Scottish wrens may be evolving into new species through island gigantism

Tiny island populations of the Eurasian Wren (Troglodytes troglodytes) on remote Scottish islands are offering scientists a rare glimpse of evolution in progress. A new study shows that several isolated island populations are diverging sharply from their mainland relatives, and in some cases becoming dramatically larger[1]. The research examined four island forms: the Shetland Wren (Troglodytes troglodytes zetlandicus), Fair Isle Wren (Troglodytes troglodytes fridariensis), Outer Hebrides Wren (Troglodytes troglodytes hebridensis), and St Kilda Wren (Troglodytes troglodytes hirtensis). Despite living in broadly similar environments, each population has followed its own evolutionary path, despite broadly similar environments.

[St Kilda wren]

The most striking change is the emergence of island gigantism in the wrens of Shetland and St Kilda. Mainland British wrens typically weigh 7 to 10 grams, but St Kilda birds reach 13 to 16 grams, with the largest individuals more than twice the size of the smallest mainland wrens. This places them among the most extreme known cases of avian island gigantism. Such size increases are common in isolated island species, where reduced predators and competition can push evolution in unusual directions.

Genetic analysis revealed that all four island subspecies are distinct from mainland wrens, with Shetland and St Kilda birds especially divergent in appearance, song, and genome. According to lead author Dr. Michał Jezierski, their genetic separation is so pronounced that they may be on the path toward becoming entirely new species.

To understand how these differences arose, researchers compared body measurements, plumage, vocal recordings, and whole‑genome data. The results provide one of the most detailed studies yet of island gigantism, a suite of traits often seen in island species, including larger size, slower reproduction, and altered behaviour.

One of the most intriguing findings is that the Shetland and St Kilda wrens, although similarly large, reached that size through different genetic routes. This suggests parallel evolution: similar environmental pressures producing similar adaptations independently. Each island population appears to have descended from mainland ancestors but evolved in isolation, developing unique songs and physical traits along the way. However, not all island wrens show the same degree of divergence. Birds from Fair Isle and the Outer Hebrides remain more genetically similar to mainland populations, highlighting how evolutionary change can vary dramatically even across nearby islands.

The Caribbean
It's entirely possible that similar patterns of rapid divergence and potential speciation may also be unfolding among certain Caribbean wrens, where isolated island populations have likewise evolved distinct forms. See here.

[1] Jezierski et al: Parallel evolution of island syndromes coincides with limited parallel genetic differentiation in a passerine bird in Evolutionary Journal of the Linnean Society – 2026.

Elephant Birds of Madagascar

Elephant birds are extinct, flightless birds belonging to the order Aepyornithiformes, native only to the island of Madagascar. There are three recognized species: one in the genus Mullerornis and two in Aepyornis. Of them, Aepyornis maximus is possibly the largest bird that ever lived, with eggs among the largest known of any amniote (flightless birds). The closest living relatives of elephant birds are kiwis, found only in New Zealand.

Elephant birds were large birds, the largest of which could reach a height of 3 meters in a normal standing position. Like most other flightless birds, they had long legs and elongated necks, with relatively small heads relative to their body size. They had straight, thick, conical beaks. The skulls of elephant bird species differ little from each other, except in size, although the front of the skull in Mulleronis is a bit less robust than in Aepyornis. The wings were rudimentary.

It is generally accepted that the extinction of the elephant bird was the result of human activities. The birds were initially widespread and lived throughout Madagascar. Research from 2021 suggested that elephant birds, along with three species of Madagascan pygmy hippopotamus (Hippopotamus lemerlei, Hippopotamus laloumena and Hippopotamus madagascariensis), became extinct somewhere between 800 and 1050 AD[1]. This timing coincided with major environmental changes in Madagascar caused by humans converting forest to grassland, likely for cattle ranching, with this habitat change likely triggered by burning the forest. This reduction in forest area may have had a knock-on effect, such as elephant birds being more frequently encountered by hunters, although there is little evidence of human hunting of elephant birds. People may, however, have eaten elephant bird eggs.

These birds fed, among other things, on the seeds of the baobab trees (Adansonia spp.). These are large, club-like seeds. When the elefant birds became extinct, it also meant that the baobab trees were in serious trouble. Because the fruits are no longer eaten, the seeds (1.5 centimeters in diameter) were no longer dispersed. Nowadays all seeds fall to the ground close to the mother tree, which does not benefit genetic diversity within populations. These trees now depend on Madagascan fruit bat (Eidolon dupreanum) for fertilization. However, these bats are heavily hunted and are therefore becoming increasingly rare. Reduced pollen exchange leads to increasing genetic isolation between baobab populations.

[1] Hansford et al: Simultaneous extinction of Madagascar's megaherbivores correlates with late Holocene human-caused landscape transformation in Quaternary Science Reviews – 2021. See here.

Moa-nalo

The moa-nalo are a group of now extinct aberrant, goose-like ducks (or duck-like goose) that once lived on some the larger Hawaiian Islands in the Pacific Ocean. They were the major herbivores on most of these islands until they became extinct after human settlement, a fate that it shared with the dodo (Raphus cucullatus).

The moa-nalo (the name literally means 'lost fowl' in the local language) were long unknown to science, having been wiped out before the arrival of James Cook in 1778, thus they were the victim of Polynesians that visited the island earlier.

Like island taxa from Mauritius, New Zealand and Polynesia, the moa-nalo were unused to mammals and were easily predated on by hunters or the animals that were introduced and became feral, such as domestic pigs or rats.

In the early 1980s, their fossil remains were discovered in sand dunes on the islands of Molokaʻi and Kauaʻi. Subsequently, bones were found on Maui, Oʻahu, and Lānaʻi, in lava tubes, lake beds, and sinkholes.

They represent four species in three genera so far:
- turtle-jawed moa-nalo (Chelychelynechen quassus) on Kauaʻi
- small-billed moa-nalo (Ptaiochen pau) on Maui
- O'ahu moa-nalo (Thambetochen xanion) on Oʻahu
- Maui Nui large-billed moa-nalo (Thambetochen chauliodous) on the prehistoric island of Maui Nui, which is composed of four modern islands: Maui, Molokaʻi, Lānaʻi, and Kahoʻolawe.

This also means that the moa-nalo isn't (yet) found on the main island.

Chelychelynechen ('turtle-jawed goose') had a large, heavy bill a bit like that of a tortoise, while the other two genera, Thambetochen and Ptaiochen, both had serrations in their bills known as pseudoteeth. All species were flightless and large, with an average mass of 4 to 7.5 kilograms.

