Erlikosaurus

Erlikosaurus andrewsi, a therizinosaur from the Late Cretaceous of Mongolia (~90 mya).

Named after Erlik, the Turko-Mongolian god of death, it’s only known from partial remains – but it was the first therizinosaur ever found with a preserved skull, helping to fill in some of our knowledge of these oddball dinosaurs’ anatomy.

It was closely related to Therizinosaurus, but was only about half the size, estimated to have measured around 4-5m long (13′-16’4″). It would have had a toothless beak at the front of its jaws, an adaption for a herbivorous diet, along with long claws on its hands and a coat of fluffy down-like feathers. I’ve also given it some longer quill-like feathers here, similar to those known in Beipiaosaurus.

Grendelius

Grendelius mordax, an ichthyosaur from the Late Jurassic of England (~155-150 mya).

Named after the monster Grendel from the epic poem Beowulf, this 4m long (~13′) marine reptile had a big robust skull with large teeth, proportionally short flippers, and smaller eyes than some of its other relatives. It also had an unusual bony “hump” on its snout above its nostrils.

(About 20 years ago Grendelius was reassigned into Brachypterygius on the basis of the two not being distinct enough from each other to justify having separate genus names – but a more recent study suggests that that they actually were different after all, and the name may be valid again.)

Diplacodon gigan

Diplacodon gigan, a brontothere from the Early Eocene of Wyoming, USA (~46-42 mya). Standing around 2.1m tall at the shoulder (~7′) it was named after the kaiju Gigan for its relatively large size – not quite as big as some later brontotheres, but still about 20% larger than other known species of Diplacodon.

It had a pair of blunt bony projections on its snout which would have been covered with skin in life, similar to the ossicones of modern giraffids, with males having larger “horns” than females.

Despite looking very similar to rhinos, brontotheres were actually much more closely related to horses, with the resemblance being a result of convergent evolution for the same sort of big-tanky-herbivore ecological niche.

Vaderlimulus

Vaderlimulus tricki, a horseshoe crab from the Early Triassic of Idaho, USA (~251-247 mya). Named for its resemblance to the shape of Darth Vader’s helmet, it’s the earliest known Mesozoic horseshoe crab from North America and was closely related to another oddly-shaped form from Australia.

It was much smaller than its modern relatives, only about 10cm long (4″), and probably lived in a brackish estuary environment where seawater and freshwater met.

Paludidraco

Paludidraco multidentatus from the Late Triassic of Spain (~237-227 mya).

This 3m long (9′10″) animal was a member of the nothosaurs, a group of semi-aquatic seal-like marine reptiles that were closely related to plesiosaurs (and both were also evolutionary cousins to modern turtles).

It had long slender jaws full of numerous tiny teeth, creating an interlocking comb that was probably used for filter feeding – scooping up mouthfuls of fine-grained sediment from the seafloor and filtering out small invertebrates or soft plant matter.

The bones of its skeleton were also highly thickened and dense, a condition known as pachyostosis that provided ballast to weigh it down in the water. This would have made it a slow and unmaneuverable swimmer, but a very energy-efficient one, using its natural neutral buoyancy to hover or walk along the seabed.

It was essentially a reptilian manatee, filling a similar sort of ecological niche.

Litovoi

Litovoi tholocephalos, a multituberculate mammal from the Late Cretaceous of Romania (~70-66 mya). Living on what was at the time the large offshore Hațeg Island, this rat-sized animal (about 25cm /10″ long) was part of a lineage of insectivorous multis called the kogaionids, with the same sort of red-colored enamel on its teeth as other species like Barbatodon.

Its brain was surprisingly tiny proportional to its size – one of the smallest known brain-to-body ratios of any mammal, and more similar to those of non-mammalian cynodonts – but it also seems have been highly specialized for processing sensory input, with relatively enormous regions associated with smell, eyesight, balance, and motor control. The olfactory bulbs of its brain were so enlarged, in fact, that they caused its skull to bulge out into an unusually dome-shaped forehead.

Its reduced brain size may have been due to limited food availability on its isolated island home. Brains are very metabolically expensive organs, and some other extinct island mammals like hippos, hominids, and goats are also known to have evolved smaller brain sizes. Modern shrews even seasonally shrink their own brains during winter for similar energy-saving reasons.

