Month: September 2019

Island Weirdness #51 — Tainotherium valei

Like much of the Caribbean, Puerto Rico originated as part of a Mesozoic volcanic island arc. While in theory this could have resulted in the region retaining some relict populations of weird Cretaceous species, there’s a major reason this didn’t actually happen: the asteroid impact event 66 million years ago. The proximity to Chicxulub would have been devastating to the proto-Caribbean at the time, with tsunamis as high as 500m (1640′) battering the islands and destroying practically everything that lived there at the time.

Afterwards subsidence in the early Cenozoic submerged many of the islands and drowned whatever was left, so it wasn’t until later tectonic uplifting that land re-emerged and was able to be recolonized by species via rafting and island hopping (or possibly via a short-lived land bridge).

Caviomorph rodents arrived from South America around the start of the Oligocene, about 33 million years ago, and became very successful due to being some of the only land mammals present on many of the islands. The only modern survivors of this lineage are a handful of hutias, but in the past they were much more diverse — and some of them were giants. 

Tainotherium valei lived in Puerto Rico during the Late Pleistocene and early Holocene, and while it wasn’t quite the largest of the giant hutias it was still enormous. It’s only known from a single partial leg bone, so its full size is difficult to estimate, but it was probably somewhere around 80cm tall at the shoulder (2’7″) and weighed about 100kg (220lbs) – similar in size to a modern black bear.

And that leg bone is especially unusual, showing anatomical adaptions associated with tree-climbing. This is strange for such a huge heavy mammal, but it may have been an ecological equivalent of something like the giant Malagasy lemurs, a slow-moving animal that climbed up trees to feed and regularly traveled over the ground from one feeding site to another.

During the Pleistocene lower sea levels meant most of the Puerto Rican archipelago was part of a much larger landmass that also included most of the nearby Virgin Islands, and the predominate climate at the time was a dry savanna. As sea levels rose at the start of the Holocene the climate shifted wetter and Puerto Rico became densely forested. This would have been advantageous for a tree-climbing animal like Tainotherium, so it was likely still around when the first humans arrived in around 3000-2000 BCE.

Unfortunately these early settlers appear to have burned large amounts of the forests for the first few centuries of their presence, and such widespread habitat destruction would have driven this giant rodent extinct very quickly.

Island Weirdness #50 — Caracara tellustris

Jamaica is unusual among the Caribbean islands for having had relatively few predatory birds.

One of the few known fossil species is Caracara tellustris, a close relative of the modern crested caracaras that probably evolved in the mid-Pleistocene between about 1.2 and 0.4 million years ago.

About 60-65cm long (2′-2’2″), it was similar in body size to larger individuals of its living relatives but was heftier built and had slightly longer legs, and its wings were reduced enough that it was either a very weak flier or entirely flightless.

It lived only in the dry scrubland around the southern coast of the island, and probably mainly preyed on reptiles, small rodents, and crabs using its strong legs — a lifestyle very similar to the modern secretarybird. Like other caracaras it would have also opportunistically scavenged on carrion, which there would have been little competition for.

The known remains of Caracara tellustris date to as recently as 100 CE, showing that it existed well into the Holocene and survived through the initial arrival of humans on its island home (about 4000 BCE). This is likely due to its inhospitable hot, arid, and thorny habitat, where it would have been left relatively undisturbed, and it may even have persisted until the time of European colonization in the 1500s.

Unfortunately the scrubland was also very limited in size and the Jamaican caracara would have always been quite a rare species. If it was still around by then it would have faced a combination of introduced predatory mammals and habitat destruction by agriculture, which would have driven it into extinction so quickly its existence was never even noticed by naturalists at the time.

Island Weirdness #49 — Sloth-Monkeys & Fighting Ibises

Jamaica is the third largest island in the Caribbean, and much like Cuba it originated as part of a Late Cretaceous volcanic island arc. It began to subside during the Eocene and was completely submerged for a large portion of the Cenozoic, then was uplifted again in the early-to-mid Miocene, reaching close to its present-day size around 13 million years ago.

Few land mammals ever colonized the island prior to human influence, and most of the known remains are from rodents. But another group did make it onto Jamaica, and became something especially weird.

