The Evolution of the Giraffe

Of all the mammals of the world, the giraffe is without a doubt one of the most fascinating. From its signature long neck, to its array of patches on its coat, to the two horn-like ossicones on its head, many aspects of the giraffe make it unique when compared to any other type of animal. It's an extremely popular creature, and yet despite its recognizability, there isn't much known about its evolution, especially compared to other species of hoofed mammals. All species of giraffe that live in the savannas of Africa are remarkably similar to one another, both morphologically and even genetically speaking. The one relative they do have outside the plains, the okapi, is also a very recluse and enigmatic mammal with only one species in its genus, and not a lot is known about it. The question that many zoologists and paleontologists alike have wondered for a very long time then, is how exactly the giraffes and their relatives came about. When did they branch out from other hoofed mammals? What were their earliest ancestors? And, in the case of the giraffe, how did it get its famous long neck? The goal of this video is to try and answer these questions and uncover the evolutionary history of this family of animals. The lineage of the giraffes and their relatives brought about some truly fascinating species in the late Cenozoic that were just as unique and majestic as the giraffes that we know today. Our stories start to the end of the Oligocene, roughly 25 million years ago. The world was undergoing a period of cooling that had started as far back as 15 million years prior in the Eocene, when India crashed into mainland Asia, raising up the Himalayan mountain range and altering global air flows. Areas of Eurasia and North America that were once dominated by dense forests were now being replaced with more open plains with tougher vegetation. This alteration of biomes and landscapes forced the herbivorous mammals of the time to make changes to the way that they ate and how they moved. One such group that proved well adapted to the shift was the artiodactyls, or even toad ungulates. They were a group of mammals who evolved shortly after the extinction of the dinosaurs, but it was only in this time period where they saw their first great expansion. Artiodactyla is an order that contains animals like pigs, hippos, camels, and even whales who share a common ancestor. But the most adapted of these ungulates to the grasslands of the Oligocene were the ruminants. The four-chambered stomachs of the ruminants allowed them to process hardier plants with ease, and the modifications on their astragalus, or ankle bones, aided them in being able to walk greater distances, not to mention run across these growing plains. Among these ruminants, a new group was beginning to grow at the time. These animals were known as the Gelocids, and during the late Oligocene they found their home in southern Eurasia. They were generally about the size of small antelopes, and showed powerful adaptations for both consuming tougher material as well as running at greater speeds via modified ankle bones. They had further built upon the blueprints of basal artiodactyls, and these developments led to the higher order of ruminants that we know as Pacora. Today the Pacorans include the Bovidae, which consist of animals such as cows, antelopes, and goats, the Moschidae, or the musk deer of Asia, the Cervidae, or the true deer, the Antelocapridae, which contains the pronghorn, and the Giraffidae, which contains the giraffe and the okapi. The only living ruminants not contained in Pacora are members of the family Trogulidae, or the mouse deer. These ruminants, also called chevrotains, demonstrate some characteristics of basal members of the taxon, including a less developed omesa, the third stomach in ruminants, as well as limb bones that aren't fully fused until adulthood. Despite not being part of Pacora, however, the chevrotains may in fact resemble the early ancestors of modern ruminants, including members of Gelocidae. The Gelocids gave rise to a new line of beasts that flourished in the early Miocene Epoch. This family of animals is known as the Palaeomericidae. The Palaeomericids were hoofed ruminants with similar morphology to antelope and deer, and they were best known for their impressive headgear. That headgear in particular was skin covered bony horns that more so resemble the ossicones of giraffes and okapis, as opposed to the antlers of deer, and this has led many to view this group of animals as an ancestral lineage to the Giraffids. The horns of the Palaeomericids are perhaps their most defining feature, and have produced forms completely unique to the fossil record. Take for example Triceromerics, with two protuberances close to its eyes that looked very much like those of the giraffe, in addition to a bifurcated horn in the back. Then there was Xenocaryx amidala, which followed in much the same vein as Triceromerics by having two giraffe-like horns near the front of its skull, with a much larger and stranger protrusion in the back. Among the Palaeomericidae, these two species were part of a group that shared strong