Cranial Morphology Confirms There Really Are Four Giraffe Species

Originally assumed to comprise just one species, new research confirms 50 years of detailed studies that find giraffes are comprised of at least four cryptic species.

How many species of giraffe are there? Originally, it was widely assumed that there is just one species of giraffe with nine or so geographic varieties that are difficult to distinguish based on their physical appearance. However, multiple studies over the past 50 years have highlighted the distinctions between different types of giraffe based on their pelage patterns, cranial and postcranial morphology, genetics, ecology, and behavior. Yet despite these identifiable differences, giraffe are still classified as just one species.

Recently, a new study reports — yet again — that there are four species of giraffe (ref). This study is based on detailed examinations of the shape and structure (morphology) of giraffe skulls and of their cranial ornaments (ossicones), and it confirmed conclusions arrived at by previous genetics studies (ref and ref). As such, giraffes are likely cryptic species that are genetically distinct and are following different evolutionary paths.

This latest finding was based on a dataset of giraffe skulls from museum collections, wild populations, and taxidermy sources across Africa that is the largest of its kind. It was assembled by the study’s lead author, Nikolaos Kargopoulos, and collaborators who are based at the University of Cape Town and the Giraffe Conservation Foundation. Dr Kargopoulos, a postdoctoral research fellow at the University of Cape Town, is studying the cranial diversity of extant giraffes using 3D geometric morphometrics. He is a palaeontologist and zoologist whose research interests mainly focus on the anatomy and diversity of extant mammals, as well as fossil mammals from the Old World.

What inspired you to study giraffes?

“After finishing my PhD I was looking for postdoc opportunities and the giraffe project came up with GCF and UCT,” replied Dr Kargopoulos in email. “The collaborators were all experts in their fields, and it was clear that we were going to do something beyond the ordinary. The topic was of course interesting, and who would reject an opportunity to live and work in Africa for some time with lots of exciting travel opportunities.”

To conduct this study, Dr Kargopoulos and collaborators examined 515 giraffe skulls from four genetically distinct giraffe populations: the northern giraffe, Giraffa camelopardalis, reticulated giraffe, G. reticulata, Masai giraffe, G. tippelskirchi, and southern giraffe, G. giraffa. The skulls were digitized using handheld surface scanners and CT imaging, and 3D models were created from those images for analysis and statistical evaluation to detect size and shape differences in cranial shape and to identify patterns of cranial variability (Figure 2).

The analysis revealed statistically significant differences between all four giraffe taxa included in this study. Although most subspecies distinctions were less conspicuous, a few, such as G. t. thornicrofti and G. t. tippelskirchi, also showed measurable differences.

Key morphological differences centered on ossicone structure, cranial crests, and palate shape. Ossicones are important for giraffe behavior and reproduction, so predictably, significant sexual dimorphism in cranial morphology was identified, with males having larger ossicones (the horn-like knobs on a giraffe’s head) and broader cranial structures than females (Figure 3).

Skull shape differences between northern and southern lineages, or clades, were also detected. Dr Kargopoulos and collaborators noted that Northern giraffe species exhibit prominent, sharply pointed median ossicones, whereas southern giraffes possess minimal or absent median ossicones — resembling ancestral traits (Figure 3).

Dr Kargopoulos and collaborators’ findings show that giraffe skulls exhibit unique developmental and morphological characteristics, once again confirming that these giraffe are indeed four distinct species. As such, these differences imply that each species has its own specific conservation needs that require distinct conservation strategies. Further, these differences indicate that using translocation or hybridization between unrelated taxa could have negative consequences.

What was most surprising or unexpected about this study?

“Honestly, when I started this project I wasn’t expecting to find significant differences between the species,” replied Dr Kargopoulos in email. “Personally, I prefer lumping taxonomic frames and I prefer to keep things simple.”

“[W]hen I first saw the diversity range of each of the studied (previous) subspecies, I really thought that we won’t really find anything significant,” Dr Kargopoulos told me in email. “So, I was amazed when step by step it became clear that we indeed had significant discrimination between them and that this study confirms the existence of four species of giraffe. I had not expected to be able to make such a significant contribution to the conservation of such an iconic animal.”

What’s next? Are you planning to continue this research?

“With the help of some collaborators, we managed to collect a huge sample of more than 500 giraffe skulls that includes all known subspecies, males and females, adults and juveniles,” Dr Kargopoulos explained in email. “Considering the physical size of giraffe and the rarity of some forms, this is an extraordinary dataset and it would be a pity not to take full advantage of it.”

Currently, Dr Kargopoulos and collaborators have three more papers going through the peer review process: one concerning the cranial diversity of West African giraffes, one about pathologies found in giraffe skulls, and one reviewing the taxonomic framework of Giraffa.

“We also have another paper in preparation that includes more advanced analyses on the dataset focusing in more detail on biology-directed topics, such as ontogeny, allometry, integration-modularity, evolution etc, which we are planning to submit soon,” Dr Kargopoulos elaborated.

“Additionally, there are many approaches that can be fruitful in the discussion of giraffe biology and conservation, such as postcranial morphology, brain anatomy etc. and I am sure that we will see many interesting results in the future.”

Dr Kargopoulos and collaborators advise that conservation efforts should focus on conserving distinct forms, avoiding admixtures and translocations between non-related populations, which could lead to hybridization and reduced fitness.

“Based on the current results and the consideration of the ossicones as a key trait of the giraffe anatomy and behavior, it is suggested that conservation effort focus on the four distinct species of giraffe, and in some cases even on their subspecies,” the researchers recommended in their study (ref).

“Our results highlight the importance of focusing future giraffe conservation efforts on each taxon to maintain their unique characteristics and biodiversity in the wild,” the researchers pointed out (ref).

Last November, the US Fish and Wildlife Service proposed listing giraffe under the US Endangered Species Act (ref). If approved, this move will affect five subspecies of giraffes.

Currently, most conservation frameworks, such as the International Union for Conservation of Nature (IUCN), treat all giraffes as one species with nine subspecies, so these latest findings suggest this classification scheme should be revised. In view of the fact that there are only an estimated 117,000 giraffes alive in the wild in Africa, these findings help raise public awareness of the ongoing silent extinction of these gentle giants.

Source:

Nikolaos Kargopoulos, Jesús Marugán-Lobón, Anusuya Chinsamy, Bernard R. Agwanda, Michael Butler Brown, Stephanie Fennessy, Sara Ferguson, Rigardt Hoffman, Fredrick Lala, Arthur Muneza, Ogeto Mwebi, Moses Otiende, Alice Petzold, Sven Winter, Abdoul Razack Moussa Zabeirou, and Julian Fennessy (2024). Heads up–Four Giraffa species have distinct cranial morphology, PLOS ONE | doi:10.1371/journal.pone.0315043

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