Some moa-nalo fossils have been found to contain traces of mitochondrial DNA which were compared to living duck species in order to establish their place in the duck family, Anatidae. The result was that the moa-nalo were not related to the large geese (Anserinae), but instead to the genus Anas, which includes the mallard or wild duck (Anas platyrhynchos). At present, the DNA analysis' resolution is not high enough to precisely determine their relationships to different species of Anas, but biogeography strongly suggests that their closest living relative is the widespread Pacific black duck (Anas superciliosa).

The unusual bill shape and size of the moa-nalo can be attributed to their role in the ecology of prehistoric Hawaiʻi. A study of coprolites (fossilized dung) of the Maui Nui large-billed moa-nalo, found in Puʻu Naio Cave on lowland Maui, has shown they were folivorous ('leaf eaters'), eating particularly fronds from ferns. This conclusion is backed up by the shapes of their beaks. This indicates they were the principal browsers on the island.

The presence of prominent spines on the leaves and soft young stems of several Hawaiian lobelioids in the genus Cyanea suggests that they evolved these thornlike prickles on new growth because they would protect against browsing by the moa-nalo. Spines are unusual in an island flora where such defenses are frequently lost.

The moa-nalo themselves filled the niche of herbivore usually filled by mammals such as goats, or the giant tortoises of Galápagos and other archipelagoes. This has implications for the ecology of Hawaiian Islands today, as a major group of species have been lost.

Orkney vole

Voles are small rodents that are relatives of lemmings and hamsters, but with a somewhat stouter body. In comparison with its family members, voles also have a longer, hairy tail; a slightly rounder head an smaller eyes and ears. They are sometimes known as meadow mice or field mice.

The Orkney vole (Microtus arvalis orcadensis) is a population of the common vole (Microtus arvalis) found only on the Orkney Islands, off the northern coast of Scotland. The common vole is absent from the rest of the British Isles.

The Orkney vole occurs on nine islands of the Orkney Islands: Orkney, Sanday, Westray, Rousay, South Ronaldsay, Burray, Eday, Shapinsay, and Stronsay.

As the Orkney vole has no natural enemies on these remote islands, they were able to grow massively. They are twice as heavy as continental voles,

The Orkney vole does not occur in mainland Britain, nor elsewhere in the British Isles. The current leading hypothesis for the development of this disjunct population is that voles were introduced to the Orkney archipelago by humans in Neolithic times, possibly concealed in animal fodder. DNA-analysis indicates transport by Neolithic humans from what is now Belgium.

The oldest known radiocarbon-dated fossil of the species in Orkney is 4,600 years old: this marks the latest possible date of introduction.

It was once hypothesized that the Orkney voles were a relict population, left behind when the land-bridge connecting Scotland and Orkney had disappeared, by the date that the more competitive Short-tailed field vole (Microtus agrestis) had reached Northern Scotland, though this theory has since been rejected based on paleontological, ecological, biological, and geological evidence.

A similar example of island gigantism is the Guernsey vole (Microtus arvalis sarniensis) that is living happily on Guernsey, one of the Channel Islands. It is (just) twenty per cent larger than its closest cousin, the European Common vole. Island farmers, simply ‘Mulots’, derived from Old French mulot, diminutive of mul, from Old Dutch muli ('moles'). Modern Dutch is still 'mol'.

A little sidenote: As so many of the islands in the region, the name 'Orkney' is derived from Old Norse. Vikings named it after the abundance of seals they encountered: orkn ('seal') and eyjar ('islands').

Rain Shadow Effect

The shaggy soft-haired mouse (Abrothrix hirta) changes in size based on which side of the Andes Mountains the individual lives on[1].

Scientists studying the skulls of 450 shaggy soft-haired mice (Abrothrix hirta), living on the Andes Mountains in Patagonia noticed something they couldn't explain: the mice from the western side of the mountains were bigger than the ones from the east, but DNA said that they were all from the same species.

The scientists put forth a new hypothesis: the mice on the western slopes were bigger because that side of the mountain range gets more rain, which means there's more plentiful food for the mice to eat.

De la Sancha and his colleagues realized this might be related to what biologists call the 'Resource Rule'."This rule suggests that where there are more resources, individuals from the same species tend to be larger than where there are fewer resources," says de la Sancha. "For instance, some deer mice that are found in deserts and other habitats tend to be smaller in drier portions of their habitats.

De la Sancha realized that the Rain Shadow Effect could explain why there was more food on the western side of the Andes, and thus, why the mice there were bigger.

The Rain Shadow Effect is a product of the way that water vapor travels over mountain ranges. "Essentially, one side of the mountain will be humid and rainy, and the other will have cold, dry air. On some mountains, the difference is extreme. One face can be a tropical rainforest, and the other side will be almost desert-like," says de la Sancha. "There is a Rain Shadow Effect in most mountains on the planet."

The 'Rain Shadow' indeed neatly matched up with the rodents' sizes—the first time, to de la Sancha's knowledge, that anyone has demonstrated the effects of the rain shadow on mammal size. And while so far it's only been shown for one species of mouse, de la Sancha suspects that he and his colleagues have hit on a larger truth—perhaps even the basis for a rule of its own someday.

This study was based on museum collections from Argentina, Chile, and the US, it's an amalgamation of years and years of collecting and big data sets.

Teta et al: Andean rain shadow effect drives phenotypic variation in a widely distributed Austral rodent in Journal of Biogeography - 2022

Island gigantism on Sakhalin and the Kuril Islands

The Russian island of Sakhalin lies north of the Japanese archipelago. During the Qing dynasty, the island was once part of China, but later it was claimed by both Russia and Japan. In 1875, Japan ceded its claims on Sakhalin to Russia in exchange for the northern Kuril Islands. Several wars made the situation problematic, because in 1949 Russia 'stole' the southern Kuril Islands from Japan, thus breaking the 1875 agreement.

But that's not what makes Sakhalin and the Kuril Islands interesting, because the islands are known for their megafauna. Plants like grass, burdock, dropwort and others can reach up to two or even three meters in height. On some Kuril Islands grass can grow up to five meters in height.

Meadowsweet (Filipendula ulmaria) can reach up to 2,5 metres in height - twice the size of the ones on mainland Russia. Buckwheat (Fagopyrum esculentum), meanwhile, grows up to four metres, despite only measuring around 50 centimetres on the continent. Local publications often publish articles on how to get rid of the annoying weed, which has a tendency to pop up in people’s vegetable patches. The plant is able to adapt quickly and is effective at spreading into new territories.

