The Grasslands of South America

South America is a changed place, though perhaps not as changed as most.

Much of the Amazon basin is now covered in swaths of temperate grassland, ranging from cool to warm from south to north and semi-humid to dry from east to west, as the gentle winds from the Atlantic blow across the continent. Though rivers are relatively common here, they are much smaller than they once were due to the reduced rainfall. With less water to carry, the Amazon river is but a stream in comparison to its older self.

Many of the inhabitants of South America are descended from those that lived in the Andes and cool pampas on old Earth. These cold-tolerant flora and fauna had such an advantage over most others that their descendants are very common in North America as well, displacing some of the less fortunate inhabitants there. Though novel in North America, they look quite familiar in the grasslands of South America where the climate isn't much different from that of the montane grasslands they hailed from.

Basal guanaco descendants are very common on the grassy expanses. Some species are more heavy-set while others are lanky, but as herds on the fields, they create a scene not too unlike ones on old South America so many years past. Basal descendants of the Darwin’s rhea have also weathered the extinction well. This they owe to their ancestor’s tactic of using failed eggs as bait for flies, giving the father birds and their chicks food in desperately lean times.

However, it is not long before examples of the inevitable divergence stand out. Among the handful of genera of rheas extant in these grasslands, one will catch the eye and ear alike. Quasistruthio, meaning "false ostrich", is a genus of very large rheas that recall the ostriches that once inhabited Africa. Tall and fast, they roam the land in small flocks of mixed age and sex, eating grass, shrubs, and the occasional small vertebrate. The males of these otherwise quiet birds will emit a growl-like booming noise when attempting to attract a mate, the strange sound carrying far over the rolling hills. However, both sexes are capable of making this noise, as they do in a threat display when cornered.

The guanacos, too, have changed, with no better example than the rearing guanaco. 

These guanacos specialize on tree leaves, often frequenting more wooded areas of the grasslands, though they are commoner in the dry subtropical forests to the east. Standing at about 220 cm (7 ft 3 in) tall, they aren't particularly giant megafauna, which might seem to restrict their ability to reach leaves high off the ground. However, their secret lies in their posture.

Rearing guanacos feed while standing upright. Their hindquarters are more developed and their hind legs are longer than their front legs. When the animal rears, the lengths of its hind legs, trunk, and long neck add up to an impressively high stance — as high as 320 cm (10.5 ft) off the ground. Using its shorter front legs to brace against the tree trunk as needed, rearing guanacos spend a large portion of their time bipedal, munching away at whatever leaves are within their range.

In other aspects, rearing guanacos aren’t much different from their ancestors. They live in comparatively small herds of mixed sex and age, organized into a hierarchy based on a pecking — or, more accurately, spitting — order. The males and females are virtually identical, which is unusual for a large animal but typical for guanacos, and they behave identically as well, save for the screaming fights the males go through for breeding rights.

Alongside these large herbivores are a plethora of flightless and nearly-flightless birds. Most of these birds are descended from tinamous (order Tinamiformes), and their presence is part of a pattern that has been repeated many times. Despite that they can fly, tinamous evolved from ratites and are technically within the ratite clade. From that and the fossil record of ratites, this implies that ratites flew to different areas of the globe and became flightless several times, as opposed to sharing descent from a flightless common ancestor. For many and various reasons, ratites appear adept at swapping out flight for a stable terrestrial niche. So, when tinamous survived the mass extinction, they once again found a variety of open niches throughout not only South America, but North America, fitting a theme millions of years in the making. 

The flora here are also oddly familiar to the continent, though they too have outliers.

The predominant shrubs and trees for the cooler parts of the grassland are descended from a rugged genus of plants in the rose family: the genus Polylepis. These common plants of the tropical Andes have exploded in diversity in these cool, dry times. Gnarled and with loose bark, the many and varied Polylepis descendants confer an air of mystery to the landscape — and also one of pollen, for their ancestor was wind-pollinated.

