Miocene antarctica

This is a substantially edited reprint of something I had done a while ago, posted on another thread, but I think it would be useful here.

Miocene Antarctica
All right, so our mission is to attempt to identify what might or might not be living on Antarctica back 20 million years ago.

As a first step, let’s look at the continental history.

* 170 Million years ago, Antarctica is part of the Southern Gondwana supercontinent. Therefore, it will share its starting biology, including flora and fauna with other remnants of the supercontinent.

* Africa breaks away from Gondwana and Antarctica 160 million years ago. Eventually links up with other plates, forms the modern African continent, and gets into a kinky Menage a Trois with Europe and Asia. It never writes, it never calls.

* Approximately 130 to 125 million years ago, Marsupial and Placental mammals evolve. The Marsupials may be first, but not by much. They both seem to emerge out of central China, and trek eastwards, into Europe and then North America, passing into to South America and perhaps Africa and India. From there, to Antractica and then finally Australia.

* Approximately 125 million years ago, India breaks away to do its own thing. It’s mammal stock is probably going to be pretty puny, archaic placentals and marsupials and likely to diverge rapidly. I don’t think its going to contribute too much to understanding Antarctica. Let’s just ignore it, as far as mammals go. Maybe some reptiles will give us hints.

* 65 million years ago, the big smackdown, the crunch, the rocca and rolla, the one, the only, the K-T event aka ‘Pop go the Dinosaurs’. An all encompassing planetary disaster the squishes the Dinos and a large number of just about every kind of species, plant and animal.

* 65 million years ago, T-Minus Rex. Antarctica is down at the pole, it’s connected to South America. It’s connected to Australia. We’re looking at a tropical climate, connifer and southern beach forests, and classical Gondwana flora, as represented by Australia, New Zealand, South America and Kerguelen.

* 50 million years ago, more or less. Placental and Marsupial mammals are found in Australia, duking it out. Antarctica is connected, so we can assume a fair overlap of placental and marsupial species with Australia, and possibly similar sets of outcomes.

* 40 to 45 million years ago at the latest, Australia leaves home to find its destiny. Let’s assume biological interchange ends then or shortly thereafter. We can assume a high degree of affinity between Australian Marsupials and Monotremes and Antarctic Marsupials and Monotremes.

* 40 million years ago, T-Minus Oops. Antarctica starts to cool. The separation of Australia and Antarctica allows cold waters to travel further along the coastline before being diverted north. It also allows cold waters to pool longer. Antarctica gets cooler and dryer, with generally less rainfall. Winter rainfalls show up as snow. Glaciers begin appearing on mountains, or climbing down the sides of mountain ranges. Also, in the deep continental interior, water freezes solid over the six month nights, and has a harder and harder time thawing completely. Circumpolar winds tend to deposit water in the center. You have your first baby glaciers.

* 23 million years ago, South America, which has been getting restless since all the kids upped and moved away, leaves on a romantic quest for that slut continent, North America, currently exchanging biological fluids with Asia. South America’s probably separated before this for quite some time, but intervening Islands and ridges have allowed for some continuing biological flow and interchange, possibly by swimmers, rafters and storm tossed types, sometimes by good old fashioned land bridges. The connection has prevented the Antarctic Circumpolar current from really getting bad. Now the Antarctic circumpolar is begining to flow fully. Getting colder and dryer faster. The only good thing is that the Circumpolar Current is probably not nearly as strong nor carrying nearly the volumes of water then as now. Australia and South America are still pretty close, which means that they don’t have the wider spaces for flow, and both of these continents may be pushing warm currents down deeper into the circumpolar, stealing its energies and making it a bit warmer and wetter. Still comparatively dryer though, and really crappy weather. Also getting in the way of the circumpolar and diverting warm currents south is Zealandia and Kerguelen.

* 20 million years ago, the Kerguelen Plateau and the Zealandia Plateau both sink. Australia and South America are slowly pulling away. The Circumpolar is now well established. The Antarctic ice age is now officially happening.

* 6 million years ago, final glaciation completed, at which point, we have a two mile thick sheet of ice over everything. It takes time to build up a two mile ice sheet, particularly in a place as dry and cold as Antarctica. So let’s say that between between 10 and 15 million years ago, the continent becomes completely uninhabitable.

Okay, so what’s living there 20 million years or so ago, in the first million years of the ice age.