The huge plants of Sakhalin interested scientists back in Soviet times. Trying to find the answer to the question of gigantism, geologists were transplanting these herbs to the European part of Russia, but the burdocks would only grow to their normal continental size. French specialists, back in 1935, tried growing Sakhalin buckwheat, but achieved the same results - it grew to its ordinary, everyday size. They only got monsters when experimenting with the species on the island.

What is the reason for this local megafauna?

It turns out that gigantism doesn’t affect all plants on the island - just those that grow above the places where the Earth’s upper crust has cracked. These places of tectonic activity contain ultra-wet soil, rich in copper, cerium and chrome, which are likely to have a positive effect on the resulting size. Therefore, this megafauna is a strictly local phenomenon.

One of the most popular dishes of Sakhalin is a starter made from gigantic marinated burdock leaves. They are sold in stores, served in cafés or prepared at home. Its taste is said to resemble that of meat.

Insular Woodiness

Insular gigantism and insular dwarfism has occured (and is occuring) on isolated islands. If there are no predators and enough food, mammals can grow to enormous sizes. If there are predators and not enough food, mammals tend to shrink in size.

But what happens to plants on isolated islands, you could wonder.

Insular woodiness, the evolution of woodiness in plant species that inhabit islands, is the most conspicuous aspect of island floras, comparable to flightlessness in birds and dwarfism and gigantism in mammals.

A recent scientific report identified more than 1,000 insular woody species on 375 islands resulting from at least 175 independent evolutionary transitions on 31 different archipelagos around the world[1]. In combination with global data on island species composition, climate, and environment conditions, the researchers tested multiple longstanding hypotheses regarding the origins of insular woodiness and find that the absence of herbivores and traits related to drought stress are best correlated with the occurrence of insular woody species across all islands.

Structural equation models reveal that the insular woody species richness on oceanic islands correlates with a favorable aseasonal climate, followed by increased drought and island isolation (approximating competition). When continental islands are also included, reduced herbivory pressure by large native mammals, increased drought, and island isolation are most relevant.

The results illustrate different trajectories leading to rampant convergent evolution toward Insular woodiness and further emphasize archipelagos as natural laboratories of evolution, where similar abiotic or biotic conditions replicated evolution of similar traits.

An example is thyme (Thymus vulgaris). It is a bushy, woody-based evergreen subshrub that is perfectly adapted to the sometimes arid environment of the Greek islands.

Moreover, the extensive research also offers an interesting look into the future. "In 2022 we had another dry summer in Europe. The fact that drought most likely has a positive influence on wood formation offers promising opportunities for agricultural research to secure our food production", co-author Lens explains. "Suppose you could make any non-woody crop woody through breeding. Then you would get a larger crop with a higher yield per plant. But just as important: you could make such more lignified crops more drought-resistant. we really can't ignore it in a world dealing with climate change and a growing global population."

[1] Zizka et al: The evolution of insular woodiness in Proceedings of the National Academy of Sciences of the United States of America - 2022

Maclear's Rat Recreated?

Maclear's rat (Rattus macleari) is also known as Christmas Island rat. It is an extinct large rat only endemic on the remote Christmas Island in the Indian Ocean. The rat is named after Captain John Maclear (1838–1907) of the British survey-ship HMS Flying-Fish, who collected the specimen from Christmas Island in 1886.

Once abundant and unfamiliar with (and seemingly unafraid) of humans, large numbers of the creatures emerged and foraged in all directions at night. Maclear's rat might have been responsible for keeping the population of the Christmas Island red crab in check, as recent numbers of the crab are greater than in the past.

According to a study, introduced black rats (Rattus rattus) possibly carried a pathogen that exterminated both Maclear's Rat and the bulldog rat (Rattus nativitatis)[1]. The last recorded sighting was in 1903, although it is possible that Maclear's rats hybridized with black rats.

A DNA study found Maclear's rat to be the sister species of Hainald's rat (Rattus hainaldi) native only to the Indonesian island of Flores[2].

Now, scientists have revealed plans to bring back the extinct Christmas Island rat[3].

For the study, the researchers extracted and sequenced ancient DNA from two dry preserved skin samples of the Christmas Island rat, originally collected between 1900 and 1902 and held as part of the Oxford University Museum of Natural History collections. Their analyses show that even when the extremely high-quality Norway brown rat (Rattus norvegicus) is used as a reference, 4.85 per cent of the genome sequence is unrecoverable, with 1,661 genes recovered at lower than 90 per cent completeness, and 26 completely absent.

The question is: Why bother with the brown rat and not use the closely related Hainald's rat?

[1] Wyatt et al: Historical mammal extinction on Christmas Island (Indian Ocean) correlates with introduced infectious disease in PLoS One - 2008
[2] Thomson et al: A perspective for resolving the systematics of Rattus, the vertebrates with the most influence on human welfare in Zootaxa -2008
[3] Lin et al: Probing the genomic limits of de-extinction in the Christmas Island rat in Current Biology – 2022. See here.

First DNA recovered from extinct Sicilian dwarf elephant

Soem 200,000 years ago, Sicily was home to two different miniature elephants, Palaeoloxodon mnaidriensis and the Sicilian dwarf elephant (Palaeoloxodon falconeri). The first species is closely related to the modern Asian elephant. The second to the straight-tusked elephant (Palaeoloxodon antiquus), an extinct species of elephant that roamed Europe and Western Asia during the Middle and Late Pleistocene (781,000–30,000 years BP).

Now, for the first-time, researchers have been able to extract and delve into the DNA of one of these extinct elephants, helping to show how the largest land mammal ever to exist shrank by at least 8,000 kilograms to become one of the smallest elephants[1].

The tiny elephants that once livedon Sicily and Malta were some of the smallest elephants ever to have existed, but quite extraordinarily they are descended from one of the biggest land mammals ever to have lived: the straight-tusked elephant.

These animals were genuine giants, with some individuals reaching up to 4.5 metres tall and tipping the scales at 14 tons. An adult straight-tusked elephant could very easily have rested its chin on the back of a bull African savannah elephant.

But new research is revealing that it took a surprisingly short period of time for this miniaturisation to occur, perhaps just 40 generations for the huge ancestors to shrink to the tiny islanders.

Co-author of the study, Dr Victoria Herridge, explains 'We have sequenced the mitochondrial genome from one of the skulls of an elephant from Puntali cave in Sicily. This is amazing, because up to now there has been no DNA evidence at all from any of the southern European population of straight-tusked elephants. We've only had ancient DNA from German specimens.'

