Non-therian Cenozoic mammals thread

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Hello, in this thread I will tell a story of the most underrated mammals of all time – Cenozoic non-therians (mostly multituberculates, of course). Their story is just as fascinating as it is tragic, and I want to share it with you.


Here I will mostly focus not on their anatomy (although it will probably be touched as well), but rather their diversity and chronology. Posts here will be organized by continents, mostly to highlight zoogeographical differences observed in these groups.


With this said, let’s start from the traditional north-west. Time to enter…


North America


Following the Cretaceous – Paleogene extinction event, two non-therian groups survived on this continent. These are, of course, multituberculates and a ghost lineage of totally unrelated relictual mammals named “symmetrodonts”. After a period of recovery, they’ve diversified, and soon enough North America became a literal Kingdom of Allotheres (group that includes multis and gondwanatheres, with the latter being unknown in this region).


Indeed, taxonomically it was the most diverse region that hosted the most families of the previously mentioned order (not symmetrodonts, of course). These are weird unclassified representatives of Paracimexomys group, (possibly) Meniscoessus, Eucosmodontids, Microcosmodontids, Ptilodontoidea and Taeniolabidids. Let’s see what genera of these group were present in Danian North America.


As I said, Paracimexomys group is present in America right after the extinction of (most) dinosaurs. All of its species were members of a sole genus Cimexomys, and were mostly found as just fragmentary teeth. Most (C. minor, C. antiquus and C. gregoryi) were the same size as modern mice, but a few (C. arapahoensis and C. grantus) have reached rat sizes. Rat-sized representatives are only known from US, while smaller ones can be also found in Canada. And sadly, that’s all we know about these animals.


Meniscoessus, a much bigger mammal that weighed around 1-3 kilograms and lived alongside T.rex in Hell Creek (plus Canada), seemingly appeared in the earliest Paleocene as M.robustus, though this find is still controversial and may be disproven in the future.


Much like the first mentioned group, Eucosmodontidae are mostly known from teeth, with very large premolar implying they were carnivorous, but still had an ability to eat grain and fruits. New Mexican representative from genus Eucosmodon were eerily similar to rats in ecology and size, while Stygimys had a much more varied weight (from 90 to 300 g) and a wider distribution (which just means they were in Canada as well).


Same problems of very poor preservation haunt another group of multituberculates, Microcosmodontidae, although studies seem to suggest they were more ecologically similar to shrews than rodents. Not much else to say, really, typical mouse-sized Canadian and US residents.


The next two groups, on the other hand, are MUCH different. Ptilodontoidea became very successful in Paleocene, spawning several families of quickly expanding multis, with some representatives (Neoliotomus) reaching 2 kg in weight. They were also not just mouse copies, with some seemingly evolving into cat-sized predators that terrified forests of this epoch. Overall, in the early Paleocene this taxon was the dominant arboreal group in North America, with almost no placentals to even match them.


Taeniolabididae, on the other hand, took a niche of terrestrial herbivores. They became very large by multituberculate standards, with the biggest representative Taeniolabis reaching 100 kg (for record, this is the same size as giant extinct beaver Castoroides)! They were not just biggest mammals of the region, but of the EPOCH.


With that said, you may think that these diversifying groups are destined to rule over the planet. But that… didn’t happen.


In the Late Paleocene, around 61 MYA, almost all of them disappear, and our own ancestors, placentals, took their spot and become dominant mammals instead. The only two group that remained, Ptilodontoidea and Eucosmodontidae, were reduced to just relics of a bygone era, most being smaller than a mouse. Surprisingly, however, non-therian predators persisted as well, and continued hunting placentals in an age of their dominance. What a peculiar paradox, don’t you think?


By the way, Late Paleocene is also the time a small insectivorous symmetrodont named Chronoperates appeared, though much like multituberculates, it was nothing but a fading memory.


Then PETM hit, and the latter group went extinct. Ptildontoidea barely survived, with only three genera remaining – Prochetodon (likely went extinct during the Azolla Event), Parectypodus (with seemingly the same story) and Ectypodus (the last multituberculate EVER, a cat-like carnivore which is one of two main arguments against “rodents outcompeting multituberculates” theory). By the time Grand Coupure happened, they had no chance against us, and by Oligocene, America became a Kingdom. Of Therians.


See you soon. Europe is next.

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Europe

Unlike North America, Europe never had an abundant non-therian fauna, with only endemic groups being an unusual genus Boffius and Kogaionids. But in terms of its history this continent is definitely more interesting than the previous one, so let us examine it in all its glory.

