Colours of Wildlife: Casea broilii

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Casea broilii

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!"

Casea by Willem

Today I have an article for you, featuring something about which we know very little. This is Casea broilii. It doesn't have a common name. The reason for that, and for why we know so little about it, is that it lived almost 300 million years ago. Even though we know more about it than about most other things that lived at that time, it is still an enormous time gap between it and us that we need to cross. The time period when Casea lived was the Permian (it lived in the earliest part of this epoch), which was the last period of the Palaeozoic Era, or the time of Ancient Life. The Palaeozoic was followed by the Mesozoic, the time of Middle Life, which was when the dinosaurs reigned; the Mesozoic was followed by the Caenozoic, the time of Recent Life, which is the age in which mammals (including ourselves) diversified and came to 'reign'. We know least about the Palaeozoic, but we need to understand that what happened in that ancient time, set the stage for everything that followed, right up to this present moment in which we live.

So it is with old Casea. This lizard-like thing lived in what is today the USA (I don't think they had a name for it back then). It was just over a metre/yard in overall length. What was it? It had four five-toed limbs, sprawling to the sides, with broad hands and feet. It had a long tail, a broad and deep rib-cage, and a proportionally tiny head. But it is that head that gives us the most clues as to what it was. Casea's head had short, blunt teeth, only in the upper jaws that overlapped the edge of the lower jaw. Such teeth would not be able to deal with biting or chewing meat. They're more suited to cropping leaves and indeed, Casea was one of the world's first four-footed vegetarians. Prior to its existence, the lizard-like things were hunters, either snapping at the many insects and other invertebrates (some huge) that lived at the time, or starting to stalk and hunt the other lizard-like things. So old Casea was taking a step that was quite revolutionary: targeting the vegetation itself for sustenance, rather than the other animal critters that the vegetation supported. Casea's big rib-cage was for containing the ample amount of entrails it needed to thoroughly digest all this plant matter. Its sprawling limbs meant that it wasn't able to move fast – but then, it didn't need to, since its food wasn't able to run. And, modest-sized as it was, there weren't at the time and place many larger predators that could eat it, so it didn't need to run very fast to escape them. Sure enough, the early Permian did see the start of the evolution of the big land predators, but at that stage these predators were rather slow and clumsy themselves.

The Palaeozoic was truly the time of beginnings. It stretches back to the origin of life itself, which happened surprisingly soon after the planet Earth came into existence. For all that, we still have only the tiniest of clues as to how that happened. Life started out as tiny single-celled organisms, using a diversity of basic metabolic systems to give them the energy they needed to live. By about two billion years ago, a crisis happened, because some of those tiny little cells had figured out the trick of using sunlight to get this life-energy; but in doing so, they generated toxic waste. That toxic waste was the gas called oxygen, a lethal poison to most living things of the time. More and more of this toxic gas was churned out, to the point where it became a significant component of the atmosphere which caused a massive catastrophe and die-off of almost all living things. But some of the ones that survived, figured out a new trick, namely using this toxic gas for their own energy needs, essentially 'burning' sugars and other organic substances in this oxygen with the release of a large amount of energy. This new trick surprisingly allowed a vast new range of living things to come into existence and to diversify.

Life thus was modifying the planet quite radically even at this early stage. The planet changed in other ways as well. The land masses and the oceans were constantly changing as a result of continental drift; bits and pieces came together and broke off, drifted and shifted; the different arrangements of the land and sea areas, together with changes in the atmosphere, caused massive climatic shifts. About six hundred million years ago, this resulted in the coldest period the planet had ever seen, called Snowball Earth. Evidence of glaciers even in equatorial regions, would suggest that a layer of ice and snow actually covered the entire surface of the planet at that time – all of the remaining life was locked up below that. Maybe it was not quite as bad as that, but still, this represented a crisis for the planet and might very well have been permanent. Once the snowball had frozen completely, would it ever thaw again?

But the snowball did thaw, we're not sure just how, but when it did, the next huge step happened. Life until then had been pretty much at the single-cell level. But somewhere in the background, revolutions were happening. Some cells were teaming up with others in strange experiments in cellular communism, where the life of the individual was sacrificed to the life of the colony. But these colonies became what we now consider to be entities in their own right – multicellular animals and plants. We don't even think about the poor single cells and how they sacrifice themselves for the good of the group; we take for granted that the wellbeing now exists only at the level of the group as a whole. And when Snowball Earth thawed, these multicellular critters started to diversify and dominate the seascapes.

