mammal – Page 12 – Nix Illustration

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 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.

Island Weirdness #15 – Deinogalerix

Thanks to the absence of large terrestrial carnivores on the Gargano-Scontrone island(s) during the Late Miocene, animals that were usually small had the opportunity to become larger, moving into the vacant ecological niches and evolving into predators unlike anything existing on the mainland.

Deinogalerix was a giant member of the gymnures – close relatives of hedgehogs without the quills – with a proportionally big head and a long snout full of large fangs at the front and bone-crushing molars at the back.

Several different species have been found, with the largest Deinogalerix koenigswaldi having a head-and-body length of around 60cm (2′). Along with its tail that would have made it at least 90cm long (2′11″), making it the biggest eulipotyphlan ever discovered.

It would probably have hunted smaller mammals, birds, and reptiles, filling a niche on the island similar to dogs or cats.

Island Weirdness #14 – Hoplitomeryx

During the mid-Miocene, about 15 million years ago, a region of central and southeast Italy around Gargano and Scontrone was cut off from the mainland by rising sea levels.

For the next 7-10 million years this island (or perhaps a cluster of islands) was left isolated, and an unusual ecosystem developed known as the “Mikrotia fauna”. With the island starting off lacking large predators, small herbivorous animals like rodents, pikas, and waterfowl became huge – and then small predators like gymnures and carnivorous birds also grew to keep up with the increasing size of their prey.

One of the strangest residents of the island(s) was Hoplitomeryx, an early type of ruminant that resembled a deer or pronghorn. Nicknamed the “prongdeer”, it had a total of five horns on its head and large protruding fangs similar to some modern deer.

Multiple species of Hoplitomeryx have been identified, representing four different size classes ranging from huge down to tiny insular dwarfs. The largest is estimated to have been similarly sized to modern moose, standing around 2m tall at the shoulder (6′6″), while the smallest would have been under 50cm (1′8″).

Each of these size classes was specialized for slightly different ecological niches, eating different types of vegetation to avoid directly competing with each other for the limited amount of food on the island.

Island Weirdness #13 – Tiny Elephants On Parade Part 1: Japan

Part of the “island rule” is that large animals often become smaller – and no group seems to exemplify this more than the elephants.

Although they’re the largest living land animals today, and in the past included some of the largest known land mammals ever, ancient elephants also frequently ended up on islands thanks to their ability to swim long distances. They produced many different dwarfed forms around much of the world, and a few of them will be featured intermittently throughout both months of this theme.

The earliest known examples were the stegodontids of Japan in the early Miocene. These animals weren’t quite true elephants, instead being close evolutionary cousins to them, and had two small additional tusks in their lower jaws similar to the related gomphotheres.

A stylized illustration of an extinct dwarf elephant. It has four tusks – two short straight ones in its upper jaw, and another two smaller ones in its lower jaw. — Stegolophodon pseudolatidens

Stegolophodon pseudolatidens first arrived in Japan about 18 million years ago, and within just 2 million years they’d developed into insular dwarfs that were probably around 2m tall at the shoulder (6′6″)– still reasonably large, but only about 60% the size of their mainland relatives.

A stylized illustration of an extinct dwarf elephant. It has long curving tusks and small ears. — Stegodon aurorae

Much later in the Early Pleistocene another small almost-elephant appeared in Japan. Living between about 2 million years ago and 700,000 years ago, Stegodon aurorae was about the same size as the then-extinct Stegolophodon but probably wasn’t descended from them. Instead it was probably the result of a separate arrival and dwarfing of a larger Stegodon species from mainland Asia.

Island Weirdness #12 – Anatoliadelphys maasae

The Pontide island 43 million years ago had no placental mammalian carnivores, and in their absence a different type of mammal took up the main predatory niches – the metatherians.

Metatherians today are represented solely by marsupials, but there were once many other branches of this mammal lineage. One group present in Europe for much of the Cenozoic were the herpetotheriids, and these rat-sized animals seem to have also occupied the small predator and opportunistic omnivore niches on the Pontide island.

And then there were the bigger metatherians.

Anatoliadelphys was a specialized carnivore, with strong jaws and bone-crushing teeth similar to the modern Tasmanian devil. It had a body size similar to a domestic cat, giving it a total length of up to 1m long (3′3″), and had opossum-like grasping digits and a prehensile tail indicating it was capable of climbing trees.

It was initially thought to be descended from another type of metatherian found in Europe at the time, the peradectids, but a later study came up with a more surprising result for its evolutionary relationships. It instead may be closer related to the polydolopimorphs, a group known mainly from South America. Quite how its ancestors got as far as Turkey is a bit of a mystery, but it’s possible they’d previously dispersed into Africa at a time when the continents were still much closer to each other than they are today, and then spread northwards until they reached the Pontide island.

