It Came From The Wastebasket #20: Colossally Convoluted Condylarths

“Insectivora” was a wastebasket taxon so bad it had to be revised multiple times, but there’s another particularly infamous case in mammal taxonomy that’s still in the process of being resolved – the “condylarths.

This group was first created in the early 1880s, during the Bone Wars, and initially was just a subgroup of odd-toed ungulates containing only the phenacodontids. But just a few years later Condylarthra was promoted up to its own order, and groups like the periptychids and hyopsodontids were added in too.

Then over the next few daceds century various groups were added and removed from the condylarths, most notably with the mesonychids and arctocyonids being brought in from their previous position with the creodonts.

By the mid-20th century the condylarths had become a big convenient dumping ground for any and all “primitive” ungulate-like mammals that didn’t easily fit into any modern groups, ranging in age from the early Paleocene through to the early Oligocene. But it soon became apparent that they had the same problem as the “insectivores” – there weren’t really any unique anatomical features that united all these animals together.

They generally had rounded-cusped molar teeth and hoof-like toes, but they also had rather generalized “primitive mammal” features and a diverse range of ecologies. Some were small herbivores, but others were coati-like or dog-like omnivores, and some were even bear-sized carnivores.

An illustration showing five different "condylarths". On the top row is Hyopsodus, a small guinea-pig-like animal with a long horse-like head; then Meniscotherium, a slightly larger animal that somewhat resembles a capybara; then the much larger Arctocyon, which has a slightly bear-like body, hoofed towes, and a dog-like head. On the bottom row is Ectoconus, a small animal with a tapir-like body and a blunt rectangular snout; then Mesonyx, a much larger dog-like animal with hoofed toes and a long tail.
From left to right, top row: Hyopsodus lepidus (hyopsodontid), Meniscotherium chamense (phenacodontid), Arctocyon primaevus (“arctocyonid”).
Bottom row: Ectoconus ditrigonus (periptychid), Mesonyx obtusidens (mesonychid)

It wasn’t even clear how the various different condylarth groups were actually related to each other. The best guess was that arctocyonids had arisen from within the “insectivores”, with a Protungulatum-like form as the common ancestor of all the other condylarths. Where exactly modern ungulates had then evolved from within the condylarths was also still uncertain.

Cladistic analysis in the 1980s began to tackle the confusing pile of assorted condylarths, and showed that they weren’t the single ancestral source of all modern ungulates, but instead a loose collection of several unrelated groups from all over the ungulate evolutionary tree. Arctocyonids, periptychids, and hyopsodontids were placed as early “primitive” lineages, phenacodontids were loosely linked with the ancestors of odd-toed ungulates once again, and mesonychids were considered to be the ancestors of whales.

An image of a diagram from a 1994 academic paper, showing the proposed evolutionary relationships of various "condylarths" with main ungulate groups. It differs majorly from modern understanding by its inclusion of elephants, sirenians, hyraxes, and their extinct relatives, along with showing whales as descending from mesonychids instead of artiodactyls.
…And if you know modern mammal phylogeny you’ll probably see some big problems here. 🐘
(Image source: https://doi.org/10.1017/S2475263000001343)

And, once again paralleling the mess of the “insectivores”, it wasn’t until genetic methods became available in the late 1990s that larger-scale ungulate relationships began to be properly resolved. The paenungulates (elephants, hyraxes, and sirenians), which had been traditionally considered to be a major branch of ungulates, were removed entirely and reclassified as afrotheres. And, along with some new fossil discoveries, whales were recognized as having actually evolved from within the even-toed ungulates instead of from mesonychids.

This shake-up threw the still-problematic “condylarth” classifications back into question – with some “condylarths” turning out to also be afrotheres instead of true ungulates.

Today the actual relationships of the main “condylarth” ungulate families are still in the process of being figured out, and there’s a lot of remaining uncertainty and disagreement about them.

Phenacodontids seem to have mostly maintained their traditional position as early odd-toed ungulates, and hyopsodontids may potentially be part of this group too – possibly as members of the hippomorph lineage, closely related to horses and brontotheres. Arctocyonids might be a wastebasket themselves, with some studies finding them to be a mix of several different archaic ungulate lineages. Periptychids may have links to the even-toed ungulates. The mesonychids, meanwhile, are now generally considered to be a separate order from the traditional “condylarths”, and may be either an early branch of the even-toed ungulates or much more basal ungulates closely related to the “arctocyonids”.