Other successful plants in this area are those descended from the genus Cortaderia, the pampas grasses. They would have been prized by humans as ornamental plants, but have done just fine without their care. Some of these gigantic grasses have become even larger, though most have gone other ways; a few are low-lying brambles while others are attractive flowers. Like the Polylepis plants, pampas grasses are wind-pollinated, and so share with them the struggle of the ever-encroaching animal-pollinated plants. Although wind-pollination was a splendid choice in their high-altitude homes, their competitors’ time-tested tactic of pollinating by insects is forcing them to change. 

Such pressures helped create this common grassland plant, the bramble-tuft (genus Cultriflores). These plants are smaller than their ancestor at roughly 60 cm (2 ft) tall, though they get to this size much faster. To facilitate their fast growth, they only have a few flowers on their stalks, allowing them to shoot up like rockets from the soil. As a trade-off, the flowers are much more precious to the plant now that there are much fewer of them. In response, the bramble-tuft has modified its vestigial flowers into sharp spines, while the pollen-catching filaments double as irritating bristles. Contact with the flowers can pierce exposed skin, while the bristles can break off and cause a burning, itching pain for hours afterward. This discourages herbivores from damaging any of the plant’s reproductive parts. All in all, the bramble-tuft manages to hold a dominant position in the grassland landscape, crowding out most competitors.

These plants and many like them fuel large swarms of locusts; specifically, descendants of the South American locust, Schistocerca cancellata. They ravage warmer areas of the grasslands during summer and overwinter as eggs in arid regions, waiting to swarm again. These plagues, fascinating in their power, have little changed from those of the locusts on old Earth. 

Though South America fared better than most places, it too lost its large terrestrial carnivores. As such, the predators of this place are descended from much smaller animals, often generalists.

One early survivor was the seriema (family Cariamidae). A characteristic predator of this continent before the extinction, it lived essentially like the secretary birds in Africa, hunting snakes and lizards in the tall grass. Unlike them, however, these birds dispatched prey not only with their beaks, but with specialized curved claws on each foot. Though most of the population didn’t live in the cooler areas of the continent, the seriema’s rudimentary ability to fly allowed it to relocate to warmer areas quickly, where it soon found a lack of competitors.

Now their predatory progeny, the sicklebirds, inhabit much of South America. 

Standing at 1.2 m (3 ft 3 in) tall and weighing 20 kg (44 lb), these birds have long forsaken their gift of flight. Instead, they prowl the grasslands atop long running legs, searching for smaller animals to prey upon. This includes medium-sized mammals and birds as well as very young individuals of large herbivores. Their form may recall that of the terror birds, another South American native whose closest living relative is, in fact, the ancestral seriema. However, sicklebirds kill with a much different tactic.

Instead of slamming the beak down and cutting into prey like an axe, sicklebirds use a more heavy-duty version of what their ancestors used. Smaller prey are picked up and pummeled into the ground, while larger prey are held in place with the mouth while one or both sickle-claws tear into it. These gruesome displays of power are effective but energy intensive, so sicklebirds maintain a territory to ensure that they get their choice of prey. They will drive conspecifics out of their territory with much fervor, usually with loud yelping calls but occasionally with violent fights.

As is perhaps a theme in the changed South America, sicklebird males and females are barely discernible both in form and behavior. Each spring they will find a mate and stay with them throughout the year, during which time they will live, hunt, and care for the chicks together. These offspring leave their parents before winter, spending a year as a subadult before reaching sexual maturity.

Sicklebirds, however, are not apex predators for most of their range. The terrestrial apex predators of this continent are derived from the culpeo (Lycalopex culpaeus), a fox-like canid that roamed the Andes, but was adaptable enough to venture into deserts and rainforests as well. With the large cats that once ruled the continent extinct, these omnivorous animals have grown to fill the niches left behind. Large carnivorous culpeos, whose males can weigh 100 kg (220 lb), now roam the land like the giant felids used to. Built like large, stocky wolves, they hunt prey alone, stalking through long grass before dashing out with hungry jaws. They can take down the adults of some of the largest herbivores here, though it is gravely dangerous and thus is used as a last resort. These culpeos’ smaller relatives find other ways to survive, such as frequenting the many small rivers in the area, hiding in the brush and targeting whatever small animals are attracted to the water or flora.