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!"

Another prehistoric special! This is Gastornis, the ancient giant goose. This species lived in the Late Palaeocene to early Eocene epochs, 56 to 45 million years ago. It is one of the most iconic of prehistoric birds, having been illustrated by Charles Knight almost a century ago and by many more paleo-artists since then. Gastornis is well-known from many fossils, found in Europe, North America and Asia as far as China. It must have been a prominent member of the ecology back then. Gastornis was very large, reaching around 2 m/7' in height, and with a much thicker and more robust build than the ostriches of today. It had a huge head with a massive bill. It was much too big to fly, and had only stunted wings, hardly visible from the outside. The genus is named for Gaston Planté of France, who discovered it in the mid-Nineteenth Century. For a long time, the American birds were considered to belong to a different genus, Diatryma, but today the consensus is that they were similar enough to the European and Asian birds as to belong to the same genus.

Note: as always, my reconstruction of this bird is imaginative. We don't really know the details of its plumage or what colours its bill, eyes and legs were.

The New Dinosaurs

Regular readers of this column will know by now that birds are actually dinosaurs. They descended from a group of small, lightly-built, feathered dinosaurs that had learned how to fly by about the midpoint of the age of the dinosaurs, and so became 'true' birds. But it's important to know that many other dinosaurs also had feathers and bird-like features. True birds were just one group of a great many feathered dinosaurs, and while the dinosaurs still reigned, there was not really a clear distinction between the true birds and the non-bird dinosaurs … there was a spectrum, from the small feathered ones that could fly very well and were clearly birds, to large ones that couldn't fly and probably used their wing and tail feathers in displays. Even the largest meat-eating dinosaurs like Tyrannosaurus rex probably had feathers of some kind, perhaps fluff rather than vaned feathers.

Things changed at the end of the age of the dinosaurs, about 65 million years ago. We are fairly sure a massive meteoroid struck the Earth then, but there could have been other factors at work also. Whatever the case, it was a massive catastrophe that caused the immediate extinction of the dinosaurs. But not all! Only the very smallest ones survived – which happened to be the birds. No non-bird dinosaur survived the extinction. Globally, pretty much all other large land and sea animals died out as well. The selective factor was for size: almost nothing larger than about the size of a cat survived.

So what happened after then? The calamity was a brief one and after it passed, life on Earth started to recover. But the global ecology was so disrupted that chaos reigned for much longer. All in all, it took about 20 million years for full ecological stability to return, for new large animals to evolve and for biodiversity to reach levels comparable to before. We should keep that in mind … we are causing a massive ecological disaster ourselves right now, one that perhaps might also end up needing millions of years for recovery! And how long is a million years?

Well, a million years is long for us, but not so long for the Earth. Twenty million years did indeed pass. New large animals evolved to replace the dinosaurs. But these were mostly members of a new group, the mammals. Almost literally the underdogs during the time of the dinosaurs, they seized their chance once their rivals were gone, and by the end of the Palaeocene they featured some new and spectacular giants. Not quite as large as the extinct dinosaurs, these were imposing all the same.

But another thing happened. The dinosaurs were not entirely gone after all. The birds were still there! And they, too, suddenly had new evolutionary opportunities. They, too, could evolve, rediversify, and indeed grow large again. So they did! Gastornis was one of the first results. It ended up very similar to many of the big and bird-like, feathery but flightless dinosaurs of about ten million years before. In this form, Gastornis could actually challenge even the largest of the mammals of the time for ecological dominance.

Predator or Plant-Eater?

For long it was believed that something as fearsome-looking as Gastornis must have been a predator. I still remember pictures in those old, lavishly-illustrated books of the nineteen seventies and eighties, of this bird hunting and killing the tiny little ancestral horses that lived at the same time. Even though you know those horses are very small, it is still shocking to see a bird hunting and killing them!

Sadly for those fond of such sensationalism, Gastornis now turns out to have probably been a much more peaceable creature. Its beak didn't have the sharp curved hook at the tip that other, fully predatory birds had and have. Its thick leg bones were not suited to fast running. The toes were not tipped with curved talons, but with shorter, thicker, blunter claws, as shown by footprints attributed to it. Still, it had an extremely powerful bill and massive jaw muscles. Some scientists thought that such a bill is overdeveloped for something that merely eats plants.

For now, however, the issue seems to be settled. We are at the point where we can make minute chemical analyses of ancient bones, to see what kinds of substances went into them. Such analyses were done on some of the bones of Gastornis. These seems to conclusively prove that it was a herbivore … the chemical traces that would have been there had it lived off meat, were entirely absent. So: Gastornis must have used its powerful beak to snip off and chew tough vegetation, instead of hunting those poor tiny horses.

Giant Geese

Another disputed aspect of these ancient giants is just what modern birds they are related to. They were indeed true birds, descended from the smaller, flying birds that survived the extinction event. Their skeletons became much changed as they grew larger, though, these changes obscuring their original ancestry. They have been classified as members of the crane order, the Gruiformes, and also in their own order, the Gastornithiformes (or Diatrymiformes). Today, however, it seems most likely that their closest relatives are the screamers, ducks, geese and swans, the Anseriformes. The anseriforms are indeed a very ancient group, probably already distinct and diverse in the time when the dinosaurs ruled, and having survived the extinction event. Gastornis seems to be a very early offshoot of this group, rapidly taking advantage of new evolutionary opportunities, growing big and powerful. Even if it was not a predator, it certainly, as an adult, did not have much to fear in the environments of the Palaeocene and Eocene epochs.

Beautiful Fossils

This is one ancient bird that is well-known from excellently preserved fossils. There is an odd beauty to the great big bones of this old thing, the thick leg bones, the intricately massive vertebrae of the neck, the huge head with the enormously deep bill. Apart from the bones, there are other remains as well attributed to it (though not with complete certainty): eggs, footprints, and even feather remains. (If the latter indeed comes from Gastornis, then it seems that it had vaned, more bird-like body feathers than the modern ostriches and other big flightless birds do.) After so many million years, it is a miracle to still have these remains preserved so well, testifying to these monster animals. One could easily believe that subsequently, they could have indeed grown bigger still, restoring the glory of the giant dinosaurs again.

Sadly (or for us, maybe fortunately) this was not to be. Only a few birds ever became as big, or bigger, and mostly only in places where there was no serious mammalian competition. For some reason, the true birds simply could never recapture the immense size of the erstwhile dinosaurs. It might have something to do with their anatomy or physiology, something in there putting an insuperable limit. The mammals, however, once rid of the dominance of the dinosaurs, proved to be extremely adaptable and indeed capable of becoming very large, even if not quite as large as the largest of the dinosaurs. And so, with its mammalian competition soon catching up, Gastornis had a limited reign, dying out with no descendants around the early Eocene. Since its reign, there have been other very large birds, and indeed we are fortunate to still have ostriches around. Giant birds are certainly likely to be with us for quite a while longer. But the true glory of the post-extinction dinosaurs actually resides in those small things with their wonderful, delicate beauty and sophisticated lifestyles – the flying birds.

Colours of Wildlife Archive

Willem

04.01.16 Front Page

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