Modern mammals are the only surviving members of a much larger evolutionary group known as the synapsids – which back in the Permian period were the dominant land vertebrates.
But much like all other life on Earth at the time, the synapsids were absolutely devastated in the “Great Dying” mass extinction at the end of the Permian, 252 million years ago. Only three lineages survived into the Triassic: the dicynodonts (who briefly took over the world), the therocephalians (who went extinct not long afterwards), and the cynodonts (who eventually gave rise to early mammals).
Diademodon tetragonus here lived right in the wake of the extinction during the Early and Middle Triassic, about 251-242 million years ago. Around 2m long (6′6″), it was one of the largest known cynodonts, and it must have been a fairly successful species since it ranged across a large chunk of Pangaea, known from modern southern Africa, South America and Antarctica.
It had pig-like cheekbones and enormous jaw muscles, along with sharp incisors and canine teeth at the front of its jaws and grinding molars at the back. This arrangement suggests that much like modern pigs it may have been an opportunistic omnivore, occasionally snacking on smaller animals and carrion – although an isotope analysis of its teeth indicates the vast majority of its diet was probably still vegetation in shady damp environments.
Did you know some crocodiles have “horns”?
Formed from the corners of the squamosal bone at the back of their skulls, just above their ears, these structures are seen in living crocs like the Cuban crocodile and the Siamese crocodile, as well as some fossil species.
But perhaps the most impressively-horned croc was Voay robustus here.
Voay lived on the island of Madagascar during the Late Pleistocene and Holocene, between about 100,000 and 2,000 years ago. At about 5m long (16′5″) it was similar in size and build to a large male Nile crocodile – but despite this resemblance its closest living relative is actually the much smaller dwarf crocodile.
It had a fairly short and deep snout and chunky limbs, adaptations associated with a more terrestrial lifestyle that suggest it was specialized for hunting its prey on land rather than just at the water’s edge.
Much like modern horned crocodiles its particularly prominent horns were probably used for territorial displays, and may have been a sexually dimorphic feature with big mature males having the largest examples.
Voay’s disappearance just a couple of thousand years ago may have been the result of the arrival of human settlers on the island, either from being directly hunted or due to the large native species it preyed on also going extinct around the same time.
Sclerothorax hypselonotus was a temnospondyl amphibian that lived in Germany during the Early Triassic, around 251-247 million years ago.
Measuring about 1.2m long (3′11″), it had some unusual features for a temnospondyl – a very rectangular skull with a wide blunt snout, and elongated spines on its vertebrae that gave its body a sort of “hump-backed” shape.
It was part of a lineage of temnospondyls called capitosaurs, which mostly occupied the same sort of aquatic predator niche as modern crocodiles – but unlike its close relatives Sclerothorax’s well-developed spine and limbs suggest it spent much more time walking around on land.
(And while there was another temnospondyl known to have similar extended vertebrae – the sail-backed Platyhystrix – the two weren’t actually closely related to each other.)
Pigs were once unicorns.
Kubanochoerus gigas lived about 15-7 million years ago during the mid-to-late Miocene, and ranged across a large portion of Eurasia with fossils known from both Georgia and China.
It was one of the largest known pig species to ever live, slightly bigger than the modern giant forest hog at about 1.2m tall at the shoulder (3′11″). But its most distinctive features were its horns, with a small pair above its eyes and a single large forward-pointing one on its forehead.
A few specimens lack the large horn, and so some paleontologists consider it to be a sexually dimorphic trait possessed only by males. But it’s currently unclear whether this was actually the case, since at least one “hornless” skull has been reported with the distinctive larger tusks also associated with male pigs – so it’s possible that the horned and hornless Kubanochoerus were actually separate species!