Tag: archosaur

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.

Almost-Living Fossils Month #22 – Some Marine Crocs

First appearing in the Middle Jurassic, about 175 million years ago, the tethysuchians were a group of neosuchian crocodilians – part of the same lineage that includes all living crocs, although they were probably more closely related to the highly marine thalattosuchians than to modern forms.

Their fossil remains have been found almost globally, except for in Antarctica and Australia, and they appear to have been highly aquatic animals living in both freshwater and marine environments. Most members of the group had very long and slender gharial-like snouts, indicating they were specialized for fish-eating, but some (like the enormous Sarcosuchus) developed broader or shorter snout shapes that suggest more generalized diets of whatever they could catch.

One lineage of tethysuchians known as the dyrosaurids evolved around the mid-Cretaceous (~100-90 mya) and quickly spread around most of the world. These crocs mainly inhabited coastal marine waters, with a few species also living full-time in estuaries or rivers.

They had tall vertebrae around their shoulders, giving them a slightly hump-backed appearance and anchoring large neck muscles that allowed them to quickly whip their jaws around to catch fast-moving fish. Their deep vertically-flattened tails were capable of an even more powerful swimming stroke than those of modern crocs, and their well-muscled limbs probably made them strong walkers when on land.

The dyrosaurids were some of the few marine reptiles to survive through the end-Cretaceous extinction (~66 mya) relatively unscathed, and several species are known from both sides of the K-Pg boundary. This may be because the marine dyrosaurids are thought to have seasonally migrated inland to breed in freshwater environments, with juveniles spending their early lives in rivers and only returning to the coasts as adults – and since freshwater ecosystems were much less affected by the mass extinction than marine ones, this allowed them to continue on while groups like the mosasaurs and plesiosaurs died out.

Dyrosaurus maghribensis here lived during the Late Paleocene and Early Eocene of  Morocco (~56-48 mya). It was similar in size to the largest living crocs, around 6m long (19′8″), but had thinner and less extensive bony osteoderm armor.

During the Eocene the dyrosaurids began to disappear, and by the Late Eocene (~37 mya) the last known species were found only in northern Africa. It’s not entirely clear why these once-successful tethysuchians began to decline, but they may have been struggling to deal with the cooling climate trends at the time. If they managed to persist until the end of the Eocene, sudden temperature and sea level drops during the Eocene-Oligocene extinction (~33 mya) probably finished them off entirely.

Almost-Living Fossils Month #10 – Big Land Crocs

First appearing in the Middle Jurassic, about 167 million years ago, the sebecosuchians were a group of terrestrial crocodilians that are known from South America, Europe, North Africa, Madagascar, and India.

They were very closely related to (or possibly descended from) the diverse and often very weird notosuchian crocs. But while notosuchians were generally small and had specialized mammal-like heterodont teeth, the sebecosuchians were much larger (around 3-4m long / 9′10″-13′) and had blade-like serrated teeth convergently similar to those of some theropod dinosaurs. Their teeth were so incredibily dinosaur-like, in fact, that Cenozoic specimens have occasionally been mistaken for evidence of late-surviving non-avian dinos.

With deep narrow snouts, powerful jaws, and upright limbs, these crocs were clearly fast active predators, and must have been directly competing with similarly-sized theropods during the Mesozoic. They were obviously doing well enough to survive alongside their distant dinosaur relatives for many millions of years, right up until the end-Cretaceous extinction – but the surprising part is how the sebecosuchians seemed to survive the extinction just fine across most of their range, while the non-avian theropods obviously didn’t. Something about these particular large terrestrial predators allowed them to pull through relatively unscathed, although whether it was to do with their metabolisms or something else is still unknown.

By the end of the Eocene the sebecosuchians outside South America seem to have died off (coinciding with the rise of placental carnivorans), but the isolated South American forms continued their success for most of the rest of the Cenozoic.

One of the best-known species is Sebecus icaeorhinus from western South America, ranging from Colombia to Patagonia, with various fossils dating from the Early Paleocene all the way through to the mid-Miocene (~66-11 mya). About 3m long (9′10″), it was named after the ancient Egyptian crocodile god Sobek and was one the first sebecosuchians to be discovered, lending its name to the entire group.

