Eons Roundup 7

It’s another PBS Eons commission roundup day!

The metatherian mammals Pucadelphysand Khasia, and lineart of the sparassodont Paraborhyaena, from “How South America Made the Marsupials”
https://www.youtube.com/watch?v=l5doyrUWFbE

The dyrosaurid crocodyliform Acherontisuchus and the bothremydid turtle Puentemys, from “How a Hot Planet Created the World’s Biggest Snake”
https://www.youtube.com/watch?v=T-hDNbM-WLk

The early penguin Waimanu and the giant penguin Anthropornis, from “When Penguins Went From The Sky To The Sea”
https://www.youtube.com/watch?v=HMArjGQwLvY

Qianshanornis

Many modern predatory birds have enlarged claws on their second toes, similar to those of their paravian dinosaur ancestors – with seriemas being a particularly good example.

Seriemas are part of a lineage known as cariamiformes, highly terrestrial birds that were widespread across most of the world but are today represented today by only two living species in South America. During the Cenozoic this group repeatedly evolved into large predatory flightless forms like the the phorusrhacids and bathornithids, and were probably the closest avians ever got to recreating the “carnivorous theropod” body plan and ecological niche.

And yet none of them ever seem to have experimented with more dromaeosaurid-like claws.

…With one known exception.

Qianshanornis rapax here lived in East China during the mid-Paleocene, about 63 million years ago. It was a small cariamiform, probably around 30cm tall (1″), and is only known from fragmentary fossil material – but part of those fragments was a fairly well-preserved foot. And the bones of its second toe were unlike any other known Cenozoic bird, shaped incredibly similarly to those of dromaeosaurids and suggesting it may have had the same sort of big hyperextendible “sickle claw”.

While it had sturdy legs and short wings, and probably spent a lot of time walking on the ground like other cariamiformes, it was probably also still a fairly strong flier based on the known anatomy of its arms and shoulders.

Unfortunately, though, its head and claws were entirely missing, so without more fossil discoveries it’s hard to say anything definite about its ecology. I’ve restored it here based on other predatory cariamiformes, but since it was also closely related to a herbivorous species it’s not clear whether Qianshanornis was truly a dromaeosaur-mimic or if something else was going on with that unique second toe.

Weird Heads Month #29: Giant Saw-Toothed Birds

The pelagornithids, or “pseudotooth birds”, were a group of large seabirds that were found around the world for almost the entire Cenozoic, existing for at least 60 million years and only going completely extinct just 2.5 million years ago.

Their evolutionary relationships are uncertain and in the past they’ve been considered as relatives of pelicaniformes, albatrosses and petrels, or storks, but more recently they’ve been proposed to have been closer related to ducks and geese instead.

Whatever they were, they were some of the largest birds to ever fly, and many of the “smaller” species still had wingspans comparable to the largest modern flying birds.

But their most notable feature was their beaks. Although at first glance they look like they were lined with pointy teeth, these structures were actually outgrowths of their jaw bones covered with keratinous beak tissue. While these bony spikes would have been useful for holding onto slippery aquatic animals like fish and squid, they were actually hollow and relatively fragile so pelagornithids must have mainly caught smaller prey that couldn’t thrash around hard enough to break anything.

The serrations also only developed towards full maturity, and the “toothless” juveniles may have had a completely different ecology to adults.

Pelagornis chilensis here was one of the larger species of pelagornithid, with a wingspan of 5-6m (16’4″-19’8″), known from the western and northern coasts of South America during the late Miocene about 11-5 million years ago.

Like other pelagornithids it was highly adapted for albatross-like dynamic soaring, with long narrow wings that allowed it to travel huge distances while expending very little energy – but with its proportionally short legs it would have been clumsy on the ground and probably spent the vast majority of its life on the wing, only returning to land to breed.

Bambolinetta

Between about 9 and 7 million years ago, the modern regions of Tuscany, Corsica, and Sardinia were once part of a single island in the ancient Mediterranean Sea.

And since evolution often goes in weird directions on isolated islands, it’s no surprise that some unusual species developed there.

One of which was a very odd duck.

A map of the Mediterranean region during the Late Miocene, showing the location of the Tusco-Sardinian island.
From fig 4 in Williams, M. F. (2008). Cranio-dental evidence of a hominin-like hyper-masticatory apparatus in Oreopithecus bambolii. Was the swamp ape a human ancestor?. Bioscience Hypotheses, 1(3), 127-137. https://doi.org/10.1016/j.bihy.2008.04.001

Bambolinetta lignitifila lived during the Late Miocene, about 7.5 million years ago. Known from a single partial skeleton discovered in the mid-1800s, it was initially thought to be a fairly normal dabbling duck and wasn’t properly re-examined until 2014, when its strange features were finally recognized.

