A giraffe, photographed at the Bronx zoo.
For me, no visit to the zoo is complete without stopping by to see the giraffes. They are among the most common of zoo animals, certainly, but I still find them fascinating. If giraffes did not actually exist and someone drew an illustration of one as a speculative zoology project the picture would likely be written off as absurd, yet the living animal is more charming than preposterous.
As with many extant large mammals, though, the giraffe is only a vestige of a once more diverse group. Its closest living relative is the okapi, a short-necked and forest-dwelling giraffe of the Congo, but many other types of giraffe lived in the not-too-distant past. Perhaps the most famous of these extinct forms is Sivatherium, a giraffe that might have survived until about 8,000 years ago and was once believed to have possessed a trunk.
An okapi (Okapia johnstoni), photographed at the Bronx Zoo.
A restoration of the skull of Sivatherium described by Falconer and Cautley.
Sivatherium was first scientifically described in 1836 by the English paleontologists Hugh Falconer and Proby Thomas Cautley. Its bones had come from the Sivalik Hills of India, and it was not quite like anything they had discovered before. In their introduction the scientists wrote;
The fossil which, we are about to describe forms a new accession to extinct zoology. This circumstance alone would give much interest to it. But, in addition, the large size surpassing the rhinoceros, the family of mammalia to which it belongs, and the forms of structure which it exhibits, render the Sivatherium one of the most remarkable of the past tenants of the globe that have hitherto been detected in the more recent strata.
Why was Sivatherium so special? In 1836 it seemed that all the large fossil mammals that had been found corresponded closely with living groups of animals. Elephants, hippos, rhinos, and antelope all had fossil counterparts. Even so, all these types of animals seemed relatively isolated from each other, and the "pachyderms" (a motley assemblage of large mammals such as elephants, rhinos, and horses) were further isolated from the numerous hooved mammals. "Connecting links" between the groups were expected, and according to the authors Sivatherium filled in a gap between the two great divisions of herbivorous mammals.
This was not necessarily an evolutionary statement. During this time paleontologists were hoping to establish a greater continuity in the fossil record. It is true that some scientists were starting to think about "secondary causes" that might cause species to change during the early 19th century, but just because an animal was the right shape to be a "connecting link" does not mean that it was considered to be equivalent to what we might now call a "transitional form." Paleontologists were looking to fill up gaps in the fossil record just as naturalists of earlier centuries searched for animals to link together in a great, graded chain that ordered animals from the "lowest" to the "highest."
Sivatherium was considered to be a suitable annectant form for several reasons. Working from a nearly complete skull Falconer and Cautley noted that Sivatherium was exceptionally large, almost the size of the fossil elephants that were also scattered throughout the Sivalik Hills. It also had a pair of "horn cores" between its eyes, like an antelope, and its nasal cavity looked that it was recessed further back into the face such that a short trunk was attached to it.
This latter point was considered by the authors to be a consequence of an increase in body size. As animals became larger(by whatever means) they required different ways of either bringing their mouths to food or food to their mouths. There was no indication that Sivatherium had a long neck, thus such a large animal would have required a trunk. Falconer and Cautley wrote;
Thus, in the Elephant nature has given a short neck to support the huge head, the enormous tusks, and the large grinding apparatus of the animal; and by such an arrangement, the construction of the rest of the frame is saved from the disturbance which a long neck would have entailed. But as the lever of the head became shortened, some other method of reaching its food became necessary; and a trunk was appended to the mouth. We have only to apply analogous conditions to a ruminant, and a trunk is equally required. In fact, the Camel exhibits a rudimentary form of this organ, under different circumstances. The upper lip is cleft; each of the divisions is separately moveable and extensible, so as to be an excellent organ of touch.
While perhaps not a "law" of nature, Falconer and Cautley identified this as a recurring trend so as to make the idea of a giant, antelope-like animal with a trunk seem less fantastic.
A restoration of a Sivatherium skeleton from Hutchinson's Extinct Monsters.
Not everyone agreed with the assessment that Sivatherium stood somewhere between camels and elephants, though. The French anatomist Geoffroy Saint-Hilaire thought that Sivatherium was a close relative of giraffes, but its strange combination of antelope-like and "pachyderm" features caused other naturalists to reject this alternate placement. The discovery of more fossils was crucial to the argument. When more skull bones of Sivatherium were found they showed that the giant mammal had a second pair of broad, pronged "horns" on the back of its head. This appeared to confirm that Sivatherium was an antelope, perhaps closely related to the pronghorn of the western United States (though even this animal, often called an "antelope", is not really a true antelope at all).
Eventually, though, naturalists came around to the conclusion Geoffroy had reached years earlier. Sivatherium was not an antelope or a "connecting link" between ruminants and "pachyderms" but an extinct form of giraffe. The features once believed to be horn cores were a major clue. In an animal like an antelope the horn core is a projection of bone from the skull that is covered in a keritanized sheath. Giraffes have similar bony projections but in life they are covered with skin and hair and are called ossicones. Upon close inspection the subtle details of the "horns" of Sivatherium, along with other features, allied it more closely with giraffes than with any antelope. The mysterious animal could finally be conclusively categorized.
A restoration of a Sivatherium family from Hutchinson's Extinct Monsters.
By 1890 Sivatherium was grouped among giraffes at the British Museum, and the skull of what had once been believed to be a hornless, female Sivatherium was by then understood to be a separate genus of extinct giraffe. Not everyone kept up with these developments, though. In his popular book Extinct Monsters H.N. Hutchinson still restored Sivatherium just as Falconer and Cautley had described, complete with a trunk that gave it the appearance of a moose with a tapir's face. A full restoration even included a hornless female laying down in the grass while the bull Sivatherium walked by.
More recent restorations of Sivatherium generally lack the short trunk and draw more inspiration from living giraffes than from moose. (Though the description of Sivatherium as "moose-like", based on the shape of its ossicones, continues to this day.) As far as I am aware there has been no specific study to address whether or not Sivatherium had any sort of trunk, but its skull differs significantly from the those of animals with short trunks such as tapirs and saiga. Even so, it is not unreasonable to hypothesize that Sivatherium had a very flexible upper lip, somewhat akin to what is seen in modern black rhinos, which could have been of assistance in browsing. More evidence will be required to support or reject this hypothesis.