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Pachydectes

Modern mammals are the only living representatives of the synapsids, but back during the Permian there were numerous other evolutionary branches – first the pelycosaurs, and later their descendant the therapsids.

Some of the first non-mammalian therapsids were the biarmosuchians, mid-sized carnivores with a more upright posture than their pelycosaur ancestors. They had large canine teeth in their jaws and powerful bites, and some of them also developed elaborate ornamentation on their skulls, with various bony bumps and crests adorning their faces.

Pachydectes elsi was a 1.5m long (~5′) biarmosuchian living in what is now South Africa during the late Permian, about 265 million years ago. Bone texture indicates its head ornamentation was covered by either tough thickened skin or a keratinous sheath, and the large bulbous bosses on the sides of its snout had a particularly rich blood supply, suggesting these structures could have been continuously growing throughout its entire life.

But despite how well-protected it looked, Pachydectes’ skull was actually relatively fragile and wouldn’t have been able to withstand the impact forces of using its headgear for fighting or defense. Instead it may have been mostly used for visual display – and the blood supply to the snout bosses might even have given it the ability to “blush” them if they had a soft-tissue covering.

Escumasia

Nicknamed the “Y animal” or “wye”, Escumasia roryi is an enigmatic fossil organism known from the Late Carboniferous Mazon Creek fossil beds in Illinois, USA, dating to about 308 million years ago.

Growing up to around 15cm tall (~6″) this strange soft-bodied creature was Y-shaped, with two slender “arms” on each side of an apparent mouth opening, a flattened sac-like body with another opening on one side, and a long stalk ending in an attachment disc. Some specimens have uneven arm lengths, which may indicate damage from predation.

Being only known from the exceptional preservation conditions of Mazon Creek, and with nothing else quite like it in the known fossil record, Escumasia‘s evolutionary relationships are still a mystery. It’s been tentatively linked to cnidarians – but this doesn’t really fit based on its anatomy, and little further study has been done on it since its discovery in the 1970s.

It was probably a filter feeder, living attached to the seafloor and capturing suspended organic material or small planktonic prey with its arms. The environment it inhabited was a shallow tropical marine bay, located close to the equator at the time, near a large river delta that would have made the surrounding waters rather brackish. This ecosystem was dominated by cnidarians, particularly the anemone Essexella, along with various arthropods, lobopodians, polychaete worms, molluscs, echinoderms, fish, lampreys, hagfish, and other difficult-to-classify weirdos like the famous “Tully monster” Tullimonstrum.

Ninoziphius

Ninoziphius platyrostris was an early beaked whale that lived during the late Miocene (~6 million years ago) in warm coastal waters covering what is now southwestern Peru. Its ancestors appear to have branched off from all other beaked whales very early in the group’s history, indicating a “ghost lineage” going back to at least 17 million years ago.

About 4.4m long (~14’5″), it was less specialized for suction feeding and deep diving than modern beaked whales. Also unlike most modern species its jaws were lined with numerous interlocking teeth, with heavy wear suggesting it may have hunted close to the seafloor, where disturbed sand and grit would have regularly ended up in its mouth along with its prey and steadily ground down its teeth during its lifetime.

Males had a pair of stout tusks at the tip of their upward-curving lower jaw, with possibly a second smaller set of tusks behind them, which were probably used for fighting each other like in modern beaked whales.

Its shallow water habitat and more abrasive diet suggest Ninoziphius’ lifestyle was much more like modern dolphins than modern beaked whales, and other early beaked whales like Messapicetus similarly seem to have occupied dolphin-like ecological niches.

These dolphin-like forms disappeared around the same time that true dolphins began to diversify, possibly struggling to compete for the same food sources, while other beaked whales that had begun to specialize for deep sea diving survived and thrived. Interestingly this ecological shift seems to have happened twice, in two separate beaked whale lineages – although only one of them still survives today – with bizarre bony “internal antlers” even independently evolving in both groups.

