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.

Seaweed-eating sheep

Sheep are herbivores and exist on a diet of grass, clover, herbs and other plants that grow in their pasture. But what happens if food supply is scarce and sheep have the choice between starvation or adaption.

The Orkney Islands form an archipelago in the north of Scotland. Conditions are harsh, the landscape is desolate and the wind can howl for days on end. But sheep still manage to live there and to survive they have adapted to feed on salty seaweed. From pure herbivores they became part-time fucivores.
Scientists wanted to know when these sheep started to add seaweed to their diet and tested remains of sheep on the island of Skara Brae using stable isotope analysis of δ13C . They found sheep began to consume moderate amounts of seaweed from the moment they arrived on the island in circa 3500 BC[1]. This adaption helped farming spread to one of the most remote areas of Europe, although on could also argue that European civilization spread from north to south.

It is not clear whether the sheep chose to consume the marine vegetation or if Neolithic farmers added it to their fodder during the winter months[2]. The authors said: 'It is not possible to establish whether Neolithic sheep turned to seaweed of their own accord or were brought to the shore by herders. These results confirm the chronology of the gradual introduction of seaweed into the Neolithic sheep diet in Orkney, which may have been the result of changes in sheep behaviour or physiology.'

The study also found that the introduction of seaweed to the diet of Orkney's Neolithic sheep was not the start of an unbroken tradition. Sheep during the Viking period on Orkney may have been separately imported, and stable isotope analyses indicate a year-round terrestrial diet for Viking-period sheep.

The modern sheep on North Ronaldsay show far higher levels of seaweed consumption, and other contemporary seaweed eating sheep are also known on Shetland and the Faroe Islands.

The practice may not have been continuous, but it is remarkable that sheep are still able to survive in such exposed environments using the same strategies their Neolithic forbearers employed thousands of years ago.

[1] Balasse et al: Seaweed-eating sheep and the adaptation of husbandry in Neolithic Orkney: new insights from Skara Brae in Antiquity – 2019. See here.
[2] Balasse et al: Stable isotope evidence (δ13C, δ18O) for winter feeding on seaweed by Neolithic sheep of Scotland in Journal of Zoology - 2006

Luzon Man

When remains of several Homo floresiensis ('Flores man') were discovered in 2003 on the Indonesian island of Flores, scientists were baffled. Scientists are still divided whether Homo floresiensis represents a distinct species from modern humans or whether they were the result of insular dwarfism.
Professor Piper showing a child's femur (collar bone).
But now the story of human evolution is getting even more diffuse, because researchers have uncovered the remains of a new species of human in the Philippines, proving the region played a key role in hominin evolutionary history[1]. The new species, Homo luzonensis ('Luzon man') is named after Luzon Island, where the 67,000 year old fossils were found during excavations at Callao Cave, located on northern Luzon. 

The researchers uncovered the remains of at least two adults and one juvenile within the same archaeological deposits. The fossil remains included adult finger and toe bones, as well as teeth. They also recovered a child’s femur. There are some really interesting features – for example, the teeth are really small. The size of the teeth generally, though not always, reflect the overall body-size of a mammal, so the researchers think Homo luzonensis was probably relatively small. Exactly how small they don’t know yet, because they have yet to find some skeletal elements from which we could measure body-size more precisely.

"So, the question is whether some of these features evolved as adaptations to island life, or whether they are anatomical traits passed down to Homo luzonensis from their ancestors over the preceding two million years, Professor Philip Piper, co-author and a lead member of the team, explained.

The Philippines is made up of a group of large islands that have been separated long enough to have potentially facilitated archipelago speciation. Homo luzonensis shares some unique skeletal features with the famous Homo floresiensis, discovered on the island of Flores to the south east of the Philippine archipelago.

So, did Homo luzonensis evolve seprately from Homo floresiensis or did both simply evolve as a result of isolated island life?

[1] Détroit et al: A new species of Homo from the Late Pleistocene of the Philippines in Nature - 2019

Irish Giant Deer

The Irish Giant Deer (Megaloceros giganteus) also called the giant deer or giant elk, is an extinct species of deer in the genus Megaloceros and, at over twee meters in height, is one of the largest deer that ever lived.
The animal was never exclusively Irish – nor, for that matter, was it an elk – but Ireland was the early treasure-house of its fossil skeletons and antlers, impeccably preserved in lake-mud beneath the bogs. It was first recorded as a fossil in 1697 and it featured in fierce debates about extinction and the impact of Noah’s flood.

Its range extended from Ireland via Siberia to China during the Pleistocene. A related form is recorded in China during the Late Pleistocene[1]. The most recent remains of the species have been carbon dated to about 7,700 years ago in Siberia.

Giant deer had clearly evolved from smaller forms, but the usefulness of bigger and bigger antlers evaporated – so it was argued – because they tangled in trees or dragged the stags down into the mud of bogs and lakes.