Since the term “condylarth” no longer has any real taxonomic meaning some paleontologists have proposed replacing it with “archaic ungulate” to distance from the historical messiness of the old name. But this hasn’t really caught on, and many papers still use “condylarth” in a very loose sense to refer to an “evolutionary grade” of early ungulates of unclear evolutionary affinities.

A cladogram showing the modern classification of several different "condylarth" families. They're shown as potentially occupying positions throughout the branches of the even-toed and odd-toed ungulates.

And while that’s the last main entry for this month, we’re not quite done yet. There’s still one weekday left in October, and after digging through so many taxonomic garbage cans there’s only one place we can go now.

…See you in the trash heap.

It Came From The Wastebasket #11: A Cetothere Change

Cetotheres were a group of small baleen whales, one of three major lineages of these cetaceans alongside the rorquals and the right whales. They first appeared in the fossil record in the mid-Miocene, about 14 million years ago (but are estimated to have actually originated 10-15 million years earlier), and disappeared during the Pleistocene about 2 million years ago.

First recognized in the mid-19th century, for a long time the cetotheres were used as a wastebasket for all fossil baleen whales that didn’t clearly fit into any modern whale families. By the start of the 21st century nearly 30 different genera representing numerous different species were all lumped into the group – and the genus Cetotherium was another wastebasket in itself with at least 12 assigned species, many of which were based on fragmentary or dubious remains.

An illustration of Ciuciulea, an extinct cetothere baleen whale. It looks similar to modern rorquals, with a streamlined and relatively slender body, but lacking the typical throat grooves of that type of whale. Its jaws are long and narrow, with a paired blowhole at the top of its head and small eyes set near the corners of its mouth. It also has fairly small flippers, a dorsal fin set about two-thirds of the way down its back, and a horizontal tail fluke. It's coloration is countershaded, mostly grey on top and white underneath.
Ciuciulea davidi

This was finally cleaned up in the 2000s, when a revision of the cetotheres cut the group down to just 6 genera. Since then a handful of additional new genera and species have been named, and while a few polyphyletic Cetotherium species may still need tidying up the cetotheres have overall gone from being a total taxonomic mess to actually being one of the best studied groups of fossil baleen whales.

Their exact evolutionary relationships with each other are still in flux, but the most surprising discovery from the improved understanding of these ancient whales is that they might not be extinct after all.

A set of three screenshots from the animated movie "Ice Age: Dawn of the Dinosaurs". The first image shows the two opossum characters Crash and Eddie asking, "Were you killed?!" The second image shows the weasel buck looking away and replying, "Sadly, yes…" The third image shows Buck leaning closer and adding "but I lived!" Buck's face has been photoshopped into that of a Cetotherium whale in both shots.

A study in the early 2010s suggested that the pygmy right whale may actually be a living cetothere. This classification was initially controversial, but further discoveries of fossil relatives of this enigmatic modern whale and comparisons of their distinctive inner ear anatomy have provided stronger evidence for an evolutionary link.

At this point it seems fairly likely that the pygmy right whale really is either the last surviving representative of the cetothere lineage, or at least is a very close evolutionary “cousin” (a “cetotherioid”) closer related to them than to any other modern baleen whales.

Spectember 2022 #04: Aquatic Brontotheres

Squeezing in one last bonus #Spectember post this year!

This one isn’t based on a specific prompt, but instead is a companion piece to a previous one.


While North American brontotheres were adapting to the spread of grasslands, some of their Asian cousins took a very different evolutionary path through the rest of the Cenozoic.

Continue reading “Spectember 2022 #04: Aquatic Brontotheres”

Spectember 2022 #02: ‘Modern’ Brontotheres and Paraceratheres

Today’s #Spectember concept is a combination of a couple of anonymous submissions:

A digital illustration of two speculative hoofed mammals, descended from extinct brontotheres and paraceratheres. One resembles a hairy rhinoceros with an odd U-shaped horn on its nose and a fork-like bony "horn" on the back of its head. The other looks like a chunky camel with a moose-like bulbous nose and short downward-pointing protruding tusks.
Crowned brontothere (left) and woolly paracerathere (right)

These two animals are the descendants of brontotheres and paraceratheres, almost the last living representatives of their kinds, hanging on in the equivalent of modern-day times in a world similar to our own.

Continue reading “Spectember 2022 #02: ‘Modern’ Brontotheres and Paraceratheres”

Tsaidamotherium

Tsaidamotherium hedini was a ruminant ungulate living around 11 million years ago during the late Miocene, in the northeastern part of the Tibetan Plateau in what is now Northwestern China. Although it’s known only from partial skull remains it was probably similar in body size to a large sheep, about 80cm tall at the shoulder (2’7″).