This is largely due to the environments in which the fossils were preserved, with the heat and humidity making it exceedingly difficult for any DNA to survive. The team were able to extract and sequence DNA from the petrous bone, a small and very dense bone found in the base of the skull.

The results have shown that the straight-tusked elephant lineage that led to the dwarf elephants on Sicily actually split away from the German elephants around 400,000 years ago, even though these miniature elephants are only thought to have been isolated on Sicily within the last 200,000 years.

This is intriguing because it suggests that in the gap between these dates, there was something interesting going on with the populations of these giant herbivores within continental Europe, perhaps a divide between those living in the north and those in the south.

[1] Baleka et al: Estimating the dwarfing rate of an extinct Sicilian elephant in Current Biology – 2021

Lord Howe Island Stick Insect

Like its name suggests, Lord Howe Island Stick Insects (Dryococelus australis) is a species of stick insect that (used to) live on Lord Howe Island. That island is an irregularly shaped volcanic remnant (about ten kilometers long and between 0.3 and 2.0 kilometers wide). It lies in the Tasman Sea between Australia and New Zealand.

Lord Howe Island Stick Insects can measure up to 20 centimetres in length and weigh 25 grams, with males some 25% smaller than females. They are oblong in shape and have sturdy legs. The insects have no wings, but are able to run quickly.

The behaviour of this stick insect is highly unusual for an insect species: the females lay eggs while hanging from branches. The nymphs are first bright green and active during the day, but as they mature, they turn black and become nocturnal.

Reproduction can happen without the presence of males, a natural form of asexual reproduction called parthenogenesis. This has allowed the species to survive when they are low in numbers.

The Lord Howe Island Stick Insect used to be abundant on Lord Howe Island. In 1918, a ship ran aground on Lord Howe Island. In addition to its crew, the ship contained a horde of black rats (Rattus rattus) that quickly invaded the island. With no larger mammals to predate on the rats, their population exploded and they ate everything that moved. The stick insect was eventually classified as extinct in 1983, along with 12 other insect species and five bird species.

[Ball's Pyramid]

Yup, the species was thought to be extinct, until some freshly dead remains were found on Balls Pyramid during the 1960s. Ball's Pyramid is an erosional remnant of a shield volcano lying 20 kilometers south-east of Lord Howe Island in the Pacific Ocean. It is 562 meters high, while measuring only 1,100 metres in length and 300 metres across, making it the tallest volcanic stack in the world.

In February 2001, a survey of Balls Pyramid led to the discovery of a small population of Lord Howe Island Stick Insects on a precipitous terrace. Two adults and one nymph (all females) were located feeding on an endemic tea tree (Melaleuca howeana). All evidence indicated that the species was confined to this single small terrace. A second survey, in March 2002, located a total of 24 Lord Howe Island Stick Insects. Twelve individuals were in the same shrub as that occupied the previous year, and 12 were dispersed among five nearby, smaller shrubs.

Coconut Crab

If you think dat insular gigantism is a thing of the past, you would be very wrong. The coconut crab (Birgus latro) is a thing that can invade your nightmares. This crab can reach a total length of one meter (from one top a a leg to the other one). It can weigh about four kilograms. It lives on remote islands in the Indian Ocean and Pacific Ocean.

The coconut crab has the same distribution as the original distribution of the coconut palm. Because the meat of this crab is very tasty, the species has been exterminated from islands where people live.

Adult coconut crabs feed primarily on fleshy fruits, nuts, seeds, and the pith of fallen trees, but they will eat carrion and other organic matter opportunistically. Anything left unattended on the ground is a potential source of food, which they will investigate and may carry away – thereby getting the alternative name of 'robber crab'.

The species is popularly associated with the coconut palm, yet coconuts are not a significant part of its diet. Although it lives in a burrow, the crab has been filmed climbing coconut and pandanus trees. No film shows a crab selectively picking coconut fruit, though they might dislodge ripe fruit that otherwise would fall naturally.

On these remote uninhabited islands the coconut crab has no natural enemies. The only potential predator is man himself. The result was that the crab could grow into an extremely large species.

That these coconut crabs even can attack a human in his or her sleep is not something that resides in the realms of impossibilities. Some think that the female pilot and adventurer Amelia Earhart (1897-1937) might have been forced to land her aircraft on Nikumaruro, a crab infested island during her final ill-fated flight on which she attempted to circumnavigate the globe.

Nikumaroro is situated in the western Pacific Ocean. Although occupied at various times during the past, the island is uninhabited today. Some theorise that Earhart and copilot Fred Noonan might have been eaten alive and their remains were then dragged into the burrows, reason why no trace of the pair has ever been found. Other claim that, because of the total lack of evidence, this theory is pure speculation.

Philippine Giant Cloud Rats

Never heard of it, would probably be your first reaction, but cloud rats (Phloeomys) do exist. At present, there are (probably) 18 different species living on several islands of the Philippines. Only two species are adequately described and several are extinct[1].

The northern Luzon giant cloud rat (Phloeomys pallidus), also known as northern Luzon slender-tailed cloud rat and buot in Filipino, is a large species of rodent. It is only found on Luzon, the Philippines.

This species is a very large rodent and weighs almost three kilograms and is around 75 centimeters long (including the tail). The colour of its relatively long pelage, which also covers the tail, is highly variable, but usually it is mostly very pale brown-grey or white with some dark brown or black patches. The northern Luzon giant cloud rats often have a black mask and collar, but can also be entirely white.

The northern Luzon giant cloud rat is only found in northern and central parts of Luzon, the Philippines. It prefers forest and scrub, but also occurs in degraded habitats such as plantations. In some areas it overlaps with the rarer giant bushy-tailed cloud rat (Crateromys schadenbergi), but that species mainly occurs at higher altitudes than the northern Luzon giant cloud rat.

The northern Luzon giant cloud rat is nocturnal and feeds on various types of vegetation. It can cause extensive damage to rice crops and are sometimes considered a pest. They are regularly hunted for food in the Sierra Madre and as a result it has been extirpated from some regions.

The only other described member of this genus, the southern Luzon giant cloud rat (Phloeomys cumingi), has a more southerly distribution, is generally somewhat smaller than its northern family member (although with some overlap), and it is entirely dark brown.

[1] Ochoa et al: Three new extinct species from the endemic Philippine cloud rat radiation (Rodentia, Muridae, Phloeomyini) in Journal of Mammalogy - 2021

Flores Giant Rat

In 'The Adventure of the Sussex Vampire', published in 1924, Sherlock Holmes already made a passing remark about the Flores Giant Rat (Papagomys armandvillei). Holmes mentions to Watson the name of a ship, the Matilda Briggs, “which is associated with the giant rat of Sumatra, a story for which the world is not yet prepared.”

