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Gaiasia

Gaiasia jennyae was a tetrapodomorph – an amphibian-like relative of early tetrapods – that lived about 280 million years ago during the early Permian in what is now Namibia.

Although it’s only known from incomplete skull and vertebral column material it probably looked quite similar to the colosteids, a closely-related group of tetrapodomorphs with elongated bodies and small limbs. If it had the same sort of body proportions as these relatives it would have been huge, the largest known stem-tetrapod at potentially around 4m long (~13′).

It had a wide flat head with a short boxy snout, and large interlocking fangs on the roof of its mouth and at the front of its lower jaw. It would have been fully aquatic and probably not a particularly fast swimmer, instead likely being an ambush predator using suction from rapidly opening its jaws to pull prey into its mouth before clamping down with its fangs.

It’s also notable for living considerably later than most other stem-tetrapods, and in an unexpected part of the world. While its close relatives are all known from the tropics of the Carboniferous, Gaiasia was in a location that was much closer to the South Pole during the early Permian (~55° S), inhabiting an immense freshwater lake in a rift valley with a cold-temperate climate.

Its presence in this habitat may suggest that other stem-tetrapod lineages survived and thrived in high latitudes for much longer than previously thought, while the true tetrapods were all diversifying nearer the equator – or it might represent a Paleozoic equivalent of Koolasuchus, an isolated straggler lurking in a cold refugium.

Lokiceratops

Lokiceratops rangiformis was a ceratopsian dinosaur that lived during the Late Cretaceous (~78 million years ago) in what is now Montana, USA. Estimated at about 6.7m long (~22ft), it was one of the largest known members of the centrosaurine branch of the ceratopsians.

It had a unique arrangement of ornamentation on its skull, with no nose horn, two long brow horns, and a pair of huge asymmetrical curving blade-like spikes on the top of its square frill – some of the largest known frill spikes of any ceratopsian.

It lived in a swampy environment near the shore of the Western Interior Seaway, in an area that seems to have had an unusually high diversity of ceratopsians – along with Lokiceratops there were three other centrosaurines (Medusaceratops, Albertaceratops, and Wendiceratops), and one chasmosaurine (Judiceratops).

(There’s also a possibility that it might not actually be a unique species. We know some other ceratopsians’ faces changed quite drastically as they aged, so Lokiceratops could instead represent a fully mature individual of Medusaceratops.)

Tachypleus syriacus

Tachypleus syriacus was a horseshoe crab from the late Cretaceous (~100-95 million years ago) of what is now Lebanon.

Closely related to modern tri-spine horseshoe crabs, it displayed a similar level of sexual dimorphism. Females grew to at least 25cm long (~10″), with rounded front edges to their carapaces and shorter rear spines, while males were around 30% smaller with a scalloped shape to the front of their carapaces.

One recently described female specimen also preserves distinctive nodules around the rim of its carapace, which may represent some sort of sensory structure.

This particular specimen is also unique for preserving a coprolite in the process of being expelled from the horseshoe crab’s body – that’s right, it died while pooping.

Xenerodiops

Xenerodiops mycter was an unusual heron from the Oligocene (~30 million years ago) of what is now Egypt.

Known only from a partial skull and an arm bone, it’s estimated to have stood around 70cm tall (~2’4″) and was probably fairly similar in overall appearance to modern night herons. Its beak was powerfully built and had a distinctive downwards curve, shaped more like some types of stork than other herons – suggesting it may have had a convergently stork-like lifestyle, slowly walking through its marshy habitat probing around for prey and snapping up whatever its beak came into contact with.

Palaeoplethodon

There are no salamanders living in the Caribbean today, but one tiny fossil shows that this wasn’t always the case.

Palaeoplethodon hispaniolae was discovered in a chunk of amber from the Dominican Republic on the island of Hispaniola. The exact age of this type of amber is uncertain, but it most likely dates to the early-to-mid Miocene, about 20-15 million years ago.

The only known specimen is a hatchling, just under 2cm long (0.8″). It’s unclear what its full adult size could have been, but based on its modern relatives it may have grown to anywhere between 4.5cm and 20cm long (~2-8″).

Its strongly webbed hands and feet suggest it was very closely related to modern tropical climbing salamanders – but Palaeoplethodon had a unique webbing arrangement, with its feet relatively elongated and its hands fully fused into small rounded pads.

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.