The theory of drowning stags had been nourished over centuries by the finding of more than 100 antlered skulls in lake sediments at Ballybetagh Bog, 15 kilometres south of Dublin (Ireland). They have made up the bulk of the remains collected in the Irish National Museum.

Whatever happened in Ireland, human hunters probably also played some part in extinguishing this great animal across the steppes of Europe.

[1] Gould: The misnamed, mistreated, and misunderstood Irish elk in Ever Since Darwin - 1977

St Kilda Field Mouse

About 100 kilometers west of the Scottish coast lies St Kilda, a remote mini-archipelago of which Hirta (Hiort in Scottish Gaelic) is the main island. Hirta. Only Hirta was once inhabited, its population probably never exceeding 180 and was slowly declining for decades. The entire remaining population of 36 intensely sombre and religious men and women was evacuated from Hirta in 1930. They were transferred to mainland Scotland, where they became even more unhappy because they missed their own little place under the sky[1].
[Image Jackhynes][St Kilda Field Mouse]
These days St Kilda is a nature reserve and is an important breeding ground for many species of seabird. But, hidden from sight, a unique species of field mouse also lives on St Kilda. The St. Kilda field mouse (Apodemus sylvaticus hirtensis) is a subspecies of the wood mouse (Apodemus sylvaticus) that is only endemic to the archipelago of St. Kilda. The mouse is unique to the islands and is believed to have arrived on the boats of Viking settlers more than a millennium ago.

Because no predators exist on St Kilda, this subspecies was able to grow to twice the size of its ancestor, the field mouse. The St. Kilda field mouse generally weighs between 50 grams and 70 grams. It has black eyes, small peaked ears, and is fairly uniform in colour: mainly brown, with a lighter shade of fur on its underside. It also has longer hair and a longer tail. The St Kilda field mice can survive by eating snails, insects, moss and seeds, can feed on the carcasses of dead sheep and birds, but and will also readily eat food brought in by visitors and intended for their own consumption.

The increased size enables the St. Kilda field mouse to preserve its heat and increase fat storage, something that is necessary in the harsh clime of St Kilda.

When the archipelago was abandoned by its human population and their houses were no longer heated, none of the islands' house mice could survive the bleak conditions and all perished within two years.

[1] Boudewijn Büch: Eilanden -1991

Flores Island Pygmies (Extant and Extinct) are the Result of Island Dwarfism

Homo floresiensis ('Flores Man') is possibly an extinct species in the genus Homo. It lived from 60,000 to 100,000 years ago.
The remains of an individual that would have stood about 1.10 m in height were discovered in 2003 in the Liang Bua cave on the Indonesian island of Flores. Partial skeletons of nine other individuals have been recovered, including one complete skull. These remains have been the subject of intense research and debate whether they represent a distinct species from modern humans or whether they were the result of insular dwarfism.

Both modern man (Homo sapiens), the Neanderthals (Homo neanderthalensis ) and the Denisovans (Homo sapiens denisova) share a common ancestor (Homo heidelbergensis). From all three species we have been able to collect their DNA. Modern humans all have bits of DNA of the Neanderthals and the Denisovans burried within their own DNA.
[Skulls of Homo floresiensis and Homo sapiens]
If Homo floresiensis was a seperate species one would expect to find bits of DNA that do not match the three related species. The problem is that scientists haven't been able to extract DNA from the fossilized remains of Homo floresiensis.

A modern pygmy population evolved short stature independently of the extinct Homo floresiensis species that lived on the same island tens of thousands of years earlier, a study reports[1]. Are they related? Scientists took DNA samples from 32 of these villagers and studied their DNA.

"They definitely have a lot of Neanderthal," said Serena Tucci, lead author. "They have a little bit of Denisovan. We expected that, because we knew there was some migration that went from Oceania to Flores, so there was some shared ancestry of these populations."

But there were no chromosomal 'bits' of unknown origins. While it is not certain that Homo floresiensis and the modern pygmies from flores are related, it is certain is that there's is no indication of gene flow from the Homo floresiensis into people living today.

Tucci and her colleagues analyzed the Flores pygmy genomes with respect to height-associated genes identified in Europeans, and they found a high frequency of genetic variants associated with short stature.
Fossil evidence indicates Homo floresiensis was significantly smaller than the modern Flores pygmies, standing about 106 centimeters, while modern pygmies average about 145 centimeters. Homo Floresiensis also differed from Homo sapiens in their wrists and feet, probably due to the need to climb trees to evade Komodo dragons, said Tucci.

Dramatic size changes in animals isolated on islands is a common phenomenon, often attributed to limited food resources and absense of predators. In general, large species tend to get smaller and small species tend to get larger on islands. At the time of Homo floresiensis, Flores was home to dwarf elephants, giant Komodo dragons, giant birds and giant rats, all of which left bones in the Liang Bua cave.

Their results show that insular dwarfism arose independently at least twice on Flores Island, she said, first in Homo floresiensis and again in the modern pygmies.

