Why Would a Herbivore Become a Fang-Feeder?

Question

In the forests of Dracoriri, one of the most dangerous herbivores is a Fangorant. This strange creature resembles an Ankylosaurus, but its entire body, even the eyelids, are covered in green scales akin to an artichoke (save the lethal tail club, which is a rugged brown and has lots of spikes, like a chestnut turned to rock), and its head is round with a flat underside and no discernible mouth, just two large fangs extending right out from its head like the canines of a sabertooth tiger, but shorter (1/3 the length) and much thicker.

My question is simple; how could a herbivore become a fang-feeder? These Fangorant have been observed stabbing their fangs into trees, shrubs, mounds of rotten fruit, and even the occasional sleeping adventurer. They clearly use these fangs to feed, but how did they get to this point?

Specifications:

1. Fangorant are descended from ankylosaurids, and the best answer will explain how such herbivores-slow, armored herbivores-could develop into fang-feeders that suck up sap, rotten fruit, honey, and occasionally blood for sustenance. And yes, just for the record, they have fangs-and a set of parallel jaws they use to clamp on prey, jaws that are not connected to a mouth or throat by the way, just a biological

2. And, going off #1, the best answer will also explain how feasible this creature's development is-how likely it's development and survival is considering biology and natural selection. I understand it's a pretty crazy creature, so if you feel it's necessary to suggest a more realistic version, that is fine.

Please note: I posted another question about a herbivore that is armed and aggressive, and at first blush this may look like a duplicate of that question. However, there is a huge difference. That question is about a herbivorous creature that looks and acts much like a predator, while this one is about an armored herbivore essentially becoming a vampire AKA a fluid-feeder.

Answer 1

A plant best-harvested by fangs

You're going to need some kind of selective pressure to accomplish this. My sense is that this particular situation will be best-served if the pressure rewards freaks rather than punishing normies.

There is a certain plant that produces sugar-rich fruit. The original species feasts on these fruits, which are full of high-calorie sugars. However, they are only able to eat fruits which have soft skins, and on this plant, those are the ripest fruits. The younger, unripe fruits of this plant have a higher sugar content, but also a much harder shell.

This creates a kind of reward gradient that effectively rewards herbivores for having piercing anatomy: any herbivore can eat some fruit, but the ones with greater piercing abilities will be able to eat more fruits on each plant, and better ones.

Lather, rinse, and repeat for a few hundred or thousand generations, and you may end up with herbivores with sharp fangs. _{Or a creepy proboscis (like a mosquito). Or wider mouths with stronger jaws. Or brains sophisticated enough to crack open the hard-shelled fruit, etc.}

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Alternatively (and more reliably):

• genetic engineering
• a wizard did it