During K-Pg, Kogaionidae managed to survive a literal hell on Earth due to their iron-coated teeth, which helped them consume insects (as you probably know, insectivores were one of the dietary groups that had lessened extinction rates in the asteroid impact). Originally endemics of famous Hateg Island, they took full advantage of this landmass merging with the mainland Europe, with genus Hainina dispersing into Western Europe (mostly Belgium, France and Spain) and becoming the most common European mammals of Early Paleocene.

There, in Danian Belgium, rapidly diversifying kogaionids met their distant relative, Boffius splendidus. And unlike those multituberculate shrews I just described to you, it was an herbivore. A big, seemingly hopping herbivore (modern studies suggest that it was related to Catopsbataar, which is often recovered as jerboa-like), in fact. The biggest European mammal at a time, with a weight of 30 kg (so, it can probably be described as some sort of European kangaroo).

Then suddenly, a period of exploration for these two groups comes to an end, but it’s not placentals that strike them down. Instead, these new invaders are Ptilodontoidea, which crossed from North America into France and settled there, seemingly nonchalant that other representatives of the group are dying elsewhere and are getting replaced by placentals. Eucosmodontidae are sometimes also described as American migrants, though no European genus was named yet.

As such, before PETM hit, Europe was already busting with non-therian life, which seemingly competed with each other. But sadly, these are the last non-therians of the region. Climatic changes in-between Paleocene and Eocene seemingly killed them all, leaving this continent to become a Kingdom. Of Placentals.

See you soon. Asia and India (a Gondwanan landmass that only connected with Asia in Eocene, but is still retrospectively related to the continent I just named) are next.

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Asia (and India)

In the Age of Dinosaurs, mainland Asia had a very diverse non-therian fauna, usually classified in a big group Djadochtatheroidea, which previously mentioned Catopsbataar was a member of. But then asteroid hit, and Asian multituberculates suddenly disappeared, with possibly related eucosmodontids and boffids surviving outside of it somehow. So, in this case, non-therians are actually unknown from Early Paleocene (especially as fossils), but indirect knowledge suggest two groups crossed through Beringia in Danian and recolonized Asia. These are Lambdopsalids, close relatives of gigantic taeniolabidids, and Ptilodontoidea (of course).

But before talking about them, let’s visit Insular India for a moment. Unlike Laurasia, which non-therian groups were mostly multis, Gondwana and its breakaways was represented by another, closely related mammal clade – gondwanatheres. India is no exception, and its sole known non-therian representative, Bharattherium, is suggested to be one of two mammalian cataclysm survivors of this small island (alongside therian Deccanolestes). And so, sudamericid allotheres had pretty much all of this landmass for themselves.

Okay, let’s now dive deep into Late Paleocene Asian oddities.

As I said, Lambdopsalidae actually diversified in this continent, even though basal rodents were already there and placentals achieved dominance over multituberculates (which is the second argument against “rodents outcompeted multis” theory). They were also fairly large for their group, only bested by taeniolabidids and roughly similar in weight to Boffius. Their ecology, however, seems to correspond with burrowing, which suggests they were somewhat of a giant marmot living alongside smaller rodents. Most fossils are from Mongolia and China, but they could’ve been even more widespread.

Ptilodontoideans are represented by a ghost lineage here btw, so don’t panic. We’ll touch on them later.

Meanwhile in India, two genera I recently named somehow disappear. Yeah, you know, in spite of Bharattherium being a very efficient grass eater. From Late Paleocene onwards, Indian fauna is represented mostly by placental island hoppers, like lagomorphs and hyaenodonts.

Then PETM hit, and lambdopsalids perished in a catastrophic global warming. Ptilodontoidea, however, managed to cling on, and actually persisted in Eocene China as a sole relictual genus Mesodmops, one seemingly similar to squirrels. Judging by the timeline, they stood no chance during the Azolla Event and were gone by the Middle Eocene.

And thus, Asia became the Kingdom. Of Placentals.

Ok, Laurasia done. Now it’s time to fully delve into Gondwana and study non-therians from South America, Antarctica (basically a continuation of South America at that point), and Africa as well. See you soon!

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Africa

Well, not much to say here. A sole known non-therian is an enigmatic gondwanathere Galulatherium, which did not survive even into Maastrichtian. Madagascar’s Maeravano Formation, on the other hand, does offer us its relative Lavanify and a more distant Adalatherium, which was featured in Prehistoric Planet. Still, no fossil record is available until Pleistocene, so we have no clue what happened to them – did they die in K-Pg, or did they meet placentals and perished in Cenozoic? Seems like we’ll never know.

South America (and Antarctica)

South America, much like its northern neighbor, was a place where quite a lot of mammalian lineages thrived after dinosaurs were reduced to just birds. These were familiar monotremates, seemingly close relatives of multituberculates named Gondwanatheria (represented here by one or two families Sudamericidae (duh) and possibly Ferugliotheriidae, plus some controversial genera) and theriiform Meridiolestida (represented by families Peligrotheriidae and Necrolestidae). Let’s discuss them.