News travelled quickly, even in those days, because the Flores Giant Rat was only described in literature in 1892. Arthur Conan Doyle was certainly keeping up to date with his knowledge of science. I can understand that Doyle changed the little known island of Flores for one of the larger Indonesian islands for literature's sake.

The Flores giant rat is a rodent of the family Muridae that occurs solely on the island of Flores in Indonesia. It has been recorded in the almost impenetrable Rutong Protection Forest. The species is found in primary, secondary and disturbed forest over a wide range of elevations.

Its length from nose to bottom is around 45 centimetres with an added tail length not exceeding 70 centimetres. The total length therefore is 115 centimetres, making it al least twice as large as those of a typical brown rat (Rattus norvegicus), which suggests about eight times the body mass.

The Flores Giant Rat is described as having small, round ears, a chunky body and a relatively small tail, and as appearing to be adapted for life on the ground with refuge in burrows. It has dense dark hair. Analysis of the teeth suggests a diet of leaves, buds, fruit, and certain kinds of insects.

The Flores Giant Rat is probably the only extant species in the genus Papagomys. The specific epithet, armandvillei, honours the Dutch Jesuit missionary Cornelis J. F. le Cocq d'Armandville (1846-1896) who was stationed in the Dutch East Indies, and later on New Guinea.

A related species, Papagomys theodorverhoeveni, is only known from subfossil remains from 3,000 to– 4,000 years ago. This species is presumed to be extinct, but may still exist on the island.

The End of the Megafauna on Madagascar

Nearly all of Madagascan megafauna - including the famous Dodo, gorilla-sized lemurs, giant tortoises, and the Elephant Bird which stood three meters tall and weighted close to a half ton - vanished between 1500 and 500 years ago. Why?

The Mascarene islands are situated east of Madagascar and are interesting because they are among the last islands on earth to be colonized by humans. Intriguingly, the islands' megafauna crashed in just a couple of centuries following human activity. In a recent study, a team of researchers found that it was likely a combination of heightened human activities in combination with a particularly severe spell of region-wide aridity that may have doomed the megafauna[1].

[By analyzing stalagmites from the La Vierge Cave located on Rodrigues the
scientists reconstructed 8000 years of the region's past climate]
[Image: Hanying Li]

The primary source of this new paleoclimate record came from the tiny and remote island of Rodrigues in the southwest Indian Ocean approximately 1600 km east of Madagascar. Li and colleagues built their climate records by analyzing the trace elements and carbon and oxygen isotopes from each incremental growth layer of stalagmites which they collected from one of the many caves from this island. Variations in the geochemical signatures provided the information needed to reconstruct the region's rainfall patterns over the last 8000 years.

Despite the distance between the two islands, the summer rainfall at Rodrigues and Madagascar is influenced by the same global-wide tropical rain belt that oscillates north and south with the seasons. And when this belt falters and stays further north of Rodrigues, droughts can strike the whole region from Madagascar to Rodrigues.

Research shows that the hydroclimate of the region experienced a series of drying trends throughout the last eight millennia, which were frequently punctuated by 'megadroughts' that lasted for decades. The most recent of the drying trends in the region commenced around 1500 years ago at a time when the archaeological and proxy records began to show definitive signs of increased human presence on the island.

While the scientists cannot say with 100 percent certainty whether human activity, such as overhunting or habitat destruction, was the proverbial last straw, the paleoclimate records make a strong case that the megafauna had survived through all the previous episodes of even greater aridity. This resilience to past climate swings suggests that an additional stressor contributed to the elimination of the region's megafauna.

The study sheds new light on the decimation of flora and fauna of Mauritius and Rodrigues. Both islands were rapidly stripped of endemic species of vertebrates within two centuries of the initial human colonization, including the well-known flightless dodo from Mauritius and the saddle-backed 'Rodrigues giant tortoise' endemic to Rodrigues.

The story our data tells is one of resilience and adaptability of the islands' ecosystems and fauna in enduring past episodes of severe climate swings for eons - until they were hit by human activities and climate change, the researchers conclude.

[1] Li et al: A multimillennial climatic context for the megafaunal extinctions in Madagascar and Mascarene Islands in ScienceAdvances - 2020

Maltese Giant Swan

The name Maltese Giant Swan (Cygnus falconeri) is a bit of a misnomer because remains have also been found on the nearby island of Sicily. On Malta itself the bird is known as Ċinju ġgant, which not surprisingly means 'giant swan'.

Some scattered remains have been unearthed and the dimensions of the Maltese Giant Swan are estimeted to be well in excess of those of the still extant mute swan (Cygnus olor), one of the largest and heaviest birds in Europe. Compared to the mute swan, the Maltese Giant Swan possibly had a total bill-to-tail length of more than 200 centimeters (Mute swan: 160 centimeters), a wingspan of 300 centimeters (Mute swan: 240 centimeters) and a potential weight of 16 kilograms (Mute swan: 10 kilograms).

The Maltese Giant Swans may be as large as or even larger than the Dwarf Elephants that roamed several islands in the Mediterranean basin.

Due to its size and lack of predators, some biologists think that it might have been flightless. This species lived during the Middle Pleistocene, a period that ran from 770,000 years ago until 126,000 years ago.

It became already extinct before human activity in the region could interfere with its demise, so its disappearance is thought to have resulted from extreme climate fluctuations or the arrival of new predators and competitors.

Its bones are on display at the Għar Dalam museum in Birżebbuġa (Malta).

Maltese Giant Dormouse

A team of paleontologists has created the first digital reconstruction of the skull of the Maltese Giant Dormouse (Leithia melitensis), an extinct gigantic dormouse that lived on Malta and Sicily around two million years ago[1]. A closely related species, the somewhat smaller Sicilian Giant Dormouse (Leithia cartei), lived on nearby Sicily.

The Maltese Giant Dormouse was first described by the Scottish naturalist Andrew Leith Adams in 1863. The genus was later named in his honour.

Roughly the size of a cat, the ancient rodent is by far the largest known dormouse species, being at least twice the size of any other insular species both extant and extinct.

The Maltese Giant Dormouse is an example of island gigantism, a biological phenomenon in which the body size of an animal isolated on an island increases dramatically.

Besides the gigantic dormice, the Mediterranean islands of Malta, Gozo and Sicily were also home to giant swans and owls as well as dwarf deer, hippos and elephants.

