Tag: convergent evolution

Weird Heads Month #28: Pig-Nosed Tanks

There’s already been quite a few Triassic weirdos in this series, so it’s probably not much of a surprise that we’ve got one more before the end of the month.

Desmatosuchus spurensis here was part of a group called aetosaurs, a lineage of heavily-armored herbivorous archosaurs which convergently resembled the later ankylosaurs but were more closely related to modern crocodilians.

Living in the Southwestern and South Central United States during the late Triassic, about 221-210 million years ago, Desmatosuchus measured around 4.5m long (14’9″) and was covered in thick interlocking bony osteoderms that protected its back, sides, belly, and tail, with longer spines over its neck and shoulders.

It had a triangular skull with a few blunt teeth at the back of its jaws and a toothless snout at the front. Its pointed lower jaw probably had a keratinous beak, while its upper jaw had an odd upturned flared tip. What exactly was going on with that snoot is uncertain, but it may have anchored a shovel-shaped upper keratinous beak – or, since there was a little bit of flexibility between its snout bones, possibly even a pig-like nose!

It probably mostly ate soft vegetation, using its shovel-like snout to dig up roots and tubers, although similarities with the skulls of modern armadillos suggest it may also have fed on insect grubs.

Weird Heads Month #27: The Weirdest Wildebeest

Earlier in this series we saw some ruminants with bizarre-looking headgear, but there was another species in that group that evolved a completely different type of strange head.

Rusingoryx atopocranion was a close relative of modern wildebeest that lived during the late Pleistocene, around 100,000 to 50,000 years ago. Its fossil remains are known from the Kenyan part of Lake Victoria, on Rusinga Island – an area which wasn’t actually an island at the time due to lower lake levels, and was instead part of a hot dry grassland environment.

Standing about 1.2m at the shoulder (~4′), it had an oddly-shaped skull with a pointed snout and a highly domed forehead. But this wasn’t the thick bony dome of a headbutting animal – this structure was narrow and fairly fragile, and had looping nasal passages running through it.

Instead it was something never before seen in any mammal: a bony nasal crest convergently similar to those of hadrosaurid dinosaurs.

Juveniles had less developed crests, developing them as they matured, and one skull that may represent an adult female also has a smaller crest, suggesting that this feature was sexually dimorphic.

Based on just the anatomy of the nasal passages Rusingoryx may have honked at a frequency similar to a vuvuzela, but the added length of its vocal tract could have lowered this pitch even further, closer to infrasound ranges – so more like a tuba! Such low frequencies can travel very long distances and are also below the hearing range of many carnivores, and would have effectively allowed Rusingoryx to shout at each other in “stealth mode”.

Weird Heads Month #25: The Case of the Missing Trunk

The rhino-like toxodontids from earlier in this series weren’t the only weird-headed South American ungulates. Another group known as the litopterns evolved in a different direction, becoming long-legged fast-moving animals convergently filling the same sort of ecological niches as modern horses, deer, bovids, camelids, and giraffids.

Macrauchenia patachonica was one of the strangest members of this lineage, living from the Late Miocene to the end of the Pleistocene, between about 7 million years ago and just 12,000 years ago.

It stood around 1.8m at the shoulder (5’11”) and resembled a large camel or llama with thee-toed hoofed feet, but its head was… confusing.

Its skull had a bizarre combination of features, with a shape closer to a sauropod dinosaur than a mammal, a cartoonish-looking set of teeth, and its nostrils set up high above its eyes, more like a cetacean blowhole than a terrestrial herbivore.

Due to its retracted nostrils it’s commonly been restored with an elephant-like or tapir-like trunk. And while a trunk gives Marauchenia a wonderfully weird and memorable appearance, there’s just one problem with that interpretation.

There’s no evidence for it.

Aside from its nostrils being far back on its head, it didn’t have any other features associated with anchoring the complex musculature of a trunk. In fact, a recent study found that its skull characteristics were much closer to those of moose than tapirs!

