It was smaller than modern pronghorns, around 70cm tall at the shoulder (~2’4″), and males had long antler-like horns with three tines. Bizarrely, one of these horns was always at least twice the size of the other, with “left-horned” and “right-horned” individuals seeming to occur in equal numbers.
Meanwhile in China another Miocene ungulate known as Tsaidamotherium hedini also had strange headgear, with an enlarged right “horn” forming a helmet-like dome on top of its head. This species was featured here on the blog just year, so check out that post for more details about it.
Tsaidamotherium hedini was a ruminant ungulate living around 11 million years ago during the late Miocene, in the northeastern part of the Tibetan Plateau in what is now Northwestern China. Although it’s known only from partial skull remains it was probably similar in body size to a large sheep, about 80cm tall at the shoulder (2’7″).
Since its discovery in the 1930s it’s traditionally been classified as part of the muskox lineage, but in 2022 it was proposed to actually be a giraffoid very closely related to the newly-discovered Discokeryx.
Tsaidamotherium had some extremely unusual headgear, with highly asymmetrical “horns” (actually ossicones if was a giraffoid). The left one was small and positioned above the eye, while the right one was shifted back and towards the middle of the forehead, and was expanded out into a wide bony disk that would have supported a large helmet-like domed keratin covering.
Its skull also had a very large nasal cavity resembling that of the modern saiga antelope, suggesting it may have convergently evolved a similar sort of complex air-filtering snout to deal with dry cold air in its mountainous habitat.
Earlier in this series we saw some ruminants with bizarre-looking headgear, but there was another species in that group that evolved a completely different type of strange head.
Rusingoryx atopocranion was a close relative of modern wildebeest that lived during the late Pleistocene, around 100,000 to 50,000 years ago. Its fossil remains are known from the Kenyan part of Lake Victoria, on Rusinga Island – an area which wasn’t actually an island at the time due to lower lake levels, and was instead part of a hot dry grassland environment.
Standing about 1.2m at the shoulder (~4′), it had an oddly-shaped skull with a pointed snout and a highly domed forehead. But this wasn’t the thick bony dome of a headbutting animal – this structure was narrow and fairly fragile, and had looping nasal passages running through it.
Instead it was something never before seen in any mammal: a bony nasal crest convergently similar to those of hadrosaurid dinosaurs.
Juveniles had less developed crests, developing them as they matured, and one skull that may represent an adult female also has a smaller crest, suggesting that this feature was sexually dimorphic.
Based on just the anatomy of the nasal passages Rusingoryx may have honked at a frequency similar to a vuvuzela, but the added length of its vocal tract could have lowered this pitch even further, closer to infrasound ranges – so more like a tuba! Such low frequencies can travel very long distances and are also below the hearing range of many carnivores, and would have effectively allowed Rusingoryx to shout at each other in “stealth mode”.
And Prolibytherium was probably the most striking of the lot.
Two different species have been identified, with Prolibytherium magnieri here living in North Africa during the early-to-mid Miocene, about 17-16 million years ago. Its exact evolutionary relationships are uncertain but it was probably part of a group called climacoceratids, deer-like giraffoids which often had thorny branching ossicones that resembled antlers.
It stood around 1.2m tall at the shoulder (~4′), and exhibited dramatic sexual dimorphism – females had slender forked horn-like ossicones, while those of the males flared out into large wide flat shapes that resembled butterfly wings.
Heavy reinforcement in the bones of the back of the males’ skulls helped to support all the extra weight of those huge ossicones, and if they actually used the structures to fight with each other then this may have also provided some protection or shock absorption.
Modern ruminants are the only living mammals with bony headgear, with four different lineages each sporting a slightly different type: deer antlers, bovid horns, giraffid ossicones, and the prongs of pronghorns.
The protoceratids were an early group of North American ruminants whose relationships are uncertain, but may have been related to modern chevrotains. They were convergently deer-like in appearance, with teeth adapted for grazing on tough grasses – and along with having a pair of horns in the usual position on their heads, males also sported an additional pair of ossicone-like growths on their noses.