“While island dwarfism is relatively well understood, as with limited resources on an island animals may need to shrink to survive, the causes of gigantism are less obvious,” said senior author Dr. Philip Cox. “Perhaps, with fewer terrestrial predators, larger animals are able to survive as there is less need for hiding in small spaces, or it could be a case of co-evolution with predatory birds where rodents get bigger to make them less vulnerable to being scooped up in talons.”

In the new study, the scientists digitally pieced together fossilized fragments from five skulls of the Maltese Giant Dormouse to reconstruct the first complete skull of the species. The reconstructed skull is 10 centimetres long — the length of the entire body and tail of many types of modern dormouse.

“Having only a few fossilized pieces of broken skulls available made it difficult to study this fascinating animal accurately,” explained lead author Jesse Hennekam. “This new reconstruction gives us a much better understanding of what the giant dormouse may have looked like and how it may have lived.”

[1] Hennekam et al: Virtual Cranial Reconstruction of the Endemic Gigantic Dormouse Leithia melitensis (Rodentia, Gliridae) from Poggio Schinaldo, Sicily in Open Quaternary - 2020. See here.

The last Woolly Mammoth died on Wrangel Island?

Mammoth is a term used to describe the various species and subspecies from the now extinct genus elephantid mammuthus that existed from the Pliocene epoch (around 5 million years ago) through to the early Holocene between (3700 and 4000 years ago).

Mammoths once roamed the continents of North America, Africa, Europe and Asia, but most species died out along with many megafauna around the time of the last ice age during the last glacial retreat some 10,500 years ago.

Various theories have been proposed to explain why the mammoth vanished, from climatic events causing rising sea levels, great cosmic catastrophes (pdf), infectious diseases, changes in fauna and habitats, to the spread of humans hunting the mammoth. There is no definitive explanation, but it could be one, a combination of some, or all the theories suggested.

Some small groups of mammoth genus survived the mass extinction in isolated pockets, with the most widely known being woolly mammoths (Mammuthus primigenius). The woolly mammoth coexisted with early humans across Eurasia and North America, where Neolithic hunters used their bones and tusks for making art, weapons, tools, dwellings, and food.

The woolly mammoth is among the best-studied of any prehistoric animal because of frozen carcasses in Siberia and Alaska, as well as skeletons, teeth, stomach contents, dung, and depictions from life in prehistoric cave paintings.

It disappeared from the mainland around 10,000 years ago, but continued to survive on Saint Paul Island (Bering Sea, Alaska) until 3,750 BC[1] and the last known population on Wrangel Island around 2000 BC[2]. Wrangel Island is located on the extreme north-eastern fringes of Russia.

So, you might think, it's a shame that such majestic creatures have disappeared forever. That is not entirely true, because scientists are busy trying to clone mammoths, hoping that in the forseeable future, mammoths will roam their icy worlds again.

[1] Graham et al: Timing and causes of mid-Holocene mammoth extinction on St. Paul Island, Alaska in Proceedings of the National Academy of Sciences - 2016. See here. 
[2] Arppe et al: Thriving or surviving? The isotopic record of the Wrangel Island woolly mammoth population in Quaternary Science Reviews - 2019

Trees that were left behind: Evolutionary anachronisms

Ever wondered what mammoths and mastodons used to eat? Well, since these species of extinct megafauna were herbivores they obviously ate large amounts of grass. But they also liked to feast on nutritious seeds. Not smallish seeds, but large, heavy, and even poisonous seeds.

[Kentucky coffeetree pods]

The Kentucky coffeetree (Gymnocladus dioicus), for example, is a species of tree that is (or rather was) endemic in northern America. Its pods are up to 25 centimeters in length. They contain six to nine seeds, that are surrounded by a thick layer of dark, sweet pulp. The pods are poisonous and can only be consumed by humans when roasted. And yes, they were used as a coffee substitute by Indians.

Mammoths and mastodons didn't care and ate these huge pods with relish. Then they trundled away and dispersed the seeds far away from the tree. That's how nature works.

The Kentucky coffeetree and other examples evolved together with the megafauna. So, when the megafauna went extinct at the end of the last ice age (around 14,000 BC) the trees were left behind. The seeds simply fell to the ground and withered away.

These plants found themselves bereft of their seed dispersers. Many of them would go extinct, while some managed to cling to survival by reproducing asexually. They were evolutionary anachronisms.

But the most successful of these anachronistic plants were those that managed to find new animals to disperse their seeds: us.

[Cocao pod]

One of these evolutionary anachronisms that found a new way to survive is cacao (Theobroma cacao). It has a big tough pod and really sweet pulp that was enticing for large herbivores. It's also got chemically protected seeds on the inside in the form of caffeine and theobromine. No other animal but a human is able to disperse the seeds.

And before avocados became popular in guacamole and on toast, they were once a favourite snack of gomphotheres, elephant-like creatures with four tusks that lived in Central and South America. Papaya, certain types of figs, pawpaw and persimmons are also examples of fruits once favoured by megafauna and later eaten by humans.

Falkland Islands Wolf

The Falkland Islands wolf (Dusicyon australis), also known as warrah or Antarctic wolf, was the only native land mammal of the Falkland Islands, situated in the colder regions of the South Atlantic Ocean. This endemic species was hunted and poisoned to extinction in 1876. Its diet is unknown, but, due to the absence of native rodents on the Falklands (rats were only brought to the islands when Europeans 'discovered' them in 1690), probably consisted of ground-nesting birds such as geese and penguins, seal pups, and even insects, as well as seashore scavenging. It has sometimes been said that it may have lived in burrows.

It diverged some 16,000 years ago from Dusicyon avus, also an extinct species of canid in the genus Dusicyon, that once roamed the Pampas and Patagonia in the southern parts of South America. It appears to have survived until very recently, perhaps no more that 400 years ago.

The Falkland Islands wolf lived on both West and East Falkland. It was about one meter in length with a weight of some 20 kilograms.

The Falkland Islands weren’t always as isolated from South America as they are today. At the height of the last ice age sea levels were up to 150 metres lower, exposing an enormous coastal plain off the Argentine coast. It seems likely that under the icy conditions of the ice age the strait between the continent and the Falkland Islands could have periodically frozen over, creating a brief window of opportunity for a cunning wolf to reach new land[1].

Of course, its 16,000 year isolation contributed to its eventual demise. Like many island species, it was totally naive to predators - including humans - and was easily killed by early European settlers.

[1] Austin et al: The origins of the enigmatic Falkland Islands wolf in Nature Communications - 2013. See here.

