insular dwarfism – Page 2 – Nix Illustration

Island Weirdness #44 — Tiny Elephants On Parade Part 4: Mammoth-Mimics & Mini-Mammoths

In the cool-temperate climate of Pleistocene Japan one type of small elephant seems to have convergently become somewhat of a mammoth-mimic, with twisting tusks and possibly even a thick coat of hair.

A stylized illustration of an extinct mammoth-like elephant. It has long twisting tusks, small ears, and a speculative coat of long hair. — Palaeoloxodon naumanni

Palaeoloxodon naumanni lived during the late Pleistocene, between about 500,000 and 16,000 years ago. At about 2-2.5m tall at the shoulder (6’6″-8’2″) it was still fairly large, similar in size to the smallest living elephant species — but it was a dwarf in comparison to its immediate ancestors, the absolutely enormous Asian straight-tusked elephant (Palaeoloxodon namadicus).

Actual woolly mammoths (Mammuthus primigenius) were also present in Japan, but the two similar-looking elephants inhabited different environments — Palaeoloxodon naumanni preferred the southern forests, while the true mammoths roamed the colder north.

Humans arrived in Japan around 40,000-30,000 years ago, so Palaeoloxodon naumanni actually coexisted with them for quite some time. Although it was hunted, it seems to have mainly been climate change towards the end of the last glacial maximum that led to its extinction.

A stylized illustration of an extinct pgymy mammoth. It has curving tusks, small ears, and a speculative coat of hair. — Mammuthus exilis

Over on the other side of the Pacific Ocean, at least 60,000 years ago, some huge Columbian mammoths (Mammuthus columbi) swam the 6.5km (4 miles) distance to the ancient island of Santa Rosae — a landmass that today is mostly submerged, with its remaining peaks forming the modern California Channel Islands.

With a lack of large predators and then steadily rising sea levels reducing the available habitat on their new home, the mammoths shrank into a dwarfed species known as the Channel Islands pygmy mammoth (Mammuthus exilis). Standing around 1.75-2m at the shoulder (5’9″-6’6″), they were less than half the size of their ancestors and had only about 10% of the body mass.

The pygmy mammoths survived until about 13,000 years ago, around the same time that early Paleoindians arrived. While they may also have been hunted by humans, the warming post-glacial climate is currently thought to be the main factor in their extinction, changing the types of vegetation on their still-shrinking islands and reducing fresh water sources.

(And if you prefer your pygmy mammoths less speculatively hairy, there’s always the version I did for PBS Eons earlier this year.)

Island Weirdness #39 — Mekosuchus inexpectatus

Along with their weird giant birds, the islands of New Caledonia were also home to a small crocodilian unlike any alive today.

It was one of the last known members of a lineage of crocodiles known as the mekosuchines, which originated in Australia during the early Eocene about 50 million years ago and later island-hopped out into the South Pacific — mostly around the Coral Sea, but with some making it as far as New Zealand. By the start of the Holocene, about 12,000 years ago, they’d already declined and disappeared from the vast majority of their range, with only a few isolated island species remaining.

Named Mekosuchus inexpectatus, the New Caledonian mekosuchine was only about 2m long (6’6″), just slightly bigger than the modern dwarf crocodile. It was much more terrestrial than living crocs, spending most of its time on land, and it had teeth in the back of its jaws that were specialized for crushing, suggesting it mainly preyed on hard-shelled invertebrates such as snails and crabs.

Based on its limbs anatomy it may also have been able to climb trees. Although this idea was ridiculed when it was originally suggested back in the 1990s, a more recent discovery has shown that modern crocs can actually climb trees too.

Like with many other Holocene island species, the extinction of Mekosuchus inexpectatus seems to be directly linked to the arrival of humans, who reached New Caledonia around 1500 BCE.

Bones in archaeological kitchen waste sites show that the settlers actively hunted and ate Mekosuchus, but dating of the last known remains is uncertain. The most generous estimate is actually as recent as about 300 CE, so much like Sylviornis these small land crocs may have persisted for some time before finally going extinct.

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.

Island Weirdness #32 — Tiny Elephants On Parade Part 3: More Indonesia

It’s finally time for part 2 of the Island Weirdness series!

(If you haven’t seen the previous installments, I suggest starting back at the beginning here.)

We left off last time with the dwarf stegodontids of Flores, but other Indonesian islands also had their own populations of unusually small elephant-relatives — so here’s a few more to start off this month!

A stylized illustration of an extinct dwarf elephant. It has long straight tusks and small ears. — Sinomastodon bumiajuensis

Sinomastodon bumiajuensis lived on the island of Java during the early Pleistocene, about 2-1.5 million years ago. It stood around 2m tall at the shoulder (6’6″), less than half the size of most other Sinomastodon species from mainland Asia. Although it looked convergently similar to modern elephants it was actually a member of the gomphotheres, much more closely related to the weird “shovel-tuskers” than to any living species.

A stylized illustration of an extinct dwarf elephant. It has long gently curving tusks and proportionalyl short legs. — Stegodon semedoensis

Stegodon semedoensis, also from the early Pleistocene of Java about 1.5 million years ago, is only known from a few isolated molar teeth — but the size of those teeth suggest it was one of the smallest known pygmy stegodontids. It was probably no more than 1.2m at the shoulder (3’11”), comparable in size to its close relative Stegodon sondaari over on Flores.