It was a medium-sized duck, probably around 50cm long (1’8″), but it had much chunkier wing bones than its relatives, with noticeably shortened forearms – looking much more like the wings of an auk or penguin, and suggesting that it was a similar sort of wing propelled diver. This is incredibly weird for a duck, since every other known diving species uses feet for propulsion instead, and so Bambolinetta may be the only known waterfowl to ever develop this type of underwater locomotion.

It’s not clear whether it was still capable of flying or not. There were few predators in its habitat, so it may well have become completely flightless – and that could also be the reason it later went extinct. Sea levels in the region began to drop around 7 million years ago, reconnecting the Tusco-Sardinian island to the European mainland, and Bambolinetta‘s high level of ecological specialization and its potential island tameness would have given it little defence against an influx of new unfamiliar predators.

Palaelodus

The closest living relatives to modern flamingos are, surprisingly, the grebes. But this relationship is especially ancient, with their last common ancestor probably living sometime between the end of the Cretaceous and the early Eocene.

Such an ancestor is thought to have been a highly aquatic swimming bird, more grebe-like than flamingo-like, but there are few fossils of intermediate forms between that and the modern wading flamingos – with the exception of a group known as the palaelodids.

Palaelodus ambiguus here lived about 29-12 million years ago in Europe, from the early Oligocene to the mid-Miocene. It was similar in size to a small flamingo at about 80cm tall (2’7″), but had proportionally shorter legs and appears to have been capable of both wading and swimming in different depths of water, leading to its nickname of “swimming flamingo”.  (Even though modern flamingos do occasionally swim too!)

Its straight pointed beak also suggests it had a much less specialized diet than its modern cousins, probably feeding on small aquatic animals like snails, insect larvae, and fish.

Various other palaelodid species have been found all around the world – even as far as New Zealand – so they seem to have been incredibly common and successful birds during their time. The last definite remains of this group come from the late Miocene, about 7 million years ago, although one Australian fossil may represent a late-surviving relict population that existed until just half a million years ago in the mid-Pleistocene.

Island Weirdness #59 — Terrestrial Otters & Owls

The Mediterranean island of Crete had very few predators during the Pleistocene, with most being birds of prey. And with the terrestrial carnivore niches in the ecosystem left vacant, it was a semi-aquatic mammal and an owl that ended up taking advantage of that opportunity.

Neither were large enough to threaten the dwarf elephants and hippos, and don’t even seem to have habitually eaten even the smallest of the miniature giant deer. Instead these Cretan predators focused much more on the smaller land vertebrates on the island, preying on birds, shrews, rodents, amphibians, and reptiles.

A stylized illustration of an extinct otter. It has a blunt snout and chunky legs.
Lutrogale cretensis

Lutrogale cretensis (previously known as Isolalutra cretensis) was a close relative of the modern smooth-coated otter. It was about the same size as its living cousin, around 1m long (3’3″), but had stronger jaws and chunkier limbs.

Its skeleton shows features associated with walking and running more than swimming, and it seems that this was something of a “land otter” — still able to swim, but spending most of its time on land similar to the modern small-clawed otter.

Shellfish were likely still the main part of its diet, indicated by its crushing teeth. But it probably also regularly ate whatever small terrestrial vertebrates it could catch, since more aquatic otters are already known to prey on those types on animals when they can.


A stylized illustration of an extinct giant little owl. It has longer legs than its modern relatives, almost resembling a large burrowing owl.
Athene cretensis

Athene cretensis was yet another weird island owl, but this time not a descendant of a Strix or Tyto species. Instead this owl was descended from the Eurasian little owl — except it had become much much larger.

It stood around 60cm tall (2′), over three times bigger than its living relative. Its legs weren’t quite as long as those of the modern burrowing owl, but they were still proportionally much longer than those of little owls and show adaptations for terrestrial movement. Little owls already sometimes chase down prey on foot, and Athene cretensis was probably even more of a ground-based hunter, convergently similar to the Hawaiian stilt-owls and the Cuban terror owls.

Preserved pellets show that it ate small mammals and birds, mainly large mice.

Its wings were still quite large, and it was probably also a good flier — and may even have spread over to some of the Dodecanese islands to the east of Crete, since a wing bone closely resembling that of Athene cretensis has been found on Armathia.

