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…April fools! Let’s turn that text the right way around:

April Fools 2026: The Backwards Elasmosaurus

In 1869, American paleontologist Edward Drinker Cope published a description and reconstruction of a newly-discovered plesiosaur, Elasmosaurus platyurus.

But there was a big problem: the head was on the wrong end.

It also didn’t have hind flippers, since no limb material had been found and Cope assumed the long “tail” was the primary means of propulsion.

By the next year the mistake had been recognized, pointed out by Cope’s mentor Joseph Leidy (and not his Bone Wars rival Othniel Charles Marsh, despite later retellings). Cope hurriedly published a corrected edition with the same title and date, and it seems he was embarrassed enough to attempt to cover up the whole affair, even recalling and replacing most of the preprint copies he’d sent out to colleagues around the world.

Tanyka

Tanyka amnicola was a tetrapodomorph closely related to both the baphetoids and true tetrapods, living in what is now northeastern Brazil during the Permian around 278 million years ago — making it one of the latest-surviving known stem-tetrapods.

Although only known from lower jaw remains it was likely about 1m long (~3’3″), and would have resembled a large chunky salamander.

Those jaws were particularly unusual, having a distinct twist in the bone that made the teeth towards the front stick out sideways when its mouth was closed. However, this twisting brought a different set of teeth into alignment with the upper jaw — “pavements” of many small denticles on the inner side of the lower jaw, which may have been used to rasp up aquatic plants or grind small invertebrates.

Tanyka’s highly specialized feeding adaptations suggest that late-surviving stem-tetrapods in Permian Gondwana weren’t just evolutionary relics but were instead actively exploring new niches, and that the extinction of these animals wasn’t quite as simple as just being outcompeted by more “advanced” tetrapods.

Saniwa

Saniwa ensidens was a varanid lizard that lived during the Eocene, about 49 million years ago, in what is now Wyoming, USA.

Closely related to monitor lizards, it would have grown to about 2m long (~6’6″) and looked very similar to modern forms, with a pointed snout, well-developed limbs, and a proportionally long tail.

But it also had something not seen in any other jawed vertebrate — a total of four eyes.

Many lizards have a single prominent parietal “third eye” on the top of their heads, which are light-sensitive and involved with both regulating circadian rhythms and hormone production for thermoregulation. However, Saniwa ensidens had two of these structures, with one formed from the parapineal gland like in other lizards, and the second positioned behind it formed by the pineal gland. The only other vertebrates with this arrangement are the jawless lampreys, suggesting that Saniwa somehow re-evolved a pineal eye hundreds of millions of years after its distant ancestors had lost it.

It’s not clear what this extra eye was used for. It would have increased the pineal complex’s sensitivity to blue-wavelength light, and may have been involved in orientation and navigation using polarized light similar to some modern lizards — or possibly magnetoreception-based navigation similar to some modern newts.

Haikouichthys

Haikouichthys ercaicunensis was one of the earliest known vertebrates, living in what is now southwestern China during the Cambrian, around 518 million years ago.

About 2.5cm long (~1″), it had a streamlined body with a long fin along its back and tail. It lacked limbs and jaws, but it did have a flexible “upper lip” that could potentially have been used to manipulate food particles, either engulfing them on the seafloor or stirring them up into the water for filter-feeding.

And a recent study revealed a big surprise — it had four eyes! Along with its already-known large sideways-facing pair of eyes, it also had another smaller upwards-facing pair in the middle of its face, giving it a much wider field of vision and the ability to watch out for predators from multiple angles at once.

The extra pair of eyes may be the evolutionary precursors to the pineal complex in later vertebrates — represented in modern forms by the pineal gland and the parietal eye.

Pygmaclypeatus

Pygmaclypeatus daziensis was a small early trilobitomorph arthropod that lived during the Cambrian, about 518 million years ago, in what is now southwestern China.

It had a wide flat carapace, about 14mm long (~0.5″), with a single pair of antennae, fourteen pairs of limbs, and a short segmented “tail”.

It also had an unusual arrangement of four eyes — one pair of fixed-in-place trilobite-like eyes on top of its headshield, and a second pair of crustacean-like mobile stalked eyes on the underside. Other four-eyed Cambrian arthropods are known, but Pygmaclypeatus is currently unique for having two completely different compound eye systems.

Its well-developed limbs with paddle-like branches indicate it could swim well, and probably also burrow into soft seafloor sediment. Its upper eyes seem to have been adapted to sensing motion in dim daylight conditions, suggesting they were used to keep a lookout for predators in shallow murky water. Its lower eyes were more sensitive, and may have been used to locate food items such as smaller soft-bodied invertebrates or organic detritus on the seafloor.

Solnhofia

Solnhofia parsonsi was a turtle that lived in the tropical seas covering what is now Europe during the Late Jurassic, about 150-148 million years ago.