The main problem with this hypothesis is the current lack of any polydolopimorphans in the African fossil record – but the African Eocene is still poorly understood, so there may be some metatherian fossils yet to be discovered that could fill in this gap.

Island Weirdness #11 – Hilalia

During the mid-Eocene, about 43 million years ago, the Pontide region of modern day north-central Turkey was an island located between the Paratethys Sea to the north and the Tethys Ocean to the south.

This island had an ecosystem of native mammals unlike anything existing today, with a unique mixture of species whose ancestors had arrived over several million years via island-hopping or temporary land connections with Europe, Africa, and Asia. There were large rhino-like embrithopods, cat-sized metatherian predators, early primates, early bats, and “enigmatic” small insectivores – but the island completely lacked any of the rodents, carnivorans, creodonts, perissodactyls, or artiodactyls which were dominating the rest of Eurasia.

But one of the most surprising inhabitants of the island were the small herbivores – a genus called Hilalia that represented a type of early ungulate known as pleuraspidotheriids. Resembling deer-dogs, this group had originated in Europe during the Paleocene and had gone extinct there around 13 million years earlier than the date of the Pontide remains, making them living fossils at the time.

These survivors of an archaic lineage thrived on their isolated island refuge and there were at least four or five species of Hilalia at different sizes, suggesting they’d diversified to each occupy a slightly different niche in their ecosystem. It’s hard to accurately measure their body size from their very fragmentary remains, but they may have ranged from around 25cm to 60cm in total length (~10″- 2′).

Island Weirdness #10 – The Kogaionids

Multituberculates were a group of rodent-like mammals that originated back in the Early Jurassic, at a point on the mammalian family tree between the origin of monotremes and the earliest therians (represented today by marsupials and placentals).

While they were an incredibly successful group, found around the world in large numbers, in Late Cretaceous Europe multis had become incredibly rare and restricted to just a single place: Hațeg Island.

Isolated there, they evolved into a unique family known as the kogaionids, diverging from their ancestral mostly-herbivorous diet to instead become specialized insectivores with distinctly red iron-pigmented teeth and huge blade-like lower premolars.

Skull of Barbatodon, from fig 2 in Smith T, Codrea V (2015) Red iron-pigmented tooth enamel in a multituberculate mammal from the Late Cretaceous Transylvanian “Haţeg Island.” PLoS ONE 10(7): e0132550. doi: 10.1371/journal.pone.0132550 | CC-BY-4.0

Some of them also had oddly domed skulls and proportionally tiny brains, along with highly acute senses of smell, eyesight, balance, and motor control.

Kogaionon ungureanui was one of the first kogaionids to be discovered, and gives its name to the group as a whole. Although known only from a skull, it was probably rat-sized, around 30cm long (~12″).

Unusually for island species, which are often ecologically fragile and vulnerable, the kogaionids’ insectivorous habits allowed them to successfully survive through the end-Cretaceous mass extinction 66 million years ago while the Hațeg dinosaurs and pterosaurs perished. And when conditions changed and their island home became reconnected to the rest of Europe they rapidly spread out and became common across the entire region for a further 10 million years, only finally disappearing in the early Eocene about 56 million years ago.

Rayanistes

Remingtonocetids were an early branch of the whale evolutionary family tree, known from about 49-41 million years ago and splitting off somewhere between the famous “walking whale” Ambulocetus and the more oceanic protocetids. With otter-like bodies, tiny eyes, and long gharial-like snouts, they lived in near-shore shallow marine habitats and probably swam using a combination of their hind feet and tails.

They were initially found only in Pakistan and India, but then Rayanistes afer here was discovered all the way over in Egypt – suggesting that these early whales were much more widespread than previously thought, dispersing through the Tethys Sea at about the same time as their protocetid cousins.

Dating to the Middle Eocene (~45-41 mya), Rayanistes was probably about 2.5m long (8′2”). It had powerful hindlimb musculature that would have given it a very strong kicking swimming stroke, but it probably couldn’t actually support its own weight on land since its femur wasn’t very well anchored into its pelvis.

Eons Roundup

This year I’ve been lucky enough to have some of my work featured in several PBS Eons videos – and I even recently got the opportunity to do some custom images for them! Since I didn’t show any of these off at the time, here they are now:

The basal temnospondyl amphibian Iberospondylus, from “When Giant Amphibians Reigned”
https://www.youtube.com/watch?v=rGthtRZl8B0

The flying paleognath bird Lithornis, from “When Birds Stopped Flying”
https://www.youtube.com/watch?v=M3h05ajJw0o

The ground sloth Nematherium, from “How Sloths Went From the Seas to the Trees”
https://www.youtube.com/watch?v=pt9tBtQoAHo

Happy new year, everybody!