Synthetoceras tricornatus lived during the Late Miocene, around 10-5 million years ago, and was one of the largest protoceratids, standing about 1.1m tall at the shoulder (3’7″). Its two nose-horns were partially fused into a single long structure with a forked tip, which may have been used for sparring in a similar manner to the antlers of modern deer.
Synthetoceras tricornatus
Meanwhile on a different branch of the ruminant family tree, closer related to deer and giraffes, a group known as the palaeomerycids independently developed a similar sort of extra head appendage – but at the opposite end of their skulls.
These ruminants were a little more heavily built than the protoceratids, and specialized in feeding on soft vegetation in humid forest environments. They were a highly successful group, existing for almost 30 million years, ranging across Eurasia, Africa, and North America, and even ventured into South America during the early phases of the Great American Interchange.
Males had two giraffe-like ossicones above their eyes, along with a third crest-like one at the very back of their heads. In some species this formed a single central “horn” shape, while in others it forked out to each side. They also often had long saber-like canine teeth similar to modern water deer and musk deer, which were probably used for fighting while their elaborate headgear was purely for visual display.
Xenokeryx amidalae lived in Spain during the mid Miocene, about 16 million years ago. It stood around 0.8-1m tall at the shoulder (2’7″-3’3″) and had a unique T-shaped “handlebar” crest which ended up inspiring its genus name – a reference to the similar shape of one of Queen Amidala’s headpieces in Star Wars, which was itself based on Mongolian imperial fashion.
The island of Crete has been isolated since about 5.3 million years ago, when the dried-out Mediterranean Searefilled — but at that time it started off as several much smaller islands, and only gained its larger modern shape thanks to tectonic uplift in the Pleistocene.
It only had a small number of endemic land mammals during the Pleistocene, whose ancestors all seem to have reached the island by swimming or rafting from southern Greece: dwarf elephants, a small hippo, an otter, a shrew, large mice, and several deer.
Deer are surprisingly good swimmers, and seem to have colonized Crete by the mid-to-late Pleistocene 300,000 years ago. They were by far the most diverse mammals on the island, with eight species in six size classes, each living in different types of habitat and specializing in their own ecological niche in a similar situation to the older Italian Hoplitomeryx. Their anatomy was modified so much that it’s unclear what their original ancestors actually were, or even if they were all descended from a single colonization or multiple arrivals, but they seem to have been close relatives of the huge Megaloceros.
All eight species are usually classified in the genus Candiacervus, and the smallest and weirdest of them all was Candiacervus ropalophorus.
Ironically for a cousin of the giant deer it was tiny, just 40-50cm tall at the shoulder (1’4″-1’8″), with proportionally short stocky legs more like a goat. It seems to have convergently evolved to occupy the same niche as wild goats do elsewhere, clambering over steep rocky mountainous terrain and eating tough prickly vegetation.
The antlers of the males were huge for their body size, around 77cm long (2’6″), and they were simplified into a long straight beam with only a single small spike at the base. The far ends were wider and rounded, described as club-like or spatula-like, and their odd shape suggests they probably weren’t much use for fighting and wrestling like in other deer. Instead they seem to have been more just for show and visual display.
Meanwhile a second dwarf species, Candiacervus reumeri, had more standard-looking antlers and probably still fought each other.
The largest species, Candiacervus major, was as big as a modern wapiti, with a shoulder height of around 1.65m (5’5″) and body proportions much more like a normal long-legged deer. Its antler shape isn’t actually known yet, but since it lived in thickly forested areas of Crete the stags may have had more streamlined antlers to avoid getting snagged on low branches.
The various Candiacervus species went extinct towards the end of the Pleistocene, around the start of the Last Glacial Maximum 21,500 years ago. Originally this was thought to be long before humans ever reached the island, but more recent discoveries have brought that into question.