Probably the two best guidelines are South American and Australia. Both continents divide into their own separate sequences of ‘mammal ages.’

South America’s would have been connected into the Deseadan age, between 29 and 21 million years ago, the middle of the break up, so we would expect the South American fauna of that period to overlap strongly with the Antarctic. After the Deseadan age, the South American mammals would have no further overlap or correspondence with Antarcticans.

So what was living in South America during the Deseadan? Damned if I know. A few minutes of searching suggests that the Marsupials were well developed, including Predator Marsupials. We’ve got placental Pyrotheres, which in South America would grow up to become elephant analogues with tusks and trunks. We’ve got placental astropotheres, whatever they are. Among edentates, we have the early ground sloths appearing in Patagonia. We also have ‘pseudoglyptodonts.’ And we’ve got Notoungulates, South American hoofed animals starting up. Overally, the biology is strongly dominated by placental mammals. So we should see some, or several representatives of Placental mammal lines showing up in Antarctica. Essentially, a lot of the key South American life forms had reached some reasonable stage of development by that time.

Here’s a bizarre candidate for Antarctic life. Monkeys! The New World monkeys rafted over from Africa to South America forty million years ago. At that time, South America was still pretty close to Antarctica, and would remain pretty close for another seventeen million years. Antarctica, and presumably the Chilean or Patagonian parts of South America would have been warm, wet and forested. So it’s just possible that Monkeys might have made it in to colonize Antarctic forests. They would have just missed Australia.

Some of these, but perhaps not all of them will make it into Antarctica. It’s more complicated than that. It appears that the Antarctic region adjoining South America is actually a big archipelago, call it west Antarctica. Depending on water levels, the whole archipelago may be above water or closely connected. So we may have scattered groups of Islands. Close contact groups of Islands. A super-island/mini-content. Or even a solid land bridge connecting to the main Antarctic continent. What this means is that in addition to the whole polar existence thing, and climactic obstacles, there may be barriers to full penetration of South American life. This means that there may be significant differences in composition of fauna in West Antarctica.

The most likely west antarctica bridging species able to cross waters to east antarctica will probably be the sloths and monkeys. I believe that both of these species made it into North America before the land bridge showed up, which indicates that they may have been able to raft, swim, or just stay alive long enough while swept in current to wash up somewhere.

We can’t guess as to whether there was a land bridge between East and West Antarctica, or whether it showed up early or late. So I’ll make a completely arbitrary guess and suggest that a handful of large placental herbivores, notably pyrotheres, made it into East Antarctica to keep the sloths and monkeys company.

Against this, we have the Australian fauna landscape which separated about 40 to 45 million years before. We’ll have Marsupial predators. The Possums. Diprodonts. Probably early representatives of all the Marsupial species. Interestingly, we also have Placental mammals in Australia during this Eocene period, but they all seem to have died off. In this one place on Earth, the Placental mammals just couldn’t seem to hack it. It’s possible that Australia was simply too impoverished an environment during this period of time. Rapidly becoming cooler and dryer, with poor soils for forest and grassland. The Marsupials metabolic rate was significantly lower, they might simply have been able to do more with less.

Antarctica may be a similarly impoverished environment - six month nights which is hard to endure, likely cooler average temperatures, water deficits, and conditions growing worse. So it’s likely, as with Australia, that the Marsupials will come to dominate the ecology. The Australian marsupials have split early, but we can assume that Antarctic species would probably develop in parallel, with a few adjustments - burrowers, hibernators, long night and cold climate adaptations.

Of course South America’s placentals will be right tough. They’ll have had an extra twenty million years of evolution under their belt across a set of biomes of about seven million square miles. So some of the Placentals will compete.

I’m thinking that the most likely outcome is that South America will predominate with big placental herbivores in Antarctica, sloths and pyrotheres, maybe a toxodont or so. Mid size herbivores will be a battleground. The small animals will all be marsupials. The carnivore mammals will all be marsupials.

What else will we have in Antarctica? Rattites - Big birds. Ostriches, Rheas, Cassowaries, Emus, Moas and Aeropornis are all common to the remnants of Gondwana. The only Gondwana fragment without its own giant bird is India. Also, ancient Australia and South America featured remarkably durable forms of giant predator bird, so if they weren’t around at the times of the splits, its likely that a mutual common ancestor or niche was there. They’re damned peculiar things, but we can probably expect one or two species to establish themselves - for sure, Antarctic versions of Ostriches or Emus or Moas, possibly a couple of lines. We might also see a single line of Terror Birds, either immigrants from South America, or more likely, a parallel home grown edition, as in Australia.