Patagopteryx

While birds are one of the few animal groups to have achieved powered flight, they’re also very prone to losing their aerial abilities. Many times over their evolutionary history, multiple different bird lineages have convergently become secondarily flightless – and Patagopteryx deferrariisi was one of the earliest known examples of this.

Living during the Late Cretaceous, about 86-84 million years ago, in what is now the northern part of Argentine Patagonia in South America, Patagopteryx was roughly the size of a modern chicken at around 50cm long.

When it was first discovered it was classified as a ratite, but soon after it was recognized as actually being a much earlier type of bird, an early ornithuromorph only distantly related to any modern groups.

It had small wings, little-to-no keel, and no wishbone, indicating it lacked the large powerful musculature required for flight. Its legs were quite long, with large feet with all four toes facing forward – proportions that suggest it was built more for walking than for high-speed running.

Growth rings in its bones also show that it had a much slower growth rate than modern birds, taking several years to reach adult size.

Hexameroceras

Hexameroceras panderi was a nautiloid cephalopod that lived during the late Silurian, about 425-423 million years ago, in what is now Czechia.

Around 5cm long (2″), it had a downwards-curving egg-shaped shell that preserved the original color pattern on one fossil specimen, showing closely-packed crisscrossing vertical and horizontal bands.

Like several of its close oncocerid and discosorid relatives, its shell also developed a highly constricted opening as it reached maturity. This eventually formed into a narrow visor-like shape with several lobes that probably correlated to the life positions of the eyes and arms, with a “spout” at the bottom for the siphon.

Diagram showing how the lobed "visor" formed in Octameroceras — Development of the “visor” in the related *Octameroceras sinuosum*
From fig 6 in Stridsberg (1981)

The function of this structure is still unclear. It may have been a defensive measure against predators – but it would have also severely limited the range of motion of the arms and the size of food that could be eaten through the mouth, suggesting that Hexameroceras may have specialized in very small prey, perhaps even filter-feeding.

Another possibility is that these visored nautiloids might represent brooding females, walling themselves into their shells to protect their eggs and dying after releasing the hatchlings through the tiny remaining gap.

Cadurcodon

Cadurcodon ardynensis was an odd-toed ungulate that lived in what is now Mongolia during the late Eocene, about 37-34 million years ago.

It was around 2m long (6’6″) and, despite its very tapir-like appearance and lack of horns, it was actually closer related to modern rhinoceroses – it was part of a group of early rhino-cousins known as amynodontids, which convergently evolved both hippo-like and tapir-like lifestyles.

Cadurcodon was the most tapir-like of the tapir-like amynodontids, with a short deep skull and retracted nasal bones that indicate it had a well-developed prehensile trunk. Males also had large tusks formed from their upper and lower canine teeth, which may have been used for fighting each other.

Wukongopterus

Wukongopterus lii was a pterosaur that lived during the mid-to-late Jurassic, about 164 million years ago, in what is now northeastern China. It was fairly small, with a wingspan of around 70cm (~2’4″), and showed a mixture of anatomical features in-between the long-tailed short-headed ‘rhamphorhynchoids‘ and the short-tailed long-headed pterodactyloids.

Its long jaws were lined with tiny pointed conical teeth, suggesting it was adapted for primarily feeding on insects. It also had a very slight overbite, with the first two pairs of teeth in its upper jaw protruding almost vertically over the end of its lower jaw.

As a fully mature adult it would have had a low bony crest on its head that probably supported a larger cartilaginous structure – similar to other known wukongopterids – although the exact size and shape is unknown since the one confirmed specimen of Wukongopterus is missing that particular part of its skull. Another fossil nicknamed “Ian” may represent a second individual of this species, showing a different crest arrangement further forward on its snout, so I’ve made two different versions of today’s image to reflect that possibility.

Lobodiscus

Trilobozoans (also known as triradialomorphs) are some of the more enigmatic members of the Ediacaran biota. In the past their unique three-way-symmetrical body plan was interpreted as linking them to groups like sponges, cnidarians, or echinoderms, but currently they’re considered to be their own weird little phylum with uncertain evolutionary affinities, classified no more specifically than “probably some sort of early eumetazoan animal“.

