Rajasaurus

Abelisaurids were a group of theropod dinosaurs characterized by short snouts, bony ornamentation on their skulls, tiny stiff arms, and stocky legs. Known mostly from the southern continents of Gondwana, they were the dominant predators in these regions and are thought to have been specialized hunters of titanosaurian sauropods.

Rajasaurus narmadensis lived in what is now western India during the Late Cretaceous, about 67 million years ago. Around 7m long (23′), it had very rough-textured thickened bone on the top of its snout, along with a short rounded horn on its forehead that was probably used for display or headbutting behaviors.

India at this time was an isolated island continent located off the east coast of Africa, and Rajasaurus‘ ancestors probably island-hopped across from then-nearby Madagascar – where its closest known relative lived, the very similar-looking Majungasaurus.

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.

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.

Squaloraja

Discovered in the late 1820s by pioneering paleontologist Mary Anning, the odd-looking fossil of the cartilaginous fish Squaloraja polyspondyla seemed to have characteristics of both sharks and rays.

It was initially thought to be a “missing link” transitional form between those two groups, but later it was identified as being something else entirely – it was actually part of the chimaera lineage, much closer related to modern ratfish, and its ray-like features were due to convergent evolution for a bottom-feeding lifestyle.

Living during the early Jurassic period, about 200-195 million years ago, Squaloraja fossils are now known from the south coast of England, southern Belguim, and northern Italy. Around 30cm long (1’), this weird fish had a massive wide flat snout that looked like an even more extreme version of the long noses seen in some of its modern relatives, and this enormous snoot would have been absolutely packed with sensory receptors to help it locate small aquatic prey hidden in the muddy seafloor.

Some specimens also have a distinctive long horn-like spine on their foreheads, and since these individuals also have claspers it seems like this was a sexually dimorphic feature. Much like the smaller head claspers on modern chimaeras, male Squaloraja probably used this “horn” to hang onto females’ pectoral fins during mating – and with it being such a large elaborate structure it may also have been used for visual display purposes, too.

Weird Heads Month #17: Trapjaw Ants From Hell

Ants first evolved sometime in the Late Jurassic or Early Cretaceous, but only really began to diversify about 100 million years ago in the Late Cretaceous after the rise of flowering plants.

One of their evolutionary experiments around that time was a group called the haidomyrmecinae – also known as the “hell ants”.

Known from Asia, Europe, and North America, hell ants had bizarre-looking heads, possessing huge upward-curving scythe-shaped mandibles and a horn-like projection between their antennae.

They were fast-moving arboreal predators that would have fed mainly on other invertebrates such as soft-bodied beetle larvae, and unlike most modern ants their workers were probably solitary hunters. They were capable of gaping their mandibles by almost 180°, and when they got close enough to their targets the long sensory hairs around their faces triggered their jaws to snap vertically upwards, impaling their prey against their horn in a unique trap-jaw mechanism.

Some species also reinforced the exoskeleton of their horns with metal particles, strengthening them against impacts from both struggling prey and their own powerful jaws.

Ceratomyrmex ellenbergeri was one of the oddest-looking of all known hell ant species. Known from a few specimens preserved in amber, with adult workers up to 6mm long (~0.25″), it lived during the Late Cretaceous of Myanmar about 100-94 million years ago.

It had an especially pronounced horn and very long mandibles, which may have been adaptations for tackling significantly larger prey items than other hell ants.

And due to this being a species known from Burmese amber, sadly we also have to address the controversy surrounding these sorts of specimens. This amber is currently mined in incredibly dangerous conditions, often using child labor, with sales of both jewellery and paleontological specimens directly funding the ongoing violent conflict in the region.

It’s the fossil equivalent of blood diamonds, and a huge ethical dilemma for the paleontology community.

Weird Heads Month #04: South American Unicorns

South America was an isolated “island continent” for a large chunk of the Cenozoic, and during that time it was home to a unique mix of species evolving completely separately to the rest of the world.

One group found there were the meridiungulates, a lineage of hoofed mammals related to modern horses, rhinos, and tapirs. Many of them convergently evolved to resemble other types of mammals, and the large rhino-like toxodontids were some of the most common and successful.

And, like rhinos, some of them may even have had horns.

Hoffstetterius imperator lived in Bolivia during the late Miocene, about 11-5 million years ago.  Standing around 1.6m tall at the shoulder (5’3″), it had a particularly oddly-shaped skull, with a deep downward-flaring lower jaw and a large bulging bony “shield” on its forehead that resembles the attachment points for horns on rhino skulls.

Keratinous structures like that only fossilize very rarely, so the actual size and shape of whatever attached there is unknown – the pointed horn shown here is one possibility – but we honestly don’t know what was going on with these guys’ heads.

Kubanochoerus

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!

Falcatus

Falcatus falcatus, a 30cm long (12″) cartilaginous fish from the mid-Carboniferous of Montana, USA (~326-318 mya).

Although it looked very shark-like it was actually much more closely related to modern chimaeras, and its most distinctive feature was the forward-pointing “unicorn horn” spine just behind its head – a sexually dimorphic structure formed from a highly modified dorsal fin, found only on mature males.

The spine’s function is unknown for certain, but it may have been a sort of clasper involved in courtship and mating, since one fossil seems to preserve a female in the act of biting onto it. Some of its close relatives like Damocles and Stethacanthus also had similarly weird dorsal fins, so whatever these fish were actually doing with these structures it must have been a fairly successful strategy.

Falcatus lived out in the open ocean, with proportionally big eyes giving it good vision in deep dark water, and its large symmetrical tail fin suggests it was a fast maneuverable swimmer that actively chased after small prey. Numerous fossils have been found together, which may also indicate schooling behavior.

Although definite fossils of falcatids are only known from the Carboniferous, recently there’s been some possible evidence of them surviving for much much longer. A few isolated fossil teeth from Europe suggest that some of these fish may have persisted for at least another 180 million years into the Early Cretaceous, living in isolated deep water refugia environments in a similar situation to the modern coelacanth – making them fossils of what would have been “living fossils” at the time!

Eospinus

Eospinus daniltshenkoi, a tetraodontiform fish from the early Eocene of Turkmenistan (~56-48 mya). Only about 5cm long (2″), it was a close relative of modern boxfish and triggerfish, as well as a completely extinct group called spinacanthids.

It was heavily armored, with large plate-like scales creating a boxfish-like carapace, but its most distinctive feature was its multiple long spines – three dorsal spines on its back, a fourth on its head resembling a “horn”, a pair of smaller spines on the sides of its body, and one on its underside formed from partially fused vestigial pelvic fins.

Linguamyrmex

Linguamyrmex vladi, an ant from the Late Cretaceous of Myanmar (~99 mya). Part of an extinct group known as the Haidomyrmecini, or “hell ants”, it measured about 5mm long (0.2″) and is known from several individuals in amber.

It had huge scythe-shaped mandibles and a horn-like appendage on its head which together formed a powerful trap-jaw mechanism, snapping vertically shut when a pair of long sensitive trigger hairs touched against a target. One specimen was preserved close to a large soft-bodied beetle larva, which may have been an intended prey item.

When closed, the mandibles formed a tube-like channel to Linguamyrmex’s mouth, allowing it to suck out the “blood” from its impaled victims – and inspiring its species name, referencing Vlad Dracula.

The horn was also reinforced with metal particles in the chitinous exoskeleton, strengthening it against the impact of its closing jaws.