Caelestiventus

Caelestiventus hanseni, a pterosaur from the Late Triassic of Utah, USA. Living about 208-210 million years ago, it was very closely related to Dimorphodon – but unlike its younger coastal-dwelling relative it instead lived in a desert environment made up of a massive sand dune sea with occasional interdunal lakes.

It’s the earliest known example of a desert pterosaur, over 60 million years older than other examples, suggesting that even fairly early in their evolutionary history these flying animals had already adapted to a much wider range of habitats than previously thought.

Although only known from a partial skull and a single wing bone, it was probably one of the largest Triassic pterosaurs with a wingspan of over 1.5m (4′11″). It had a “keel” on its lower jaw that may have supported a soft-tissue crest or a pelican-like throat pouch, and there were several different types of teeth in its mouth – large pointed fangs at the front, “leaf-shaped” blades further back in its upper jaw, and numerous much smaller teeth along its lower jaw.

The skull roof also preserved the impression of Caelestiventus’ brain shape, showing that it had very well-developed vision but a poor sense of smell.

Thanahita

Thanahita distos, a recently-named species from the mid-Silurian of the UK (~430 mya).

This little lobopodian was very closely related to the famous Cambrian Hallucigenia, but it lived over 70 million years later – giving us the first evidence that these weird worms weren’t just short-lived “evolutionary experiments”, but must have actually been a very successful lineage that thrived for quite a long time.

Measuring around 3.5cm long (1.4″), it had seven pairs of legs tipped with one or two claws each, and at least two pairs of shorter tentacles on its neck. The head region of the only known fossil specimen wasn’t preserved, so it’s unclear exactly what its front end looked like – but it would have probably been quite similar to Hallucigenia with a slender oval head, two simple eyes, and a small round mouth ringed by tiny teeth.

Unlike its spiky relative, however, Thanahita’s back was covered in rows of numerous small raised soft-tissue “tufts”. I’ve reconstructed it here with them brightly warning colored, mimicking stinging coral polyps.

Almost-Living Fossils Month #27 – Those Giant Sharks

For the final entry this month, let’s look at a particularly famous lineage: the megatooth sharks.

More formally known as the otodontids, the megatooths were a group of sharks that first appeared in the Early Cretaceous, about 115 million years ago. They were a branch of the mackerel shark lineage – making them evolutionary cousins to a variety of modern species like the great white shark, basking shark, and goblin shark – and had a near-worldwide distribution, with fossils known from every continent except Antarctica.

Early otodontids in the Cretaceous were usually small-to-medium sized, around 2-3m long (6′6″-9′10″), but after surviving through the end-Cretaceous extinction they took over the marine apex predator niches left vacant by the vanished mosasaurs and plesiosaurs and began to get very big. Species of Otodus in the Paleocene and early Eocene may have reached sizes of at least 9m long (29′6″), twice the size of an average great white.

Their teeth gradually became proportionally larger in their jaws, losing their side cusplets and taking on a chunky triangular shape with finely serrated edges. This gave them an incredibly powerful bite force, and they would have probably fed on pretty much any other large marine vertebrates they could catch, including bony fish, smaller sharks, turtles, and early penguins – and then when marine mammals like early whales and sirenians appeared in the mid-Eocene, they adapted to this new food source too.

By the Late Eocene (~35 mya) the Otudus lineage was still developing even chunkier and more serrated teeth, and by the Early Oligocene (~28 mya) Otodus chubutensis reached even larger sizes rivaling the modern whale shark at around 12m long (39′4″).

But the most well-known member of the group evolved just a few million years later in the Early Miocene (~23 mya) – the absolutely enormous “megalodon”.

There’s some debate about what genus name megalodon should be assigned to – at the moment its formal name is usually considered to be Otodus megalodon, but some paleontologists place it in Carcharocles or Megaselachus or Procarcharodon instead. Whatever you want to call it, it was a ridiculously big shark – size estimates range up to about 18m (59′), which would make it potentially the largest fish to have ever lived.

