Burdles of the Hothouse

It is now 285 million years post-establishment on Serina, and the middle hothouse transitions into the late. This temporary interim in the climate has now lasted fifteen million years, and we are now closer to its end than to its beginning. Yet biodiversity only continues to increase as this age progresses, and has not yet reached its ultimate peak. Animals, plants, and habitats over the world of birds are still growing more derived, and more complex.

Fifteen million years have passed since the burrowing burdle rafted from a drowning Meridian Islands to a newly-thawed Serinaustra. With the climate then favoring their metabolism, and with far more ecological room to diversify than their ancestral home allowed, these last surviving mucks have undergone an incredible radiation of forms in the years since. These burdles were prominent predators on their island habitat, but here, once the carrion stopped washing up from a dying sea, they found stronger competitors from Serinaustra's two native carnivores, the long-present snowscrounger and later-introduced foxtrotter, both of which were smarter and more cunning. Though some earlier large carnivorous burdle species rose to brief dominion here, they have largely died out now as these two other predators, and others, have diversified and taken over most large predatory roles in the recovered ecosystem. Yet far from going extinct as a whole, the last burdle has given rise to an incredible assortment of descendants that have evolved to exploit many other niches left unfilled upon this new and unusual landscape. Its recovery from the brink has been rapid, and thousands of burdle species exist, most - but not all - of them endemic to Serinaustra.

The burdles' greatest success upon their new homeland has come to those which have become far smaller than their ancestors, and so dropping below their competitor's sights. Some, such as the spadewing, specialized further into their digging adaptations and have become fossorial like the molebirds and bumblets of earlier epochs. Now spending most of their lives in dark tunnels and hunting insects and worms, they favor damp and partially flooded soils and remain capable swimmers. Closely related, the penguipus has then taken this evolutionary route a different direction, and become semi-aquatic and piscivorous, only using tunnels to rear its young.

Another group of burdles, known as murds, specialized to different diets and so avoided their competing predators altogether. Rodent-like and rapidly reproducing, these burdles now eat mostly seeds - and usually still insects - and have larger cracking beaks to handle increasingly large grass and tree seeds produced by contemporary plants, which lends them a more bird-like appearance than most of their ancestors, if only in the face. Murds such as the jirdbird are much more social than their ancestor species, and often live in social groups and even communally incubate their eggs and young Their offspring are more altricial than they used to be, and now rely on adults to feed them for several weeks prior to independence, with the trade-off that they can now grow up much more quickly. Though murds are still reliant on environmental temperatures to stay warm, their habitat is so mild and tropical even through the polar winter as a result of the greenhouse gas-rich atmosphere, and so murds can be as active as similarly sized birds or tribbetheres while still devoting less energy to maintaining their body temperatures, giving them an advantage in this climate. While most species still nest below ground, some are arboreal, and perhaps the most specialized of all is the hurtle, a tree-dwelling omnivore which has evolved gliding membranes between its limbs in order to parachute between trees and avoid the dangerous forest floor. This species is still solitary, and females rear their eggs in tree holes, abandoning the chicks shortly after they hatch, for they can take care of themselves immediately.

Not all burdles have needed to become small or drastically shift their diets to survive here, though. The beaver-sized rivercarver is a morphologically primitive burdle that structurally has changed very little from its ancestor. Its innovations are behavioral - it is a complex ecosystem engineer, adapted to shape and redesign its environment and thus become a keystone of the southern forest. 

above: a rivercarver pond providing habitat for many other species including a stingfisher, a type of highly derived flying insect, and a variety of other birds.

The rivercarver lives in monogamous pairs which maintain territories, and their favorite food is crustaceans such as crayfish and shrimp. These animals occur in most inland freshwater, but are preyed upon by many animals and so competition is fierce. The rivercarver has evolved to control its own food supply by digging out refuges for its preferred prey along rivers, making small ponds that these invertebrates seek out as calm shelters to hide and reproduce. The rivercarver then surrounds its pond with earthen walls three to six feet high to prevent the prey from leaving again, while also excluding larger aquatic predators. Plant life quickly takes over the edges of the sheltered pools, while the owners of the territory drive away terrestrial predators that overstay their welcome. Crustaceans proliferate within, along with small fishes that the rivercarver will also eat, particularly when young, and the rivercarver can raise its young with a predictable source of food in a refuge safe from the threats that lurk in deeper, wilder waters.  

above: a simplified cutaway view of the inside of a rivercarver's den, showing its two underwater entrances and fish that make use of them to dig their own hiding places.

Pairs of rivercarvers dig their breeding dens into the mounds they form along the edges of their ponds, always channeling out two entrances so that the brooding female, as she sits with her eggs, can make a hasty escape in the event one entrance is compromised by their only significant predators - large, toothy eel-snakes descended from the sea dragon that can maneuver themselves through the tunnels and ambush a brooding female, or just eat her eggs. These underwater tunnels may also be utilized by a variety of small fish, which dig their own smaller tunnels into the sides in which to safely rear their own eggs or young. Though the male rivercarver doesn't take part in incubation, he does provide the female with food as she does so, as well as protecting her and their offspring from any predators that attempt to enter the pond. He is highly aggressive, chasing and biting animals even many times his size, and is a formidable defender. Parental care in this species extends well after the chicks hatch, as both adults will collect food for the young and crush hard-shells to make it easier for them to eat. Young are only driven out of their natal pool once their parents hatch a second brood, usually 3 months after the last one. Now fully able to hunt for themselves, the juveniles must navigate the pools of many neighboring pairs which are not very welcoming to intruders before they find their way back to the river that feeds all of the rivercarvers' breeding ponds. There they will grow until maturity, when they will pair up and begin to make their own ponds, or to take over that of an older pair which can no longer defend their territory well enough to hold claim over it.

Rivercarvers contribute the swampy of most of Serinaustra's environments, as they channel out rivers and gradually turn upland forest into wooded wetlands.Though they try to exclude competing predators from their ponds, they cannot do so all the time, and their pools attract a wide variety of other wildlife. Their actions upon the land open up many more spaces for prey to survive and reproduce than is possible in a natural river alone, therefore increasing the productivity as well as the biodiversity of their habitat considerably.