The last definite fossils of Sebecus and its relatives come from the mid-Miocene, but they may possibly have survived up until at least the Miocene-Pliocene boundary about 5 million years ago. It’s not clear exactly why these big land crocs finally went extinct, but it was likely due to a combination of factors such as the influx of placental predators from North and Central America, along with climate changes from the continuing rise of the Andes mountains and the formation of the Isthmus of Panama.

Zby

Zby atlanticus, a sauropod dinosaur from the Late Jurassic of Portugal (~156-151 mya). While its genus name might look like a keyboard smash, it was actually named after the Russian-French paleontologist Georges Zbyszewski, who spent much of his career studying Portuguese fossils.

(As for how to pronounce it, according to the original paper it’s “zee-bee”.)

It was a close relative of Turiasaurus, the largest dinosaur currently known from Europe – and although Zby itself wasn’t quite so enormous it was still pretty big, probably measuring somewhere around 15-19m long (49′2″-62′4″).

In fact, all the sauropods known from Late Jurassic Portugal seem to have grown to very large adult sizes. The complete lack of medium or small forms suggests that other types of herbivorous dinosaurs may have dominated the region’s lower-browsing niches at the time.

Tarjadia

Tarjadia ruthae from the Middle Triassic of Argentina (~242-235 mya).

Originally known only from a few fragments, this 2.5-3m long (8′2″-9′10″) animal was first considered to be an indeterminate early archosaur, then a non-archosaurian doswelliid. But new fossil material and a recent analysis have instead placed it as a member of the erpetosuchids, an early group of pseudosuchians (the branch of the archosaurs that includes modern crocodilians).

Erpetosuchids were some of the earliest well-armored archosaurs, with several rows of bony osteoderms along their neck, back, and tail, and scattered oval osteoderms covering their limbs. Their fairly gracile build and slender limbs suggest they were active terrestrial carnivores – but it’s hard to say exactly what they were preying on due to their somewhat odd skulls.

Skull of Tarjadia, from Fig 2 in Ezcurra, M. D., et al (2017). Deep faunistic turnovers preceded the rise of dinosaurs in southwestern Pangaea. Nature ecology & evolution, 1(10), 1477. doi: 10.1038/s41559-017-0305-5

They had only a few teeth at the very front of their upper jaws, with the rest being toothless, but meanwhile the lower jaw was fully-toothed. Their skulls had narrow snouts at the front but became much wider further back, suggesting the presence of powerful jaw muscles, and they had slightly upward-facing eye sockets.

Smaller erpetosuchids are speculated to have been specialized for insect-eating, catching their small prey with their front teeth and then crushing it with the semi-toothless part of their jaws further back. But something the size of Tarjadia probably couldn’t have survived on a purely insectivorous diet, and it must have been doing something else with its weird jaws.

Copepteryx

Copepteryx hexeris, a plotopterid bird from the Late Oligocene of Japan (~28-23 mya).

Known from around the North Pacific rim from about 33-15 million years ago, plotopterids were flightless diving birds which used their small but powerful wings to propel themselves through the water. They were convergently similar to penguins in body shape and lifestyle, but not actually closely related to them – instead being relatives of gannets, cormorants, and anhingas.

Smaller plotopterids were about the size of modern cormorants, around 70cm long (2′4″), but the larger known genera like Copepteryx rivalled the southern giant penguins at around 1.8m (6′).

And a second species of Copepteryx known only from a single leg bone (Copepteryx titan) may have been ever bigger. Estimated at over 2m in length (6′6″), it was possibly one of the largest diving birds to have ever lived.

Medusaceratops

Medusaceratops lokii, a ceratopsid from the Late Cretaceous of Montana, USA (~77.5 mya).

About 6m long (19′8″), it had long brow horns and large curved spikes on its frill – an arrangement very similar in appearance to the centrosaur Albertaceratops, and initially its fossils were misidentified as belonging to that particular ceratopsid. But in 2010 it was recognized as a different genus, and based on some partial frill remains it was classified as a very early chasmosaur (a different branch of the ceratopsids which includes Triceratops), related to other early forms like Mercuriceratops.