Since these huge sharks are all known mostly from just their fossilized teeth (and occasionally a few exceptionally preserved cartilaginous vertebrae), it’s hard to tell what they actually would have looked like in life. Megalodon is frequently depicted as simply a scaled-up great white, but it’s unclear how accurate that really is – it may have convergently resembled a giant great white due to their similar predatory habits, or it could have had a build more like the larger basking shark or whale shark.

A preserved megalodon skull has actually been found, but no studies of it have been published yet. It might give us some important clues about the head shape of this giant shark, but until there’s some official information all we can do is continue to speculate.

Megalodon was a highly successful species, living all around the world in warm and temperate ocean waters for around 20 million years. Its teeth have been found in association with the bones of many different smaller whale species, suggesting it frequently ate marine mammals, and the patterns of the bite marks indicate it probably used different hunting strategies than modern great whites. Some whales seem to have been heavily rammed and then had their ribcages bitten into, targeting their hearts and lungs, while others had their flippers ripped off to immobilize them.

During the Pliocene (~5-2.6 mya), however, megalodon began to struggle. Cooling oceans and changes in the abundance of the marine mammals it ate began to restrict its available prey. Baleen whales started to grow too large for it to effectively hunt, since it preferred to target smaller species, and they also shifted their ranges towards the cold polar waters that megalodon didn’t seem to be able to survive in. In addition, dropping sea levels may have destroyed most of its shallow warm-water nursery sites, making it harder for newborn young to survive into adulthood.

By the end of the Pliocene, somewhere between 3.6 and 2.6 million years ago, megalodon went completely extinct. Despite some very pseudoscientific claims, there’s definitely no living “Meg” out there anymore – if there was, we’d be constantly finding freshly-shed teeth and whales with giant bite marks on their bodies!

Almost-Living Fossils Month #26 – Angry Land-Flamingo-Ducks

The presbyornithids were an early group of waterfowl birds – relatives of modern ducks, geese, swans, and screamers – that first appeared in the Late Cretaceous, about 71 million years ago. With their long necks, long legs, and duck-like bills adapted for filter-feeding, they seem to have essentially been primitive ducks converging on the body shape and lifestyle of flamingos – and as a result they’re sometimes even nicknamed “flamingo ducks”.

They lived in shallow freshwater environments all around the world, and after surviving through the end-Cretaceous extinction they even became some of the most common waterbirds in the early Cenozoic. Some species have been found in large bonebeds containing fossils from thousands of individuals all in one place, suggesting they were very social and lived in huge flocks.

Around the mid-to-late Eocene (~40-37 mya) they seemed to disappear completely, until some fossils from Australia that were originally thought to be from a species of ancient stone-curlew were reassessed in 2016 and found to actually represent the latest-surviving members of the presbyornithids.

Named Wilaru, this bird lived in South Australia during the Late Oligocene and Early Miocene (~28-20 mya). Two different species have been identified: Wilaru tedfordi and its slightly larger and stockier descendant Wilaru prideauxi. With only partial pieces of their skeletons known it’s difficult to estimate their full life size, but based on similar presbyornithids they were probably both somewhere around 1m tall (3′3″).

As well as outliving the rest of their kind, the two Wilaru species were also rather weird compared to the other known flamingo-ducks, with adaptations that indicate they were spending much more time walking around on land than wading in water. Their feet resembled those of modern screamers (which are also more terrestrial) and may have partially or fully lost their webbing, and since they lived alongside various other species of waterfowl and early flamingos they clearly weren’t competing for the same ecological niches. It’s possible they might have also shifted away from their ancestral filter-feeding diet, perhaps becoming more herbivorous, but without any preserved skulls we can’t tell for certain.

Unlike other presbyornithids they also had large spurs on their wings – and based on the behavior of modern spurred waterfowl this suggests they were much less social. They were probably rather aggressive animals, living solitary or in pairs and fighting each other over mates and territory.

This major departure from the lifestyle of their ancestors may have been what allowed Wilaru to survive for so much longer than all the other presbyornithids. They might potentially have lasted a few more million years into the mid-Miocene, but a cooling and drying climate – especially a sudden temperature drop about 14 million years ago – may ultimately have altered their habitat and food sources too quickly for them cope with.