Channel Islands Fox

The Channel Island Fox (Urocyon littoralis) is a small fox (or rather foxes) that is (are) native to six of the Channel Islands of California, an eight-island archipelago along the Santa Barbara Channel in the Pacific Ocean, off the coast of Southern California.

[Image: Jessica Sanchez - Channel Island Fox]

There are six subspecies, each unique to the island it lives on, reflecting its evolutionary history. The island fox shares the genus with the mainland gray fox (Urocyon cinereoargenteus), the species from which it once descended.

[The six subspecies]

Channel Island foxes are significantly smaller than the grey fox and are the smallest foxes in North America. Typically, they measure 50 centimeters in length with a 30 centimeters long tail attached. Island foxes weigh between 1.0 and 3.0 kilograms. Their small size is a result of insular dwarfism.

“They’re definitely very clever and mischievous, but they also have a kind of fearless confidence that comes with having been a top predator for so long. They will come right up to you,” said Jessica Sanchez, a wildlife biologist, veterinarian and epidemiologist.

Sanchez has been working with the Channel Island foxes since 2006, when she joined in the efforts to repopulate the fox populations following a rapid decline which brought the species to the brink of extinction.

The foxes have no immunity to parasites and diseases brought in from the mainland and is especially vulnerable to those that the domestic dog may carry. In addition, predation by the golden eagle and human activities devastated fox numbers on several of the Channel Islands in the 1990s. In the late 1990s, the foxes were on a precipice. On Santa Catalina Island, an epidemic of canine distemper virus — likely introduced from the mainland — killed 95% of all the foxes on the island by 1999, while up north on Santa Cruz, Santa Rosa and San Miguel Islands, invasive golden eagles began feasting on the foxes in large numbers.

“The eagles were initially attracted to the islands because there was an abundance of livestock like pigs and goats for them to feed on. There were also open territories that were left because the native bald eagles had also been declining at the same time due to DDT,” Sanchez said.

Unfortunately for the foxes, their fearless nature and diurnal lifestyle made them easy targets. Better yet, they were the perfect size to be scooped up and brought to nests as a nutritious meal for infant chicks.

“They didn’t really have a lot of the evasive behaviours that mainland foxes have so they really suffered predation by these eagles and that just led to dramatic population declines,” Sanchez said.

The only way to save the Channel Island foxes was to remove the golden eagles (by removing their favourite food supply: pigs and goats) and to reintroduce bald eagles to the islands to occupy their former territory and drive away any wayward golden eagles that were inclined to return.

Source.

Giant trees have role in protecting forests

Scientists have shown to be true what JRR Tolkien only imagined in the Lord of the Rings: giant, slow-reproducing trees play an outsized role in the growth and health of old forests. In the 1930s, the writer gave his towering trees the name 'Ents'. Recently, scientists concluded that these 'long-lived pioneers' contribute more than previously believed to carbon sequestration and biomass increase[1].

The authors said their study highlights the importance of forest protection and biodiversity as a strategy to ease global heating. They say it should also encourage global climate modellers to shift away from representing all the trees in a forest as essentially the same.

“This analysis shows that that is not good enough for tropical forests and provides a way forward,” said Caroline Farrior, an assistant professor of integrative biology. "We showed that the variation in tropical forest species’ growth, survival and reproduction is important for predicting forest carbon storage."

Long-lived pioneers – a term that has been around for decades – include species such as mahogany, Brazil nut trees and Ceiba pentandra, which are visible far above the rest of the canopy because they grow fast (at up to twice the speed of plants lower in the canopy) for hundreds of years. Researchers believe this is the result of a trade-off between stature and reproduction: they are able to put more energy into putting on biomass than into producing offspring.

The study is based on more than 30 years of data collected from old growth and secondary rainforest on Barro Colorado, an island in the middle of the Panama Canal.

The scientists grouped the 282 different species of trees into five categories determined by growth, reproduction and longevity. This showed the relative roles of 'fast' species that grow and die quickly, versus 'slow' species that grow slowly and reach an old age. Others are 'infertile giants' that live long and reproduce over a long time, and 'fertile dwarfs' and small shrubs and low treelets that grow slowly, die young, but produce a large number of offspring.

By simulating different combinations of these groups, the scientists were able to build a model that reproduced the dynamics of the recovery of nearby young forests.

This knowledge of how quickly trees grow, how long they live and how many offspring they produce could help in the restoration of tropical forests, which are currently being cut down at an alarming rate. It could also dispel a theory that such giant trees disappear once a forest reaches maturity.

"Our results show long-lived pioneers are not transient but an important feature in old forests. They represent about 40% of the biomass and there are no signs that this declines over time," said the paper’s lead author, Nadja Rüger. However, she cautioned that others forest might have different patterns.

[1] Rüger et al: Demographic trade-offs predict tropical forest dynamics in Science - 2020

Gough Island Giant Mice

Gough Island (also known as Ilha de Gonçalo Álvares) is a remote British Overseas Territory, a rugged volcanic island in the South Atlantic Ocean. It is a dependency of Tristan da Cunha and is part of the British Overseas Territory of Saint Helena, Ascension and Tristan da Cunha. It is considered to be one of the world's most important seabird colonies, hosting more than 10 million birds.

It would be some sort of paradise but for the mice. Mice were inadvertently introduced to the 91 square kilometers island by sailors during the 19th Century. The rodents have adapted to the limited resources on the small piece of land by developing a taste for seabird eggs and chicks.

Video cameras have recorded groups of up to nine mice eating the chicks alive. As a result of their success, the mice have become 'super-sized'. They are about 50% larger than a regular domestic mouse.

Many of the seabirds on Gough are small and nest in burrows. The chicks are smaller and have no escape route, so for an opportunistic mouse these chicks constitute relatively easy prey. The mice have done so well that they've grown bigger and are now attacking all seabirds, even endangered Tristan albatross chicks, which are far bigger than other, smaller sea-going birds.

Watch the documentary 'Tristan da Cunha – the Monster Mice of Gough Island' here.

Recently, a plan has been hatched to completely eradicate the mice. The operation is due to start in 2020. A ship will carry two helicopters and a load of poisonous, cereal pellets. These will then be spread across the island by the helicopters. They contain an anticoagulant which should kill the mice within 24 hours. They hope.

The Gough Island Giant Mice is an example of how quickly a species can adapt and become an example of island gigantism.

Congreso Island Rat

Isla de Congreso (or Congreso Island) measures just 0.256 square kilometers and is part of the small Spanish archipellago of the Islas Chafarinas, a group of three small islets located off the coast of Morocco. Obviously, the ownership of the islands is disputed by Morocco.

