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.
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.
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.
Standing at an adult height of about 1.1m tall (3′7″), they were smaller than any population of modern humans and are thought to represent an unusual case of insular dwarfism.
They also had much smaller brains than would be expected for their size, similarly to the miniature hippos of Madagascar, which was probably an energy-saving adaptation in an island environment with limited resources, since brains are metabolically expensive organs. An area of their brains associated with higher cognition was about the same size as in modern humans, however, so they weren’t necessarily less intelligent – stone tools and butchery marks on dwarf elephant bones suggest they were cooperatively hunting, and there’s also possible evidence of fire use for cooking.
It’s not clear exactly where they belong on the human family tree, and attempts at extracting DNA from the known remains have so far failed. They might be descendants of a population of Homo erectus who arrived on Flores about 1 million years ago, or they may even have been part of a much older unknown lineage that dispersed from Africa over 2 million years ago.
Although they were initially thought to have lived on Flores from 190,000 years ago up to about 12,000 years ago, more accurate dating of the cave where their skeletal remains were discovered suggests they actually disappeared about 50,000 years ago – about the same time that modern humans arrived on the island.
While some of the lemurs of Madagascar were surprisingly sloth-like, another lineage of these primates evolved in a different direction entirely.
Megaladapis was built similarly to a koala, with a rather squat body and hands and feet adapted for clinging onto branches. Three different species have been identified, with the largest measuring around 1.5m long (4′11″).
Its skull resembled that of a cow, with eyes on the sides of its head, a long snout, and powerful chewing jaw muscles for processing its diet of tough leaves. It also had a very unusual nose for a primate, with nasal bones similar to rhinos – suggesting it may have had an enlarged prehensile upper lip used for grasping foliage.
Much like some of the sloth lemurs, carbon dating of subfossil remains indicates that these “koala lemurs” may have survived until surprisingly recently – possibly only going extinct about 500-600 years ago.
The small and medium-sized sloth lemurs of Madagascar were incredibly convergent with modern tree sloths, and the biggest member of the group likewise seems to have been the closest they came to evolving a ground sloth equivalent.
Archaeoindris was the largest known lemur – and one of the largest primates – similar in size to a modern gorilla at about 1.5m tall (4′11″). It would have been a slow-moving animal which fed mostly on leaves, and while it was still capable of climbing around in larger trees it was probably much too bulky for upside-down suspension like its smaller relatives, and would likely have had to regularly traverse the ground to reach new feeding sites.
It seems to have been a fairly rare member of the ecosystem, living only in the Central Highlands, and the last known remains date to just over 2000 years ago – around the same time that humans first reached that area of the island. Sadly a combination of factors such as the giant lemurs’ slow reproductive rate, habitat loss, and hunting pressure was too much for their population to recover from all at once, and they probably went extinct very soon after that date.
The island of Madagascar has been isolated from other landmasses for almost 90 million years, and as a result there are many lineages present there found nowhere else on Earth.
Lemurs are one of the island’s most famous residents, having arrived from Africa via a rafting event sometime early in the Cenozoic and evolving to fill the ecological niches occupied elsewhere by monkeys and apes. But while there are around 100 lemur species alive today, there used to be more before the arrival of humans – subfossil remains from the last 25,000 years hint at an ecology with even greater diversity, and types of lemurs much larger than any still living today.
The sloth lemurs, as their name suggests, resembled modern sloths in a remarkable case of convergent evolution. With long limbs and long hooked fingers and toes they were adapted for swinging through trees and hanging from branches, feeding on a wide range of plant material such as leaves, fruit, and seeds.
Palaeopropithecus was one of the larger members of this group, and the most specialized for sloth-like upside-down suspension. Three different species have been identified, with the biggest (Palaeopropithecus maximus) possibly measuring around 1m long (3′3″).
It probably spent almost its entire life in the trees, and would have been slow and awkward on the ground. Malagasy folklore about a creature known as the tretretretre or tratratratra, which couldn’t navigate on smooth flat surfaces, may even represent a cultural memory of Palaeopropithecus from before its extinction – which may have happened as recently as within the last 500-1000 years.