It seems more likely that it had a moose-like bulbous fleshy nose – possibly giving it an enhanced sense of smell or functioning as a resonating chamber – perhaps with slightly retracted external nostrils like a giraffe or sauropod to prevent it from being stabbed in the nose when feeding on spiky vegetation.

Whatever it was doing with its weird schnoz, it was clearly a highly successful species, since it was found across most of South America in a wide range of habitats.

Weird Heads Month #23: Dome-Headed Claw-Horses

Much like Platybelodon from a few entries back, chalicotheres look like a fictional creature design rather than something that actually existed.

These animals were odd-toed ungulates related to modern horses, tapirs, and rhinos, who ranged across Africa, Eurasia, and North America for a large chunk of the Cenozoic. Instead of hooves they had large claws on their feet, and they appear to have occupied the same sort of ecological niche as ground sloths or therizinosaurs – sitting or rearing up on their hind legs to browse on high vegetation, using the hook-like claws on their forelimbs to pull down and strip branches.

There were two different lineages of chalicotheres which developed along slightly different evolutionary paths: the knuckle-walking gorilla-like chalicotheriines and the more goat-like schizotheriines.

Tylocephalonyx skinneri here was one of the latter group, known from the Miocene of North America about 16-13 million years ago. Standing about 2m tall at the shoulder (6’6″), it had the same sort of chunky body as other schizotheriines and walked around with its large front claws held up to keep them raised away from the ground.

But there was also an unusual feature on its otherwise rather horse-like head – a large bony dome on top of its skull, like a mammalian version of a pachycephalosaur.

It probably used its dome in the same way as the dinosaurs it convergently resembled, headbutting or flankbutting in fights with each other.

Weird Heads Month #16: Big Honking Snoots

The dinoceratans featured here a few days ago were some of the first large mammalian herbivores to evolve in the Cenozoic, but during the Eocene they were joined by another group: the even bigger brontotheres.

Part of the odd-toed ungulate lineage, brontotheres convergently resembled rhinos but were actually much more closely related to horses. And much like the dinoceratans they also had some unusual heads, with some species evolving concave foreheads and sexually dimorphic ossicone-like pairs of blunt horns on their noses.

But others went really weird.

Embolotherium andrewsi lived in Mongolia during the late Eocene, around 37-34 million years ago. Standing around 2.5m tall at the shoulder (8’2″), it was one of the largest brontotheres and also one of the oddest-looking.

It had a large bony “battering ram” at the front of its snout, formed from modified nasal bones – and while some reconstructions tend to shrinkwrap this structure as a horn, the fact that the nasal cavity appears to have extended all the way to its tip suggests that it was actually supporting a huge bulbous nose.

Since Embolotherium also doesn’t seem to have been sexually dimorphic like other brontotheres, its enormous ridiculous-looking snoot may instead have been a resonating chamber used for sound production and communication.

Weird Heads Month #13: Many-Horned Mammals

The dinoceratans were a lineage of hoofed herbivorous mammals whose evolutionary affinities are a little uncertain, but may have been related to the South American meridiungulates. Found in Asia and North America from the late Paleocene to the late Eocene, they had bulky rhino-like bodies and were some of the largest terrestrial animals of their time.

Eobasileus cornutus was one of the biggest of them all, measuring around 2.1m tall at the shoulder (~7′) and living in the Western United States during the early Eocene, about 46-40 million years ago.

And it had a very odd-looking head, with six blunt ossicone-like horns, large sabre-like fangs, bony flanges on its lower jaw, a concave forehead, and a proportionally tiny brain for its body size. The horns and fangs were sexually dimorphic, much smaller in females, suggesting they were mainly used for display or combat between males.

Weird Heads Month #12: Double-Crested Dinosaurs

Dilophosaurus wetherilli is a fairly recognizable dinosaur thanks to its memorable appearance in the Jurassic Park franchise – but unfortunately that also means the popular image of it is completely wrong.