ancestral roots with a line that would lead to the giraffes. The strangeness of the Palaeomericids weren't limited to these two species, of course. They represented a bizarre line of prehistoric ruminants that were widespread throughout both Eurasia and North America during the Miocene. Unfortunately, the Palaeomericids went extinct in the Pliocene Epoch, possibly due to further global cooling and the subsequent reduction in their wetter homes and the dense brush they were so accustomed to. But the question remains, with all the similarities to Giraffids, were the Palaeomericids their ancestors? Anatomical evidence suggests that they're more closely related to deer, making many classify them as a sister taxon to the family that contained the progenitors of the Giraffinocopy. But genetic analysis has shown that the relationship between the two groups is closer than what was once thought. A study by Fernandez and colleagues in 2007 combined morphological, ethological, and molecular information from all 197 recently extinct and currently living ruminants and created a phylogenetic tree showcasing two major results. It not only managed to group together the ancestors of giraffes, okapis, and pronghorns into a larger group that's now known as the superfamily Giraffoidea, but it also provided evidence that the ancestors of this family were the Palaeomericidae. Later, a 2015 research study done by Sanchez and colleagues on the systematics and evolution of Palaeomericidae grouped these animals together with the giraffes to form the clade Giraffamorpha. This clade saw a great radiation throughout the later legacine through the Miocene, resulting in an incredible diversity of forms. From the Palaeomericids arose the subfamilies Dromomericidae and Palaeomericinae. The Dromomericidae led to the North American group of ruminants whose only living member is the pronghorn, whereas the Palaeomericinae led to the Giraffanocopy. While recent studies found that ruminants such as Xenocaryx and Tricerameryx were part of Palaeomericinae, the earliest giraffeid was a Palaeomericinae known as Teruelia. Named after the Teruel Basin in Spain where it was found, it was a small deer-like animal that would have lived in the country around 25 million years ago at the end of the Oligocene and the beginning of the Miocene. Fossils of this Palaeomericinae are incredibly scarce, with the only ones being found at the Spanish Basin. As a result, it has been hard to piece together an accurate reconstruction. Teruelia branched off into two groups of giraffids, the Climacoceratidae and the Canthumericidae. Climacocerus was one of the earliest members of Climacoceratidae and lived around 17 million years ago. These animals were abundant in Miocene Africa and were said to live in herds. They measured about 1.5 meters or 4 foot 9 inches in height and had ossicones that looked a lot more like the headgear of deer and antelope than what we typically see on a giraffe. That being said, the size of Climacocerus and the design of their ossicones varied depending on the species. Climacocerus africanus was a species that was around average height for the genus and had straight and thorny ossicones. Climacocerus gentry on the other hand had ossicones that looked very similar to the antlers of deer. Their differences to giraffes were slightly understandable when taken into account that Climacocerus would lead to a sister group of giraffids that lived at the same time as the line that led to the modern day Shortly after Climacocerus came Prolibotherium, a Climacoceratid that existed roughly 16 million years ago. This genus lived in both Miocene Africa and Pakistan and was about a foot taller than Climacocerus, coming in at about 1.8 meters or 5 foot 11 inches in height. But what really set Prolibotherium apart from its ancestors were the shape of its ossicones. Prolibotherium had a pair of large palm-shaped ossicones that measured 35 centimeters or 14 inches across. However, these ossicones were only found on the males, indicating sexual dimorphism in the species. It's unclear what the exact purpose of these structures were. They could have been used for bouts between rival males or simply as accessories to attract females. Female ossicones were far simpler, looking more like slender horns that pointed back. Prolibotherium eventually led to the final group of Climacoceratids, a group that contained perhaps the most spectacular giraffids of all time. These were the Shivatheres, enormous mammals that while shorter than the giraffe, at only 2.2 meters or 7 foot 2 inches tall, rivaled it in weight. These giraffes are stated to be heavier than 1,200 kilograms or about 2,700 pounds. At over 1.3 tons, Shivatherium and many others of its genus rival the weights of some of the heaviest land mammals alive today. Shivatherium's ossicones are very similar to the antlers of the moose, leading many early reconstructions of the animal to look moose-like. However, this animal would have more likely looked like an overgrown okapi in life. Shivatherium is known from fossils ranging from Africa to India, and while the genus originated in the Miocene at around 7 million years ago, African