afrotheria – Nix Illustration

Arsinoitherium

Arsinoitherium zitteli was a large herbivorous mammal living in what is now northern Africa during the late Eocene and early Oligocene, about 36-30 million years ago.

Despite looking like a double-horned rhino this resemblance was only superficial, and for most of the 20^th century it was actually the only known representative of an entire order of mammals – the embrithopods – with its wider evolutionary relationships being unknown. Since the 1970s, however, more members of this group have been discovered and embrithopods are now understood to be afrotheres, a very early offshoot of the tethythere lineage, with their closest living relatives being modern elephants and sirenians.

Arsinoitherium was by far the most abundant embrithopod, with numerous fossil remains making it one of the most completely known African fossil mammals. It stood around 1.8m tall at the shoulder (6′), similar in size to modern white rhinos, and would have been a massively-built slow-moving animal with elephant-like columnar limbs.

Its pair of enormous nose horns (and smaller brow horns) were structurally more similar to those of bovids than rhinos, with large hollow bony cores that probably bore thick keratinous sheaths that would have increased their apparent size even more. Both males and females appear to have had these horns, and muscle attachments at the back of the skull suggest Arsinoitherium could powerfully swing its head upwards – possibly wrestling with each other in combat over territories, competing for mates, or in establishing dominance hierarchies.

Postschizotherium

Postschizotherium intermedium was a large hyrax that lived during the late Pliocene and early Pleistocene, about 2.5-2.2 million years ago, in what is now northern China.

About 1.5m long (~5′), it had very high-set and sideways projecting eye sockets similar to those of modern hippos, indicating it probably had a similar sort of semi-aquatic lifestyle. The shape of its skull also suggests it may have had a short tapir-like trunk.

Much like modern hippos or capybaras Postschizotherium probably spent much of its time wallowing in bodies of water, and emerging onto land to graze on grasses. Its habitat would have been humid forest and grasslands, alongside other animals such as large horses and bovines, one of the last chalicotheres, woolly rhinos, beavers, macaques, bears, big cats, early lynxes, and scimitar-toothed cats.

Notiomastodon

Notiomastodon platensis was a gomphothere – a relative of modern elephants – that lived across much of what is now South America from the mid-Pleistocene to the early Holocene, between about 800,000 and 10,000 years ago.

Similar in size to an Asian elephant, it stood around 2.5m tall at the shoulder (~8’2″) with a domed head and thick tusks that varied in length and curvature between different individuals. It had a stockier build than modern elephants with thicker and slightly shorter limbs, and fossilized footprints suggest it had five nails on its front feet and at least three on the hind feet.

Isotope analysis and wear analysis of Notiomastodon’s teeth suggest it was a generalist browsing herbivore, with different populations adapting their dietary habits to local conditions. As one of the largest South American herbivores of its time it was probably an important seed disperser for plants such as bamboo and palms – and some of the plants that once depended on it may now be “evolutionary anachronisms“.

Miosiren

Miosiren kocki was a sirenian (sea cow) that lived during the early Miocene (~20-15 million years ago) in what is now the North Sea basin in northwestern Europe.

Similar in size to the very largest modern manatees, about 4-4.5m long (~13-14’10”), it has traditionally been classified as an early member of the manatee lineage – but a study in 2022 suggested it may instead represent a much earlier stem of the sirenian evolutionary tree, with its ancestors potentially having diverged around 34 million years ago.

It had unusually thickened bones in its skull, especially around the roof of its mouth, which would have given its jaws a very strong chewing force. Isotope analysis of its teeth show it was part of a marine algae-based food web, unlike the seagrass-based diets of other sirenians, so it may have been specialized to feed on a much tougher diet. Possibly it was eating something like calcareous algae, or more speculatively it might even have been crunching on hard-shelled algae-consuming marine invertebrates.

Phosphatherium

Phosphatherium escuillei was one of the very earliest known members of the proboscideans, a lineage today represented only by the three living species of elephants.

