The giant panda with its distinctive black and white colouration and its diet of bamboo is almost always thought of as the most unique bear species in existence. In fact, it has been suggested by some that the giant panda is so uncommon that it is not a bear at all, and should be categorized in its very own Family. However, you might be surprised to learn that in many ways the sloth bear is more unique than the giant panda. True, the sloth bear may superficially not look quite as unique as the giant panda, but if you look below the surface you might be surprised at what you find.
The Family Ursidae split off from other lineages in the Order Carnivora roughly 40 million years ago and is composed of 8 living bear species: brown bear, polar bear, American black bear, Andean bear, sun bear, Asiatic black bear, sloth bear and giant panda. The giant panda split from other existing bear species roughly 17 million years ago. This is, by far, the earliest any bear species lineage has been separated from other existing bear species. The sloth bear, by contrast, only split from other bear species roughly 3.5-4.0 million years ago when it split from the sun bear. Therefore, the sloth bear has had less than a quarter of the time to evolve in its own individual manner.
Giant pandas are known for their nearly exclusive diet of bamboo. While most bears are omnivorous (polar bears are almost exclusively carnivorous) and therefore eat plant matter, no other bear is a specialist in the manner that giant pandas are to bamboo. In fact, giant pandas have evolved a small thumb-like appendage, called a sesamoid bone (the thumb-like appendage is actually an elongated wrist bone), that allows them to maneuver bamboo in a manner that makes it easier to eat. Sloth bears have a specialized diet as well. Sloth bears are the only bears that are myrmecophagous (a fancy word that means they eat termites and ants). Roughly 50% of a sloth bear’s diet is made up of termites and ants. The sloth bear, like the giant panda, has evolved physical adaptations that have allowed them to more efficiently eat their food. They have long claws for digging into termite mounds and have a raised palate that allows them to suck in with great force. They can suck up hundreds of termites in one go. They are even able to independently close their nostrils, most likely an adaptation for keeping termite soldiers out of their nasal passages. But perhaps what is most surprising is that a sloth bear’s gut microbes are the most unique of any bear, including that of the giant panda.
Gut microbes are microorganisms, including bacteria, archaea, fungi, and viruses, that live in the digestive tracts of animals. The gut microbiota is very important for digestion and the health of the animal. It can even affect behavior. It turns out that specialized gut microbes are necessary for digesting chitin exoskeletons (which termites and ants have) for protein intake. And the gut microbiomes of placental myrmecophagous mammals have shown a “textbook example of evolutionary convergence driven by extreme diet specialization”. The giant panda, despite its unique diet, hosts a gut microbiome similar to other bear species.
And finally, there is but one bear on the planet that is known to chase off tigers, and it’s not the giant panda. Sloth bears are known for being defensively aggressive and unpredictable. This is a problem when it comes to living near humans, but a necessity when living among tigers.
Giant pandas are a beautiful bear and an amazing animal known the world over. In many ways they are the pride of China. It would be nice to see India embrace the sloth bear, a black fuzzball of a bear, in the same way they have embraced the tiger and Indian rhinoceros. In many ways, the sloth bear is just as unique and interesting as the giant panda, and in some ways even more so!