cave paintings and Sumerian figurines of the creature indicate that it could have been alive as late as 8,000 years ago, which would put the creature's date of extinction well into the Holocene epoch. Shivatherium had many other close relatives that lived during the same time. Bromotherium, for example, was a giraffid of a similar weight and height, measuring 2.5 meters tall, being even slightly taller than its cousin, although it was not as heavy. Rather than being found in Africa, these Climacoceratids lived from India to Turkey, making them much more of an Asiatic group of species. Bromotherium also possesses its own unique ossicones, the purpose of which, as with many other giraffids in this lineage, is largely unknown. These animals all made up the terminal group that ended the lineage of the Climacoceratids. Around the time that the first members of Climacoceratidae evolved, another animal had begun venturing into the plains of the Middle East. This creature was known as Canthumerix. Canthumerix was a medium-sized creature that resembled an antelope or a deer in shape and measured about 1.5 meters in height, similar to Climacocerus. While its head ornamentation didn't get as extravagant as the one possessed by that animal, only having two horns that flared out in opposite directions, it bore far more similarities to the giraffes that we know today. A key aspect to take note of Canthumerix for was its bilobed canines that are found in giraffes, and just like in giraffes, these teeth were most likely used for stripping brows. The teeth of this animal would lay the foundation for the dentition of giraffids to come. This animal lived from 18 to 15 million years ago, and there were many giraffids similar to it at the time. However, one key fact to note is that the range of these animals was primarily centered in the Middle East, as opposed to Sub-Saharan Africa where giraffes are found today. Giraffo Carex was the next major member of Canthumericidae. It lived from 14 to 11 million years ago during the Miocene in India and Pakistan, and had several features that bore a strong resemblance to modern giraffes. This is seen not only in the greater length of its neck, but also in its ossicones, which look very similar to the ones seen on giraffes today, of which Giraffo Carex had four. Giraffo Carex is part of a new group of giraffids that arose in the middle of the Miocene. This group differentiated itself from its earlier ancestors by showing far more giraffe-like features. These animals were Besides Giraffo Carex, the other two genres of Palaeotragines are Palaeotragus and Samotherium. Palaeotragus evolved in the late Miocene roughly 12 million years ago. The genus also had many species that were very giraffe-like in anatomy, with longer muzzles and similar wear patterns on their teeth that would have been gained from their diet. This animal also grew to much greater heights, with taller members of the species measuring 3 meters or 9.8 feet tall. Palaeotragus It's argued from fossil deposits that it originated in North Africa, where Giraffo Carex was beginning to become extinct. Palaeotragus would have been able to occupy the niches it would leave behind before other ungulates arrived, such as the Miocene horse Hipparion. It then migrated to Europe, producing a line unrelated to the modern giraffe, as well as to Asia, where it would lead to the modern genus of giraffes. The other major member of Palaeotraginae was Samotherium. Living roughly 7 million years ago during the late Miocene, this species of giraffe inhabited areas of Eurasia, including Greece. The first thing to notice about Samotherium was the size of its neck. The neck of Samotherium major was roughly 1 meter or 3.3 feet long, and while it doesn't exceed the 1.8 meter long neck of the giraffe, it was far longer than that of its ancestors. This animal is often cited as a transitional fossil between the earlier giraffids with shorter necks that look more okapi-like in appearance and more modern giraffes with longer necks, making Samotherium an important genus in the history of giraffe evolution. With many of these Palaeotragines showing similarities to both the giraffe and the okapi, it begs the question as to how exactly the split between those two animals occurred. It's generally agreed upon that the okapi branched off first, but which species led to this branch remains a heated topic. Zoologist Kathleen Hunt believes that both the giraffe and okapi split off from Samotherium, with the modern genus Okapia splitting off during the Miocene, and then Giraffa splitting off during the Pliocene. These statements were part of a 1999 post known as Transitional Vertebrate Fossils FAQ, and looking through them in the modern age, we can see that there are more than a few problems. The biggest issue comes from how soon the modern Okapi genus splits off so close to when Samotherium evolved 7 million years ago, as well as stating that Giraffa split off during the Pliocene. As we'll soon find out, Giraffa emerged during the Miocene itself, and it most likely came from the genus Bolinia, not Samotherium. Paleontologist J.D. Skinner has another stance on the matter, stating