The land was still barren, but that changed too. Tiny films of algae and other critters soon covered rocks and mud at the edges of the rivers and seas; by about 400 million years ago, the first complex and large, multicellular land plants (a few inches in height) came to grow well inland, and soon there sprouted vast forests of truly large trees over much of the continents. They were composed of ancient plants like ferns, horsetails, lycopods, and groups that have by now vanished. But these first forests made possible the invasion of the continents by animal life. Again at first, these land-dwelling animals were small, and mainly insects and other invertebrates. The first forests had nothing preying on these, and some became huge. But by about 375 million years ago the large sea-dwelling animals were taking important steps that would change that. And these important steps were literal steps: the ability to walk, using strong legs and feet, amazingly seems to have happened in fish-like things that were still entirely water-living. But once the feet and legs were there, they could crawl from the bottom of the seas and rivers out onto the dry land, where the feast of insects awaited. From the initial very fish-like things, which could leave the water only for short periods, evolved what we call the amphibians, which could live on land all the time, only needing to return to water to lay their jelly-like eggs. But just over 300 million years ago the final step was taken, breaking the dependence on the oceans, rivers and lakes entirely. That was the invention of the shelled egg. Inside this egg the water needed for the development of the baby critter was contained, as well as a big store of energy in the yolk. The egg could be laid on land, the shell protecting it against damage and desiccation, the critter inside developing until large and strong enough to break out and to seek its own food and life. The critters who laid these shelled eggs were called reptiles. And this is where old Casea comes in.

The first reptiles all looked like lizards – testimony to how amazingly well the lizard shape and lifestyle suits generalist land-living four-footed things. But even at the start they were diverging; even 300 million years ago we can start tracing the lines of evolution that culminated in the full diversity of land-living things (and also many things that decided to go back to a life in the water) that we find today. To see where Casea fit in, let's again look at its tiny skull. The first reptiles had solid, box-like skulls, with openings only for eyes and nostrils. These are called anapsids. We still have reptiles with such box-like skulls, namely the tortoises and turtles, but strangely they may not be true anapsids. From the first anapsids, the skulls changed. Some developed two new openings just behind the eyes, an upper and a lower opening on each side. These reptiles are called diapsids, and their descendants were legion. The two openings meant skulls that could be light and flexible or strong and solid, depending on the size and arrangement of bones around the openings. Lizards and snakes are diapsids; the dinosaurs were diapsids, and their descendants the birds, and their cousins the crocodiles. Even tortoises and turtles, which as I've said today have no skull openings behind the eyes, may turn out to be diapsids in which the openings secondarily closed up again.

There was one other kind of skull that also appeared a bit over 300 million years ago. That skull type also had openings behind the eyes, but this time only a single opening behind each eye. This skull type is called synapsid. The single opening helped reduce skull weight, while retaining strength and robustness, and the opening also provided new attachment sites for muscles. And this is the skull type old Casea had. The openings were right at the sides of its broad, flaring cheekbones. Casea was not the first synapsid, but it was one of the earliest types. Want to guess what group of modern animals it was that were the descendants of these first, ancient synapsids? It is us – the mammals! So, incredible as it seems, this old thing was one of the first of a group that today includes mice and men, bats and badgers, horses and cows, wolves and tigers, hippos and elephants, whales and dolphins. And it all came down to the possibilities opened up by that single temporal opening in that ancient skull. Changes in skulls drove changes in diets which drove changes in lifestyles which drove changes in body forms which enabled new environments to be colonized which then drew more and greater changes still. Even in its turn to vegetarianism, from meat-eating synapsid ancestors, Casea demonstrates the start of that adaptation drive.

But there is much, much that we still don't know about old Casea and its world. We're not sure if it was entirely terrestrial or semi-aquatic. Its thick body might have floated well in the shallow waters of an ancient swamp, and its broad hands and feet might have been great for swimming. We don't know just why its head was as small as it was. Presumably it didn't chew much, leaving most of the digestion of its food to happen in its big gut. Did it use bacteria to help ferment and digest the food in its belly, like modern cows and other herbivores do? Just how fast did it grow, how long did it live? Just how fast could it move, and which animals of the time preyed on it? We don't know much about this first experiment in herbivory. How, and how rapidly, did the change-over from meat eating to plant eating happen? From mid-sized animals like Casea, there soon evolved very big plant eaters like Cotylorhynchus which had proportionally even smaller heads. But these all died out in the early Permian – why? Other vegetarian relatives of Casea included strange animals with huge, bone-supported skin 'sails' on their backs. What were these for? We don't know; these animals also died out in the early Permian, along with other sail-backed animals that were meat-eating. But some of the meat-eating synapsids of the time diversified into an amazing variety of forms. Yet, most of these also died out, at the end of the Permian, which was perhaps the greatest global extinction of all. But a tiny fraction survived and diversified yet again, only again to be driven to the edges of existence in the Mesozoic, the time of the dinosaurs. But some of these through good fortune survived the catastrophe that killed the (non-avian) dinosaurs, and these finally became us modern mammals. And Casea and its kin were the start of all that! So spare a thought for this strange and ungainly old critter.

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