We can also expect Antarctica to have super-sized crocodilians, because those show up in South America and India. The Australian Saltwater crocodile is the largest surviving Reptile on Earth. And we’ve got interesting adaptive radiations of crocodilians in several Gondwana fragments, including Australia and South America. So warm Antarctica is likely to have some big and powerful crocodile forms, and possibly some interesting niche creatures. Mega-sized turtles also show up in India, Australia and South America. So they’re a pretty safe bet here, either because the giants were common, or ancestral species to the giants with fledgling potential, or similar circumstances. The bad news is that the reptiles are likely to be the first victims of the big cool.

So, the players are all in place. How does it all sort out?

Let’s take a look at Antarctica. The interesting thing about it is that it is located at the pole. Yep, captain obvious at work. But at the pole, we have some interesting things. First, the relative intensity of light, the ‘light energy’ is a fraction of what it is at the equator. The Equator gets light straight on. The polar region gets light at a relatively steep angle. So it’s likely getting 1/8th or 1/16th (more or less) of the intensity of light energy of the equator.

That’s still plenty to keep things nice and bright. But plants are metabolising solar energy - light and heat, so dial down the intensity, and you dial down the available energy for plants to metabolise. That’s why as a general rule, flora of equatorial regions, all other things being equal, are much more biologically active than the flora of temperate regions. So, in terms of the available energy output for biological activity, the south pole is something of an energy desert, compared to the tropics or even temperate zones.

But there’s two factors that tend to ease this problem a bit. The first is that at the tropics, plants likely don’t metabolize all the energy available from the sun, but just the fraction they need. I've read that on average, most plants metabolize between 3 and 4% of the energy of sunlight, with sugar cane topping out at around 8%.

As you go further north or south, into temperate regions, the fraction they need grows larger and larger. And at the polar regions, this would be a very big fraction indeed. But it's possible that there's enough available sunlight that metabolisation could take up a lot of slack. The other factor is that during the polar day, you’re getting sunlight pretty much 24/7, which means longer time periods to metabolize than tropical plants which make do with only 12 hours of light a day.

The result is that you still get an energy desert at the pole, but its more like a third or a quarter than an eighth or a sixteenth. Which means that you get a lively, but vulnerable flora. You get trees and bushes and grasses, the whole nine yards. But they tend to grow comparatively slowly compared to more energetic regions further north and into the equator.

There’s another Antarctic factor at work. With axial tilt, you get the polar region tilting towards the sun for half the year, and 24 hour days. When it tilts away, you get 24 hour nights. That sucks. Now, you probably don’t get six months of darkness. Probably more like five months, because the atmosphere scatters daylight around a lot. But even four or five months of darkness is pretty harsh. That’s four or five months where there’s no photosynthesis going on, no plant growth, and where it’s going to be getting relatively cold.

Antarctic flora has to cope with this. It’s likely not too too different from temperate or subarctic flora which experiences strong winter seasons. Plants go into shutdown mode and regenerate during the winter. In which case, you've got big plants with heavy trunks or root systems which metabolize like crazy during the summer. Some interest agricultural potentials there, but its risky. Press too hard... and poof.

Or you'll have flora have periods of summer growth and bloom, die and spread seeds in autumn around for the new generation next spring and summer. This implies fast growing, opportunistic vegetation, living season to season. Probably not large, and a lot of the growing energy goes into seeds and proliferation.

Animals are also probably going to be strongly seasonal. In North America and Eurasia, northern hemisphere animals compensate for seasons by migrating back and forth. Not an option here. Antarctic animals have nowhere to migrate too. They’ve only got two options. Either they stay active during the winter night, or they don’t.

For those who are not active through the winter night, their only real choice is some form of hibernation. So you’d see lots of burrowing. Lots of fat building, heavy eating, food gathering and storage tactics.

Some animals probably remain active through the winter period. But to do so, we’ll need to see major changes in the animal’s lifestyle. Diurnal animals must become nocturnal, and must adapt to getting around in the dark. A summer omnivore/herbivore might become a scavenger/ carnivore. A carnivore might migrate to shorelines and take up fishing. Winter herbivores might see their diet change dramatically, or might shift to digging up frozen grasses or roots buried in snow.