[1] Tucci et al: Evolutionary history and adaptation of a human pygmy population of Flores Island, Indonesia in Science – 2018

Javan Dwarf Wolf

Several canid fossils, which were originally discovered in the early 20th century, are known from Early and earliest Middle Pleistocene of Java (Indonesia). There's bit of confusion as to which genus these canids belong. Most scientsts now say they belong to Xenocyon ('strange wolf'), an extinct subgenus of Canis, while others place them within Megacyon, that seems to have been diverged from Xenocyon.
On the Indonesian island of Java, fossils of two variants of Xenocyon have been unearthed near Trinil, a palaeo-anthropological site on the banks of the Bengawan Solo River on eastern Java[1].

The larger-sized fossils belonged to Merriam's Wolf (Xenocyon merriani), a canid that lived in the early Pleistocene (ca. 1.2-1.0 million years ago). It was gradually replaced by the small-sized Javan Dwarf Wolf (Xeoncyon trinilensis) during the earliest Middle Pleistocene (1.0-0.8 mya). The latter is probably an anagenetic dwarf derived from the larger form of the preceding period. The change in body size of Xenocyon on Java over time is likely the effect of increased competition within the carnivore guild within the restricted boundaries of the island.
More competition meant less food. Less food meant more hunger and – eventually – a pronounced body size shift. That smaller size allowed the Javan Dwarf Wolf to shift to (and survive on) much smaller prey, like mice.

The degree of endemism of terrestrial mammals of the earliest Middle Pleistocene horizon of the site Trinil, which has also yielded Homo erectus erectus fossils, indicates that during this period, Java was marginally isolated which allowed for a corridor dispersal to the island with subsequent vicariance.

The following continentalisation enabled the invasion by mainland terrestrial mammals, as is seen in younger layers at Trinil, and eventually by Homo sapiens and Cuon in the Late Pleistocene to early Holocene.

[1] Van der Geer et al: Insular dwarfism in canids on Java (Indonesia) and its implication for the environment of Homo erectus during the Early and earliest Middle Pleistocene in Palaeogeography, Palaeoclimatology, Palaeoecology

Minorcan Giant Rabbit

The small island of Minorca, Menorca or Minorca is one of the Balearic Islands located in the western Mediterranean. There, researchers have recently unearthed the fossilized remains of a giant rabbit[1].
[Image: Nobu Tamura]
This massive rabbit (Nuralagus rex), measuring 60 centimeters in length and 30 centimeters in height, weighed in at 12 kilograms, some ten times the size of its extinct mainland cousin (Alilepus sp.) and six times the size of the living European rabbit (Oryctolagus cuniculus).

The scientific name, Nuralagus rex, roughly translates as 'Rabbit King of Minorca', because nura is the ancient Phoenician name for the island of Minorca, lagos is the Greek word for 'hare' or 'rabbit', while rex 'means 'king'.

This 'rabbit king of Minorca' lived approximately 3 to 5 million years ago and may be one of the oldest known cases of the 'island rule' in mammals. This rule states that when on islands, big animals will get smaller and small animals will get bigger.
This size change on islands may be due to [1] reduced quantities of food or [2] lack of mainland predators. On Minorca, Nuralagus rex lived with few other vertebrate species. Some of its neighbours included a bat (Rhinolophus cf. grivensis), a large dormouse (Muscardinus cyclopeus) and a giant tortoise (Cherirogaster gymnesica). In the case of the Minorcan giant rabbit, the lack of predators allowed this rabbit to reach its giant size.

The researchers found that this giant rabbit had also lost its ability to hop. The long springy spine of a mainland rabbit was replaced by a short, stiff spine that would make jumping difficult. Instead, this rabbit was most likely a digger, searching for roots and tubers to eat. This is an indication of a lack of fresh green grass.

Additionally, because of lack of predators to worry about, Nuralagus rex developed reduced eye socket size and reduced auditory bullae, suggesting smaller eyes and ears. Which means that this creature didn't have large flappy ears, but relatively diminutive ears for its size.

[1] Quintana, Köhler, Moyà-Solà: Nuralagus rex, gen. et sp. nov., an endemic insular giant rabbit from the Neogene of Minorca (Balearic Islands, Spain) in Journal of Vertebrate Paleontology - 2011

Balearic Islands Cave Goat

Remains of the Balearic Islands Cave Goat (Myotragus balearicus) have been found on the islands of Majorca and Menorca. This clear example of island dwarfism went extinct some 5,000 years ago. While it still bears the name 'goat', genetic analysis has revealed that it was more akin to sheep than to goats.
The Balearic Islands Cave Goat was standing about 50 centimetres high at the shoulder and weighed between 50 and 70 kilograms[1]. It had rather short legs, which meant that the Balearic Islands Cave Goat could not have run very fast. They had no need to do so, because on these isolated islands no predators except for some birds of prey, from which they probably hid in the vegetation. The Balearic Islands Cave Goatwas able to grow at flexible rates, halting the growth process when food was unavailable. This species was probably the only mammal ever to adapt in this way, and it probably helped the goat survive for five million years before - as some scientists believe - being driven into extinction by human hunters.