Since its discovery in the 1930s it’s traditionally been classified as part of the muskox lineage, but in 2022 it was proposed to actually be a giraffoid very closely related to the newly-discovered Discokeryx.

Tsaidamotherium had some extremely unusual headgear, with highly asymmetrical “horns” (actually ossicones if was a giraffoid). The left one was small and positioned above the eye, while the right one was shifted back and towards the middle of the forehead, and was expanded out into a wide bony disk that would have supported a large helmet-like domed keratin covering.

Its skull also had a very large nasal cavity resembling that of the modern saiga antelope, suggesting it may have convergently evolved a similar sort of complex air-filtering snout to deal with dry cold air in its mountainous habitat.

Casatia

Modern beluga whales and narwhals are the only living representatives of the monodontid lineage, found only in cold Arctic and sub-Arctic waters. But this whale family actually first evolved in much warmer climates – and some of them were downright tropical.

Casatia thermophila lived about 5 million years ago during the early Pliocene, in the Mediterranean Sea around Tuscany, Italy. Although known only from a couple of partial skulls and a few vertebrae it was probably similar in size to its modern relatives, around 5m long (16’4″).

It seems to have had a larger number of functional teeth than modern monodontids, and probably didn’t suction feed like its modern close relatives. Instead it may have fed more like most porpoises and dolphins, relying more on speed and snapping jaws to capture prey.

It inhabited the Mediterranean at a time not long after the sea there had mostly dried up and then been rapidly refilled. The presence of warm-water marine species such as bull sharks, tiger sharks, and dugongs in the same fossil beds as Casatia indicates the local climate at the time was hotter than it is today, with tropical temperatures – and suggests that this whale’s ancestors must have originally moved into the replenishing Mediterranean from lower latitudes alongside these other warmth-adapted animals.

This tropical monodontid was also much closer related to modern belugas than modern narwhals are, which raises the possibility that the two living monodontid species actually specialized for colder conditions completely independently of each other rather than descending from a cold-adapted common ancestor. Instead modern belugas and narwhals may have originated from separate warm-water monodontid ancestors who evolved similar cold-tolerant adaptations in parallel as the climate cooled during the onset of the Quaternary ice age, while the rest of their relatives all went extinct.

Retro vs Modern #16: Uintatherium anceps

Discovered in the Western United States during the early 1870s, Uintatherium anceps was part of one of the earlier major conflicts in the the Bone Wars. Nearly 30 different scientific names were applied to various fossil specimens of this mammal in under two decades, and the taxonomic tangle wasn’t properly sorted out until nearly a century later in the 1960s when they were recognized as actually all being the same species.


1870s

Paleontologist Edward Cope considered Uintatherium (under the name “Loxolophodon”) and its close relatives to be proboscideans – part of the elephant lineage – due to some of the similarities in their anatomy. The first reconstruction of these animals showed this version, depicting elephant-like animals with downward-pointing tusks, short tapir-like trunks, and the multiple bony projections on their skulls speculatively shown as attachment points for large antler-like horns.

Cope’s rival Othniel Marsh heavily criticised that interpretation of Uintatherium, arguing that these huge mammals were instead a separate group within the ungulates named dinoceratans – although this wasn’t really as huge of a classification difference as it seems today, since at the time proboscideans were also considered to be ungulates!

The dinoceratan ungulate interpretation quickly won out, and for a while in the 20th century Uintatherium actually became a fairly popular and well-known prehistoric mega-mammal, commonly included in collections of cheap plastic “dinosaurs” and usually depicted as more of a knobbly-headed sabertoothed rhino.


2020s

In recent years the dinoceratans seem to have fallen into obscurity and some degree of paleontological neglect, with little modern work on the group and no major studies for the last couple of decades – although this might be starting to change.

Despite the early ideas about them being ungulates, the evolutionary relationships of dinoceratans have become much more murky over the last century or so. Due to different elements of their anatomy being highly convergent with various other mammals it’s easy to find “false positives” in morphological comparisons, and they’ve been proposed as being connected to a wide variety of groups including “condylarths“, “insectivores“, rodents, and cimolestans. But some mid-2010s research suggests they were in fact ungulates after all, closely related to early South American forms like Carodnia – a lineage whose own evolutionary relationships are murky, but may have close affinities with modern horses, rhinos, and tapirs.