Humans do actually seem to have encountered living Candiacervus ropalophorus, since petroglyphs in Asphendou Cave appear to depict the dwarf deer and so must be at least 21,500 years old. Additionally, even older stone tools on the southern coast of Crete from at least 130,000 years ago match those made by archaic humans (probably Homo erectus) who may have arrived over sea from northern Africa.
So it’s possible the weird Cretan deer survived alongside humans for some time, but then their habitat started to degrade as the climate shifted rapidly colder and drier. Some remains show that many individuals were suffering from secondary hyperparathyroidism and metabolic bone disease, signs of severe nutritional deficiencies, and their weakening population may have ultimately been unable to deal with both the malnutrition and the additional pressures of human hunting.
5.3 million years ago the Strait of Gibraltar formed, re-establishing the connection with the Atlantic, and the Mediterranean refilled incredibly rapidly, possibly in as little as two years. As a result, various species that had colonized across the dried-out Mediterranean from the continental mainland were left stranded out on islands that had been re-formed throughout the sea.
And on what is now Menorca a population of rabbits found themselves isolated, with little competition and no large terrestrial predators.
Nuralagus rex
Nuralagus rex was the evolutionary result, an enormous rabbit 50cm tall at the shoulder (1’8″). It was heavily built with a stiff spine — making it unable to hop — and had weaker senses than its ancestors, with small eyes and stubby ears. It would have been a slow-moving animal ambling around the scrublands of Menorca, digging for its main foods of roots and tubers.
It’s unclear what happened to this big bunny, but it seems to have disappeared around the end of the Pliocene, about 3-2.5 million years ago. Possibly the onset of global cooling at the beginning of the Pleistocene ice ages changed the climate too quickly for it to adapt to, or the dropping sea levels that connected Menorca with nearby Mallorca introduced new competition from the other island that Nuralagus couldn’t cope with.
Myotragus balearicus
And one of the animals that spread into Menorca from Mallorca was Myotragus.
About the same size as the giant rabbits, at 50cm tall (1’8″), Myotragus balearicus was a close relative of modern sheep that had undergone dwarfing on Mallorca since its ancestors’ isolation 5.3 million years ago.
It was possibly one of the most unusual mammals ever, with a combination of features not seen anywhere else. Its snout was relatively short and rabbit-like, with ever-growing front teeth in its lower jaw, and its eyes faced directly forward, giving it stereoscopic vision more like a primate than a herbivore. Its brain and sense organs were highly reduced compared to its ancestors, its legs were shorter and stockier, and its feet had lost much of their flexibility, making it unable to run or jump.
But strangest of all was its metabolism, as indicated by growth lines in its bones. It was essentially cold-blooded, functioning more like a reptile than a mammal, growing at a slow rate that varied or even stopped entirely depending on the conditions of its environment. It would have taken around 12 years for it to reach maturity, an incredibly long time for its size, and so it would have reproduced very very slowly — but this metabolic strategy also allowed it to conserve a lot of energy and survive long periods of scarce food availability.
Myotragus‘ extreme weirdness obviously worked to its advantage, because it was quite common on Mallorca-Menorca and unlike many of the other native species it survived through the much colder drier conditions of the Pleistocene.
It was still around in the Holocene when humans reached the islands in about 3000 BCE, and this slow-moving sluggish goat-like animal with a rather uncanny face must have been a very strange sight to them.
There was a hypothesis that the early settlers actually attempted to domesticate Myotragus, based on remains found in caves with what appeared to be trimmed horns. But in recent years this has been disputed, since some of the “trimmed” horns pre-date human arrival and may be better explained as the result of Myotragus individuals chewing on the bones of others for the mineral content.
Shortly after the arrival of humans Myotragus and the other remaining endemic mammals on the islands (a giant dormouse and a giant shrew) disappeared entirely, suggesting that a combination of hunting, competition from introduced livestock, and predation from dogs was finally too much for these strange sheep to handle.
