Teeth are durable witnesses to the past. They can survive when much of a skeleton disappears, and their shape can help identify an animal. But a species known only from teeth leaves large questions about the body that carried them.
For the earliest named members of Giraffa, the genus containing living giraffes, that was a substantial gap. Melinda Danowitz, John C. Barry and Nikos Solounias addressed it in a 2017 PLOS ONE study describing three sets of fossils from Pakistan. An ankle bone, fragments of a long foot bone and an ossicone offered a view of early giraffe anatomy beyond the dentition.
Separate finds, separate ages
The specimens came from the Siwalik deposits of the Potwar Plateau. They were found through expeditions involving the Geological Survey of Pakistan, Harvard University and collaborating institutions, then studied in established museum collections.
Their geological ages were not identical. The ankle bone, or astragalus, dated to 9.4 million years ago; the metatarsal fragments to 8.9 million; and the ossicone to 8.1 million. The dating framework drew on rock sequences correlated through magnetic polarity and radiometric information.
Those differences matter. The fossils cannot be assembled into one individual, and the researchers could not show that they belonged to a single species. Each is a separate observation of anatomy assigned to Giraffa through comparison with corresponding modern bones.
The team examined several giraffe museum specimens, including ossicones at different developmental stages. That gave them a way to ask whether a fossil difference might reflect age as well as evolutionary change.
An ankle carried a recognisable combination
The astragalus is a compact bone at the ankle, where several joint surfaces transmit forces between the lower leg and foot. Its form includes ridges, grooves and areas that articulate with neighbouring bones. A useful identification comes from their combination, not merely from size.
The fossil shared a particularly flattened upper groove and a characteristic twist between parts of the bone with the giraffe comparison. Other similarities included the shape of a supporting joint surface and a lateral notch.
It also differed. The fossil was more rectangular, while modern giraffe astragali in the comparison were broader and boxier. The authors suggested that this might reflect a smaller-bodied animal, while acknowledging that shape can have several explanations.
Thus, the oldest specimen preserved a mixture of familiar and differing anatomy. It supported recognition of Giraffa-like skeletal features at 9.4 million years without establishing that the entire animal had modern giraffe proportions.
A shallow groove in an incomplete foot bone
The metatarsal is one of the elongated bones below the ankle. Only two shaft fragments from the same individual were available, so the complete length could not be measured.
Even so, their form was informative. The groove along the rear surface was exceptionally shallow, resembling the corresponding region in modern giraffes. The relatively uniform width along the preserved fragments also suggested an elongated original bone.
This inference is more limited than holding a complete limb. The fragments could establish a distinctive surface pattern and support elongation, while leaving total length and overall body proportions uncertain. Their value came from adding a different anatomical system to evidence previously dominated by teeth.
The head appendage resembled a young giraffe’s
The ossicone preserved a backward-curving shaft, a rounded tip and secondary bony growth concentrated towards its apex. Its concave, pitted underside resembled the attachment surface of young giraffe ossicones before complete fusion to the skull.
The developmental comparison helped explain why a fossil might have less extensive secondary growth than an older giraffe. It could represent a juvenile or young adult, although age, sex and species differences could not be fully separated.
This is where O’Brien and colleagues’ anatomical growth series provides a useful connection. Their scans of newborn, juvenile and adult giraffe heads showed changes in the blood supply around developing ossicones. That work concerns living-species development, but it explains why an appendage’s growth stage belongs in a fossil comparison rather than being treated as irrelevant variation.
The fossil ossicone was not enough to identify the sex of its owner. Nor could it be linked confidently to either of the early named Giraffa species known from isolated teeth. A skull preserving both would be needed to connect those categories of evidence.
Familiar anatomy does not establish an unchanged animal
Danowitz and colleagues concluded that several characteristic skeletal features of Giraffa had a long history. The discovery extended the genus’s early record beyond teeth and supported a substantial Asian component in that history.
It did not show a modern giraffe standing unchanged nine million years ago. The oldest ankle differed in proportions; the limb remained fragmentary; and no neck vertebra belonged to these finds. The larger neck-evolution question requires its own evidence.
More associated remains could connect teeth to limbs and headgear, distinguish one species from several and test how body proportions changed. The three finds have already made those questions more specific. An early genus that had been recognised largely by its teeth could now be compared through joints, limb structure and the growth of its head appendages.
Sources
Melinda Danowitz, John C Barry, Nikos Solounias (2017). The earliest ossicone and post-cranial record of Giraffa. PLoS ONE. DOI: 10.1371/journal.pone.0185139. Read the full paper.
