New giraffe taxonomy discovery stands tall: Four species, four unique skulls

When palaeontologist and zoologist Nikolaos Kargopoulos embarked on a research project two years ago to analyse the skull morphology of giraffes, he believed that “a giraffe was just a giraffe”.

Kargopoulos travelled the world to 3D-scan a huge dataset of giraffe skulls — 515 to be exact — from African national parks, game farms, taxidermists and museum collections. 

“I did not expect to find such clear differences in the skull shapes of giraffes — before I started looking more closely, I thought a giraffe is just a giraffe,” the post-doctoral fellow at the University of Cape Town (UCT) and the Giraffe Conservation Foundation, said.

Kargopoulos is the lead author of a new study, led by UCT, which has further confirmed, through their skull shapes, that there are four distinct species of giraffes. It was published in the journal, PLOS One, in December. 

Nearly a decade ago, scientists discovered four species of giraffes — based on their genetics — and not, as previously assumed, only one species. They are the Masai, northern, reticulated and southern giraffe. 

Although there were theories of differences in the appearance of giraffes, no study had analysed this until UCT and the Giraffe Conservation Foundation began their research project, working with the Universidad Autónoma de Madrid in Spain, other European universities and numerous African government partners. 

Using 3D geometric morphometrics analysis, the study’s authors were not surprised that the research revealed distinct differences between male and female giraffe skulls. 

What was unexpected was that the results confirmed the existence of four giraffe species, in line with previous genetic analysis. The four species have different cranial morphologies, largely linked to their ossicones (the bony protrusions on their heads).

The problem with giraffe skulls is that, because of their size, museums rarely have the space for more than five to 10 giraffe skulls, Kargopoulos noted.

“This meant that, if we were to gather as much data as possible, we had to combine our efforts and to sample everything that we could. Considering that at the end of our sampling we managed to scan 515 skulls from 39 different sources, this required very efficient scheduling and a lot of coordination.” 

With only 117 000 giraffes remaining in the wild in Africa, the study’s findings are vital in “finally shining a light on the silent extinction of these gentle giants”, the authors said.

While the world’s tallest mammal is found in many countries in sub-Saharan Africa, not all the species are equally represented and, “as a result, some species are in more urgent need for protection than others”, said Kargopoulos.

“For example, there are less than 6 000 northern giraffes remaining in the wild and they live in rather ‘difficult’ regions such as Central and West Africa, while the southern giraffe is comparatively numerous with almost 50 000 individuals in Southern African countries, which are often under better conservation governance. 

“Now that we know that there are different giraffe species, it becomes clear that some giraffe species require much more urgent measures than others.” 

While the International Union for Conservation of Nature (IUCN) — the global authority on the status of the natural world — “is not a taxonomic expert”, many people continue to look to it for guidance, he said. 

“A main problem that has been affecting giraffe conservation is the fact that the IUCN has not yet officially split giraffe into four species … but we are optimistic that this will change soon.” 

If this happens, regulations and measures will apply separately to each giraffe species, allowing for targeted conservation strategies to be applied.

In a statement, Julian Fennessy, the director of conservation at the Giraffe Conservation Foundation and a co-author of the study, said: “For almost a decade our genetic research has proved that four giraffe species exist and now our collaborative morphological research has further confirmed this. It is about time that the world stands tall for giraffes, in particular the IUCN, and changes the outdated taxonomy of giraffes that some still hang on to.”

Conservation efforts need to target all four species, in particular those with precariously low numbers, before it is too late, Fennessy added. “Science is science and facts are facts. I hope that any debate around giraffe taxonomy is now finally put to bed.”

The team’s sampling required the acquisition of 3D models of the skulls, which was performed using 3D scanners, and in some cases, CT scanners. The Giraffe Conservation Foundation — the initial driver behind the study — saw the value and purchased such a scanner, Kargopoulos added.

Geometric morphometrics is used to compare shapes. “To compare the skulls, we placed specific landmarks on the 3D objects [using specialised software] which, when combined, captured the overall shape of the skull.”

The software can identify the coordinates of these landmarks — their 3D distance from the centre of mass of the skull — and then compare their exact position between all the skulls using statistical tools. 

“At the end, we can tell whether the position of the landmarks is different between defined groups, such as sexes, species, age classes etcetera.”

Although geometric morphometrics has been used in biology for several decades, sampling and analysing tools have recently developed to such a degree that they enabled complex tests that weren’t previously possible, Kargopoulos pointed out.

There is a lot of variation in giraffe skulls, especially in the ossicones. 

“If we dive deeper into our analysis, we can see small differences in many regions of the skulls, such as the orbits, the rostrum, the back part of the skull etcetera. However, the most striking difference between the four species can be seen in the development of the central ossicone, which is located above their eyes, especially in males.” 

There seems to be a clear trend in the development of this ossicone that follows geography and taxonomy. 

“As we move from the south to the north, this ossicone gradually becomes bigger. 

“The two extremes are the southern giraffe, in which this ossicone is practically a faint hill, and the northern giraffe, in which this ossicone is very high and pointy. The Masai giraffe and reticulated giraffe occupy intermediate positions.”

Giraffe ossicones are important because they affect selection for reproduction and, therefore, evolution. Males with more developed ossicones look more intimidating and are more likely to win in a direct fight between males, Kargopoulos said.

“Thus, they are more successful in territorial claims but also more successful in their mating efforts with females. In this framework, ossicone shape is a key aspect of giraffe anatomy that affects their life and evolution.”

The study’s authors are preparing additional scientific papers based on the data. “It’s fascinating how much we can learn from just by looking at the skulls,” he said.