Monotremata, the only group of non-therians that survives to this day, is only known in South America during Cretaceous and Paleocene. Its only Cenozoic representative was Monotrematum, which was basically a clone of modern platypus, but in Argentina. Judging by the fact that Australia and Americas were connected through Antarctica, it is quite possible egg-layers lived there as well.

Gondwanatheres, meanwhile, were more enigmatic during Danian and for whole 5 million years they were only represented through ghost lineages, although Sudamerica did indeed first appear alongside previously mentioned Monotrematum.

But the most interesting are Peligrotheriidae, since this was definitely their golden age. A sole member of this family, Peligrotherium, reached the size of a dog and became the biggest South American mammal of its era. Its ecology was also peculiar, as its bunodont teeth crushed very hard plant matter and basically helped to eat through everything, just like a pig.

Don’t ask about Necrolestidae btw. They won’t appear in a fossil record for a while.

Then the Late Paleocene started, and in South America both Peligrotheriids and monotremes disappeared (although the latter could’ve survived for longer in Antarctic rivers). Gondwanatheres, however, were seemingly not affected by a happening that killed most multis, or even arrival of marsupial and ungulate invaders (yeah, ironically, they first came from the North). In fact, it seems like Sudamerica actually expanded its range, crossing into Antarctica and adapting to its still warm forests. Necrolestids probably did the same, but we’ll get to that.

PETM, Azolla Event and cavimorph rodent’s arrival also didn’t do shit to these groups, and in Eocene gondwanatheres remained abundant on both continents. Aside from Sudamerica, there also existed Argentinian genus Greniodon of uncertain affinities, LACM 149371 (a weird, partially degraded tooth which possibly represents a sole known Cenozoic ferugliotheriid) and the whole new family Groeberiidae (to be fair, they may be marsupial as well). Still, all were small- to mid-sized herbivores (with the first two being adept grass eaters) and never managed to get at least as big as Peligrotherium.

A sole necrolestid tooth (which is now lost) was also found in Eocene Antarctica. One can only wonder what would’ve happened if them and gondwanatheres managed to reach the safety of Australia.

Not much is known about Oligocene though. Unlike previous extinctions, Grand Coupure definitely managed to weaken these groups, and they declined drastically. Antarctic representatives, meanwhile, likely froze to death.

And so, we reach our final destination. Miocene. Here, in Argentina, two relics cling on in a fauna dominated by metatherians, SANUs and xenarthrans. The first one is Patagonia, a small digging herbivore similar to tuco-tuco, the last gondwanathere (although it may be some sort of marsupial as well). Alongside it lives the last necrolestid, Necrolestes, a mole rat analogue that hunted for soil invertebrates. Both were representatives of a bygone era. In the Kingdom of Therians.

Conclusion approaches. Let’s end this on a higher note.

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Ok, let’s finish this. One continent to go.

Australia

Australia, much like Africa, only had one non-therian group – Monotremata. Unlike Africa, however, these critters are still with us, which is something that must be appreciated. They are the last remnants of Mesozoic mammals.

But let’s get back to the past first. Not much is known about Paleocene and Eocene, aside from the fact that archaic platypuses survived metatherian arrival and a cascade of climate-related extinctions with a morphology virtually unchanged from Mesozoic. Oligocene was the first period where we get Australian monotreme fossils, these being representatives of genus Obdurodon. By Miocene, these animals reached a meter in length, becoming truly dominant in rivers of Queensland. This was also a time modern platypuses appeared, by the way.

One lineage, however, got stranded on a New Guinea – big island that had no mammals at a time. So there, in isolation, they evolved into a more terrestrial niche and eventually returned to their homeland. Meet Megalibgwillia, a first echidna.

Meanwhile, New Zealand, which was mostly submerged in Paleogene, reappeared, providing us with fragmentary bones of a yet unnamed Saint Bathans mammal. It was a survivor of an archaic non-therian lineage, which sadly, stood no chance against global cooling trends.

Pliocene is not particularly interesting, but in Pleistocene echidnas suddenly got larger, which is very noticeable in genus Murrayglossus, which reached 30 kilograms in weight. And much like other Australian megaphauna, these giant monotremes suddenly went extinct when Holocene began (likely thanks to us).

But what about current day? Tachyglossus echidna is a fairly widespread species that lives in all of Australia and some parts of New Guinea. Ornithorhynchus platypus is threatened with habitat destruction, but is still somewhat common, and was introduced to Kangaroo Island. Zaglossus echidnas, however, are on the verge of extinction (except eastern species which was a little bit more lucky), and if we don’t do at least something to save them, Age of Monotremes will get closer and closer to ending.