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 #61 — Tiny Elephants On Parade Part 6: Eastern Mediterranean

Alongside the weird deer, otters, and owls, the island of Crete also had dwarf elephants — and much like Sardinia to the west the Cretan elephants were actually descendants of mammoths rather than the Palaeoloxodon seen in the rest of the Mediterranean.

A stylized illustration of an extinct pygmy mammoth. It has gently curving tusks, small ears, and a body shape more like a baby elephant.
Mammuthus creticus

Mammuthus creticus was originally thought to also be a palaeoloxodontine, but more recent studies of its anatomy and ancient DNA have confirmed it was indeed another tiny mammoth. It was probably descended from either the Southern mammoth or Mammuthus rumanus, which would have arrived on Crete during the late Pliocene or early Pleistocene between about 3.5 and 1 million years ago.

Isolated on Crete, with no predators and living at a time when the island was much smaller, it quickly dwarfed and became the tiniest known mammoth to ever exist, standing just 1.1m tall at the shoulder (3’7″). Not much is known about its ecology, but its teeth suggest it was a browser feeding on leaves and shrubs, possibly filling a similar niche to the mid-sized deer that came later.

This mini-mammoth seems to have gone extinct by the mid-Pleistocene, about 1 million years ago, around the time when rising sea levels during an interglacial phase may have submerged so much of the smaller proto-Crete that its population could no longer be supported.

Later in the mid-to-late Pleistocene, after the sea level dropped again and tectonic uplift brought Crete close to its modern dimensions, the small mammoths were replaced by both newly-arriving deer and Palaeoloxodon elephants, which evolved into the much more moderately dwarfed forms of Palaeoloxodon creutzburgi and Palaeoloxodon chaniensis.


A stylized illustration of an extinct dwarf elephant. It has long thin tusks and small ears.
Palaeoloxodon tiliensis

To the north and east of Crete the Cyclades and Dodecanese islands had endemic dwarf elephants on at least eight islands, with the best known being the species that lived on Tilos.

Palaeoloxodon tiliensis stood about 1.8m tall (5’11”), on the larger side for a dwarf Mediterranean elephant but still one of the smallest palaeoloxodontines in the Aegean region. Several thousand specimens have been found, and radiocarbon dating shows it was a fairly recent evolutionary development, appearing just 45,000 years ago in the late Pleistocene.

This dwarf elephant was also the very latest surviving of its entire kind, living well into the Holocene until at least 4000 BCE. This is several thousand years after humans first arrived on Tilos, suggesting it was a rare case of an island elephant that managed to endure the effects of a human presence for quite some time.

In fact there’s some speculation that Palaeoloxodon tiliensis (or a similar unknown species) may have survived for even longer than that, since one Ancient Egyptian tomb from around 1480-1400 BCE contains a painting depicting traders with exotic animals, including what appears to be a small hairy elephant with slender limbs and thin upward-curving tusks. We may never know for certain if this was actually a late-surviving dwarf, a mutant modern elephant, or just artistic license with scaling, but the possibility is still intriguing.

A stylized illustration of an extinct dwarf elephant. It has long gently curving tusks and small ears.
Palaeoloxodon cypriotes

Over on isolated Cyprus further to the east, the only native large mammals were the miniature hippos and an equally miniature elephant.

Palaeoloxodon cypriotes was smaller than the Aegean palaeoloxodontines, about 1.4m tall (4’7″), and much like its cousin on Tilos seems to have evolved very recently towards the end of the Pleistocene, sometime around 20,000 years ago.

It wasn’t the first dwarf elephant on Cyprus — there was a larger, earlier species known as Palaeoloxodon xylophagou at least 200,000 years ago — but it’s not clear whether these two species represent a single evolutionary line or two entirely different colonizations of the island.

Similarly to the hippos it lived alongside, Palaeoloxodon cypriotes disappeared shortly after humans arrived on Cyprus, between 12,000 and 10,000 years ago. Collections of its bones have been found in a rock shelter with evidence of having been burnt, suggesting that it was being actively hunted and cooked.


And that’s all for the Island Weirdness series! Even over two months there are still plenty of species I didn’t have time to feature, so this definitely won’t be the last we see of strange endemic species.

Thank you for following along — with a shoutout to my Patreon supporters! — and regular weekly art posts will resume here next Monday.