that Samotherium wasn't the last common ancestor between the giraffe and Okapi, but rather that the two species branched off as far back as with Canthumerics. He then goes on to state that the Okapi is simply an extant Paleotrigine. When looking at the history of giraffe evolution, that view does make sense. If anything, giraffes seem like the odd one out when compared to all its prehistoric relatives and even the Okapi, which shares much more in common with Paleotrigines than its living cousin. Among both zoologists and paleontologists, the general discussion around which species was the last common ancestor between giraffes and Okapi seems to circulate around two animals in particular, those being Paleotrigus and Samotherium. A 2016 genetic study found that the last common ancestor of the giraffe and the Okapi might have lived around 11.5 million years ago, which might possibly make that animal Paleotrigus, or another closely related animal alive at the time. The genus definitely has strong characteristics linking it to both animals, so it is a possibility. Following the Paleotrigines came Bolinia in the late Maya scene. At first glance, this animal looks indistinguishable from giraffes that we'd see today, and in truth there is very little that separates this animal from the modern genus of giraffe. Apart from being slightly smaller, it shares all basic giraffe characteristics, from its ossicones to dentition to its general body plan. Bolinia created an evolutionary radiation in Asia, particularly around India and China, where it led to the potential first member of Priscilla. Very little exists in the way of fossils for this creature, making it hard for scientists to determine whether this species should be a member of Bolinia or Giraffa. To find our first undisputed member of Giraffa however, we need to go to the Pliocene Epoch. This species was Giraffa Punjabiensis from the Indian subcontinent. It lived around 7.3 to 7.1 million years ago, and was able to distinguish itself from Bolinia with its even more developed and giraffe-like teeth. However, while the early history of Giraffa was characterized by Asian expansion, it was a later African species that would pave the way for the giraffes of today. The earliest known African Giraffa was Giraffa gracilis, and was known from fossil deposits from the Pliocene and Pleistocene in areas such as Kenya. Later members such as Giraffa Jumai also inhabited these same regions, surviving until about the early Pleistocene. It was in East Africa that the modern giraffes, historically grouped together as Giraffa camelopardalis, first evolved around 1 million years ago. In looking at the evolution of the giraffe, it's hard not to wonder why their long neck developed in the first place. A common theory is that it allows giraffes to access hard-to-reach food up in the trees. While this theory does make sense given their feeding habits in the branches of trees, another theory has emerged stating that the long necks could be to attract mates. The necks could be used as signals of attraction in males, but the problem with that is that there is no large difference between male and female neck sizes. Another use in relation to mating, however, could be as weapons for bouts between rival males, who can use the necks to club one another. Regardless of why the necks of giraffes are the way they are, it's interesting to note that the evolution of the neck came about rather suddenly in the fossil record, and didn't show many gradual steps from a species like Samotherium to Boelenia, despite the fossils of those giraffids being so close together. The evolution of the giraffe's neck is still a subject for debate, and one that more fossil evidence can hopefully clear up. Today we only have two genera of giraffes alive. The first is Okapia, with Okapia johnstonii being the only member of this genus. While it was believed for a long time that the genus Giraffa had only one living species as well, Giraffa camelopardalis, recent genetic evidence has found that the genus can be split up into as many as four different species. These are the Reticulated Giraffe, Giraffa reticulata, the Maasai Giraffe, Giraffa typoskirchi, the Southern Giraffe, Giraffa giraffa, and the Northern Giraffe, which keeps the old Giraffa camelopardalis species name. While these species all look very similar, there is a significant amount of genetic variation among them, and they do not interbreed with one another in the wild. Some species even show as much, if not more, genetic distinction than that of polar bears and brown bears. Unfortunately, this poses another major issue for the animal in the wild. Prior to the four species distinction, giraffes have never been thought of as a threatened species. However, now that many agree upon this distinction, it's easy to see that some species are at a high risk of extinction, with giraffes like the Northern Giraffe having as few as 5,600 individuals in the wild. The greatest threats to giraffes today are poaching and habitat loss, and if humanity continues contributing to the decline of both the giraffes and the okapi, the earth will lose a group of fascinating animals.