Living in what is now Morocco during the late Paleocene and early Eocene, around 56 million years ago, it would have been about the size of a cat, roughly 30cm at the shoulder (~1′) and 60cm long (~2′). It had a fairly low flat head with a proportionally short snout, while the back end of its skull behind it eyes was elongated, supporting large powerful jaw muscles.

Wear patterns on its teeth suggest it ate a lot of tough vegetation, and it may have been a semiaquatic animal behaving somewhat like modern tapirs or pygmy hippos – spending a lot of the daytime lounging in water, and emerging onto land to forage during the night.

Spectember/Spectober 2023 #09: Things With Wings

(Apologies for the abrupt absence – I’m okay, just having everything break down at once. ~~This is fine.~~)

So— back to the speculative evolution request list!

TheBigDeepCheatsy requested a “cactus-dwelling/germinating evolution of introduced rosy-faced lovebirds”:

A shaded sketch of a speculative symbiotic relationship between lovebirds and saguaro cactus. The lovebird is shown on the left, a small parrot that looks very similar to modern rosy-faced lovebird except with hints of a more mottled color pattern. The cactus is shown on the right, a large fasciated saguaro with its top fanning out into a wide "crown", with several nest holes dug into it and multiple lovebirds occupying them.

While Agapornis cheatsyi is still quite physically similar to its introduced ancestors, this lovebird has developed a close symbiotic relationship with the cactus Carnegiea ornipolis, a descendant of the modern saguaro.

Naturally fasciated, this cactus grows a splaying fan-like crown which the lovebirds excavate their shallow nest burrows into. Feeding on the cactus’ fruit in early summer, the lovebirds then disperse the seeds via their droppings – a process that significantly improves propagation chances, both due to the birds commonly foraging and defecating around suitable nurse plants and the passage through their gut speeding up germination.

Someone calling themself “LB” asked for some “flying afrotherians”:

A shaded sketch of a speculative flying tenrec. It's a bat-like animal with membranous wings supported by three elongated fingers, and a large shrew-like head with long toothy jaws and an elephant-shrew-like nose.

Elbeitandraka venenifer is a descendant of tree-climbing Malagasy tenrecs that developed gliding membranes – and its lineage is now just about achieving true powered flight.

About 25cm long (~10″), its proportionally short broad wings require it to fly very fast to generate enough lift for its weight. It mostly only actively flies when traveling between roosts and feeding sites (or when escaping from threats), alternating between gliding to save energy and flapping to recover altitude.

It’s an opportunistic omnivore, crawling around in the tree canopy foraging for vegetation, fruits, fungi, invertebrates, and the occasional smaller vertebrate, using its flexible sengi-like nose to probe around in crevices.

Much like modern common tenrecs it’s capable of hibernating for months at a time through periods of scarce food availability. It also accumulates alkaloid toxins in its body from its arthropod prey, advertising its unpalatability to predators with bold contrasting warning coloration on its wing membranes.

And here’s a combination of a couple of anonymous requests for both “flying heterodontosaurs” and “dragons with hind leg wings, a la sharovipteryx”:

A shaded sketch of a speculative flying predatory heterodontosaurid dinosaur, show both on the ground in a quadrupedal posture and in flight. Its hind legs form its main wings, with elongated outer toes supporting large pterosaur-like flight membranes. It also has a hooked beak at the front of fanged jaws, an s-curved neck, a compact fuzzy body, short forelimbs with taloned hands and small stabilization membranes, and a long vaned tail.

Inversodraco rapax is a highly specialized Jurassic descendant of heterodontosaurids that took to climbing and gliding, developing delta-wing-like membranes on their hindlimbs convergently similar to those of the earlier sharovipterygids.

Around 75cm long (~2’6″), it has unusually flexible hip joints for a dinosaur, able to splay its legs out to the sides to deploy wings supported by an elongated outer toe on each foot. Its arms form small forewings for stability, and its long tail ends in a vane of stiffened feathers that aid in steering.

Unlike its herbivorous-to-omnivorous ancestors it’s primarily a carnivore, swooping down onto small prey and grabbing it with its talon-like forelimbs.

Strange Symmetries #22: The Whalerus And The Twisted Tusks

Mammalian tusks usually grow in symmetrical pairs with only minor developmental asymmetry, but a few species have evolved much more uneven arrangements.