The island is uninhabited, but it is home to some rabbits and a pigeon colony. This rocky islet offers just some grass to herbivores. However, the young rabbits and the eggs of the pigeons can be a meal for the indigenous population of black rats (Rattus rattus).

These black rats constitute one of the westernmost insular populations of the species in the Mediterranean region. Considering this later fact and the geographical proximity between Chafarinas and the Morocco coastline, it seems likely that Congreso black rats had their source in North-African populations.

To evaluate the influence of insular conditions on body and skull dimensions, scientists measured the biometric characteristics of a Congreso Island Rat and compared these with specimens from nearby mainland populations from Malaga (southeastern Iberia) and Morocco[1].

Results show that Congreso Island Rat was similar in size to Iberian specimens, but the skull shape resembled Moroccan rats. Actually, the specimens from Malaga correspond to one of the largest mainland forms of rat from western Europe. The size of Congreso Island Rat might constitute another case of gigantism that appears as an adaptive response to insularity in black rat populations from small western Mediterranean islands.

Lack of interspecific competition and low predation pressure on Congreso Island could have contributed to the black rat size increase.

Queija, López Fuster: Morphometric analysis of the black rat: Rattus rattus, from Congreso Island (Chafarinas Archipiélago, Spain) in Geography – 2000

Admiralty Giant Rat

The more isolated an island, the more likely a species will develop island gigantism.

Manus Island is the main island of the Admiralty Islands that are located to the northwest of Papua New Guinea. Today, the island is best known for its detention centre for Australian asylum seekers.

As recently as 2016, a new species of rats was discovered on Manus Island. To 'honour' the 'recent use of the island to detain people seeking political or economic asylum in Australia', this new addition to the genus Rattus was named Rattus detentus.

The Admiralty Giant Rat weighs nearly half a kilogram and is larger than almost any other rat across the Melanesian archipelago. It measures more than 40 centimeters in length. It has coarse, spiny, and dark fur with prominent black guard hairs; and sharply contrasting cream ventral pelage. The rat has a short tail. This species of rat may have been on the island hundreds of thousands of years.

Over millennia of isolation on Manus Island, the rat has adapted to specific conditions. It has powerful front incisors but small molars, suggesting it uses its front teeth to break open hard nuts.

Before confirmation of the Admiralty Giant Rats existed, scientists had suspected there was a large rat endemic to the island.

Sightings of the Admiralty Giant Rat are rare, thus it is possibly seriously endangered. Residents report it has previously been seen across Manus Island and sometimes on adjacent Los Negros Island (the two islands are connected by a bridge) but efforts by zoologists to find further evidence of it have been fruitless.

Tenerife Giant Rat

Now, a popular tourist destination, the island of Tenerife once was home to the fearsome Tenerife giant rat (Canariomys bravoi). This rat is an extinct species of rodents that was endemic to the largest of the (Spanish) Canary Islands, that are situated off the African coast in the Atlantic Ocean.

The Tenerife Giant Rat honoured his name, because it really was a big rat, measuring over 1.15 meters in length, including its tail. It had a weight of about 1.5 kilogram[1]. Its skull reached up to zeven centimeters in length. The Tenerife Giant Rat was the most imposing of its family: a related species, the Gran Canaria giant rat (Canariomys tamarani) reached a body length of 'just' 25 centimeters, similar to the size of the 'modern' brown rat.

Isolation, an abundance of food and absence of predators is the reason that some species develop extreme sizes. 

Tenerife Giant Rat was a strong and powerfully muscled rodent able to move on different substrates from the ground to the trees and probably had digging skills[2].

[Image by Ghedoghedo]

The Tenerife Giant Rat probably infested the island, because many remains have been found during archaeological digs. Most remains are from the Pleistocene. Radiocarbon dating has placed some of the finds in the late Pleistocene, a dating that places the extinction of the Tenerife giant rat at about 11,700 years before the present era or about 10,000 BC.

After the Tenerife giant rat became extinct, the island was devoid of rodents until the Vikings arrived around 1000 AD. Mice accompanied the Vikings in their boats and disembarked when they reached the islands[3].

[1] Moncunill-Solé et al: How large are the extinct giant insular rodents? New body mass estimations from teeth and bones in Integrative Zoology - 2014
[2] Michaux et al: Body shape and life style of the extinct rodent Canariomys bravoi (Mammalia, Murinae) from Tenerife, Canary Islands (Spain) in Comptes Rendus Palevol - 2012 
[3] Rando et al: Radiocarbon evidence for the presence of mice on Madeira Island (North Atlantic) one millennium ago in Royal Society Proceedings - 2014. See here.

Channel Islands Dwarf Mammoth

To be absolutely clear: the Channel Islands Dwarf Mammoth has not lived and died on the European Channel Islands, situated between England en France in the English Channel or la Manche, depending on which coast you're standing.

The Channel Islands (or Archipiélago del Norte) we're talking about is an archipelago consisting of eight islands in the Pacific Ocean, off the coast of Southern California. On some of these islands (Santa Cruz, Santa Rosa and San Miguel) remains have been found since 1856 of the Channel Islands Dwarf Mammoth (Mammuthus exilis). It is thought that this species of dwarf elephant descended from its larger family member, the Columbian Mammoth (Mammuthus columbi) of mainland North America[1].

The Channel Islands Dwarf Mammoth became extinct during the Quaternary extinction event (of still largely uncertain causes) in which many megafauna species disappeared from the face of the earth due to changing conditions to which these species could not sufficiently adapt.

From a recent analysis in 2010 it was determined that the Channel Islands Dwarf Mammoth was on average, 1.70 meters tall at the shoulders and weighed around 750 kilograms.

The Channel Islands Dwarf Mammoth appears to have survived on the islands until the arrival of the humans around 13,000 years ago as the last known mammoth occurrence was around the same time.

Since modern elephants are excellent swimmers, the ancestors of the Channel Islands Dwarf Mammoth could probably swim the six kilometers from the coast to the island of Santa Rosa. As the population of mammoths increased, the lack of large predators and the loss of habitat caused by the rise of sea levels at the end of the ice age. As a result, Santa Rosae split into four islands favoured smaller animals. Because of this, the Dwarf Mammoth began to evolve through generations as a survival mechanism to stay alive on the ever-shrinking Santa Rosa Island; their body size became smaller because it required less food and resources to remain energized and alive. The mammoth had become a distinct species, the Channel Islands Dwarf Mammoth.

[1] Agenbroad, Morris: Giant Island/Pigmy Mammoths: The Late Pleistocene History of Channel Islands National Park. See here.