Hey there every peoples!
Ever been to a museum and seen a big skeleton and thought it was some kind of rhino? So it goes with brontotheres. While I’m sure you read the sign and found out you were wrong, I can’t really blame you. With their bulky bodies, pillar-like legs, and massive heads adorned with long (or short) horns, it’s easy to see why people think they are rhinos. While distantly related to rhinos, brontotheres are a more ancient group and were the largest land animals for at least 10 million years. While they are best known from North America, they have been found extensively in Eurasia as well. And one of those asian brontotheres is the subject of this post (but more importantly, something I recently found out about it).
The animal is known as Embolotherium andrewsi, which translates as “Andrew’s battering ram beast”. You may remember this animal (though not by name) from the BBC special Walking with Prehistoric Beasts. And this post is concerned with a claim made by that show and a recent revelation of mine. In the show the animals was shown with a great rhino-like horn (as it has always been). The show explained that the horn was made of bone, not hair. Rhino horns are made of keratin, the same material as your finger nails, which consists of thousands of tightly backed hairs. And this is true, brontothere horns were made of bone. The show claimed that these structures were too brittle to be used in combat (which the show later contradicted by showing a female brontothere ramming a carnivore full force with her horn). Was this really the case? Well as I found out a few weeks ago, perhaps not.
Embolotherium as it appeared in the BBC special "Walking with Prehistoric Beasts"
About a month ago I visited the California Academy of Sciences in San Francisco for the exhibit Extreme Mammals. The exhibit discussed the incredible abilities and adaptations of mammals throughout their evolution. Early on the exhibit discusses the many elaborate forms mammalian headgear has taken. Sure enough there was a brontothere skull in the mix and it happened to be Embolotherium.
Skull of Embolotherium andrewsi at the California Academy of Sciences exhibit Extreme Mammals
What struck me though was the new hypothesis for the purpose of the animal’s horn. Unlike other brontotheres who had horns on their noses or snouts, new research (as explained by the exhibit plaque) found that Embolotherium’s horn was actually a hyper extended nasal bone. Here, compare Embolotherium’s nose with that of another brontothere:
Skull of Brontops robustus (from Wikipedia)
As you can see, the brontothere above has a nasal bone separate of the horns. But on the Embolotherium skull, there is no separate nasal bone. The nasal bone itself is forming the horn. According to the exhibit, this radically alters the look and behavior of the beast. The exhibit said that the new research found that this hyper extended nasal bone would have created a very tall nasal cavity. The conclusion was that instead of being a ram made of bare bone, the horn instead supported a large fleshy structure:
The new look of Embolotherium
The huge nasal cavity may have acted as a resonating chamber, allowing the animals to make loud booming calls. The exhibit also said males may have fought with them now that we think they were covered in flesh. I imagine these fights may have resembled those of modern pigs where they used their extraordinary structures to push and shove in an up close tussle as opposed to the more violent fights seen amongst bovids (but then again I’m no expert). This doesn’t mean that all brontotheres are going to undergo makeovers. Brontotheres were very diverse with a wide variety of headgear. As the picture further up the post demonstrates, other brontotheres had independent nasal bones and horns. But as I was searching for pictures to use, I came across a rather intriguing one:
Skull of Megacerops coloradensis with a hypothosized reconstruction (from Wikipedia)
I noticed that the horn resembles that of Embolotherium where there doesn’t appear to be a separate nasal bone. Did this species of Megacerops have a nasal chamber like Embolotherium? If so, what does it mean for brontothere taxonomy? Was this a feature of a specific clade or did it independently evolve in different members of the group?
The media is dominated by discoveries of new species (almost overwhelmingly dinosaurs) and breakthroughs in the study of dinosaurs. But as Embolotherium’s massive nose reveals, there is still much to learn about the mammals of earth’s past. Ancient mammals were as diverse and as magnificent as the dinosaurs that over shadow them. Brontotheres in particular have a quality about them that is a little hard to pin down. Needless to say they are among the tops reasons I want to scour the Eocene and Oligocene beds of western North America.
Till next time!
A Central Coast Paleontologist 