A colored line drawing of the extinct toothed whale Odobenocetops. Its body is beluga-like but it has a face more like a walrus than a whale, with a big fleshy bristly upper lip and a pair of protruding tusks. The right side tusk is much longer than the left. It's depicted with a mottled brown and white color scheme. — *Odobenocetops peruvianus*

Odobenocetops peruvianus was a small toothed whale that lived during the Miocene, about 7-3 million years ago, in shallow coastal waters around what is now Peru. Around 3m long (~10′), it was a highly unusual cetacean with binocular vision, a vestigial melon, muscular lips, and a pair of tusks – features convergent with walruses that suggest it had a similar lifestyle suction-feeding on seafloor molluscs and crustaceans.

In males the right tusk was much more elongated than the left, measuring around 50cm long (~1’8″) in this species and up to 1.35m (4’5″) in the closely related Odobenocetops leptodon. Since these teeth were quite fragile they probably weren’t used for any sort of combat, and they may have instead served more of a visual display function.

And despite being closer related to modern narwhals and belugas than to other toothed whales, Odobenocetops’ long right-sided asymmetric tusks actually seem to have evolved completely independently from the iconic left-sided asymmetric spiral tusks of narwhals.

An edited meme image using screenshots of Dr. Doofenshmirtz from "Phineas and Ferb". The text reads: "If I had a nickel for every time whales evolved asymmetric tusks, I'd have two nickels. Which isn't a lot, but it's weird that it happened twice."

A colored line drawing of an extinct woolly mammoth. It's an elephant-like animal covered in a thick coat of brownish hair, with a high domed forehead, small ears, and long curving tusks. The tusks are noticeably asymmetrical, one curving more downwards than the other. — Woolly Mammoth (*Mammuthus primigenius*)

The woolly mammoth (Mammuthus primigenius) lived across Eurasia and North America during the last ice age, mostly from the Pleistocene about 400,000 years ago to the early Holocene about 10,000 years ago – altohugh a few relict populations survived until around 4,000 years ago in isolated areas of Alaska, Siberia, and eastern Russia.

Around 3m tall at the shoulder (~10ft), these hairy proboscideans had very long curving tusks that were used for digging out vegetation from under snow and ice, scraping bark from trees, and for fighting.

The tusks showed a lot of variation in their curvature, and were often rather asymmetrical, a condition also seen in the closely related Columbian mammoth. Like modern elephants mammoths may have also favored using one side over the other for certain tasks, which over their lifetimes could result in uneven wear exaggerating the natural asymmetry even more.

It Came From The Wastebasket #03: The Gomphothere In The Room

The three living species of elephants are the last surviving members of the proboscidean lineage – but up until the end of the last ice age about 11,000 years ago their relatives were much more numerous and widespread, found on every continent except Australia and Antarctica. Mammoths are probably the most famous of these recently-extinct proboscideans, closely related to modern Asian elephants, but there were also the more distantly-related stegodonts and mastodons…

…And also the gomphotheres.

A cladogram showing the traditional classification of gomphotheres as a poorly-defined group evolutionarily between mastodons and modern elephants.

Traditionally any proboscideans that fell into the evolutionary grade between mastodons and elephants-and-stegodonts were all labelled as gomphotheres. As a result by the late 20^th century this group ended up as a wastebasket full of elephant-like forms that didn’t easily fit anywhere else, defined more by what they weren’t rather than by any features they all had in common.

This big collection of gomphotheres was highly diverse. Some species independently evolved similar convergent features, and there was also considerable individual physical variation within species, making the actual taxonomy of these animals very difficult to figure out. But over the last few decades there’s been a lot of revision of proboscidean evolutionary relationships, and gradually the gomphothere wastebasket has been clearing up. Groups like the choerolophodontids, amebelodontids, and anancids have been split off, leaving a more defined lineage of gomphotheres that do have shared anatomical characteristics – distinctive three-lobed trefoil-shaped wear patterns on their molar teeth.