Both of these predators seem to have disappeared around the end of the Pleistocene, at the same time as many of the other native Cretan species about 21,500 years ago. Much like the situation with Candiacervus, this may have been a result of a combination of a rapidly shifting climate and the presence of humans disrupting the already fragile island ecosystem.

Island Weirdness #57 — Cygnus falconeri

The island of Sicily was isolated about 5.3 million years ago when the Mediterranean rapidly refilled. During the next few million years changes in sea level and tectonic uplift allowed repeated colonizations by mainlaind species via the sea strait separating Sicily from Italy, and opened up occasional connections with nearby Malta, resulting in a series of different ecosystems over time.

During the mid-Pleistocene, between about 900,000 and 500,000 years ago, a lack of large land predators on Sicily and Malta allowed a weird mix of endemic species to evolve. Most famous are the tiniest elephants (Palaeoloxodon falconeri), but there were also a couple of giant owls, a small long-legged owl, a giant crane, a big lizard, a giant tortoise, an otter, and giant dormice.

And then there were the swans.

Cygnus falconeri was enormous, at least a third larger than the biggest living swans, at least 1.5m tall (4’11”) — taller than the native elephants, although not nearly as heavy. Its wings were large, with a span of around 3m (9’10”), but at such a hefty size it would have been either a very poor and reluctant flier or functionally flightless.

Its legs were better adapted for walking around on land than for swimming, with shorter toes and possibly reduced webbing. It would have been one of the biggest terrestrial herbivores on Siculo-Malta, probably mainly a grazer but also capable of reaching much higher vegetation than the elephants or tortoises.

It lived alongside another unique swan species, the goose-like dwarf swan Cygnus equitum. Both the giant and dwarf swans probably evolved from the same whooper swan-like ancestor species, but each resulted from separate colonization events — otherwise interbreeding would have probably prevented them from developing such a huge difference in size.

Or an alternative scale comparison to highlight the utter ridiculousness of this island:

A scale comparison between a dwarf elephant and a giant swan. The swan is the taller of the two.
Palaeoloxodon falconeri vs Cygnus falconeri

Between 500,000 and 200,000 years ago multiple sea level fluctuations allowed new species to colonize Siculo-Malta from the mainland, including various large mammalian herbivores and carnivores. With new competition and predators, Cygnus falconeri probably disappeared around the same time as the tiny elephants and most of the other mid-Pleistocene endemic animals.

The dwarf swan, smaller and still a strong flier, may have survived the altered ecosystem for a bit longer, but would have gone extinct during the rapid climate changes at the start of the last glacial period 115,000 years ago.

Island Weirdness #50 — Caracara tellustris

Jamaica is unusual among the Caribbean islands for having had relatively few predatory birds.

One of the few known fossil species is Caracara tellustris, a close relative of the modern crested caracaras that probably evolved in the mid-Pleistocene between about 1.2 and 0.4 million years ago.

About 60-65cm long (2′-2’2″), it was similar in body size to larger individuals of its living relatives but was heftier built and had slightly longer legs, and its wings were reduced enough that it was either a very weak flier or entirely flightless.

It lived only in the dry scrubland around the southern coast of the island, and probably mainly preyed on reptiles, small rodents, and crabs using its strong legs — a lifestyle very similar to the modern secretarybird. Like other caracaras it would have also opportunistically scavenged on carrion, which there would have been little competition for.

The known remains of Caracara tellustris date to as recently as 100 CE, showing that it existed well into the Holocene and survived through the initial arrival of humans on its island home (about 4000 BCE). This is likely due to its inhospitable hot, arid, and thorny habitat, where it would have been left relatively undisturbed, and it may even have persisted until the time of European colonization in the 1500s.

Unfortunately the scrubland was also very limited in size and the Jamaican caracara would have always been quite a rare species. If it was still around by then it would have faced a combination of introduced predatory mammals and habitat destruction by agriculture, which would have driven it into extinction so quickly its existence was never even noticed by naturalists at the time.

Island Weirdness #49 — Sloth-Monkeys & Fighting Ibises

Jamaica is the third largest island in the Caribbean, and much like Cuba it originated as part of a Late Cretaceous volcanic island arc. It began to subside during the Eocene and was completely submerged for a large portion of the Cenozoic, then was uplifted again in the early-to-mid Miocene, reaching close to its present-day size around 13 million years ago.

Few land mammals ever colonized the island prior to human influence, and most of the known remains are from rodents. But another group did make it onto Jamaica, and became something especially weird.

