Eons Roundup 4

Some more recent commission work for PBS Eons!

The entelodonts Eoentelodon and Brachyhyops, from “The Hellacious Lives of the Hell Pigs”
https://www.youtube.com/watch?v=trJpxwMGoCw

The early ichthyosaur Tholodus and the mosasaurPluridens, from “When Ichthyosaurs Led a Revolution in the Seas”
https://www.youtube.com/watch?v=V342aXQs9XY

The early bats Onychonycteris and Icaronycteris, from “When Bats Took Flight”
https://www.youtube.com/watch?v=zWeYCULC0UQ

Livyatan

The modern sperm whale is already an impressive animal, being by far the largest of the living toothed whales and famous for its ability to dive over 2km down (1.2 miles) to feed on deep-sea animals like giant squid.

But some of its ancient relatives were terrifying.

Livyatan melvillei here has an appropriately monstrous name, inspired by both the Hebrew name for the Leviathan and Herman Melville, the author of Moby-Dick. Known from the Pacific coast of South America during the late Miocene, around 10-9 million years ago, it’s estimated to have measured somewhere between 13.5m and 17.5m long (~44′-57′) – comparable in size to an adult male sperm whale.

Unlike the relatively slender mouth of its modern cousin, however, it instead had thick strong jaws full of enormous teeth.

Livyatan melvillei skull by Ghedoghedo | CC BY-SA 4.0
(for an idea of the sheer size of this reconstructed skull – some of those teeth are almost the length of your forearm)

It was part of a loose grouping of what are known as “macroraptorial sperm whales“, which all had similarly toothy jaws and occupied the same sort of ecological niche as modern orcas, specializing in hunting prey like large fish, squid, seals, and other whales.

Livyatan‘s main food source was probably smaller baleen whales about half its own size, and its only real competition for this prey was the equally huge megalodon shark that shared the same waters.

A huge fossil tooth found in Australia suggests that Livyatan or a very close relative of it survived at least into the early Pliocene, about 5 million years ago. Around this time a cooling climate and dwindling numbers of its preferred prey would have eventually made a population of such enormous apex predators unsustainable, and driven this “killer sperm whale” into extinction – probably around the same time megalodon disappeared, about 3.6 million years ago.

Island Weirdness #60 — Hippopotamus minor

Cyprus is one of the most isolated islands in the Mediterranean, having had no close connections to the mainland for the last 5.3 million years and being uplifted to close to its modern size during the Pleistocene. As a result it had very few land mammals, all of which arrived by swimming or rafting: rodents, shrews, a genet, dwarf elephants, and a dwarf hippopotamus.

Hippopotamus minor (sometimes called Phanourios minor) seems to have been descended from the common hippo, which probably swam across to Cyprus from the Levant region sometime in the mid-to-late Pleistocene, around 400,000 years ago. Isolated with no predators and limited space it rapidly became dwarfed compared to its ancestors, reaching at most 75cm tall at the shoulder (2’6″) — making it the tiniest known island hippo, and slightly smaller than the modern pygmy hippo.

It became much more terrestrial, with more digitgrade feet adapted for walking and climbing over rugged rocky terrain. Its teeth suggest a diet of pig-like browsing on forest vegetation — and much like pigs (and other hippos) they may have been opportunistic omnivores occasionally also eating small animals and carrion.

Despite being so small for a hippo, it was still one of the largest animals living on Cyprus, weighing about the same as the dwarf elephants it lived alongside. It also seems to have been the most common of the mammals on the island, with remains of thousands of individuals having been found.

While larger dwarf hippos are known from several other Mediterranean islands, the Cypriot species is the only one that seems to have survived into the early Holocene.

The earliest known evidence of humans in Cyprus comes from a rock shelter on the southern coast, dating to about 12,000 years ago, consisting of stone tools and a massive concentration of burned animal bones — with over 200,000 of them coming just from Hippopotamus minor. It’s possible that in addition to being so abundant on the island, the dwarf hippos’ evolution in the absence of predators meant they had no fear of humans and were much less aggressive than their larger relatives, making them particularly easy to hunt and kill.

…Or they were just especially tasty.

Later deposits from about 2000 years later show no sign of the hippos at all, with their role in the Cypriot ecosystem completely replaced by introduced species like deer, sheep, and goats.

Island Weirdness #58 — Candiacervus ropalophorus

The island of Crete has been isolated since about 5.3 million years ago, when the dried-out Mediterranean Sea refilled — 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.