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 #59 — Terrestrial Otters & Owls

The Mediterranean island of Crete had very few predators during the Pleistocene, with most being birds of prey. And with the terrestrial carnivore niches in the ecosystem left vacant, it was a semi-aquatic mammal and an owl that ended up taking advantage of that opportunity.

Neither were large enough to threaten the dwarf elephants and hippos, and don’t even seem to have habitually eaten even the smallest of the miniature giant deer. Instead these Cretan predators focused much more on the smaller land vertebrates on the island, preying on birds, shrews, rodents, amphibians, and reptiles.

A stylized illustration of an extinct otter. It has a blunt snout and chunky legs.
Lutrogale cretensis

Lutrogale cretensis (previously known as Isolalutra cretensis) was a close relative of the modern smooth-coated otter. It was about the same size as its living cousin, around 1m long (3’3″), but had stronger jaws and chunkier limbs.

Its skeleton shows features associated with walking and running more than swimming, and it seems that this was something of a “land otter” — still able to swim, but spending most of its time on land similar to the modern small-clawed otter.

Shellfish were likely still the main part of its diet, indicated by its crushing teeth. But it probably also regularly ate whatever small terrestrial vertebrates it could catch, since more aquatic otters are already known to prey on those types on animals when they can.


A stylized illustration of an extinct giant little owl. It has longer legs than its modern relatives, almost resembling a large burrowing owl.
Athene cretensis

Athene cretensis was yet another weird island owl, but this time not a descendant of a Strix or Tyto species. Instead this owl was descended from the Eurasian little owl — except it had become much much larger.

It stood around 60cm tall (2′), over three times bigger than its living relative. Its legs weren’t quite as long as those of the modern burrowing owl, but they were still proportionally much longer than those of little owls and show adaptations for terrestrial movement. Little owls already sometimes chase down prey on foot, and Athene cretensis was probably even more of a ground-based hunter, convergently similar to the Hawaiian stilt-owls and the Cuban terror owls.

Preserved pellets show that it ate small mammals and birds, mainly large mice.

Its wings were still quite large, and it was probably also a good flier — and may even have spread over to some of the Dodecanese islands to the east of Crete, since a wing bone closely resembling that of Athene cretensis has been found on Armathia.

Both of these predators seem to have disappeared around the end of the Pleistocene, at the same time as many of the other native Cretan species about 21,500 years ago. Much like the situation with Candiacervus, this may have been a result of a combination of a rapidly shifting climate and the presence of humans disrupting the already fragile island ecosystem.

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 #56 — Cynotherium sardous

Despite being decent swimmers, canids are surprisingly rare in island ecosystems, only seeming to end up there when able to move over land connections with larger landmasses (or when brought there by humans). Even the most remote species, the recently-extinct Falkland Island wolf, is thought to have crossed over a short stretch of sea ice during the last glacial period.

So the existence of a unique canid on the Mediterranean islands of Sardinia and Corsica is quite unusual.

The Sardinian dhole (Cynotherium sardous) was a small fox-sized canid, just 50cm tall at the shoulder (1’8″), related to the modern African wild dog and dhole. It was probably descended from the much larger wolf-like Xenocyon, which would have been able to reach Sardinia-Corsica during the early-to-mid Pleistocene about 1.2 million years ago, at a time when lower sea levels connected the island to the European mainland via Tuscany.

Isolated with very little large prey, it instead evolved to specialize in hunting small fast-moving animals, flattening its body low to the ground while stalking in a similar manner to modern foxes or Ethiopian wolves. Powerful shoulder muscles allowed it to launch into sudden high-speed lunges, and it had an especially strong flexible neck that would have been used to grab at its zig-zagging targets and shake them to death.

Cynotherium went extinct sometime in the early Holocene, around 11,000 years ago, after the arrival of humans on Sardinia and Corsica.

The earliest definite human remains on Sardinia are at least 20,000 years old, and while it’s unclear if those were permanent settlers it still seems like Cynotherium was able to deal with the effects of a human presence for several thousand years, probably due to its main prey (the Sardinian pika) also surviving at the time. So its disappearance may have been caused by a combination of problems that slowly whittled away at its population, like the warming climate, gradual habitat destruction, and competition from introduced predators like feral dogs — or possibly even new diseases caught from them.

Island Weirdness #55 — Megalenhydris barbaricina

Along with its miniature mammoths, the Mediterranean island of Sardinia (and neighboring Corsica) had an unusually large amount of endemic mustelids during the Pleistocene and early Holocene. There were at least four different otters — probably all descended from a single species of Lutra — that occupied various ecological niches in both the rivers and the coasts, and also an enigmatic grison-like terrestrial species.

