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?
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
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.