Around 20cm long (~8″), it had a long pointed beak and a large triangular head that would have supported powerful jaw muscles, which it may have used to crush hard-shelled invertebrate prey.

Its relatively short limbs are more similar to those of freshwater turtles than the long flippers of oceanic-swimming sea turtles, suggesting Solnhofia was adapted to shallow coastal waters and lagoons rather than the open sea.

Some specimens have considerably shorter tails than others, which may represent the same sort of sexual dimorphism as seen in modern sea turtles – with the longer-tailed individuals being males, and the shorter-tailed ones females.

One fossil’s carapace also shows predation tooth marks from a marine crocodilian similar to Dakosaurus.

Gomphos

Gomphos elkema was an early lagomorph – closely related to the ancestors of modern rabbits, hares, and pikas – that lived during the Early Eocene, about 56-47 million years ago, in what is now Mongolia and northern China.

Around 20cm long (~8″), it had some anatomical features surprisingly similar to modern rabbits and hares, such as long feet and hindlimbs capable of hopping. But unlike its modern relatives it also had a longer tail, and more “primitive” features in its jaw and teeth that link it to lagomorphs’ shared ancestry with rodents.

Tyrannoroter

Tyrannoroter heberti lived in a lush tropical coal forest covering what is now Nova Scotia, Canada during the late Carboniferous, about 307 million years ago.

It was a member of the pantylid family in the recumbirostran lineage, a group of tetrapods whose evolutionary relationships are still a little uncertain. Traditionally they were classified as lepospondyl “amphibians”, but more recently some studies have found them to be either very early sauropsids or convergently reptile-like stem-amniotes.

Known only from a partial skull and jaw, based on the proportions of its pantylid relatives Tyrannoroter was probably around 30cm long (~1′) and would have resembled a squat lizard with a large blunt triangular head.

It would have had small bony scales within its skin, with interlocking polygonal “armor” on the underside of its jaw and chest, and irregular pebbly scales on other parts of its body. It may also have had claws on its toes, and potentially was capable of burrowing using a combination of its stout limbs and its shovel-like snout.

The roof of its mouth and the inside of its jaw were covered in extensive “batteries” of blunt teeth that show evidence of shearing and grinding motions – suggesting it may have been primarily processing tough plant matter, and making it one of the earliest known herbivorous tetrapods.

Arsinoitherium

Arsinoitherium zitteli was a large herbivorous mammal living in what is now northern Africa during the late Eocene and early Oligocene, about 36-30 million years ago.

Despite looking like a double-horned rhino this resemblance was only superficial, and for most of the 20^th century it was actually the only known representative of an entire order of mammals – the embrithopods – with its wider evolutionary relationships being unknown. Since the 1970s, however, more members of this group have been discovered and embrithopods are now understood to be afrotheres, a very early offshoot of the tethythere lineage, with their closest living relatives being modern elephants and sirenians.

Arsinoitherium was by far the most abundant embrithopod, with numerous fossil remains making it one of the most completely known African fossil mammals. It stood around 1.8m tall at the shoulder (6′), similar in size to modern white rhinos, and would have been a massively-built slow-moving animal with elephant-like columnar limbs.

Its pair of enormous nose horns (and smaller brow horns) were structurally more similar to those of bovids than rhinos, with large hollow bony cores that probably bore thick keratinous sheaths that would have increased their apparent size even more. Both males and females appear to have had these horns, and muscle attachments at the back of the skull suggest Arsinoitherium could powerfully swing its head upwards – possibly wrestling with each other in combat over territories, competing for mates, or in establishing dominance hierarchies.

Manipulonyx

Manipulonyx reshetovi was an alvarezsaurid theropod dinosaur that lived during the Late Cretaceous, about 70 million years ago, in what is now Mongolia.

Although only known from a partial skeleton, based on its close relatives it would have been about 50cm long (~1’8″), with a narrow snout, a coat of fluffy down-like feathers, long slender legs, and short stout arms with massively enlarged thumb claws.

Notably the fossil specimen has the best preserved hands known from the parvicursorine subfamily of alvarezsaurs, revealing a surprising arrangement of three ossified conical spikes around the thumb. These hand spikes were positioned pointing forwards, backwards, and inwards, and may have improved the ability to grip with just one functional finger.

“Spike-like” hand bones were also previously reported in 2009 in another parvicursorine, Ceratonykus, suggesting that these structures weren’t unique to Manipulonyx.

The paper describing Manipulonyx proposes that alvarezsaurs were ovivores, using their hands to carry and then break open eggs, but I’m personally very skeptical of this idea. I think the myrmecophagy interpretation for these little dinosaurs is still much more likely – they probably did opportunistically raid eggs when they could get them, like many modern predators do, but being specialized for just egg-eating is a big claim that definitely needs more evidence.