The biological advantage in Antarctica in the miocene goes to multi-taskers rather than specialists. We can make some reasonable predictions: Its easier for low light or night animals to adjust to day conditions, than it is for day animals to adjust to night. So eyes will be primarily nocturnal adapted, likely larger than animals elsewhere, with reflecting pupils and large irises. We can also expect other senses to become comparatively more important - hearing and scent. The hoofed animals are probably not going to do well. They’re specialized for their environments, but its likely that animals with digging claws for either digging burrows, or for digging up roots or snow covered grasses will do well. The advantage probably goes to the rodents, who have sussed out hibernation among the placentals. Also, advantage to marsupials and to monotremes, who have lower energy metabolisms and at least some capacity to adapt their metabolic rates. Nonspecialized, opportunistic herbivores will probably do well. But lack of specialization is a handicap as well, since it puts some food sources out of reach, and means less than optimal utilisation of specific food sources.

In our universe, the circumpolar current is a cold water current that will acts as a barrier to moisture and rainfall moving inland. In this Universe, contact of warm air with the circumpolar current produces rains which sweep inward, leaving us with fairly wet and watered shores and coastal areas.

There is an inland Antarctic sea within the current that might allow some regional precipitation, but down there at the polar region, its going to receive minimal energy from the sun and that will cause less evaporation and precipitation. You’ll get rainfall along the coasts, a lot less inland. Even with rains, its a relatively dry continent, though not as dry as Australia.

The continent won’t be completely dry, there will still be rainfall and especially snowfall, and summer glacial melt will be a major factor for rivers and streams. In the Interior, glacial melt feeding the river systems will be the major source of water. Which means that during the long nights, water drains out of the ecology. The Antarctic interior turns into a desert punctuated with lakes and oasis.

If we want to, we can postulate a period or periods of interior glaciation in which the baby glaciers were quite extensive - deforming local geography and leaving sections of the interior studded with lakes.

It’s definitely going to get a few degrees cooler, even in the beginning. The circumpolar current is going to be blocking warm water currents similar to the Gulf stream that might have transported warm air down to the continent. From here on in, the Antarctic is restricted to its weak sun-drench for warmth. Assuming that this warmth is trapped, and stays in Antarctica, we won't have a tropical climate - best chance is a temperate European type climate, something somewhere between Paris and Moscow, say.

It'll warm up fast in the summer, 24 hour antarctic days, you know what I mean. When the Antarctic night comes, it may take time for that accumulated heat to dissipate. So there may be two winters - Early winter, which is still tolerable, and deep winter which can be ferocious.

Finally, we have the famous glaciers, because hey, what's Antarctica without at least a few glaciers. Where are the going to be? Mountains to start with. There are three highland/mountain regions. One almost in the center of the continent near the polar center itself. The other two are on coasts. The coastal glaciers will be fairly active due to more coastal precipitation. The areas inland of them, in their rain shadow will alternate between deserts and zones with brief flowerings during summer glacial melts. The inland glacier will likely expand more slowly but steadily, its summer melts will contribute to the water ecology of the inland. Keep in mind that the Glaciers are stable or slowly expanding.

So how do these conditions affect the Antarctic flora? Well, first of all, I think that the Southern Beech forests are going to be in serious decline. A lot of Antarctic forests are going to be replaced with pine scrub. Only in some coastal areas will there be enough warmth and water for the Beech to hang on. The trees won’t be all that huge, no more old growth forest giants. And they’ll be very slow growing trees.

We’re also going to see in the interior, a preponderance of dryland grasses and dry bush. As with the Canadian prairie, the grasses are going to develop very deep root systems to access increasingly more difficult moisture. In fact, most of the biological investment of plants is going to be in deep and extensive root systems which will survive the long winter/nights and simply crown new foliage in the spring. These will perrenials will gradually outcompete the seed annuals, which have to do all their growing in a light poor, cool, dry climate. Root systems will be used to store energy for growth, so things like potatoes, tubers, yams, turnips, etc., will tend to predominate. Shorelines and river basins (including lakes and marshes) fed by glacial melt will be the wettest places in Antarctica, and likely have the most biodiversity, and the most annual plants.

What animals do we get? Well, Antarctica is a harsh landscape breeding hardy generalist animals.