A stylized illustration of an extinct titi monkey. It has long soft fur and a very long tail.
Xenothrix mcgregori

Xenothrix mcgregori is a primate only known from fragmentary remains, but what is known of its skeleton shows a unique combination of features for a New World monkey. It had a reduced number of teeth in its jaws, with enlarged molars, and oddly-shaped heavily-built leg bones that resemble those of slow quadrupedal climbers like lorises.

It was probably about 70cm long in total (2’4″), including the tail, and is thought to have lived a lot like a tree sloth, spending most of its time moving slowly around in the trees and possibly even feeding while hanging upside down.

Its anatomy was so ununsual that its evolutionary relationships were a mystery until ancient DNA was recovered from subfossil bones and confirmed it was actually a titi monkey very closely related to the genus Cheracebus. Its ancestors probably arrived on Jamaica in the late Miocene, around 11 million years ago, and it had some close relatives on a couple of other Caribbean islands — the terrestrial Paralouatta on Cuba, and Antillothrix and Insulacebus on Hispaniola — although they likely all independently colonized the Caribbean via different rafting events from South America.


A stylized illustration of an extinct flightless ibis. It has stout legs, and has its wings raised as if threatening to hit something with its heavy club-like arm bones.
Xenicibis xympithecus

Another inhabitant of Jamaica was an equally strange bird.

Xenicibis xympithecus was one of only two lineages of ibis ever known to have become completely flightless (the other being Apteribis from Hawaii).

Around 60cm tall (2′), it had some of the most unique wings of any bird. The hollow bones were thickened, its forearm was proportionally short, and the hand was modified into a large heavy “club” — and blunt-force injuries on some of these birds’ remains suggest that they used their wings as weapons when fighting, clobbering each other with powerful blows.

Radiocarbon dating suggests the Xenothrix monkeys survived well into the Holocene, until around 1100 CE. Since various groups of humans had been present on Jamaica since about 4000 BCE the sloth-monkeys must have coexisted with them for several millennia, and their extinction may have been caused by more of a “slow fuse” of gradual habitat destruction than direct exploitation.

Dating on Xenicibis‘ extinction is less precise, with the youngest known remains being somewhere between 10,000 and 2200 years old. It may have still been around when the earliest humans arrived, but unlike the native monkeys it seems like it didn’t last long beyond that point.

Island Weirdness #48 — Chunky Cranes & Terror Owls

Like many other isolated islands ancient Cuba lacked any large land predators, allowing some birds to exploit more terrestrial lifestyles.

A stylized illustration of an extinct flightless sandhill crane. It has a somewhat chunkier beak than its modern relatives, along with smaller wings and thicker legs.
Grus cubensis

The Cuban flightless crane (Grus cubensis, or possibly Antigone cubensis) lived during the Late Pleistocene and Holocene. It was probably a descendant of the sandhill crane — and although an endemic variety of sandhill crane still exists in Cuba today, the two aren’t directly related to each other and instead are the result of two different colonization events.

It was about the same size as modern sandhill cranes, around 60cm tall at the back (2′) with a full height of about 1m (3’3″), but it was much more heavily built. It had stockier legs and a thicker beak, suggesting it may have been specialized for a different ecological niche than its ancestors, and its wings were reduced enough that it was probably completely flightless.


A stylized illustration of an extinct giant owl. It has proportionally short wings and long stilt-like legs.
Ornimegalonyx oteroi

And, once again, there was also a weird owl on this island.

Ornimegalonyx oteroi was closely related to true owls in the genus Strix, and in a great example of convergent evolution did the exact same thing as the Grallistrix stilt-owls — it evolved into a long-legged short-winged ground-based apex predator.

But it was almost twice the size of its Hawaiian cousins, measuring about 1.1m tall (3’7″) and potentially being the largest owl to ever exist. Its remains were so big, in fact, that they were initially mistaken for those of a terror bird.

It was powerfully built and was probably a good runner, mainly preying on giant rodents and dwarf ground sloths. While its wings and flight muscles were reduced it might not have been entirely flightless, and it may have been still been capable of turkey-like short bursts of flight.

Three other species of Ornimegalonyx also stalked ancient Cuba at the same time, varying slightly in size from each other and probably each specializing in a different size class of prey.

Remains of both of these birds have been found in natural petroleum seeps on the northern coast of Cuba that date to as recently as about 6000 years ago, around the same time that humans first arrived. After that point they probably both went extinct very quickly — the flightless cranes were probably actively hunted and eaten into extinction, and the terror owls would have disappeared as their prey species dwindled away due to the same hunting pressures.