A cladogram showing a more modern classification of gomphotheres, with the gomphotheriids as just one of several different lineages originating between mastodons and modern elephants.

These gomphotheriids were widespread, found across Africa, Europe, Asia, and the Americas – and they were especially successful in the latter. They arrived in North America during the Miocene (~16 million years ago) via the Beringia land bridge, and rapidly spread across the continent and down into Central America. They went on to become the only proboscideans to disperse into South America during the Great American Biotic Interchange, with two different lineages arriving at separate times – Notiomastodon around 2.5 million years ago, and Cuvieronius around 750,000 years ago.

An illustration of Cuvieronius, an extinct elephant-like gomphothere. It has a longer flatter head than modern elephants, and its tusks have a spiral twist to them. — *Cuvieronius hyodon*, a 2.3m tall (7’7″) South American gomphotheriid with distinctive spiraled tusks.

The exact relationships of the gomphotheriids to other elephant-like proboscideans are still a little uncertain. Both protein sequences and mitochondrial DNA have recently been recovered from 35,000-13,000-year old Notiomastodon specimens, but these studies have given different taxonomic conclusions – with the protein results suggesting gomphotheriids were most closely related to mastodons, and the DNA results suggesting they were much closer to true elephants.

Sobrarbesiren

Since the last couple of weeks have featured marine mammals, let’s have one more! This time not a cetacean but a member of the other group of fully aquatic mammals still alive today: the sirenians.

Although commonly known as “sea-cows” due to their herbivorous grazing habits, sirenians’ closest living relatives are actually modern elephants. They’re thought to have originated in Africa over 50 million years ago, starting off as pig-like or hippo-like semi-aquatic animals — but they must have been good swimmers capable of crossing oceans very early in their evolutionary history, since some of the earliest known sirenian fossils actually come from the other side of the Atlantic on the Caribbean island of Jamaica.

Sobrarbesiren cardieli here extends some of our knowledge of early four-legged sirenians to Europe, dating to the mid-Eocene about 42 million years ago. Hundreds of bones were found in Northeastern Spain, representing at least six different individuals and giving us a fairly complete idea of this species’ anatomy.

It was smaller than modern sea-cows, reaching about 2m long (6’6″), and seems to represent a transitional point between the semi-aquatic ancestral sirenians and fully aquatic later forms. It had a head very similar to its modern relatives, and probably a tail fin, but also still retained small functional hind limbs.

It was initially thought to still be somewhat semi-aquatic and capable of quadrupedal locomotion on land, but a later analysis of its hind limb bones suggests that it may actually have been much more aquatic than that. Its hind legs had a wide range of motion and were probably used for otter-like swimming, undulating the body while paddling, but might not have been capable of supporting its weight on land. So if Sobrarbesiren did still haul out of the water, it may have had to move more like a seal.

Weird Heads Month #20: Shovel-Tuskers

With their odd-looking skulls, long tusks, and their noses and upper lips modified into tentacle-arm-like trunks, modern elephants are the sort of animal that would seem completely unbelievable if we only had fossils of them.

But not nearly as strange as some of their ancient relatives.

Platybelodon is probably the most famously weird member of the proboscideans (the group that contains both modern elephants and their extinct cousins), looking like some sort of deliberately outrageous speculative creature design.

Living during the mid Miocene, around 15-4 million years ago, several different species of Platybelodon ranged across Africa, Europe, Asia, and North America, with Platybelodon grangeri here known from abundant fossils in Asia.

These strange-looking proboscideans stood around 2.2m tall (7’3″) and had fairly standard elephant-like bodies, but also heads with bizarre-looking elongated lower jaws that ended in a wide flat shovel-like shape tipped by two flat tusks, leading to their nickname of “shovel-tuskers”.

It was originally interpreted as a swamp-dwelling animal using its weird jaw to scoop up soft aquatic vegetation, with a fairly short flat trunk. But more recent studies of the wear patterns on its teeth suggest it actually used them more like a scythe than a shovel, cutting through tough grasses and branches – a feeding style that would also require it to have a much more modern-elephant-like trunk, using it to hold on to plants while it was sawing through them.