A stylized illustration of an extinct dwarf elephant. It has four straight tusks, two longer ones in its upper jaw and two shorter ones in its lower jaw. — Elephas celebensis

Meanwhile on Sulawesi, Elephas celebensis (sometimes called Stegoloxodon celebensis) was an actual true elephant closely related to the modern Asian elephant. Living during the late Pliocene and early Pleistocene, between about 2.5 million and 800,000 years ago, it was only 1.5m tall (5′) and had a second set of tusks in its lower jaw, a “primitive” feature retained from the gomphothere-like ancestors of modern elephants.

A stylized illustration of an extinct dwarf elephant. It has long curving tusks and small ears. — Stegodon sompoensis

At the same time Sulawesi also had yet another small stegodontid, Stegodon sompoensis, also around 1.5m tall.

Both of these dwarfs lived alongside a larger Stegodon species, as well as giant tortoises and large-tusked pigs.

The cooling climate of the Pleistocene and dropping sea levels eventually connected the islands of western Indonesia to the Sundaland landmass of mainland Asia. Influxes of new predators and competitors — and early humans — probably drove these endemic small elephants to extinction.

Eons Roundup 2

California Channel Island pygmy mammoth (Mammuthus exilis) and Columbian mammoth (Mammuthus columbi)

And speaking of island elephants, I recently illustrated some for PBS Eons’ episode on the California Channel Island pygmy mammoths:

https://www.youtube.com/watch?v=dXwoKEDtdlM

Island Weirdness #31 – Tiny Elephants On Parade Part 2: Flores

Much like Japan, ancient Flores had a succession of dwarf stegodontids – close relatives of modern elephants that were capable of island-hopping through Indonesia by swimming.

A stylized illustration of an extinct dwarf elephant. It has curved tusks, small ears, and very proportionaly short stumpy legs. — Stegodon sondaari

Stegodon sondaari lived on Flores during the Early Pleistocene, about 900,000 years ago, and was the size of a small water buffalo at just 1.2m (3′11″) tall at the shoulder. It was probably descended from the larger Stegodon trigonocephalus, known from Java, and it had proportionally short legs which may have been an adaptation to clambering over rough terrain and steep inclines.

Around 850,000 years ago Stegodon sondaari disappeared from Flores, probably due to a large volcanic eruption, but a new wave of stegodontids quickly recolonized the island. The mid-sized Stegodon florensis probably originated from either Java to the west or Sulawesi to the north, and eventually evolved into a new dwarfed subspecies.

A stylized illustration of an extinct dwarf elephant. It has long gently curving tusks and small ears. — Stegodon florensis insularis

Stegodon florensis insularis wasn’t quite as small as its predecessor, standing around 1.8m tall (5′10″). It probably didn’t shrink quite so much due to the existing presence of various predators on Flores, since it was likely the main prey of large Komodo dragons, it was hunted by Homo floresiensis, and it may also have been occasionally targeted by giant storks.

It seems to have disappeared around the same time as several other unique endemic species, between 50,000 and 20,000 years ago, due to either climate change, another volcanic eruption, or the arrival of modern humans – or perhaps a combination of all of those factors.

And that’s all for this month… but Island Weirdness will be back later for part 2, with more giants, more dwarfs, and so many elephants.

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.

Island Weirdness #14 – Hoplitomeryx

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 modern deer.

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.

Island Weirdness #13 – Tiny Elephants On Parade Part 1: Japan

Part of the “island rule” is that large animals often become smaller – and no group seems to exemplify this more than the elephants.

Although they’re the largest living land animals today, and in the past included some of the largest known land mammals ever, ancient elephants also frequently ended up on islands thanks to their ability to swim long distances. They produced many different dwarfed forms around much of the world, and a few of them will be featured intermittently throughout both months of this theme.

The earliest known examples were the stegodontids of Japan in the early Miocene. These animals weren’t quite true elephants, instead being close evolutionary cousins to them, and had two small additional tusks in their lower jaws similar to the related gomphotheres.

A stylized illustration of an extinct dwarf elephant. It has four tusks – two short straight ones in its upper jaw, and another two smaller ones in its lower jaw. — Stegolophodon pseudolatidens

Stegolophodon pseudolatidens first arrived in Japan about 18 million years ago, and within just 2 million years they’d developed into insular dwarfs that were probably around 2m tall at the shoulder (6′6″)– still reasonably large, but only about 60% the size of their mainland relatives.

Much later in the Early Pleistocene another small almost-elephant appeared in Japan. Living between about 2 million years ago and 700,000 years ago, Stegodon aurorae was about the same size as the then-extinct Stegolophodon but probably wasn’t descended from them. Instead it was probably the result of a separate arrival and dwarfing of a larger Stegodon species from mainland Asia.

Island Weirdness #07 – Telmatosaurus transsylvanicus

The hadrosauroid dinosaur Telmatosaurus was another resident of Hațeg Island, and while it wasn’t quite as small or specialized as its cousin Tethyshadros it was still dwarfed compared to their other relatives, only growing to about 5m long (16’4″).

It was also the first dinosaur fossil found with a specific type of non-cancerous tumor known as an ameloblastoma on its lower jaw – a surprising discovery, since ameloblastomas were previously only known to occur in mammals and a single snake species. Various other types of abnormal tissue growth have been identified in other hadrosauroids and hadrosaurs, however, suggesting that this particular lineage of dinosaurs may have been unusually susceptible to developing tumors.