#allotheria

[harpagornis]

Plummobaatar diathagoia, a new submission for Multituberculate Earth: https://multituberculateearth.wordpress.com/2024/07/30/example-site-messel-pit/

[alphynix]

Even for a fossil species from an isolated island, Adalatherium hui is very weird.

This mammal was part of an enigmatic group known as gondwanatheres, which were probably early members of the theriiform lineage – slightly closer related to modern marsupials and placentals than to monotremes. Found in the southern continents of Gondwana between the Late Cretaceous and the Miocene, these animals were adapted for herbivory with convergently rodent-like ever-growing front teeth that helped them chew through tough plant matter.

They were previously known mainly from isolated teeth and jaw fragments, with some rare full skull material, but Adalatherium is remarkable for being represented by a complete skeleton.

And it's turned out to be far stranger than anyone expected.

Living in northwestern Madagascar during the Late Cretaceous, about 70-66 million years ago, Adalatherium was one of the larger known Mesozoic mammals at around 60cm long (2') – although the one known specimen seems to have been a juvenile, so mature individuals were probably slightly larger.

(And based on its body proportions, its close relative Vintana may actually have been even bigger than previously thought. Whether this sort of large size was common in Cretaceous gondwanatheres or if this was just island gigantism is still unknown, though.)

It was probably a marmot-like digging animal, excavating burrows with its large claws and powerful limbs, and since it likely evolved from ancestors that had become isolated on Madagascar over 20 million years earlier it had developed a very unusual mixture of both "primitive" and highly specialized anatomical features. It had more back vertebrae than any other known Mesozoic mammal, upright forelimbs, sprawling hind legs with bowed-out tibias, strong back and leg musculature, and a therian-like pelvis with epipubic bones.

And then there's the snoot.

The snout region of Adalatherium's skull was pockmarked with a large number of foramina, holes that allow the passage of nerves and blood vessels through the bone. It had more of these than any other known mammal, and their presence suggests that it probably had a very sensitive upper lip and whiskery snout. Most mammals with a lot of whiskers just have one very big foramina, but Adalatherium seems to have evolved a different solution to the same problem.

It also had one other bizarre feature – a hole in the top of its nose. A large "internasal vacuity" between its nasal bones is a unique feature not known in any other mammal, and its function is a total mystery.

Since this hole was also surrounded by many foramina it may have supported some sort of soft-tissue sensory structure on top of its nose. So I've speculatively depicted it here with a leathery horn-like "shield".

[ From fig 2 in Krause, D. W. et al (2020). Skeleton of a Cretaceous mammal from Madagascar reflects long-term insularity. Nature 581, 421–427. https://doi.org/10.1038/s41586-020-2234-8 ]

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Nix Illustration | Tumblr | Pillowfort | Twitter | Patreon

[harpagornis]

New Multituberculate Earth content: https://multituberculateearth.wordpress.com/2022/03/29/kogaionidae-old-dogs-do-learn-new-tricks/

[harpagornis]

We take evolution for granted. It is easy to imagine ourselves as the end goal, regardless of whereas there is a God or not. That the current state of affairs is the destined one.

But evolution is nothing if not chaos. Life is the result of many chances and happenstances, which resulted in our status quo. The most frequent “what if” scenario when imagining different possibilities of how life would have evolved different is perhaps the famous “what if [non-avian] dinosaurs never died out”, but I believe this project will illustrate this point even better.

In our timeline, Theria, the group of mammals composed of placentals, marsupials and any extinct cousins that descended from their last common ancestor, came to dominate the world. From the hopping kangaroos to majestic tigers, to the flying foxes and enormous whales, they’re the definition of “mammal” in most people’s minds.

But it wasn’t always like this.

Even today, monotremes still live in Oceania, but the beginning of the “Age of Mammals” actually had another group as far more dominant than therians: multituberculates. This ancient lineage were the most common and diverse mammals in the Mesozoic, and their entrance into the Cenozoic was promising: surviving a mass extinction event, they proliferated and came to dominate the mammalian fossil reccord for the first 5 million years.

