Neolicaphrium recens here might look like some sort of early horse, but this little mammal was actually something else entirely.

Known from southern South America during the late Pleistocene to early Holocene, between about 1 million and 11,000 years ago, Neolicaphrium was the last known member of the proterotheriids, a group of South American native ungulates that were only very distantly related to horses, tapirs, and rhinos. Instead these animals evolved their remarkably horse-like body plan completely independently, adapting for high-speed running with a single weight-bearing hoof on each foot.

Neolicaphrium was a mid-sized proterotheriid, standing around 45cm tall at the shoulder (~1’6″), and unlike some of its more specialized relatives it still had two small vestigial toes on each foot along with its main hoof. Tooth microwear studies suggest it had a browsing diet, mainly feeding on soft leaves, stems, and buds in its savannah woodland habitat.

It was one of the few South American native ungulates to survive through the Great American Biotic Interchange, when the formation of the Isthmus of Panama allowed North and South American animals to disperse into each other’s native ranges. While many of its relatives had already gone extinct in the wake of the massive ecological changes this caused, Neolicaphrium seems to have been enough of a generalist to hold on, living alongside a fairly modern-looking selection of northern immigrant mammals such as deer, peccaries, tapirs, foxes, jaguars… and also actual horses.

Some of the earliest human inhabitants of South America would have seen Neolicaphirum alive before its extinction. We don’t know whether they had any direct impact on its disappearance – but since the horses it lived alongside were hunted by humans and also went extinct, it’s possible that a combination of shifting climate and hunting pressure pushed the last of the little not-horses over the edge, too.

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.

Strange Symmetries #21: Uneven Ungulates

Asymmetry is commonly seen in the headgear of modern even-toed ungulates, with natural genetic variation, developmental stress, and injuries during life sometimes causing very wonky-looking horns or antlers.

No living species have asymmetry as a standard trait, however – but some fossil ungulates did.

Ramoceros osborni was a relative of the modern pronghorn living during the mid-Miocene, about 13 million years ago, in open plain habitats of what is now the Midwest and Mountain states of the USA.

It was smaller than modern pronghorns, around 70cm tall at the shoulder (~2’4″), and males had long antler-like horns with three tines. Bizarrely, one of these horns was always at least twice the size of the other, with “left-horned” and “right-horned” individuals seeming to occur in equal numbers.

It’s not clear how this asymmetry affected combat between males. Could they only properly lock horns with “opposite-sided” rivals, or did this uneven arrangement actually prevent physical fights and restrict them more to just visual displays?

An illustration of the head of Tsaidamotherium, an extinct hoofed mammal distantly related to modern giraffe and okapi. It has a vaguely moose-like head with a bulbous fleshy snout. Its left ossicone "horn" is above its eye and very small, while the right ossicone is much larger and positioned towards the middle of its forehead, forming a wide blunt helmet-like structure like a very stubby fat unicorn horn.
Tsaidamotherium hedini

Meanwhile in China another Miocene ungulate known as Tsaidamotherium hedini also had strange headgear, with an enlarged right “horn” forming a helmet-like dome on top of its head. This species was featured here on the blog just year, so check out that post for more details about it.

Strange Symmetries #19: Wonky Whales

Toothed whales – the branch of cetaceans that includes modern dolphins, porpoises, beaked whales, and sperm whales – have surprisingly asymmetrical skulls, with some of the bones skewed to one side and just the left nostril forming their blowhole.

Some of the most obvious external manifestation of this lopsidedness can be seen in sperm whales, which have their blowhole at the front left side of their head, and in male narwhals, which usually have a single left-side tusk.

This sort of asymmetry first appeared in the skulls of early toothed whales around 30 million years ago. And since the highest amounts of wonkiness have gone on to develop in lineages that hunt in dark, cluttered, or murky waters, this suggests that the trait is somehow linked to the evolution of complex echolocation.

Some ancient members of the river dolphin lineage also had some additional unusual asymmetry, sometimes having slightly sideways-bending snouts.

Ensidelphis riveroi was one of the weirdest of these, living around the coasts of what is now Peru during the Miocene, about 19 million years ago. Around 3m long (~10′), it had a very long narrow toothy snout that curved distinctly off to the right along its length.

A sketch showing Ensidelphis' bizarre side-curving snout. A hypothetical straight snout is shown outlined in blue, while the actual curvature is overlaid in red.
Expectation vs reality

It’s not clear what the function of this bend was, or even if the only known skull actually represents the normal condition for this species. But Ensidelphis’ bendy snoot might have been used to probe around in muddy seafloor sediment or to extract prey from crevices, possibly like an underwater version of the modern wrybill.


Antaecetus aithai was an early whale that lived during the late Eocene (~40 million years ago) in what is now Morocco, at a time when northern Africa was covered by a warm shallow sea.

It was part of the “basilosaurids“, some of the first fully aquatic cetaceans – traditionally considered to be a single defined group, but more recently found to be more of an “evolutionary grade” of multiple early whale lineages – and much like Basilosaurus it had elongated back vertebrae that would have given it a very long slender body shape.

Antaecetus also had a proportionally smaller head and smaller teeth than other basilosaurids, along with much denser bones and a stiffer spine that would have made it a rather slow swimmer with reduced maneuverability. It was also fairly small overall compared to most of its relatives, probably around 6m long (~20′).

It was probably a slow-moving coastal water animal somewhat like modern sirenians – except unlike manatees and dugongs it was carnivorous. Its relatively delicate teeth suggest it was feeding on soft-bodied prey like cephalodpods, and with its lack of speed it must have been some sort of ambush predator, waiting around for potential prey to come within striking range.

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:

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 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.