But Brontornis might not actually have been a terror bird at all – it may have instead been a giant cousin of ducks and geese.
The known fossil material is fragmentary enough that it’s still hard to tell for certain, but there’s some evidence that links it to the gastornithiformes, a group of huge herbivorous birds related to modern waterfowl.
If it was a gastornithiform, that would mean it represents a previously completely unknown lineage of South American giant flightless galloanserans. And, along with the gastornithids and the mihirungs, it would represent a third time that group of birds convergently evolved this sort of body plan and ecological role on entirely different continents during the Cenozoic.
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.
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.
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.
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:
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.
The big herbivorous moa-nalo weren’t the only unusual waterfowl on the ancient Hawaiian islands — and the island of Kauaʻi had a very odd duck indeed.
The Kauaʻi mole duck (Talpanas lippa) was fairly small, about 50cm long (1’8″), and although it lived alongside one of the moa-nalo species they don’t seem to have been closely related at all. It instead appears to have come from a different duck lineage entirely, with it’s closest living relatives potentially being the stiff-tailed ducks.
It had short chunky legs and an especially weird skull, with eyes so tiny and underdeveloped that it must have been near-blind and flightless. But the areas of its brain associated with the sense of touch were proportionally huge, and although the exact shape of its beak currently isn’t known it seems to have been very wide and flat.
It was probably a nocturnal bird that used an incredibly sensitive bill to grub around in the undergrowth for invertebrates, sort of an equivalent of the modern kiwi but with a face more like a platypus.
The only known Talpanas remains come from mid-Holocene deposits about 6000 years old, but since Kauaʻi is the geologically oldest of the main Hawaiian islands it may have existed there for several million years prior.
Like the moa-nalo it was likely driven to extinction due to human influences on its environment once Polynesian settlers reached the island, sometime between 300 CE and 1200 CE.
The islands of Hawaii are part of a larger archipelago formed via hotspot volcanism in the Pacific, and are quite geologically young — the oldest of the main islands was formed just slightly over 5 million years ago, and the youngest less than 0.5 million years ago.
Located almost 3700km (2300 miles) from the nearest continental shore, they’re the most isolated islands on Earth. Their native species are all descended from the rare colonization events that reached such a remote location, either via ocean rafting or island hopping from much older now-submerged islands northwest in the chain.
Like many other Pacific islands no land mammals ever reached Hawaii prior to human arrival, and so it was birds that ended up filling many of the vacant ecological niches.
The Maui Nui large-billed moa-nalo (Thambetochen chauliodous) was one of the biggest species, about 90cm tall (~3′). It originally lived in the highlands of Maui Nui, a large island that formed over 1 million years ago — and when Maui Nui subsided and flooded about 200,000 years ago, it would have then occupied the resulting modern islands of Maui, Molokaʻi, Lānaʻi, and Kahoʻolawe.
Polynesians reached the Hawaiian islands sometime between 300 CE and 1200 CE (the exact dating seems to be controversial). The moa-nalo would have suffered the same fate as many other flightless island birds, lacking any instinctive fear of the new arrivals and falling prey to the invasive pigs, dogs, and rats they brought with them.
Between Australia and Fiji lie the islands of New Caledonia, an archipelago at the northern end of the mostly-submerged continent of Zealandia. Having split away from Australia at the end of the Cretaceous, 66 million years ago, New Caledonia’s Cenozoic isolation has resulted in the islands acting as a refugium for a number of “living fossil” lineages, including the kagu, a small nautilius, and the “primitive” flowering plant Amborella.
Sylviornis had a massive skull with a large deep beak, topped with a bony crest, along with reduced wings and stout legs. It also had no wishbone, extra tail vertebrae, and a ribcage and pelvis that looked more like a non-avian dinosaur.
It was probably a slow-moving herbivore, browsing on plant matter and digging up roots and tubers with its beak and feet.
Thousands of subfossil remains of Sylviornis individuals have been found, but a large proportion of them are all juveniles, suggesting that this species’ reproductive strategy was to have large numbers of young at a time. It also seems to have had a surprisingly short lifespan for its size — just 5-7 years.
New Caledonia was first settled by humans around 1500 BCE, and it’s likely that Sylviornis was hunted by both them and the invasive mammals they brought along like dogs, pigs, and rats.
The folklore of the Kanak people features stories of a large flightless bird known as the du, described as being reddish-colored with a star-shaped crest, so it’s possible Sylviornis actually persisted alongside the new arrivals for some time — but eventually the environmental disruption was too much for these odd primitive dino-chickens, and they were gone.
Standing around 50cm tall (1′8″), it had a slender body, long legs, a long neck, and a narrow goose-like beak. It also had an unusual pair of bony bumps on its skull which may have supported some sort of small crest superficially similar to the knob on the head of the modern magpie goose.
Temperatures in Antarctica at the time were much warmer than today, and the area where its fossils were found would have been a temperate estuary or river delta. It was probably an omnivorous wading bird, feeding on vegetation, small fish, and invertebrates in shallow freshwater.
Although it somewhat resembled a presbyornithid it was actually part of an even earlier branch of the waterfowl evolutionary tree – so its ancestors must have originated much further back in the Late Cretaceous – and their similar body shapes hint that the common ancestor of all waterfowl may also have been a rather leggy bird. Conflicto’s closest known relative might actually be the similarly-aged Anatalavis (which was previously though to be a primitive magpie-goose) from North America and Europe, suggesting that its lineage was quite widespread and already taking advantage of vacant niches in the immediate wake of the Cretaceous-Paleogene mass extinction.
Garganornis was an enormous anatid bird, closely related to modern ducks, geese, and swans. Although only known from fragments of its skeleton it’s estimated to have stood up to 1.5m tall (4′11″), making it the largest known waterfowl to have ever lived.
It probably reached such a size thanks to the lack of large terrestrial predators, and possibly also as protection against the island eagles and owls – literally growing too big for them to be able to eat.
It was flightless, with small wings, and had reduced webbing between its toes, suggesting it spent most of its time walking around on land. It also had bony knobs on its wrists that would have been used to give some extra force to wing-slaps when fighting with each other over territory or mates.