But they declined rapidly, for reasons still poorly understood, giving way to therian mammals. This is why you’re here, and why only some paleontologists know what a multituberculate is.

So what if they didn’t die out?

Ectypodus arctos devouring a basal rodent by Dylan Bajda. Already a carnivorous animal, this scene could have taken place in both timelines, but in this one it heralds the end of placentals, and the era of the allotheres.

Table of contents

What is a multituberculate?

An alternate history:

Paleocene

Eocene

Oligocene

Animal Groups (note: only until Oligocene for now)

Multituberculate Diets

Multituberculate Saberteeth

Multituberculate Sounds

Kogaionidae

Taeniolabidoidea

Microcosmodontidae

Meniscoessidae

Ptilodontoidea

Djadochtather[i]oidea

Gondwanatheria

Flying Mammals

Sea Mammals

Marine Reptiles

Birds

Dryolestoidea

Monotremata

A world with no lizards

Alternate Timelines Of The Timeline

Nyctosaurid Earth

Meta

The three Multituberculate Earths

[alphynix]

Month of Mesozoic Mammals #16: So Many Gliders Maiopatagium

The haramiyidan featured yesterday was a ground-dwelling animal, but most others in the group were actually highly adapted for tree-climbing. They were very squirrel-like in appearance, with grasping hands and feet and tails that may have been prehensile -- and some took this lifestyle even further, becoming specialized gliders.

Living during the Late Jurassic of China (157-163 mya), Maiopatagium is one of at least four known gliding haramiyidans. It was about 25cm long (10″), around half of which was its long tail, and had a gliding membrane extending between its wrists and ankles. The proportions of its hands and feet were very similar to modern colugos and the feet of bats, which has been interpreted as evidence of the same sort of upside-down roosting behavior.

Its close relative Vilevolodon had rodent-like teeth highly adapted for crushing and grinding, suggesting these haramiyidans were herbivores feeding mainly on seeds and soft plant matter.

And these gliding haramiyidans also contribute to the confusing classification of haramiyidans -- because although Megaconus’ anatomy suggested they might be mammaliaformes, studies of another glider, Arboroharamiya, give a very different result. Its ear bones and jaw show the characteristics of true members of Mammalia, supporting the hypothesis that haramiyidans were actually close relatives (or ancestral to) the multituberculates.

[alphynix]

Month of Mesozoic Mammals #17: Awesome Ankles Rugosodon

Moving on to the next major group of the theriiform mammals, we have the multituberculates -- or “multis” for short.

First appearing in the Early Jurassic, about 183 million years ago (possibly descending from haramiyidans), multis were one of the most successful and long-lived mammal lineages of all time, found throughout the world and making up more than half the known mammal species in some fossil deposits. They even made it through the end-Cretaceous mass extinction and became even more diverse in the Paleocene, although shifts in vegetation, climate change, and the rise of new predators seem to have sent them into decline by the mid-Cenozoic. The last surviving group of multis, the gondwanatheres, finally went extinct in the Miocene (~17.5 mya).

Multis had rodent-like teeth, except with huge blade-like lower premolars, and likely occupied similar ecological niches to their modern counterparts. The structure of their pelvises also suggests they were some of the earliest mammals to give live birth to tiny undeveloped young, similar to marsupials.

Ptilodus skull by Nobu Tamura || CC-BY-3.0

Rugosodon is known from the Late Jurassic of China (161-155 mya) and is one of the earliest multituberculates represented by near-complete fossil remains.

About 25cm long (10″), it was a ground-dwelling chipmunk-like animal with highly flexible ankle joints that would have made it very a fast and agile runner, capable of navigating uneven surfaces. These specialized ankles were a defining trait of multis, allowing later forms to adapt to lifestyles ranging from tree-climbing to burrowing to jerboa-like hopping.

And while many later multis were primarily herbivores, Rugosodon’s teeth show it was an omnivore, indicating that a more generalized diet was ancestral to the group.

[harpagornis]

Multituberculate Colors

Afroptilodontoidean Nunduapis tricolor drunk on fermented fruit. By HodariNundu. Note the reconstruction with vibrant structural colors, aki