Lobodiscus tribrachialis is a newly-described member of this mysterious lineage. It lived in warm shallow marine waters covering what is now Southwestern China, and with an age of around 546 million years it’s currently the youngest known trilobozoan, extending the group’s time range by several million years.

About 3.7cm in diameter (~1.5″), it had the characteristic trilobozoan disc-shaped shield-like body, with a central depression surrounded by three triradially-symmetric lobes with branching ridges and grooves.

Its body would have been soft but fairly rigid, and it’s not clear if it was capable of moving over the seafloor or if it had a more static lifestyle. Like its relative Tribrachidium it was probably a filter feeder, with the grooves on its surface directing water flow towards the central depression – and this surface ornamentation may also have been covered with cilia that actively caught and transported suspended food particles.

Jiangxichelys neimongolensis

Jiangxichelys neimongolensis was a terrestrial turtle that was part of an extinct group known as nanhsiungchelyids, whose closest living relatives today are the aquatic softshell turtles.

(This species was previously known as “Zangerlia” neimongolensis, but has since been moved into the genus Jiangxichelys instead.)

It lived towards the end of the Cretaceous, about 75-71 million years ago, in what is now the Gobi Desert – which at the time was more of a semi-arid climate with both rivers and sand dunes.

Its 60cm long (~2′) carapace had a long wide shape that made it appear rather flattened from the front, but not to quite as much an extreme as its larger American cousin Basilemys.

Several fairly well-preserved specimens have been found that appear to have been buried alive, probably either engulfed by sudden sandstorms or trapped in collapsing burrows. This has preserved some anatomical details previously unknown in nanhsiungchelyids, such as the pattern of scales on top of the head and the presence of large bony osteoderms on the underside of the front toes, which may have aided with traction on loose sandy ground.

April Fools 2024: The Curious Case Of The Chunky-Necked Ceratopsians

Much like the aquatic Compsognathus featured here a couple of years ago, not every novel idea that came out of the Dinosaur Renaissance was a winner.

And one of the oddest examples came from author/illustrator John C. McLoughlin.

His 1979 book Archosauria: A New Look at the Old Dinosaur featured an unusual interpretation of ceratopsian dinosaurs’ characteristic bony frills, proposing that they were actually muscle attachment sites for both powerful jaw muscles and enormous back muscles to help hold up their large heavy heads. This would have completely buried the frill under soft tissue, giving the animals massive thick necks and humped shoulders, and resulted in an especially weird reconstruction of Triceratops with a grotesque sort of wrinkly sewn-together appearance.

This concept didn’t entirely originate from McLoughlin – three years earlier in 1976 he’d illustrated Ronald Paul Ratkevich’s book Dinosaurs of the Southwest, which seems to have been the inspiration for Archosauria’s fleshy-frilled ceratopsians. A few paleontologists had also proposed jaw muscles attaching onto the frills during the 1930s and 1950s, and there’s even a book from as far back as 1915 that also shows the top of a Triceratops’ frill connected to its back! But McLoughlin’s Archosauria image is still by far the most extreme and infamous version of the idea.

There were a lot of things in Archosauria that were actually very forward-thinking for the time period, such as putting fuzz and feathers on small theropods and depicting non-avian dinosaurs as active fast-moving animals. The unique ceratopsian reconstructions, however, never caught on for several big reasons:

Firstly, all that hefty muscle tissue would have locked ceratopsians’ heads firmly in place, unable to move at all, which just doesn’t make sense biomechanically. Then there was the lack of skeletal evidence – muscles that big should have left huge visible attachment scars all over the frill bones, and there was no sign of anything like that on any fossil specimens. Finally, it turns out the ceratopsian head-neck joint was actually highly mobile, suggesting their heads were free to make a wide range of motions in life.

As wrong as they were even at the time, McLoughlin’s ceratopsians were still an interesting speculative idea, and notable for advocating for fleshier dinosaur reconstructions at a time when paleoart was trending towards shrinkwrapping.