A stylized illustration of an extinct titi monkey. It has long soft fur and a very long tail.
Xenothrix mcgregori

Xenothrix mcgregori is a primate only known from fragmentary remains, but what is known of its skeleton shows a unique combination of features for a New World monkey. It had a reduced number of teeth in its jaws, with enlarged molars, and oddly-shaped heavily-built leg bones that resemble those of slow quadrupedal climbers like lorises.

It was probably about 70cm long in total (2’4″), including the tail, and is thought to have lived a lot like a tree sloth, spending most of its time moving slowly around in the trees and possibly even feeding while hanging upside down.

Its anatomy was so ununsual that its evolutionary relationships were a mystery until ancient DNA was recovered from subfossil bones and confirmed it was actually a titi monkey very closely related to the genus Cheracebus. Its ancestors probably arrived on Jamaica in the late Miocene, around 11 million years ago, and it had some close relatives on a couple of other Caribbean islands — the terrestrial Paralouatta on Cuba, and Antillothrix and Insulacebus on Hispaniola — although they likely all independently colonized the Caribbean via different rafting events from South America.

A stylized illustration of an extinct flightless ibis. It has stout legs, and has its wings raised as if threatening to hit something with its heavy club-like arm bones.
Xenicibis xympithecus

Another inhabitant of Jamaica was an equally strange bird.

Xenicibis xympithecus was one of only two lineages of ibis ever known to have become completely flightless (the other being Apteribis from Hawaii).

Around 60cm tall (2′), it had some of the most unique wings of any bird. The hollow bones were thickened, its forearm was proportionally short, and the hand was modified into a large heavy “club” — and blunt-force injuries on some of these birds’ remains suggest that they used their wings as weapons when fighting, clobbering each other with powerful blows.

Radiocarbon dating suggests the Xenothrix monkeys survived well into the Holocene, until around 1100 CE. Since various groups of humans had been present on Jamaica since about 4000 BCE the sloth-monkeys must have coexisted with them for several millennia, and their extinction may have been caused by more of a “slow fuse” of gradual habitat destruction than direct exploitation.

Dating on Xenicibis‘ extinction is less precise, with the youngest known remains being somewhere between 10,000 and 2200 years old. It may have still been around when the earliest humans arrived, but unlike the native monkeys it seems like it didn’t last long beyond that point.

Island Weirdness #48 — Chunky Cranes & Terror Owls

Like many other isolated islands ancient Cuba lacked any large land predators, allowing some birds to exploit more terrestrial lifestyles.

A stylized illustration of an extinct flightless sandhill crane. It has a somewhat chunkier beak than its modern relatives, along with smaller wings and thicker legs.
Grus cubensis

The Cuban flightless crane (Grus cubensis, or possibly Antigone cubensis) lived during the Late Pleistocene and Holocene. It was probably a descendant of the sandhill crane — and although an endemic variety of sandhill crane still exists in Cuba today, the two aren’t directly related to each other and instead are the result of two different colonization events.

It was about the same size as modern sandhill cranes, around 60cm tall at the back (2′) with a full height of about 1m (3’3″), but it was much more heavily built. It had stockier legs and a thicker beak, suggesting it may have been specialized for a different ecological niche than its ancestors, and its wings were reduced enough that it was probably completely flightless.

A stylized illustration of an extinct giant owl. It has proportionally short wings and long stilt-like legs.
Ornimegalonyx oteroi

And, once again, there was also a weird owl on this island.

Ornimegalonyx oteroi was closely related to true owls in the genus Strix, and in a great example of convergent evolution did the exact same thing as the Grallistrix stilt-owls — it evolved into a long-legged short-winged ground-based apex predator.

But it was almost twice the size of its Hawaiian cousins, measuring about 1.1m tall (3’7″) and potentially being the largest owl to ever exist. Its remains were so big, in fact, that they were initially mistaken for those of a terror bird.

It was powerfully built and was probably a good runner, mainly preying on giant rodents and dwarf ground sloths. While its wings and flight muscles were reduced it might not have been entirely flightless, and it may have been still been capable of turkey-like short bursts of flight.

