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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.

Kermitops

Despite being named after the famous Muppet frog, Kermitops gratus here wasn’t actually a frog itself. Instead it was a close relative of the common ancestor of all modern amphibians, part of a grouping of amphibian-like animals known as amphibamiform temnospondyls.

Living in what is now Texas, USA, during the mid-Permian, about 275 million years ago, Kermitops would have resembled a chunky salamander. Only its fossil skull is known, so its full body size is uncertain, but based on the proportions of related amphibamiformes it was probably around 15-20cm long (~6-8″).

Although its discovery helps to fill in the very sparse fossil record of the early evolution of modern amphibians, it’s also complicated matters more than expected. Previously it was thought that the characteristic skull anatomy of modern amphibians evolved in a clear sequence, but Kermitops has a unique mix of features that doesn’t fit this idea – suggesting that there was a lot of convergent evolution going on in amphibamiformes at the time.

Eurotamandua

Eurotamandua joresi lived during the mid-Eocene, about 47 million years ago, in the lush subtropical forests that covered what is now central Germany.

When it was first described in the early 1980s it was classified as an anteater due to its close resemblance to some modern species… but there were big problems with this interpretation. Anteaters have a sparse fossil record, but they’re known to have originated during the early Eocene in the isolated island continent of South America – so Eurotamandua’s ancestors making it all the way to Europe within just a few million years would be pretty remarkable!

Also, on closer inspection it didn’t have the distinctive skeletal features of a xenarthran mammal, suggesting it wasn’t an anteater after all.

Instead more recent studies have identified it as a close relative of pangolins, part of an early branch of the group that didn’t have the characteristic large scales.

About 90cm long (~3′), Eurotamandua would have a lifestyle much like the anteaters it convergently resembled, using its large claws to rip open ant nests and a long sticky tongue to feed.

Dinocephalosaurus

Dinocephalosaurus orientalis was a fully aquatic protorosaur reptile living in what is now southwest China during the mid-Triassic, about 244 million years ago.

Up to 6m long (~19’8″), it had a long serpentine body with paddle-like limbs and an especially elongated neck – but despite the superficial similarities to its semi-aquatic cousin Tanystropheus, Dinocephalosaurus’ long neck appears to have been independently evolved.

Much like the similarly-shaped elasmosaurs, its neck may have had a “stealth” function, allowing it to bring its jaws closer to targets before the rest of its body was visible, then using side-to-side snapping bites to catch its prey in its interlocking “fish-trap” teeth.

A preserved well-developed embryo inside one specimen also suggests that Dinocephalosaurus gave birth to live young, making it one of only two archosauromorph lineages known to have ever evolved this reproductive strategy.