploying their long sticky tongues to snag the insects inside. These anteaters have special musculature that allows them to flick their tongues in and out over 150 times per minute! [1].

Aardvark

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Fig. 2 The aardvark (Orycteropus afer) is another ant and termite specialist with a scientifically adorable snout. Image source: Heather Paul via Flickr.

The aardvark is another ant and termite specialist that shares many traits with the giant anteater, such as powerful forelimbs and a long, sticky tongue. However, aardvarks belong to a much older branch of the mammal family tree, and these similar features are a result of convergent evolution. Aardvarks forage for termites on the African savannahs, and scientists used to assume they were most closely related to giant anteaters and sloths. However, new studies indicate that aardvarks share a common ancestor with other African mammals such as manatees, elephants, and hyraxes [2]. Like the anteaters, they use powerful forelimbs to dig open termite mounds, have long cone-shaped skulls, and snag termites with their sticky prehensile tongues; unlike the anteaters, they actually have teeth! However, these teeth lack enamel (the hard outer surface that protects the tooth from damage) and are extremely soft. Rather than chew its food, the aardvark has a muscular stomach that acts like a gizzard to grind up insects after swallowing [3].

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Fig. 3 The aardwolf (Proteles cristata) is like the hyena’s smaller cousin who won’t stop talking about how great it feels on this amazing all-insect diet. Image source: Dominik Käuferle via Wikipedia.

Despite its similar name, the aardwolf is separated from its fellow termite specialist the aardvark by millions of years of evolution. This African mammal belongs to the hyena family (part of the larger group Carnivora that includes dogs, cats, and bears), and it looks like a travel-sized, pointy-faced, less threatening hyena. Apart from their sharp canine teeth (used mostly for looking tough and defending territory), aardwolves have tiny reduced tooth nubs where their bone-cracking relatives have terrifying blade-like molars. Their skulls are also longer, flatter, and weaker than a hyena’s. Like the giant anteaters and aardvarks, aardwolves use long sticky tongues to consume exclusively termites [3].

These three mammals are just a few examples of species that have convergently evolved specializations for feeding on ants and termites—there are many more! Ant-eating is a great example of convergence because it has evolved multiple times in very distantly related animals. In each case, species show similar adaptations to their specialized diet, including long conical skulls, reduced or absent teeth, and exceptional tongues. These traits make sense when you think about the functional demands of their diets—they need to be able to insert their snouts into insect colonies and slurp up thousands of insects daily in order to survive on such tiny prey, but they don’t need to bite very hard or chew very much.

Finding these connections between body shape, behavior, and diet is my favorite part of studying evolutionary biology in animals. When extreme modifications like this pop up in different parts of the mammal tree, it’s always interesting to think about why a particular set of traits is best suited to a certain feeding strategy. Many animals eat insects as all or part of their diet, but these convergent ant and termite specialists have taken it to a whole new level.

If convergent evolution lights your fire, tell us your favorite example of a convergent trait in the comments and we can discuss it!

References:

  1. Naples, Virginia L. “Morphology, evolution, and function of feeding in the giant anteater (Myrmecophaga tridactyla*).” *Journal of Zoology 247 (1999): 19-41.

  2. Seiffert, Erik R. “A new estimate of afrotherian phylogeny based on simultaneous analysis of genomic, morphological, and fossil evidence.” BMC Evolutionary Biology 224 (2007).

  3. Taylor, W.A., Lindsey, P.A., and Skinner, J.D. “The feeding ecology of the aardvark Orycteropus afer.” Journal of Arid Environments 50 (2002): 135-152.

  4. Richardson, P.R.K. “Aardwolf: The most specialized myrmecophagous mammal?” South African Journal of Science 83 (1987): 643-646.

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