Three other species of Ornimegalonyx also stalked ancient Cuba at the same time, varying slightly in size from each other and probably each specializing in a different size class of prey.

Remains of both of these birds have been found in natural petroleum seeps on the northern coast of Cuba that date to as recently as about 6000 years ago, around the same time that humans first arrived. After that point they probably both went extinct very quickly — the flightless cranes were probably actively hunted and eaten into extinction, and the terror owls would have disappeared as their prey species dwindled away due to the same hunting pressures.

Island Weirdness #47 — Megalocnus rodens

Just 21km south of the Bahamas (13 miles), Cuba is the biggest island in the Caribbean and has a complex geological history. It originated as part of a volcanic island arc in the Late Cretaceous and during its existence in the Cenozoic it was colonized by a richer variety of mammals than the Bahamas ever had, including rodents, the enigmatic solenodons and nesophontes, and ground sloths.

The Caribbean ground sloths were all part of the megalonychid lineage — which eventually reached North America and produced giants — and they arrived on Cuba by the early Miocene, about 20 million years ago.

Megalocnus rodens lived during the Late Pleistocene and Holocene, between about 125,000 and 5000 years ago. It had unusually rodent-like front teeth, and while it was dwarfed compared to its mainland relatives it was actually one of the largest of the Cuban ground sloths — close to the size of a modern black bear, about 80cm tall at the shoulder (2’5″).

Subfossil remains show that Megalocnus survived well into the Holocene, and there’s been speculation that it may even have still been around in the highland forests as late as the time of European colonization in the 1500s.

However, radiocarbon dating of remains has given no dates younger than about 5000-4000 years ago, about 1000 years after the earliest arrival of humans in Cuba.

Island Weirdness #46 — Tyto pollens

The islands of the Caribbean looked very different during the Pleistocene ice ages, when changing sea levels meant larger areas of land were exposed — and one of the most extreme examples of this was the Bahamas, much larger than they are today, with most of the Bahaman Banks exposed and over 10 times more land area.

Tyto pollens was an enormous barn owl, around 1m tall (3’3″), the size of a large eagle and one of the biggest owls to ever exist. It lived in old-growth pine forests on what is now the Andros Island archipelago and preyed mostly on Bahamian hutias, which were originally the only terrestrial mammals in the Bahamas.

It probably evolved in Cuba, and colonized the Bahamas shortly after the hutias did, sometime in the last 400,000 years during a glacial period when a particularly low seal level meant the islands were only about 30km apart.

It was the main nocturnal predator in the Bahamas, and much like its older Italian relative Tyto gigantea it also had a giant hawk counterpart in the daytime: the huge Titanohierax.

Although many popular online sources refer to Tyto pollens as being flightless, it actually had large robust wings and could probably fly quite well. This might be due to some confusion between it and a completely different giant Caribbean owl, Ornimegalonyx.

The Lucayan people probably reached Andros Island sometime around 1000 CE, and coexisted with the giant owls for several centuries. It was only after European arrival in the 1500s and the felling of their forest habitat that they seem to have vanished.

Local legends of an owl-like creature called the chickcharney may have been inspired by historical encounters with Tyto pollens, and suggest that they were aggressively territorial.

Island Weirdness #45 — The Pedro González Dwarf Deer

Isla Pedro González is part of the Pearl Islands in the Gulf of Panama, about 48km (30 miles) offshore. It was formed after the end of the last glacial period, as steadily rising sea levels cut it off completely from mainland Panama about 8500 years ago — and isolating the population of deer that lived there.

Although Pedro González is the third largest of the Pearl Islands it’s still fairly tiny, just 6.5km long (4 miles). As a result of this small space, limited available food supplies, and a lack of any large predators, these deer rapidly shrank down into a dwarfed form to survive. By 6000 years ago they were the size of a small dog, just 35-40cm tall at the shoulder (1’2″-1’4″) and weighing less than 10kg (22lbs).

The Pedro González dwarf deer haven’t been given any official scientific name just yet, but since they’re thought to be descendants of brocket deer they’d be a part of the genus Mazama, either as their own separate species or as a subspecies — similar to the larger native deer on nearby Isla San José, which are probably their closest living relatives.