Another unsusual feature of the Balearic Islands Cave Goat was that it had eyes that were directed towards the front like nearly all primates and carnivorans. It gave the species stereoscopic vision.
Before human colonisation, the Balearic Islands were once covered by forests. In this habitat, the Balearic Islands Cave Goats would probably move about in solitude or in small groups.

At first, the Balearic Islands Cave Goat only colonized the island of Majorca. On nearby Ibiza a strange ecosystem without terrestrial mammals developed in which birds and bats were the main vertebrates, while in Menorca a giant rabbit, the Minorcan giant lagomorph (Nuralagus rex) evolved that covered the same niche as the Balearic Islands Cave Goat on Majorca[2]. With sea levels falling during the last ice age, Majorca and Menorca were united and the Balearic Islands Cave Goat replaced the great Menorcan lagomorphs. Both islands separated again at the beginning of the Holocene.

[1] Lalueza-Fox et al: Molecular dating of caprines using ancient DNA sequences of Myotragus balearicus, an extinct endemic Balearic mammal in BMC Evolutionary Biology - 2005. See here.
[2] Quintana et al: Nuralagus rex, gen. et sp. nov., an endemic insular giant rabbit from the Neogene of Minorca (Balearic Islands, Spain) in Journal of Vertebrate Paleontology - 2010. See here.

Australian Dwarf Emus

Island dwarfism can be found on virtually every Mediterranean island of a certain size. But it is not just an Mediterranean feature. Island dwarfism happens everywhere around the world where mammals were forced to depend on less food and had no other species hunting them.
Australia's iconic emu (Dromaius novaehollandiae novaehollandiae) is the only living representative of its genus, but fossil evidence and reports from early European explorers suggest that three island forms (at least two of which were dwarfs) became extinct during the nineteenth century.

While one of these – the King Island emu (Dromaius novaehollandiae ater) – has been found to be conspecific with Australian mainland emus, little is known about how the other two forms – Kangaroo Island emu (Dromaius novaehollandiae baudinianus) and Tasmanian emu (Dromaius novaehollandiae diemenensis) – relate to the others, or even the size of Tasmanian emus[1].
Now research has found that that all the island populations represent sub-populations of mainland Dromaius novaehollandiae[2]. Further, the size of island emus and those on the mainland appears to scale linearly with island size but not time since isolation, suggesting that island size – and presumably concomitant limitations on resource availability – may be a more important driver of dwarfism in island emus, though its precise contribution to emu dwarfism remains to be confirmed.

This was the surprise finding of a study that analysed the DNA and bone measurements of the now extinct small emus, using both ancient and modern museum specimens. The study revealed that the small stature of the island emus evolved relatively quickly.

“Our results have shown that all the island emus are genetically closely related to the much larger mainland emu," says lead author Dr Vicki Thomson, an Australian scientist. "The leg bones, a measure of overall body size, show size differences from the smallest, found on King Island, to the largest, on the mainland, with Kangaroo Island and Tasmanian emus in between," she says. "The smallest, the King Island emus, are typically two-thirds of the size of our mainland emus, with others ranging upwards according to the size of their island."

Co-author Dr Kieren Mitchell says: "This suggests that island size, and presumably the associated reduced food resources available, may have been important in causing smaller body size in island emus."

"We do know that prior to European arrival, Kangaroo Island, King Island and Tasmania had these smaller bodied emus and they would have been isolated from the mainland after sea-levels rose around 10-15,000 years ago.

"The change in body size thus appears to have happened quite quickly, and independently on each island."

[1] Heupink et al: Ancient DNA Suggests Dwarf and ‘Giant’ Emu Are Conspecific in PloS One – 2011
[2] Thomson et al: Genetic diversity and drivers of dwarfism in extinct island emu populations in Biology Letters – 2018. See here.

Ancient DNA: Minoans and Mycenaens were (almost) the same

The discovery of the Minoan and Mycenaean civilizations on the island of Crete and on mainland Greece in the late 1800s gave birth to modern archaeology and opened a direct window into the European Bronze Age. This period of history had previously been glimpsed only through Homer’s epics, the Iliad and Odyssey.
The Minoan civilization flourished on Crete beginning in the third millennium BC and was very advanced both artistically and technologically. The Minoans were also the first literate people of Europe. The Mycenaean civilization developed in mainland Greece in the second millennium BC. It shared many cultural features with the Minoans.

The origins of the Minoan and Mycenaean peoples, however, have puzzled archaeologists for more than a century. It is widely believed that they derived from different ancestral populations.

Researchers reported the first genome-wide DNA sequence data on the Bronze Age inhabitants of mainland Greece, Crete and southwestern Anatolia[1]. They analyzed tooth DNA from the remains of 19 ancient individuals who could be definitively identified by archaeological evidence as Minoans of Crete, Mycenaeans of mainland Greece and people who lived in southwestern Anatolia.

