Myotragus: The Forward-looking Lizard Goat of the Balearic Islands

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Myotragus: The Forward-looking Lizard Goat of the Balearic Islands

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!"

Myotragus by Willem

An interesting prehistoric thingy for this week! Myotragus balearicus ("Balearic mouse-goat") was one of the strangest 'goats' of all time. It looked strange: while all living goats, sheep, antelopes, gazelles and their kin have eyes facing sideways, Myotragus had forward-facing eyes. This means it had good binocular vison, like we humans do. Some reconstructions of this goat indeed look 'wrong', giving it a creepily human expression. I've tried to make it look more properly goat-like! Another very weird thing about Myotragus was that it was, apparently, 'cold-blooded'! Well, not completely. When we use the term 'cold-blooded' today, we actually mean that the blood is not always warm. Lizards, snakes, crocodiles etc. may be called cold-blooded, but actually their blood is only cold when it's cold around them. On a hot day, they may be more hot-blooded than many birds and mammals! But the key about them is that they don't keep a constant blood temperature. It goes up and down depending on the outside climate. And that is what old Myotragus seems to have done as well: allowing its blood temperature to rise and fall, and its metabolism to speed up and slow down, depending on its environmental conditions. It was a mammal, but it had a metabolism more like that of a lizard.

Let's look at just how these strange features came to be. Evolution is constantly molding all things to fit their environments, those environments not only encompassing the air, water and features of the land, but also the other living things every being comes into contact with. Myotragus was a close relative of goats and sheep, being a member of the subfamily Caprinae of the family Bovidae. If you've been reading my articles these names should be familiar to you by now. It was apparently a fairly close relative of the modern Takin, which is not very goat-like in appearance itself. Myotragus is first known from about 5 million years ago, the early Pliocene. Its fossils were found on the Balearic islands Mallorca and Menorca (now belonging to Spain). Its ancestors reached the islands from likely the European mainland, and what made that possible was that around that time the Mediterranean ocean dried up! It first became a landlocked lake, with no outlet to the ocean. Then, over centuries to millennia, because the rivers feeding into it were not enough to offset the evaporation from it, it disappeared entirely. Now animals could walk over dry land to reach what used to be islands. Thus, the ancestors of Myotragus landed on the Balearics. When the ocean re-invaded the Mediterranean basin, and event known as the Zanclean Flood, the islands became islands again, and the goats were cut off from the mainland.

Though quite small, standing only 45 cm/18" or so at the shoulder, these goats were then the top herbivorous mammals on the islands. There were no large predators. They were at risk mainly from large eagles, but could hide from them in dense vegetation. Thus, they didn't need to keep constant watch. Modern goats and many other herbivores have those sideways-facing eyes mainly so they can see danger approaching from as many directions as possible. But because Myotragus didn't need such vigilance, it could free up its vision to mainly show it what's happening ahead of it. Living in rocky, mountainous terrain, it could use its binocular vision to judge distances for precise leaps. But that doesn't appear to explain everything. First of all, its short limbs don't appear much suited for leaping; second, modern goats can execute spectacular leaps in mountainous terrain even despite having sideways-facing eyes. Myotragus had a small brain, with reduced areas dedicated to all its senses. It might have needed the forward-looking eyes to enable it to walk around with minimal attention other than what it needed for getting where it wanted to be.

The reduction of the sensory abilities of Myotragus were likely to enable it to save on resources, as the islands became less hospitable. In the early Pliocene, the climate of the Mediterranean was warm, moist, subtropical. The climate subsequently cooled and the end of the Pliocene marked the onset of the Ice Ages. The Mediterranean region never became freezing cold, but there was a drop in temperature as well as rainfall, and the islands became covered mostly in stunted scrub. With the islands not being very extensive, there wasn't much food to go around. Myotragus was descended from grazing goats, but on the islands started browsing, likely eating everything it could get at. In its lower jaw, it had a single pair of ever-growing incisor teeth, like the gnawing teeth of rodents. This it could use to snip off tough vegetation.

In addition, Myotragus decreased its need for food, by reducing its own levels of activity. The brain-shrinking was part of that, as was its decrease in body size (a phenomenon known as island-dwarfing) and the shortening and stiffening of its limbs. That brings us to the other amazing specialization, the evolution of a reptilian-style metabolism. What clued the scientists in to that, was that when they examined this old goat's bones, they saw that, instead of having an even internal texture, it was deposited in layers. This means growth happened periodically: a layer of bone was deposited over a period, then over a subsequent period, no bone was deposited. It didn't grow evenly, but in spurts. This is unlike other mammals, but similar to reptiles. The times when it stopped growing, must have been times during which it could not get enough food for growth – perhaps during the winters. It could adjust its growth needs to match its nutritional circumstances, slowing its metabolism down when provisions were low. This also means that overall its growth rate was slow. A newborn Myotragus kid was the size of a large rat, and probably needed about 12 years before it would reach adulthood. Adults could regulate their body temperature in the way of reptiles, by lying around basking in the sun to heat up, using shade when it got too hot, and perhaps sheltering in caves when it was raining or snowing.

With such adaptations, these little goats managed to successfully survive on the islands for about five million years. They shared their environment with some other strange things; the Balearic Islands also hosted enormous rabbits (competition with Myotragus might actually have driven them extinct), dormice, and shrews. But about three thousand years ago, humans arrived on the islands. Within a short time, all the unique mammals of the Balearic islands were extinct. The small, slow goats were easy prey. There are signs that the humans caught them and kept them for a while before eating them. At a time, it was believed that humans had managed to domesticate them, but this apparently wasn't possible. They went extinct as a result of hunting, destruction of their native habitat, competition with newly-introduced domestic cattle, horses, pigs, sheep and goats, and predation by the equally newly-introduced dogs. They took many of their secrets to the grave with them; we still don't quite know how these highly unique goats actually lived.

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