Isla Pedro González is part of the Pearl Islands in the Gulf of Panama, about 48km (30 miles) offshore. It was formed after the end of the last glacial period, as steadily rising sea levels cut it off completely from mainland Panama about 8500 years ago — and isolating the population of deer that lived there.
Although Pedro González is the third largest of the Pearl Islands it’s still fairly tiny, just 6.5km long (4 miles). As a result of this small space, limited available food supplies, and a lack of any large predators, these deer rapidly shrank down into a dwarfed form to survive. By 6000 years ago they were the size of a small dog, just 35-40cm tall at the shoulder (1’2″-1’4″) and weighing less than 10kg (22lbs).
The Pedro González dwarf deer haven’t been given any official scientific name just yet, but since they’re thought to be descendants of brocket deer they’d be a part of the genus Mazama, either as their own separate species or as a subspecies — similar to the larger native deer on nearby Isla San José, which are probably their closest living relatives.
Paleoindian settlers arrived on Pedro González just over 6000 years ago, and we know they hunted and ate the tiny deer because all the known remains come from a preserved trash heap and show signs of human butchering and chewing.
Younger deposits have gradually less and less deer bones, and although those particular settlers had left again by about 5500 years ago the damage was already done — layers from another group of people about 2300 years ago show no deer bones at all, so the dwarf deer had to be already extinct by that time.
Located on the Pacific Ring of Fire, the islands of the Philippines were formed by volcanic activity at the junction between several tectonic plates. Most of the 7461 islands that make up the archipelago have never been connected to any other landmass, leading to a huge number of unique endemic species evolving from whatever managed to arrive via ocean rafting events.
Celebochoerus cagayanensis
Celebochoerus cagayanensis was a giant species of pig, known from the island of Luzon. Living around 800,000 years ago in the mid-Pleistocene, it had enormous tusks and stood around 1m tall at the shoulder (3’3″) — similar in size to the very largest modern pigs, the African giant forest hogs.
The giant forest hogs are also some of its closest living relatives, along with the river pigs, and back in the Miocene and Pliocene similar pigs were present in Asia. Celebochoerus‘ ancestors probably arrived in the Philippines from Taiwan, and eventually spread onwards to the Indonesian island of Sulawesi to the south, where another species of Celebochoerus existed.
Bubalus cebuenesis
In contrast to the huge pigs of Luzon, the Cebu tamaraw (Bubalus cebuensis) was a particularly tiny species of wild cattle related to modern water buffalo. Just 75cm at the shoulder (2’6″), it was an example of insular dwarfism even smaller than the modern tamaraw which still survives on the island of Mindoro.
The spotty fossil record of these animals makes it difficult to determine when they disappeared, but it’s likely that they went extinct sometime around the arrival of early humans about 700,000 years ago.
During the mid-Miocene, about 15 million years ago, a region of central and southeast Italy around Gargano and Scontrone was cut off from the mainland by rising sea levels.
For the next 7-10 million years this island (or perhaps a cluster of islands) was left isolated, and an unusual ecosystem developed known as the “Mikrotia fauna”. With the island starting off lacking large predators, small herbivorous animals like rodents, pikas, and waterfowl became huge – and then small predators like gymnures and carnivorous birds also grew to keep up with the increasing size of their prey.
One of the strangest residents of the island(s) was Hoplitomeryx, an early type of ruminant that resembled a deer or pronghorn. Nicknamed the “prongdeer”, it had a total of five horns on its head and large protruding fangs similar to some moderndeer.
Multiple species of Hoplitomeryx have been identified, representing four different size classes ranging from huge down to tiny insular dwarfs. The largest is estimated to have been similarly sized to modern moose, standing around 2m tall at the shoulder (6′6″), while the smallest would have been under 50cm (1′8″).
Each of these size classes was specialized for slightly different ecological niches, eating different types of vegetation to avoid directly competing with each other for the limited amount of food on the island.
