Willem is a wildlife artist based in South Africa. He says "My aim is simply to express the beauty and wonder that is in Nature, and to heighten people's appreciation of plants, animals and the wilderness. Not everything I paint is African! Though I've never been there, I'm also fascinated by Asia and I've done paintings of Asian rhinos and birds as well. I may in future do some of European, Australian and American species too. I'm fascinated by wild things from all over the world! I mainly paint in watercolours. . . but actually many media including 'digital' paintings with the computer!"

Some time ago I told y'all about Waller's Titan, a huge prehistoric predatory bird that lived in North America some time before the first people arrived there. Now this bird was just one species in a whole family of birds, the Terror Birds, scientific name the Phorusrhacidae. This family was actually primarily South American. It evolved on that continent while North and South were completely disconnected, separated by a wide stretch of ocean. Only when the Isthmus of Panama formed, a process finished by about 2.7 million years ago, were the continents connected, allowing an interchange of species between them. For most of the Cenozoic, the era of life after the extinction of the non-avian dinosaurs, South America was an 'island continent' (together with Antarctica to which it was sometimes connected) on which mammals, birds and other things could evolve independently.

Thus the terror birds arose. In fact there still exists a small remnant of close relatives of theirs, the Seriemas. Only two species remain, which are long-legged hunting birds that stalk the grass very much like the Secretary Bird of Africa does. They're not closely related to it, or to any other remaining present-day group of birds, however. But back in South America's island continent stage, this group of birds consisted of many species of a great diversity. The terror birds count as just one group among these.

The extinction event that killed off the dinosaurs also killed off a huge number of other things, and left a landscape brimming in opportunities for new lifestyles for the survivors. As plant-eaters became big again, there were now ecological niches available for animals to hunt them. In South America, the principal land predators to fill these niches were the sparassodonts, a marsupial-like group of mammals; the sebecids, which were fast-running, land-living crocodiles; and the terror birds. In fact, the terror birds grew bigger than the sparassodonts, and were the top (or apex) predators of South America for a long time – they first appeared about 62 million years ago and held on until just a hundred thousand years ago, or maybe even less.

Not all the terror birds were very big, but all as far as we know were flightless. They had tiny and weak wing bones, but long and powerful legs with sharp, curved claws. They certainly were all capable of fast running, likely to chase down their prey. Their speed made them dominant over the sparassodonts on the open, grassy plains. It appears they were great at running in a straight line, but not so good at making rapid turns. They might have used their feet for kicking and gouging but perhaps mostly dispatched their prey with their bills. They had proportionally large heads and huge bills, especially in the larger species. The bills had hooked tips and were deep but narrow. They were strong in the up/down plane, but not so resistant to side-to-side-forces, thus likely the killing was done by one or a few strong, downward blows. To wield these huge axe-like heads and beaks, they had long and powerful necks.

Now let's look at a few specific terror bird species. As always when it comes to long-vanished critters that we now only know from their bones, the colours and plumage details are my own speculation.

Psilopterus bachmanni, 'Bachmann's Bare Wing', is one of the smallest terror birds known, standing only about 70-80 cm/28"-32" tall and weighing 5-7 kg/11-15 lbs. It had a rather eagle-like beak. It had sharp, curved, cat-like claws and may have used its feet for killing. Four species of Psilopterus are currently recognized. The genus lived from 29 million to less than 100 000 years ago, making it very successful and one of the latest-surviving members of the family.

Llallawavis scagliai, 'Scaglia's magnificent bird', is another small species, standing about 1.2 m/4' tall and weighing about 18 kg/40 lbs. It is known from a magnificent skeleton, with the trachea, voice box, palate and even the eye bones wonderfully preserved. I restore it looking a bit like the cartoon roadrunner! It may have been one of the fastest-running birds ever. Its skull bones were fused to increase its strength and resistance to shocks, supporting the beak-hunting hypothesis. It appears to have had a deep voice, with inner ears adapted to hearing low frequencies. It lived in the Pliocene, about 3.5 million years ago.

Mesembriornis milneedwardsi was quite large, standing 1.5m/5' tall. It had a long, low skull and beak with a sharply-curved tip. It likely used speed for hunting. I show it here preying on a baby toxodont, one of those strange and special uniquely South American mammals. Mesembriornis lived about 5.3-4 million years ago.

Andalgalornis steuletti was similar in size to Mesembriornis but had a deeper bill. Proportionately it had the largest skull of them all. Its remains are well-preserved and the skull has been studied in detail to see how it could withstand forces. This lead to the general understanding of terror birds hunting with rapid and powerful bill-strikes.

Paraphysornis brasiliensis was a very large terror bird. It stood about 2.4 m/8' tall, with a skull 60 cm/24" long (as long as that of a hippo), and likely weighed over 150 kg/330 lbs. It lived about 23 million years ago.

Kelenken guillermoi was one of the largest terror birds of all time, standing about 2.5 m tall. It had the largest skull known of any bird species, reaching 71 cm/28"! It is named for the demon Kélenken of the Tehuelche people, and after its discoverer, Guillermo Oscar Aguirre Zabala, a student at the time of the discovery. It lived in the mid-Miocene, about 15 million years ago, in a habitat that was transitional between forest and more open grassland, that supported a rich assemblage of mammal and reptile species.

Enigmatic Extinction

All the terror birds are gone today – but we don't quite know why. It is true that when the land bridge formed, new carnivorans like wolves, foxes, dogs, cats and bears moved into South America, meaning stiff competition for the local predators. But this process was happening for many millions of years, during most of which at least some terror birds seemed to hold up quite well. Others went extinct well before this faunal interchange even started. It is not possible that humans had anything to do with their extinction, since the last terror birds vanished thousands of years before the first humans arrived. What we have is thus a group that had its heyday, flourishing and diversifying, and then ultimately dwindling and disappearing, as if it simply gave up on life.

Willem

13.04.20 Front Page

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