Paraceratherium: Beast of the Week

This week let's take a look at the largest land mammal of all time. (That we know of.)  Make way for Paraceratherium transouralicum!  Paraceratherium was a plant-eating mammal that lived all over what is now Eurasia during the late Paleogene Period, between 34 and 23 million years ago.  It was gigantic, towering over all other land mammals, including elephants, at up to sixteen feet tall at the shoulder (not including the long neck and head), and almost twenty five feet long. (Keep in mind this animal did NOT have a long tail.  A 25-foot long dinosaur isn't as large because of the long tail in the back takes up a lot of that length.)

Paraceratherium life reconstruction by Christopher DiPiazza

Paraceratherium has changed its name since its discovery a few times.  This is because specimens of it have all been pretty fragmentary, and therefore given names when initially discovered until it was realized they were all from the same kind of beast.  It may be more recognizable by the name, Indricotherium, which has since been lumped with Paraceratherium.  This was what it was called when it was featured on the BBC miniseries, Walking with Prehistoric Beasts. (Sequel to Walking with Dinosaurs)  Within the genus, Paraceratherium, there have been a few species named, but P. transauralicum is the most well-studied.

Paraceratherium skull on display at the American Museum of Natural History in New York

So what kind of mammal was Paraceratherium exactly?  It doesn't quite resemble any of the other large land mammals we know today.  The answer can be found when you look at its skeleton more closely.  Even though all specimens of it are mostly fragmentary, we do have good skull material.  If you look at the teeth of this animal, you will see large molars for grinding in the back, and pointed incisors in the front on both the upper and lower jaws.  This gives it away as  belonging to the order, perrisodactyla, which includes modern horses, tapirs, and rhinos.  So think of Paraceratherium as a really huge, hornless rhino.  The shape of the nasal cavity also tells us, by comparing it to skulls of its living relatives, that it likely had flexible, strong lips, or perhaps even a short trunk, like tapirs do.  Reconstructions of this animal's face seem to vary since horses, rhinos, and tapirs all have varying versions of a similar adaptation in this area.

It is likely, judging by the wear found on its teeth, that Paraceratherium was a browser, eating leaves from the tops of trees in life.  Since leaves have very little actual nutritional value as a food, animals, like Paraceratherium, need to eat large quantities in order to sustain themselves.  They also have large guts for fermenting tough-to-digest plant material, and and long digestive tracts to get as much nutrition out of the food as possible before its finally pooped out.  Because of this leafy diet (as oppose to grass which can just be sucked up with a wide mouth)

Perrisodactylids are known for their flexible lips. However, among them there is a wide variety of lips. Rhinos can have wide, or pointed lips.  Horses have rounded lips, and tapirs have short trunks.  This is all dependent on their feeding style.  My reconstruction of Paraceratherium has something between a White Rhino's wide lip and a tapir's short trunk.  This would allow Paraceratherium to select as many edible leaves as possible with less effort, something very important for large animals that rely on low-nutrition foods like leaves.  (It may have had something different. That's just my hypothesis.)

It was recently suggested that because of it's immense size, Paraceratherium would have needed an efficient way to have regulated its body temperature, especially when it came to cooling off.  Some scientists have suggested that Paraceratherium had large ears, like an elephant, where blood could be closer to the cooler outside temperatures before flowing back into the rest of the body, ultimately preventing the animal from overheating.  Many mammals from desert environments today have large ears for this reason.

The Fennec Fox, which lives in the Sahara, has extremely large ears for heat dissipation.  Larger animals like elephants use this same adaptation, and Paraceratherium may have as well.

 That is all for this week!   As always feel free to comment below or on our facebook page!

References

 Antoine, P. O.; Karadenizli, L.; Saraç, G. E.; Sen, S. (2008). "A giant rhinocerotoid (Mammalia, Perissodactyla) from the Late Oligocene of north-central Anatolia (Turkey)". Zoological Journal of the Linnean Society 152 (3): 581–592. 

Martin, C.; Bentaleb, I.; Antoine, P. -O. (2011). "Pakistan mammal tooth stable isotopes show paleoclimatic and paleoenvironmental changes since the early Oligocene". Palaeogeography, Palaeoclimatology, Palaeoecology 311: 19–29.

Prothero, 2013. Rhinoceros Giants: "The Paleobiology of Indrichotheres". pp. 87–106

Wang, Y.; Deng, T. (2005). "A 25 m.y. Isotopic record of paleodiet and environmental change from fossil mammals and paleosols from the NE margin of the Tibetan Plateau". Earth and Planetary Science Letters 236: 322–338.