Rather than a small frill-necked venom-spitting creature, this early theropod was actually rather large, reaching around 7m long (~23′), and along with its distinctive double crests it also had a narrow snout with large teeth and a distinctive notch at the front of its lower jaw.

It lived in North America during the early Jurassic, about 196-183 million years ago, and while it wasn’t venomous its notched jaws were probably capable of delivering powerful bites to small struggling prey, much like the similar-looking ornithosuchids in the Triassic. Some structural similarities to the skulls of spinosaurids suggest it may have primarily eaten fish.

Its two bony crests were probably used for visual display, with juveniles only having small crests that fully developed as they matured. They also may have had a more extensive keratinous covering, so it’s not clear what their actual shape and full extent was in life.

Weird Heads Month #10: Permian Crowns

The tiny-headed Cotylorhynchus we saw earlier in this series wasn’t the only synapsid with a weird head.

A little more closely related to modern mammals, the dinocephalians were a a diverse group that were found across Pangaea during the middle of the Permian period. Many of them had thickened skulls that may have been used for headbutting each other, and some also developed bony horn-like projections around their faces.

And Estemmenosuchus mirabilis here was particularly elaborately ornamented, earning it a name meaning “wondrous crowned crocodile”. It lived in the Perm region of Russia during the mid Permian, about 268-265 million years ago, and was one of the largest dinocephalians, reaching at least 3m long (9’10”).

It had two big antler-like structures on its head, two wide cheek flanges, and a small nose horn, almost looking like the synapsid version of a ceratopsid dinosaur – and with its big bulky body, fairly erect-legged posture, and herbivorous-or-omnivorous diet it may have been a fairly close ecological equivalent to them, too.

But it’s also possible it was semi-aquatic, and it certainly does have a very hippo-like appearance when reconstructed with a decent amount of soft tissue.

One specimen of Estemmenosuchus even preserved skin impressions around its face, which were described in Russian in the early 1980s. They show scaleless glandular skin with a slightly bumpy texture, similar to that of hairless mammals or some amphibians. Since it occupied a point in the synapsid family tree close to where hair may have originated (somewhere in the Permian therapsids), it’s not clear if it was entirely hairless or if it had just secondarily lost some of it.

Weird Heads Month #05: Crested Snorkelers

Phytosaurs were a lineage of incredibly crocodile-like archosauriformes – essentially “crocodiles before crocodiles” – convergently evolving an incredibly similar appearance at a time when the ancestors of modern crocs were still small and terrestrial.

But while they had toothy snouts and bodies heavily armored with bony ostederms, unlike crocodilians their nostrils were far back on their heads up near their eyes, often in a sort of bony “snorkel” so they could breathe while almost fully submerged underwater.

Mystriosuchus westphali lived in Germany during the Late Triassic, about 215-212 million years ago. Around 4m long (~13′), it was even more aquatic than other phytosaurs, with paddle-like limbs and long slender gharial-like jaws adapted for catching slippery prey.

And along with the typical phytosaur snorkel, it also had raised crests along its upper jaw – which may have supported even larger keratinous display structures.

Weird Heads Month #03: Big Head Mode

In the last entry we had heads that looked much too small… so now how about heads that were too big?

Erythrosuchus africanus was part of an early branch of the archosauriformes, related to the ancestors of crocodiles, pterosaurs, and dinosaurs. Living in South Africa during the mid Triassic, around 247-242 million years ago, it was the largest predator of its time, reaching about 5m long (16’5″).

It was one of the earliest archosaurifomes to develop a more upright-limbed posture, and convergently evolved a very theropod-like head with a deep narrow snout full of large serrated teeth.

A head that was absolutely massive proportional to the rest of its body, measuring about 1m long (3’3″).

As a result of such a big noggin, Erythrosuchus must have also had some bulky musculature in its neck and forequarters to support it. And while its fairly short neck wouldn’t have been very flexible buried in all that tissue, it probably didn’t need to be – some of its main prey would have been large slow-moving dicynodonts, and its hunting strategy may have consisted of simply “aim at food and lunge”.