The Placental Mammals are likely on the way out. Antarctica probably features sloths and pseudoglyptodonts. Sloths, although they look like feebs, are incredibly tough and adaptable. In our timeline they made it into North America before the continents joined, and they infiltrated all the way to Alaska. They survived in the human era for almost 10,000 years. So likely they’ll be one of the last big dominant herbivores, most likely forest species. The other big herbivore are likely the Pyrotheres, whose tusks and trunks will allow aggressive ground feeding, think giant plains dwelling warthogs. Expect pyrothere herds inland.

There might be a few other large animals roaming around. Actually, in these harsh conditions, size becomes an advantage. Easier to conserve body heat, easier to store fat, more bang for the buck metabolically. Probably no giants. The largest animal will be smaller than the Indian Elephant. Likely no larger, and possibly smaller than a Rhino or Hippo. The upper size ranges are probably those of big musk ox, moose or reindeer.

If Monkeys have made it to Antarctica, they’re in big trouble now. Similar climactic changes resulted in monkey extinction in Europe. But Monkeys are smart and adaptable, so it’s possible that through a combination of physical adaptation and behavioural complexity, they might be able to survive. Perhaps monkeys form cooperative groups to feed, forage and nest, competing effectively with rodents. It’s likely that any Antarctic monkeys are now extinct, but if they are around they’re likely the smartest monkeys on Earth, and effectively social enough to be potentially domesticateable.

Rodents are also likely to be hanging in there for all they’re worth. We might see a lot of development of Antarctic marsh rodents - possible beaver or muskrat analogues. Given the increasing importance of meltwater and river/pond/lake/marsh systems to the drying Antarctic ecology, I wouldn’t be surprised to see something like beaver behaviour, with dam building and ponding to retain water showing up as behaviour.

The Marsupials are going to be increasingly important. Large marsupials may well be starting to compete with the Pyrotheres and Sloths for the top of the herbivore food chain. The dry inland grasslands may be marsupial country with some deer/kangaroo analogue running about. Monotremes, with their low metabolisms and ability to reduce further may be in their glory days. The Platypus are in the catbird seat as far as niches go as a riverine small predator. But if the monotremes have any diversity at all, expect them to spread and grow.

The reptiles and crocodilians probably don’t make it. They’re on the way out and the big ones are now extinct. Remarkably, a surprising number of snakes and turtles manage to survive at remarkably high Canadian latitudes, so we can expect some around the coasts and rivers.

As for giant flightless birds, we have no records of any big flightless subarctic birds in our timeline, so there’s no precedent. On the other hand, the Ostrich and Emu both seem pretty tolerant of dryland conditions near deserts in Australia and the Sahara. We might see some of them hanging around for a while.

As for predators, Marsupial carnivores will predominate. Most likely, open country pack animals like wolves, african wild dogs or lion prides. Also likely are some sort of big forest and river ambush predator, think perhaps a marsupial grizzly or polar bear (monotremes-perhaps)

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monotremes-perhaps

Would have an added benefit of eggs for the hunters.

Monotremes are unlikely. They seem to be stuck at low end carnivores, niche critters. There's too much other competition from both Marsupials and Placentals for them to make much of a dent.

As for eggs, Antarctica will have a full complement of bird species, and even seabirds. The circumpolar currents and winds, however, mean no migratory waterfowl or other species.

On the other hand, if you want eggs, think Penguins. I'm assuming that Penguins, or an indistinguishable equivalent, will inhabit the outer islands and secure rocky shores, much as the northern hemisphere Auks did. Look for them to become a domesticated or semi-domesticated species.

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The Antarctic Archipelago, which has more South American influenced flora and fauna will likely remain wetter than the main Antarctic continent, although its going to get colder. There’ll be more diversity of life forms there, and placentals will do better.

Most animals will tend to reproduce slowly, have slow growth rates and longer life spans. This is the best strategy, when resources are limited and can’t take much pressure, you keep the population relatively low and very stable. The problem is that while a slow reproducing, slow growing, long lived population is very stable under normal conditions, it doesn’t respond to new pressures very well. Short lived and fast reproducing species can respond to new conditions by upping the birthrates to take advantage of new opportunities and adapt to new pressures.

Ideas and input welcome, anyone wants to design or contribute new species of plants or animals, including potential agricultural plants, domesticateable animals or even riding critters, welcome aboard.