Its genus name was based on the snake-haired Medusa from Greek mythology, while its species name comes from the Norse trickster god Loki – both in reference to the years of confusion about the identity of Medusaceratops’ fossils, and the distinctive curved horns on the helmet of Marvel’s Loki.

And, true to its name, the confusion wasn’t over yet.

Recently more fossil material and a new study have shown it was still being misclassified. Now it seems like Medusaceratops was actually part of the centrosaur lineage all along, and was indeed a very close relative of Albertaceratops.

It also turns out that what were thought to be numerous Albertaceratops fossils found in the same location were all just even more Medusaceratops. Instead of a mixture of two different ceratopsids there’s a single big bonebed representing some sort of mass-mortality event of only this one animal.

Similar mass bonebeds have been found for other centrosaurs in the same area and around the same age. Perhaps there were frequent flash floods at the time, or they were attempting to migrate across fast-flowing rivers like some modern animals, but we still don’t actually know for certain why they died en masse so frequently.

Australovenator

Australovenator wintonensis, a megaraptoran dinosaur from the Late Cretaceous of Queensland, Australia (~100-94 mya). It was a medium-sized member of the group, about 6m long (19′8″), and despite only being known from a partial skeleton it’s still one the best-known megaraptorans – and also the most complete predatory dinosaur from Australia.

Megaraptorans were a group of fairly large theropod dinosaurs, currently known from Australia, South America, and Japan (and maybe Egypt). Their relationships to other theropod groups are rather uncertain, with different studies placing them as neovenatorids, tyrannosaurids, or most recently as an early branch of the coelurosaurs.

They had very lightly-built bodies, with bird-like bones full of weight-reducing air spaces, proportionally small heads with long slender snouts, and leg bones adapted for running. But their most distinctive feature was their hands, featuring massively enlarged claws on the first and second fingers, with the third finger being much smaller and somewhat vestigial-looking. While some other theropods like allosaurids and spinosaurids also had big hand claws, megaraptorans’ almost tyrannosaurid-like mostly-two-fingered arrangement is rather odd.

Their arms and fingers were much more flexible than those of most other non-avian dinosaurs, allowing them to reach out, grab onto prey with those claws, and then pull it in close to their bodies, restraining it in a sort of death-hug while their relatively weak jaws finished it off.

A distinctive injury to the second toe of Australovenator also suggests these dinosaurs may have been able to deliver powerful kicks like modern cassowaries.

Caviramus

Caviramus schesaplanensis, a pterosaur from the Late Triassic of Switzerland (~205 mya). Known from two fossil specimens – a partial jaw and a much more complete skull and skeleton – it was about the size of a modern raven, with a length of around 60cm (2′) and a wingspan of 1.35m (4′5″).

(The more complete fossil is also sometimes considered to be a separate genus and species, Raeticodactylus filisurensis, depending on which pterosaur specialist you ask. If it was a different animal it still would have been very closely related to Caviramus, though, and the two would likely have looked very similar to each other.)

It had some odd anatomy for an early pterosaur, with proportionally long and slender limbs and a fairly heavily-built skull. There were bony crests on both its upper and lower jaws, with the upper crest probably supporting a much larger soft-tissue structure.

Powerful jaw muscles along with a combination of fang-like teeth at the front of its jaws and and serrated slicing-chewing teeth further back suggest it was specialized for eating particularly tough foods such as hard-shelled invertebrates – and it may even have been omnivorous, capable of eating plant matter as well.

Boverisuchus

Boverisuchus magnifrons*, a crocodilian from the early Eocene of Germany (~50-40 mya). Reaching about 3m long (9′10″) it was much more heavily armored than its modern cousins, with an interlocking “exoskeleton” of bony osteoderms covering its body and limbs – leading to it being given the nickname “panzer croc”.

It was adapted for walking and running on land, with relatively long legs and surprisingly hoof-like claws. It may even have carried its weight directly on these hooves similar to mammalian ungulates.

And if that’s not unusual enough, its hind leg musculature suggests it also might have been capable of short bursts of bipedal sprinting.

[ * Originally known as Pristichampsus rollinatii before being reassigned in 2013.]