Next, they compared the Minoan and Mycenaean genomes to each other and to more than 330 other ancient genomes and over 2,600 genomes of present-day humans from around the world.

The results show that Minoans and Mycenaeans were genetically highly similar – but not identical – and that modern Greeks descend from these populations. The Minoans and Mycenaeans descended mainly from early Neolithic farmers, likely migrating thousands of years prior to the Bronze Age from Anatolia, in what is today modern Turkey[2].

"Minoans, Mycenaeans, and modern Greeks also had some ancestry related to the ancient people of the Caucasus, Armenia and Iran," explained Lazaridis.

[1] Lazarides et al: Genetic origins of the Minoans and Mycenaeans in Nature – 2017
[2] Lazarides et al: Genomic insights into the origin of farming in the ancient Near East in Nature – 2015

When humans arrived, megafauna died

The late Pleistocene, from around 125,000 years ago, megafauna started to disappear. A new study puts the blame squarely on humans and our hominin relatives.

By looking at how mammals have changed in size over time, scientists discovered that, whenever humans are around, the mammals that disappear tend to be 100 to 1000 times bigger than those that survive[1]. The new analysis shows that this pattern occurred in every continent except Antarctica, and throughout at least the last 125,000 years.
“Size-selective extinction is a hallmark of human activity,” lead-author Smith says. In other words, when we’re around, big animals die.

The distribution of body size is generally related to the size of a land mass. Africa is smaller than Eurasia but bigger than the Americas, so you’d expect its animals to weigh in somewhere in the middle. But by the time hominins left Africa, the average mammals there were about 50 percent smaller than the average ones in either Eurasia or the Americas. For that reason, Smith thinks these size-specific collapses started well before the rise of Homo sapiens, and probably dates back to the origins of Homo erectus, roughly 1.8 million years ago. “That was the species that marked the shift from hominins that depend heavily on plants to ones that depend more on meat,” says Smith. “Being a good predator is a general feature of our genus.”

When hominins like Neanderthals and modern humans spread through Europe and Asia, the average mass of mammals there halved. When Homo sapiens later entered Australia, the mammals there became 10 times smaller on average. And when they finally entered the Americas, with effective long-range weapons in hand, they downsized the mammals there to an even steeper degree. By around 15,000 years ago, the average mass of North America’s mammals had fallen from 216 pounds to just 17.

Even during huge changes in climate, including several ice ages and warm spells, large mammals weren’t especially vulnerable. “When it got warmer or colder, it didn’t select for bigger or smaller mammals,” says Smith. “It’s only when humans got involved that being large enhanced your extinction risk.”

Smith calculates that if all the species that are currently threatened eventually go extinct, the largest mammal left on land will be the domestic cow. In terms of body size, our order will be back to where we were around 45 million years ago. “And that’s largely because of humans,” Smith says.

[1] Smith et al: Body size downgrading of mammals over the late Quaternary in Science - 2018

Maltese Dwarf Hippopotamus

The Maltese dwarf hippopotamus (Hippopotamus melitensis) is an extinct species of hippopotamus or pigmy hippo, remains of which have been found on Malta. It first arrived after the Messinian salinity crisis.
The Messinian salinity crisis was a geological event during which the Mediterranean Sea went into a cycle of partly or nearly complete desiccation and dessertification. It ended with the Zanclean Deluge, a flood that ensued when the Strait of Gibraltar opened and that must have refilled the Mediterranean Basin some 5.33 million years ago when water from the Atlantic Ocean again reclaimed the basin.

The absence of predators combined with a scarcity of food led to the dwarfing of the hippos. The majority of findings of this species on Malta are from Għar Dalam, a cave on Gozo famous for its Pleistocene fossil deposits. They stood just 80 centimeters high.

The Maltese dwarf hippopotamus lived during the Pleistocene, better known as the Last Ice Age that ended around 11,700 years ago.
Some think that dwarf hippopotamuses from Malta, Crete (Hippopotamus creutzburgi), Cyprus (Hippopotamus minor) and Sicily (Hippopotamus pentlandi) all belonged to the same species. The name Hippopotamus pentlandi has since then regularly used for the four species. However, the Sicilian species is somewhat larger than the species from Malta, but still smaller than the living species (Hippopotamus amphibius).

The Cyprus dwarf hippopotamus survived until the end of the Pleistocene or early Holocene. Evidence from an archaeological site at Aetokremnos continues to cause debate on whether or not the species was encountered by man[1].

[1] Grayson: Faunal extinction in an island society: Pygmy hippopotamus hunters of Cyprus in Geoarcheaology – 2000

Cretan Dwarf Deer

In a cave in Crete, archaeologists have discovered what is probably the earliest Greek art, dating back to the last Ice Age[1]. The artwork found in Asphendou Cave is the earliest known Greek portrayal of extinct animals and is more than 11,000 years old.
Speaking to the journal, Dr Thomas Strasser of Providence College (Rhode Island, USA) said: "This is the first palaeolithic art ever found in Greece and it’s significant because it deepens the history of art there by many thousands of years, and is like an eyewitness account of Ice Age Crete. Archaeological and palaeontological information, as well as new technologies unavailable to earlier scholars, offer evidence to confirm a palaeolithic date for the earliest carvings."

