#gondwanathere

[harpagornis]

Gondwanatheria: World Domination

(As with all animal pages so far, this only goes so far into the Miocene… for now) Fusuamys, from the early Paleocene of Bolivia. By pale.re

Manik xtabay from the Oligocene of Colorado. Here speculatively using tools much like modern cows. By astraplatina

[rave-lord-nito]

I couldn’t have wished for a better birthday gift on the 29th than being bombarded with fantastic palaeontology news, what a day

[harpagornis]

Multituberculate Earth: Gondwanatheria

Gondwanatheria is a mysterious but highly successful clade of allothere mammals. As previously noted it is unclear if these are multituberculates, close relatives or unrelated non-mammalian synapsids; it’s even unclear if they form a natural group, as ferugliotheriids are sometimes considered true multituberculates while other gondwanatheres aren’t. For the sake of simplicity they are treated as a monophyletic group here that may or may not be related to multituberculates (otherwise represented only by cimolodonts). Its worth to not that, unlike virtually all other multituberculates, gondwanatheres have a seperate septomaxilla from the premaxilla, whereas the normal multituberculate condition is just a single bone that may be a premaxilla or an entirely new bone as mentioned in the link above.

In our timeline, gondwanatheres first appear in the Late Cretaceous. They were widespread, with remains found in South America, Antarctica, Africa, Madagascar and India; they crossed the KT boundary in all, but the fate of African, Indian and Malagasy species is unknown. In South America and Antarctica they continued to thrive even as marsupials and placentals took over, but ultimately became rare by the Oligocene. One possible species, Patagonia peregrina, might have endured as recently as the Miocene, though this taxon is controversial and some studies claim it is a polydolopiform instead (the latest on the matter seems to cautiously favor the gondwanathere interpretation).

Thus, in our history gondwanatheres are potentially the last of the multituberculates, or of the non-mammalian synapsids at any rate.

In this timeline, fortune nature kept smiling on this resilient clade, whose plausible deniality is even more effective thanks to their real life success. The Paleocene saw them in all of the southern continents, albeit with some provincialism, with sudamericids, greniodontids and ferugliotheriids in South America, Australia and Antarctica, sudamericids and adalatheriids in India and Madagascar and galulatheriids in Africa. Not long after they aimed for the north; ferugliotheriids, already found in the Late Cretaceous of Mexico, were quick to migrate to North America and soon after to Europe.

The PETM brought about an even greater interchange. India joined with Asia, and with it herds of sudamericids and adalatheriids marched into the continent. More efficient herbivores – unlike most [other] multituberculates, many species have ever-growing cheek and incisor teeth like rodents -, they displaced the local taeniolabidids and nearly all lambdopsalids above 10 kg. Adalatheriids would later colonise North America, but sudamericids would only expand further with the Grand Coupure, taking advantage of the forest collapse to invade Europe and North America. This is less fortunate for local ferugliotheriids, which go extinct.

As of the Oligocene, gondwanatheres are essentially cosmopolitan, found in pretty much every major landmass. In this respect they resemble the hadrosaur dinosaurs of the Cretaceous, another cosmopolitan clade of herbivores with sophisticated teeth. Though they are more diverse, ranging from tiny hamster-sized granivores to massive aquatic herbivores and some of the tallest land mammals of all time.

Ferugliotheriidae

Ferugliotheriids are the most basal of gondwanatheres; as mentioned previously, some authorities don’t even considered them gondwanatheres at all. They lack the refined teeth of their more derived relatives, having brachydont rather than hypsodont cheek teeth and retaining a plagiaulacoid. Consequently, they generally feed on soft plant matter, though the plagiaulacoid allows them to explore some harder food stuffs like seeds and tubers.

Ferugliotheriids have the second widest distribution after sudamericids, ocurring across the Americas, Europe, Antarctica, Australia and the Caribbean islands, though the Grand Coupure killed them off from the northern continents, and even in the southern ones the spread of grasslands is threatening their long term survival, seeing as they can’t process grass as easily as other gondwanatheres. Most remained comparatively small, from hamster to sheep size, but both Australia and the Caribbean saw the rise of large browsing species, using their forelimbs to bring down branches like gorillas or sloths. Several species have taken to an arboreal lifestyle, being more efficient folivores than other tree-climbing mammals like ptilodontoideans or leonardid dryolestoids.

Galulatheriidae

Africa in our timeline bears a singular gondwanathere, Galulatherium jenkinsi. Although sometimes placed in Sudamericidae, sharing similar hypsodont teeth, it differs in other respects, like the absence of enamel and the presence of what appears to be a plagiaulacoid. If Adalatherium – which is pretty similar to sudamericids – can get its own family, I don’t see why Galulatherium can’t.

In this timeline, galulatheriids pretty much evolved in parallel with our world’s paenungulates. They diversified in the isolation of Africa, the only mammals in the Paleocene alongside kogaionids, where they took herbivorous niches while the latter became predators. Being relatively bulky animals, they left plenty of room for the arrival of other groups like the arboreal afroptilodontoideans and cursorial boffiids, diversifying in rather unique ways. Some became mole-rat-like burrowers, while others became chalicothere-like tall browsers. While lacking enamel, their ever-growing hypsodont molars allowed them to consume grass efficiently, though most species remained mixed browsers even into the Oligocene.