Island Weirdness #54 — Big Bunnies & Strange Sheep

At the end of the Miocene, about 6 million years ago, the movement of tectonic plates caused the narrow connection between the Mediterranean Sea and the Atlantic Ocean to close — and over the next several hundred thousand years the Mediterranean dried up almost completely.

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.

A stylized illustration of an extinct giant rabbit. It doesn't resemble a modern rabbut much at all, with a small head, tiny eyes and ears, a fat body and thick somewhat bear-like limbs.
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.


A stylized illustration of an extinct goat-like sheep. It has a short snout, oddly forward-facing eyes, short pointed horns, and a chunky body.
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.

Island Weirdness #45 — The Pedro González Dwarf Deer

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.

Island Weirdness #33 — Big Pigs & Tiny Buffalo

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.

A stylized illustration of an extinct giant pig. It has four long thick tusks and long legs..
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.


A stylized illustration of an extinct dwarf water buffalo. it has short curved horns, drooping ears, and a chunky body.
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.

Inticetus

While most modern toothed whales have jaws full of teeth that are all the same simple pointed shape – an adaptation for better holding onto slippery prey – their ancient ancestors had teeth much more like other mammals, with differentiated incisors, canines, and molars.

In-between them were whales like Inticetus vertizi, which lived off the coast of southwestern Peru during the Early Miocene, about 18 million years ago.

At over 3.5m long (11′6″) it was one of the larger known toothed whales around at the time, but it wasn’t the direct ancestor of any living whales. Instead it was more of an evolutionary “cousin” to them, part of an older offshoot lineage that lived alongside the early members of modern toothed whale groups.

Inticetus had a long and unusually wide-based snout, somewhat croc-like in appearance, with sharp pointed teeth at the front and multi-lobed cheek teeth further back. A lack of obvious wear on its back teeth suggests it wasn’t using them to chew up its food, and it may have had a fairly specialized diet – possibly using those back teeth to sieve small prey out of the water in a similar manner to modern lobodontine seals.

An close-up view of Inticetus' jaws, showing the differences in tooth shape from front to back.
Closeup of Inticetus‘ jaws

Inticetus-like teeth have also been found in Miocene-aged deposits in the eastern USA, the Atlantic coast of France, and southeast Italy, indicating that this ancient whale lineage was quite widespread.

Kubanochoerus

Pigs were once unicorns.

Kubanochoerus gigas lived about 15-7 million years ago during the mid-to-late Miocene, and ranged across a large portion of Eurasia with fossils known from both Georgia and China.

It was one of the largest known pig species to ever live, slightly bigger than the modern giant forest hog at about 1.2m tall at the shoulder (3′11″). But its most distinctive features were its horns, with a small pair above its eyes and a single large forward-pointing one on its forehead.

A few specimens lack the large horn, and so some paleontologists consider it to be a sexually dimorphic trait possessed only by males. But it’s currently unclear whether this was actually the case, since at least one “hornless” skull has been reported with the distinctive larger tusks also associated with male pigs – so it’s possible that the horned and hornless Kubanochoerus were actually separate species!

Island Weirdness #21 – The Malagasy Mini-Hippos

Much like elephants, hippos have frequently made their way onto islands and developed dwarfed forms. These mini-hippos are mostly known from the Mediterranean, but further south they also occurred on Madagascar.

Hippopotamus madagascariensis (also sometimes called Hexaprotodon madagascariensis or Choeropsis madagascariensis; its exact classification is uncertain) was similar in size and appearance to the modern West African pygmy hippo – which it might have been closely related to, or may have just ended up resembling through parallel evolution.

Standing under 1m tall at the shoulder (3′3″) and measuring about 1.8m long (5′11″) it lived in the forested highlands and was much more terrestrial than its larger cousins. Its eyes were further down on the sides of its head, and it was better adapted for walking and running around on land, with proportionally longer legs and a more digitigrade posture.

It also had an unusually small brain for its size – about 30% smaller than expected – which may have been an energy-saving adaptation.

Two other species of dwarf hippo have been identified on Madagascar – the similarly-sized but more aquatic Hippopotamus lemerlei in the west of the island, and the larger and poorly-known Hippopotamus laloumena in the east. It’s not clear when exactly the ancestors of these various hippos first arrived on the island, and they may even represent three independent colonization events.

The last known subfossils date to about 1000 years ago, but surprisingly accurate accounts of similar creatures in Malagasy folklore raise the possibility that small isolated populations of these hippos may have survived into more recent times. One of the most intriguing examples is the kilopilopitsofy, described as having large floppy ears and supposedly being sighted as recently as the 1970s.