We now know Uintatherium anceps lived across the Western and South Central USA during the mid-Eocene, about 46-40 million years ago, at a time when warm wet climates extended up into the Arctic and lush tropical-style rainforests covered much of the continent.

It was similar in size and build to a modern white rhino, about 4m long (13′) and stood around 1.7m tall at the shoulder (5’7″). It had three distinctive pairs of “horns” on its forehead, snout, and nose, that were similar in structure to the ossicones of giraffids, probably covered in skin and hair rather than keratin. Its elongated canine teeth were protected by bony flanges on its lower jaw, and seem to have been a sexually dimorphic feature that was much more prominent in males.

It also had an oddly concave skull, with its forehead dipping inwards, and an unusually tiny braincase for its size. It probably wasn’t a particularly intelligent animal, but it didn’t really need to be – as one of the first types of herbivorous mammal to get truly huge in the early Cenozoic, a fully-grown Uintatherium probably had no natural predators at all.

Kogiopsis

Kogiopsis floridana was a physeteroid whale that lived near the coast of the southeastern United States from the mid-Miocene to the early Pliocene, about 14-4 million years ago.

Known just from fossilized lower jaws and teeth, with some teeth up to nearly 13cm long (~5″), its full life appearance and size are uncertain – but it may have been slightly larger than a modern bottlenose dolphin at around 4.5m long (~14’9″). It’s traditionally been considered to be part of the kogiid family, closely related to modern pygmy and dwarf sperm whales, but some studies disagree with that classification and instead place it in the true sperm whale lineage.

It was probably a predator in a similar ecological role to modern orcas, adapted for hunting prey like squid, fish, and smaller marine mammals. But unlike orcas it wouldn’t have been the apex predator of its ecosystem, subject to predation pressure by even larger carnivores like macroraptorial sperm whales and everyone’s favorite ridiculously huge shark – and as a result it probably had a “live fast and die young” lifestyle similar to modern kogiids and other small-to-medium-sized Miocene physeteroids, rapidly maturing and only living to around 20 years old.

I’ve reconstructed Kogiopsis here as a kogiid-like animal, with a similar sort of shark-like head shape and “false gill” markings. In the background a second individual is depicted displaying “inking” behavior, releasing a defensive cloud of reddish-brown fluid from a specialized sac in its colon.

Elasmotherium

Elasmotherium sibiricum was a giant rhinoceros that lived during the mid-to-late Pleistocene epoch, between about 800,000 and 39,000 years ago. Found across much of the Eurasian steppe dry grassland environments, it stood around 2.5m tall (8’2″) at the top of its humped shoulders and weighed about 4 tonnes (4.4 US tons), making it close in size and mass to a modern elephant.

It was the last known representative of a particularly ancient lineage of rhinos, last sharing a common ancestor with modern forms over 40 million years ago.

A large bony dome on its forehead is traditionally thought to have supported an enormous keratinous horn like the distantly-related woolly rhino, but a 2021 study has recently challenged that interpretation. The dome structure was actually rather thin-walled and wouldn’t have been able to support the weight of a giant horn, instead probably being covered by a much stumpier backwards-pointing nub – while an enlarged nasal cavity inside the dome also suggests it may have actually functioned as a resonating chamber, similar to the crests of hadrosaurs or the extinct wildebeest Rusingoryx.

It also had a smaller toughened “pad” on its nose that may have been used along with a prehensile upper lip to dig around in the soil for plant roots and tubers.

Phiomicetus

Named after the canine-headed Ancient Egyptian god, Phiomicetus anubis is the first fossil cetacean to discovered, described, and named entirely by a team of Arab paleontologists.

Living during the mid-Eocene, about 43 million years ago, in a shallow sea-covered region that is now part of Egypt‘s Western Desert, Phiomicetus was an early protocetid – an amphibious foot-powered swimmer, at a transitional point in the evolution of whales from deer-like terrestrial animals to fully aquatic screaming torpedoes.

About 3m long (~10′), it had large jaw muscles and sharp teeth with wear patterns that suggest it was a raptorial hunter grabbing and snapping at prey with powerful bites. It would have probably tackled fairly big prey compared to other protocetids, hunting things like large fish, turtles, and even smaller whales in an ecological role similar to that of modern orcas.

Along with the distantly-related long-snouted Rayanistes it’s one of the earliest known whales from Africa, giving us further glimpses at a time period when early cetaceans were first dispersing out from the South Asian subcontinent via the ancient Tethys Sea.