Many species became semi-aquatic, even as taeniolabidids took hold over the world’s seas and freshwater habitats. Several have swam across the Tethys to Balkanatolia, where they became established as the largest herbivores while one genus, Termagantus, established itself in southern Europe (though in fairness it could have also arrived there via a brief land bridge). Both European and Balkanatolian species became extinct in the Grand Coupure, but another group had far more sucess: in the Eocene, some galulatheriids crossed the then-thinner Atlantic Ocean into South America. Arriving to a crowded landmass, they currently remain in semi-aquatic niches.

Hvalros tropicalis, an Oligocene form known from European and Caribbean marine sites. It used its tusks to scrape off algae from corals, sometimes even eating corals thanks to its ever-growing molars. By corvarts.

Uniquely among allotheres galulatherids (as well as some greniodontids) have converted their vestigial plagiaulacoid into a tusk (notoptilodontoideans also converted the peg-like relictual plagiaulacoid into a canine-like tooth, but the main one remains blade shaped as usual). Used both for fighting predators and rivals as well as for digging tubers and scrapping tree bark, these tusks allow them some control of their environment, allowing them to uproot undesirable plants. In some regards, it can be said that galulatheriids mimic elephant evolution, though they have not developed trunks.

Adalatheriidae

Adalatherium hui is probably one of the most publicised gondwanatheres, the first to show a significantly complete skeleton. It was rather similar to sudamericids – many of which co-existed with it in the Cretaceous of Madagascar – sharing similar ever-growing hypsodont teeth coated in thick enamel, but it was an unexpectedly gracile animal with erect limbs and lacking some of the latter’s features like facial flanges. As such it was given its own family, which in this timeline has found great success.

Adalatheriids were originally constrained to Indo-Madagascar. But as India collided with Asia in the PETM, they quick spread across Asia, and even into North America through Beringia. They would latter colonise Europe during the Grand Coupure, spanning the entire North Hemisphere plus the island of Madagascar. Still, North America and Madagascar would be the hotspots of their radiation.

In the northern continents, adalatheriids grew increasingly gracile and tall. While its easy to compare these now long-necked herbivores to indricotheres (barring their wider distribution), they in truth more closely resemble elephants and sauropod dinosaurs at least in terms of function, feeding both from tall trees as well as picking grass and small shrubs (well, I guess camels are a good analogue, but it’s not quite as romantic, you know). Like most mammals they have only seven neck vertebrae, so while their neck are not terribly flexible they anchor powerful muscles that allow the skull to pull vegetation powerfully. Their necks are proportionally longer than those of giraffes, allowing them to drink more gracefully. Conversely, some species have short necks and more closely resemble rhinos ecologically, and a few species remained small and gopher-like.

I’m not supposed to reveal this yet, since there is no Oligocene fossil reccord of Madagascar, but there they instead became arboreal, analogous to our giant lemurs.

A notable feature of Adalatherium is the presence of many holes in this skull; this normally correlates to blood vessels supporting a soft tissue structure, like a horn or a wattle. We thus choose to portray adalatheriids in this project with all manner of horns on the snout, some similar to those of rhinos while other more bizarre structures.

Sudamericidae

Sudamericids were the most successful gondwanatheres in both timelines, having spread across South America, Antarctica, India and Madagascar and possibly lasted until the Miocene. In this timeline, they further colonised Australia, and through India first Asia in the Eocene, then North America and Europe in the Oligocene (though they remain less diverse in the former, where adalatheriids are more common instead; see below for the future in the southern continents). Only Afro-Arabia remains free of them… for now…

These are rather robust animals, which can be best thought of as mix between heavy rodents like gophers and herbivorous xenarthrans like sloths and glyptodonts. Like the former they have ever growing hypsodont teeth, a rarity among allotheres, and like the latter they developed massive jugal flanges likely anchoring powerful cheek muscles. They were most certainly capable of processing hard plant matter from cycads to the now increasingly dominant grass, and this has been key to their success.

Many gondwanatheres in this timeline attained massive sizes, with Oligocene Asia species in the upwards of 5 tons. However, a myriad of small taxa as small as a guinea pig still persist, some of which even competing with lambdopsalids in digging niches, and having more successfully produced mole-rat-like forms. When larger species die, these ones are among the first to step in to replace them. Many species have also taken to the tree canopies in Eurasia, acting as the main local sloth-analogues.

Sudamericids may lack the tusks of galulatheriids and the horns of adalatheriids, but their resilience makes the hard to get rid of. But perhaps a new rival has come to challenge them…

Greniodontidae

Greniodon is an enigmatic gondwanathere from our timeline’s Late Eocene of Patagonia. They strong resemble sudamericids, but they differ in having an occlusal surface more similar to that of ferugliotheriids. Thus, they are here interpreted speculatively as a sort of “bridge” between the basal ferugliotheriids and derived galulatheriids, adalatheriids and sudamericids, retaining plagiaulacoids that in some species formed tusks like their galulatheriid cousins. In our world, these bizarre animals was a tenacious survivors, having lasted until the end of the Eocene.

… and so it makes sense that, in this timeline, its relatives too are highly successful, having “the best of both worlds” in terms of derived and primitive molar features, allowing them to feed on a wider variety of vegetation. They for now occur in South America, Australia and Antarctica, and as early as the early Paleocene they have been displacing their sudamericid cousins in the south. For now both clades co-exist, but southern sudamericids are being driven to increasingly specialised niches in the light of these new, more efficient grazers and browsers, and combined with the arrival of African galulatheriids they may be ironically removed from South America altogether.

Greniodontids: our new saviours… or an even greater evil to be unleashed?