Island Weirdness #21 – The Malagasy Mini-Hippos

Much like elephants, hippos have frequently made their way onto islands and developed dwarfed forms. These mini-hippos are mostly known from the Mediterranean, but further south they also occurred on Madagascar.

Hippopotamus madagascariensis (also sometimes called Hexaprotodon madagascariensis or Choeropsis madagascariensis; its exact classification is uncertain) was similar in size and appearance to the modern West African pygmy hippo – which it might have been closely related to, or may have just ended up resembling through parallel evolution.

Standing under 1m tall at the shoulder (3′3″) and measuring about 1.8m long (5′11″) it lived in the forested highlands and was much more terrestrial than its larger cousins. Its eyes were further down on the sides of its head, and it was better adapted for walking and running around on land, with proportionally longer legs and a more digitigrade posture.

It also had an unusually small brain for its size – about 30% smaller than expected – which may have been an energy-saving adaptation.

Two other species of dwarf hippo have been identified on Madagascar – the similarly-sized but more aquatic Hippopotamus lemerlei in the west of the island, and the larger and poorly-known Hippopotamus laloumena in the east. It’s not clear when exactly the ancestors of these various hippos first arrived on the island, and they may even represent three independent colonization events.

The last known subfossils date to about 1000 years ago, but surprisingly accurate accounts of similar creatures in Malagasy folklore raise the possibility that small isolated populations of these hippos may have survived into more recent times. One of the most intriguing examples is the kilopilopitsofy, described as having large floppy ears and supposedly being sighted as recently as the 1970s.

Island Weirdness #20 – Megaladapis

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.

Island Weirdness #19 – Archaeoindris fontoynontii

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.

Island Weirdness #18 – Palaeopropithecus

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 humanssubfossil 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.