Located in the mountainous Sphakia region of western Crete, Asphendou Cave has been known for its petroglyphs, described by Strasser as "a confusing jumble of engravings that had previously eluded dating".

The confusion was caused because several layers of engraving were superimposed upon one another. Initially it was believed that the animal depictions were feral goats and possibly as late as the Bronze Age. However, archaeologists exposed the oldest layers, now showing the recently identified Cretan Dwarf Deer (Candiacervus ropalophorus), which became extinct more than 11,000 years ago.

With the use of photogrammetry, the depictions of the quadrupeds were recorded and then extracted. Then they were compared with those made from excavated Candiacervus remains.

The 37 deer engravings identified are about 5 centimeters long and the engravings shallow. They represent "a palaeolithic animal herd without ground line or background," Strasser said.

When fully grown the species stood about 40 centimeters at the shoulders, which makes it a textbook example of insular dwarfism[2], which also included the Cretan Dwarf Mammoth, the Cyprus Dwarf Elephant and the Tilos Dwarf Elephant. The Cretan Dwarf Deer had unusually long spatula-shaped antlers. Specimens found not far north of Asphendou in caves on the north coast of Crete are dated to between 21,500 and 11,000 years ago, which means that humans lived on Crete before the species went extinct.

[1] Strasser et al: Palaeolithic cave art from Crete, Greece in Journal of Archaeological Science - 2018. See here.
[2] Kolb et al: Growth in fossil and extant deer and implications for body size and life history evolution in BMC Evolutionary Biology - 2015. See here.

The lost world of island dwarfs and giants

Until 12,000 years ago, the native faunas on the islands of the Mediterranean were very different than they are now. They included pony-sized elephants, pig-sized hippos, dwarf gorals with continuously-growing teeth like those of rodents (Myotragus balearicus of Mallorca), dwarf deer with simplified antlers that are longer than their bodies (Candiacervus of Crete), giant rabbits (Nuralagus rex of Menorca) and giant dormice (Leithaia of Sicily and Malta). Those were the days of dwarfs and giants. The smallest elephant that ever roamed the Earth lived on Sicily (Palaeoloxodon falconeri). It had a shoulder height of about one meter and a mere 2-4% of the body mass of its mainland ancestor (Palaeoloxodon antiquus), one of the largest elephants to have roamed the Earth. The smallest hippo on record is from Cyprus (Hippopotamus minor), which had dwarfed to 4% of its ancestral size.

The largest mouse (Kritimys catreus) was native to Crete. It was at least eight times the size of its ancestor and would today be mistaken for a large rat. The giant dormouse of Sicily (Leithia melitensis) was up to almost fourteen times as heavy as its ancestor.

These dwarfs and giants were the norm, rather than exceptions. Once isolated on an island, large mammal species evolve dwarf sizes and small mammal species evolve giant sizes. The pattern is so consistent that ecologists call it the 'island rule'.
[Sicialian dwarf elephant compared to its present day cousin]
Food limitation appears to be an obvious factor. The absence of predators is also an essential factor. Absence of competition has perhaps the greatest effect. With no competitors animals are free to occupy new ecological niches that are appropriate for different body sizes and lifestyles.

Extinct dwarf and giant animal forms have been unearthed on practically all islands around the world, and the Mediterranean islands are no exception. Dwarf elephants in particular had extremely wide distributions in both time and space. They are known from about thirty islands, ranging from the Californian Channel Islands (Mammuthus exilis) in the west to Timor (Stegodon timorensis) in the east.

The dwarf elephant of the Greek island of Tilos (Palaeoloxodon tiliensis) may well have continued to exist into the Holocene and protohistoric age. See here. The Aetokremnos site on Crete is known for its rich fossil deposit containing many thousands of hippo bones from the Cyprus dwarf hippo (Hippopotamus minor), apparently in association with artifacts from Palaeolithic people.

Why did mammoths and mastodons really disappear?

Dinosaur went extinct some 65 million years ago. The rock layers of that time tell a story of a cosmic impact: iridium is found in a thin layer that marks the end of the Cretaceous era and the beginning of the Tertiary era. Which is why scientists call the event Cretaceous-Tertiary (or K-Pg). But it wasn't only iridium that was found in that layer, a similar anomaly was the presence of platinum.

Both anomalies represent the atmospheric fallout of rare elements resulting from an extraterrestrial impact.
Around 12,800 years ago, the mammoth, mastodon and saber-toothed tiger suddenly disappeared. This was the onset of the Younger-Dryas. Although early humans are blamed, nobody knows for certain what the exact cause of the extinction was. The discovery of widespread platinum at archaeological sites across the United States has provided an important clue in solving this enduring mystery[1].

