“Palaeontology, in truth, is based on a narrow but solid foundation of fact, propped up by much that is uncertain or unstable, which future time must test, try—or reject.” So said anatomist James Murie to his peers at a meeting of the British Association, Edinburgh in 1871, and the inspiration for his big picture claim was a strange beast that had been dug up from India’s Siwalik Hills.
Named Sivatherium giganteum over three decades earlier, the hefty mammal seemed to be a mashup of deer, ox, giraffe, and other parts. Murie, for his part, believed the mammal was something distinct but related to America’s pronghorn, acting as a bridge to giraffes, but one can only hope he believed his own words. His hypothesis turned out to be wrong. As paleontologists eventually confirmed, Sivatherium was a burly giraffe.
All the same, I was struck by how Murie framed his argument about “Shiva’s beast” for another reason. Sivatherium is something of a forgotten celebrity. It was commonly included in books and lectures about “prehistoric monsters” in the 19th century, often touted as being a hoofed mammal as big as an elephant, but it eventually faded from view as dinosaurs soaked up almost all of our prehistoric affection. Sivatherium was pushed to the background, mostly known to fossil mammal aficionados, but now there’s something a revival in extinct giraffe studies.
Close on the hooves of a study that placed Sivatherium and its relatives in the context of giraffe neck evolution last year, a different team of anatomists consisting of Christopher Basu, Peter Falkingham, and John Hutchinson have gone back to revise just how large the impressively-ossiconed mammal really was.
What drew Basu to Sivatherium? “The real honest answer is that this animal just looks so cool,” Basu says. The “charisma” of the giraffe’s skull and bones sparked Basu’s imagination. But in fossiliferous terms, Basu says, Sivatherium was so widely different from what we envision when we think “giraffe” that studying the animal offered the opportunity to get a better handle on all the different ways it was possible to be a giraffe.
In order to piece the fossil mammal together, Basu and his coauthors turned to the Cautley Collection house at the Natural History Museum, London. This included the original Sivatherium bones used to describe the animal back in the 1830s as well as “key anatomy” for estimating body size such as neck vertebrae and limb bones. And for the parts that haven’t been found yet, Basu says, the modern giraffe and okapi provided a guidebook since some of their bones are very similar despite their disparate forms.
But how to put flesh on the bones of an animal that’s been extinction for thousands of years? There are two popular methods these days, Hutchinson says. Paleontologists can use an equation relating the bones of an extinct animal to a living species of known mass, or they can build a model – physical or virtual – of the whole animal to get a species-specific estimate of body mass, and often times both of these methods are used together as a check against each other. In this case, the two were in accord – Sivatherium had to be downsized.
Sivatherium came out “at least as heavy as a heavy large bull giraffe, or as heavy as a common hippo”, Hutchinson says, in excess of 3,000 pounds. There could have been larger ones, he notes, but even so they wouldn’t have been anywhere close to the 6,600 pounds of a typical elephant. This puts a lower cap on how large ruminant mammals got to be, even though Sivatherium is still among the largest of them all.
Not that such superlatives really matter. The animals themselves didn’t care. The more important point is that this conclusion came from the first rigorous reconstruction of what a Sivatherium skeleton looked like, assembled nearly two centuries after the animal was named.
Basu is right. Sivatherium is too strange to be left collecting dust, and, as I’ve been arguing lately, we really shouldn’t let dinosaurs have all the fun. HowSivatherium actually lived still teases my brain, and I’m glad that Basu, Falkingham, and Hutchinson have cleared some of the mythology surrounding the herbivore to give us a clearer view to the mammal, especially as new discoveries will continue to change this fantastic beast.
By Brian Switek