Megalenhydris barbaricina was the largest of the Sardinian-Corsican otters, reaching lengths of over 2m (6’6″), slightly bigger than the modern South American giant river otter. Its crushing teeth indicate it specialized in crunching through hard-shelled invertebrates like molluscs and crustaceans, and its highly flexible backbone and flattened tail suggest it was a strong swimmer that may have been even more aquatic than most other otters.

It was possibly an equivalent of the modern sea otter, spending most of its time in the water, although it’s not clear whether it was a river or marine species.

Dating on the one known partial skeleton of Megalenhydris is uncertain, but it may be late Pleistocene to early Holocene in age, between about about 70,000 and 10,000 years old. Unfortunately this puts it within the same age range as the arrival of humans on Sardinia and Corsica, and its extinction may have been a direct result of being hunted for its meat and pelt.

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 #53 — Tiny Elephants On Parade Part 5: Western Mediterranean

During the Pleistocene elephants colonized many of the islands in the Mediterranean Sea, with each island independently developing its own unique dwarfed form.

A stylized illustration of an extinct pygmy mammoth. It has long tightly-curved tusks, small ears, and a coat of hair over its body.
Mammuthus lamarmorai

Mammuthus lamarmorai lived on the island of Sardinia during the middle and late Pleistocene, between about 450,000 and 40,000 years ago. Standing around 1.4m tall at the shoulder (4’7″), it was a dwarf form roughly one-third the size of its ancestor, the huge Eurasian steppe mammoth.

Its remains are known only from the west and south of the island. Strangely it appears to be have been absent from the nearby island of Corsica, despite the two being joined as a single landmass a few times during lower sea level periods in the Pleistocene.

It’s not clear why this mini-mammoth disappeared. The date of the earliest human settlement of Sardinia is controversial (ranging from 250,000 to 20,000 years ago), so Mammuthus lamarmorai might never have actually encountered them. Instead it may have struggled to cope with climate changes during the last glacial period towards the end of the Pleistocene, which rapidly turned Sardinia colder and drier.


A stylized illustration of an extinct dwarf elephant. It has long thin tusks and tiny ears, and its body shape resembles a chubby baby elephant.
Palaeoloxodon falconeri

Over on Sicily and Malta (which were also occasionally a single island when sea levels were lower), there were several different species of miniature elephant during the mid-to-late Pleistocene, each with a different body size and occupying its own ecological niche. They were all descendants of the massive straight-tusked elephant (Palaeoloxodon antiquus) but each resulted from independent colonization waves swimming over to the island(s).

Palaeoloxodon falconeri lived during the mid-Pleistocene, about 550,000 years ago, and was both the smallest of the Mediterranean dwarfs and possibly the smallest elephant to ever exist. Just 0.8-1m tall (2’7″-3’3″), it had adult body proportions resembling the juveniles of its ancestors, limbs adapted for running and clambering over rough terrain, and a proportionally enormous brain relative to its body size.

Around 200,000 years ago a sea level drop allowed new colonization from the Italian mainland. If Palaeoloxodon falconeri was still around at that time it likely didn’t survive long with new competition from large herbivores like bison and deer, and being preyed on by newly-arriving large carnivores like wolves, lions, and hyenas.

Another small elephant soon evolved to take its place, although due to the presence of predators it was never able to get nearly so tiny.

A stylized illustration of an extinct dwarf elephant. It has short thick twisting mammoth-like tusks and small ears.
Palaeoloxodon mnaidriensis

Palaeoloxodon mnaidriensis was in fact one of the largest dwarf elephants in the Mediterranean, standing about 1.8-2m tall (5’11”-6’6″), but despite its larger size its limbs still show signs of adaptation for more fast and agile movement. Its tusks also show a lot of variation in shape, with some much more curved and twisted than others.

This elephant had disappeared by about 13,000 years ago, probably due to the climate significantly warming towards the end of the last ice age. Much like Sardinia, the earliest arrival of humans on Sicily and Malta is controversial, and it’s unclear whether they ever encountered Palaeoloxodon mnaidriensis — the earliest definite date for Sicily is about 16,000 years ago, so a human-induced extinction can’t be ruled out entirely.

The subfossil remains of the Siculo-Maltese elephants may have also ended up inspiring legends of the cyclops, as their skulls would have resembled large human ones with the nasal cavity forming a single big “eye socket”.