“Platinum is very rare in the Earth’s crust, but it is common in asteroids and comets,” says Christopher Moore, the study’s lead author. He says the K-Pg dinosaur extinction was the result of a very large asteroid impact, while the Younger-Dryas onset impact is likely the result of being hit by fragments of a much smaller sized comet or asteroid, possibly measuring up to a kilometer in diameter. The Younger-Dryas impact event is not yet associated with any known impact crater.

He says the Younger-Dryas coincides with the end of the Clovis paleoindian culture and the extinction of more than 35 species of ice-age animals. Moore says that, while evidence has shown that some of the animals were on the decline before Younger-Dryas, virtually none are found after it. Moore thinks that this would indicate an extinction event for North America.

Current views tell us that the mastodon became extinct in the New World 130,000 years ago, but recently the bones of a mastodon were found under a freeway construction site in California. These bones were battered and broken by modern humans[2]. The problem is that Homo sapiens reached North America only about 15,000 years ago. So, you see, there's a problem. Scientists now speculate about a radical new early date for the arrival of ancient humans in America.

The problem can more easily be solved by stating that mastodons were still alive around 15,000 years ago.

[1] Moore et al: Widespread platinum anomaly documented at the Younger Dryas onset in North American sedimentary sequences in Scientific Reports - 2017
[2] Holen et al: A 130,000-year-old archaeological site in southern California, USA in Science - 2017. See here

Tilos Dwarf Elephant

When fossil remains of dwarf elephant or dwarf mammoths were found in the Mediterranean basin, these remains were once usually attributed to trade[1].
Two groups of remains of dwarf elephants have been found on the island of Tilos. Since no migration route between the any other island can be proved, the species should be named Tilos Dwarf Elephant (Elephas tiliensi). It was the latest paleoloxodontine to survive in Europe. They didn't become extinct until around 4000 BC, so this elephant survived well into the Holocene and thus was alive during the the start of the Egyptian civilisation.

The Tilos dwarf elephant is the first dwarf elephant whose DNA sequence has been studied. The results of this research are consistent with previous morphological reports, according to which it is more closely related to Elephas than to Loxodonta or Mammuthus[2].

The most recent research confirms that the origin of the Tilos and Cyprus elephantids is consistent with a lineage within the genus Elephas, while the DNA-sequence from the Cretan sample falls clearly within the mammoth clade[3]. Thus, the scientific name of the Cretan Dwarf Mammoth Mammuthus creticus rather than Elephas creticus, seems to be justified for this form.

[1] Theodorou, Symeonides : The excavations of the last ten years at Charkadio cave on Tilos Island, Dodekanese, Greece in The World of Elephants – 2001
[2] Poulakakis et al: Molecular phylogeny of the extinct pleistocene dwarf elephant Palaeoloxodon antiquus falconeri from Tilos Island, Dodekanisa, Greece in Journal of Molecular Evolution – 2002
[3] Poulakakis et al: Ancient DNA forces reconsideration of evolutionary history of Mediterranean pygmy elephantids in Biology Letters – 2006

Did dwarf elephants survive until the Bronze Age?

Earlier I wrote about the Cretan Dwarf Mammoth and the Cypriot Dwarf Elephant that once roamed the Mediterranean islands. On a beautifully decorated tomb wall of Rekh-mi-Re, vizier during the reigns of Thutmosis III and Amenhotep II (from about 1470 to 1445 BC), we can find a strange image: a small, tusked, hairy elephant, shown as being waist-high to the accompanying people[1].
[Part of Rekh-mi-Re's tomb]
Suppose that the elephant in Rekh-mi-Re's tomb is a depiction of one of the dwarf Mediterranean island-dwelling species. Most of the dwarf Mediterranean elephants were Pleistocene animals that were long extinct by the time of the Pharoahs, but one researcher noted that a population of dwarfed elephants (Elephas tiliensis) seems to have lingered on in isolation on the Greek island of Tilos (located between Rhodes and Kos)[2].
[Detail of image above]
Radiocarbon dating of the Tilos Dwarf Elephants apparently puts some of them as recent as about 4300 years old (+/- 600 years), meaning that they overlapped with the presence of Bronze Age people on the island[2]. If we stretch the dates to its absolute maximum, we get 4300 minus 600 minus 2017 is 1683 BC. As Rekh-mi-Re died around 1445 BC, we're still around 240 years short, but maybe the artist pictured a dwarf elephant as it was known to exist.

Therefore, the remote possibility exists that one or more of these dwarf elephants from Tilos were captured by ancient Aegeans and then traded between Aegeans, Near Eastern people and Egyptians – in fact, trade was already occurring between these regions during the late Bronze Age. This sequence of events might be the answer as to why an image dwarf elephant appears on a wall in a tomb of Rekh-mi-Re

[1] Rosen: Mammoths in ancient Egypt? in Nature – 1994
[2] Masseti: Did endemic dwarf elephants survive on Mediterranean islands up to protohistorical times? in La terra degli Elefanti – 2001. See here.