Paleoindian settlers arrived on Pedro González just over 6000 years ago, and we know they hunted and ate the tiny deer because all the known remains come from a preserved trash heap and show signs of human butchering and chewing.

Younger deposits have gradually less and less deer bones, and although those particular settlers had left again by about 5500 years ago the damage was already done — layers from another group of people about 2300 years ago show no deer bones at all, so the dwarf deer had to be already extinct by that time.

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

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

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

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

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

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

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

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

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

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

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

Island Weirdness #43 — Flightless Flies

One of the most defining features of the true flies is a pair of wings, but various different lineages have actually become flightless.

Flightlessness is very rare in the long-legged fly family (Dolichopodidae), however, with only about 12 out of over 5000 species known to have lost functional wings — and eight of those are endemic to the Hawaiian islands.

The Koʻolau spurwing long-legged fly (Emperoptera mirabilis, sometimes classified as Campsicnemus mirabilis) was found only on Mount Tantalus in the southern Koʻolau Range of Oʻahu, close to Honolulu. About 2mm long (>0.1″), its wings were reduced to thin stiff spines, and it moved around by walking and hopping in leaf litter in the moist cool forest at elevations of about 300m (~1000ft).

Like most other long-legged flies it would have been predatory, hunting other tiny invertebrates.

The Koʻolau spurwing was actually still common on Tantalus as recently as the early 1900s, but multiple searches since the 1980s have failed to find any more of them at all. The species is most likely completely extinct, probably due to a combination of predation from invasive ants and habitat destruction from feral wild boar rooting up the forest floor.

Of the other flightless Hawaiian long-legged flies several other species are now possibly extinct — only one out of the five known Emperoptera species still definitely survives on the highest slopes of Mount Kaʻala, and one of the three Campsicnemus is either very rare or also extinct.

The Hawaiian islands also have three endemic species of flightless crane fly in the genus Dicranomyia, all of which are incredibly rare.

Island Weirdness #42 — Tall Owls & Short Ibises

The complete lack of land mammals on the Hawaiian islands left the terrestrial predator niches available to birds — and it was owls who ended up taking advantage of that role in the ecosystem.

The Grallistrix owls were found on Kauaʻi, Oʻahu, Molokaʻi, and Maui, with each island having its own endemic species. They were a type of true owl, probably descended from a species of Strix, and developed especially long legs that led to their nickname of “stilt-owls”.

A stylized illustration of an extinct owl. It has short wings and very long stilt-like legs.
Grallistrix geleches

The Molokaʻi stilt-owl (Grallistrix geleches) was the largest of the four known species, about 60cm tall (2′). Although it had proportionally short wings it was still capable of flying, and probably specialized in stalking and ambushing smaller birds like Hawaiian honeycreepers in the dense forests.

(These owls were also the inspiration for the pokémon Decidueye!)

A stylized illustration of an extinct flightless ibis. It has a downward-curving beak, small wings, and relatively short thick legs compared to other ibises.
Apteribis glenos

Meanwhile the forest floor insectivore niche was occupied by Talpanas on Kauaʻi, but on the other main islands a different type of bird took up the same role.

Apteribis was an ibis closely related to the modern white ibis and scarlet ibis, with three different species found on the islands of Maui, Molokaʻi, and Lānaʻi.

The Moloka’i flightless ibis (Apteribis glenos) was a typical example of the genus, about 50cm long (1’8″). It was flightless, with reduced wings, and had unusually short stocky legs that gave it proportions much more like a kiwi than an ibis. And it probably lived very much like a kiwi, too, probing around in the forest litter with its beak searching for snails and other invertebrates.

We even have an idea of the coloration of these birds, thanks to subfossil remains with preserved feathers. They seem to have been brown and beige, similar to the juvenile plumage of their close relatives.

The arrival of humans at least 1000 years ago would have unfortunately been devastating to both the stilt-owls and the flightless ibises. The combination of hunting, habitat destruction, and invasive dogs, pigs, and rats attacking them and their ground-based nests probably drove them all into extinction very quickly.