Cretan Dwarf Mammoth

The smallest dwarf mammoth, standing at about 1 meter at the shoulders, has been uncovered on the Greek island of Crete. As explained here, with little or no predators and limited amounts of food, insular dwarfism might occur in large mammals. In other words: insular dwarfism helps giants survive within the limits imposed by islands.

Over the course of less than 800,000 years — a short stint on an evolutionary scale — these dwarf elephantsare thought to have descended from larger European elephants, weighing 100 times as much, which lived on mainland Europe.

Scientists analyzed dwarf fossils first discovered in Crete more than a century ago[1]. Paleontologists have long argued whether the remains belonged to curvy-tusked mammoths or straighter-tusked elephants. Teeth discovered more recently in the same area in Crete now suggest the animal was in fact a mammoth (Mammuthus creticus). A newly found foreleg bone suggests it was the smallest mammoth known, standing little over a meter high at the shoulders and weighing only approximately 300 kilograms, making it about the size of a modern baby African or Asian elephant.
These dwarf mammoths were not woolly mammoths. "When most people think of mammoths, they think of woolly mammoths," lead-scientist Victoria Herridge said. "We think this dwarf was more adapted to warmer environments, more in appearance like modern African or Asian elephants, with a sparse covering of hair, although they would have had curvy tusks like all mammoths."

The Cretan mammoth is the first evidence for extreme island dwarfism in mammoths. It would have been comparable in size to the smallest dwarf elephant known, the extinct Cyprus dwarf elephant (Palaeoloxodon cypriotes) from Crete or the Maltese dwarf elephant (Palaeoloxodon falconeri )from Sicily and Malta, which stood only about 1 m high at the shoulder and weighed only approximately 240 kg.
The fossils suggest this dwarf mammoth was descended from one of the first mammoth species to arrive in Europe from Africa. As such, the researchers suggest dwarf mammoths may have evolved much earlier than previously thought — possibly as far back as 3.5 million years ago.

Given the scant fossils and the uncertainty about Crete's environment during this period, not much is known about how this dwarf might have lived. Still, its teeth do suggest it browsed on shrubs as opposed to grass like woolly mammoths.

Insular mammoths are further known from Sardinia (Mammuthus lamarmorai) and the Californian Channel Islands (Mammuthus exilis), as well as Wrangel Island (northeast Siberia) and St Paul (Pribilof Islands, Alaska) (Mammuthus primigenius).

[1] Herridge, Lister: Extreme insular dwarfism evolved in a mammoth in Proceedings of the Royal Society B – 2012

Cyprus Dwarf Elephant

The Cyprus dwarf elephant (Palaeoloxodon cypriotes) is an extinct species of elephant related to the living Asian elephant. It was among the only mammals on Cyprus before humans arrived, and it is thought the Cyprus dwarf elephant came to the island during the last Ice Age.

This species was only about one meter in height and is a case of 'insular dwarfism'. The factors responsible for the dwarfing of island mammals are thought to include the reduction in available food, a reduction or even absence of predation and competition. The Cyprus dwarf elephant became extinct around 11,000 BC.
Believed to be descended from the straight-tusked elephant, this much smaller species inhabited Cyprus. Closely related species roamed some other Mediterranean islands. Remains of the Maltese dwarf elephant (Palaeoloxodon falconeri) were found on Sicily and Malta (at Għar Dalam, pronounced 'ar dàlam' in Maltese and meaning 'Cave of Darkness'), while those of the Cretan dwarf elephant (Palaeoloxodon chaniensi) were found in Stylos and in the Vamos cave, near Chania, western Crete.

The estimated body weight of the Cyprus dwarf elephant was only some 200 kilogrammes, a staggering weight reduction of about 98% from its ancestors which weighed about 10 tonnes or more. Their molars however were about just 40% of the size of the mainland straight-tusked elephants.

Remains of the first Cyprus dwarf elephant were first discovered by British palaeontologist Dorothea Bate (1878–1951) in 1902. She found the fossilized bones of the elephant in a cave in the Kyrenia hills of Cyprus.
Human interference leading to the extinction to the Cyprus dwarf elephant has been a controversial topic over the last couple of decades. A rising theory is that most of the elephants died during the settlement of the Mediterranean islands. A claim to support this theory is that the early Greek settlers thousands of years later incorporated the dwarf elephant into their mythology calling them Cyclopses (one-eyed monsters)[1]. An alternative theory is that these early Greeks found a skull of an extinct Cyprus dwarf elephant and, not knowing that it belonged to an extinct elephant, thought it must belong to a mythical figure because the central nasal cavity - where the trunk was attached - could easily have been mistaken for a single eye socket.

[1] Massetti: Did endemic dwarf elephants survive on Mediterranean islands up to protohistorical times? See here.