It is now 200 million years post-establishment. The world comes alive with the raucous squawks of birds as they awake with the dawn. In just a few million years since the Thermocene's catastrophic end, a handful of surviving species have evolved into many thousands. Some remain recognizable, songbird-like creatures whose ancient forms continue to serve their uses, but others are becoming ever more unusual. 

On a sandy dune that was not here just six months ago, a small flock of gullglings descend. As large as a pigeon, the gullgling still a conservative-looking bird, but already exhibits some very remarkable adaptations - most apparently, the ability to drop from two legs to four, and to walk using their wings as additional legs. The gullgling is a changeling, or metamorphic bird, and is one of a new lineage of these strange creatures which has evolved only since the start of the Pangeacene. Though it often walks as a biped, especially for speed, the gullgling is capable of bearing weight on its wings, too; an ancestry of birds with freely-crawling, larval infants has resulted, here, in a slightly neotenic adult bird which retains the altered forearm anatomy of the larval life stage, and which remains a faculative quadruped into adulthood. The strange life cycle of the metamorph bird, which begins life so differently from the adult, has paved the way for the anatomical development of the gullgling to be "reset", to an earlier, less-specialized condition than is seen in birds with less extreme development. A need for these "bird grubs" to crawl along in their earliest days and weeks by using their wings to pull themselves along has produced new wing musculature and restructured the bones of the wing to produce, in the gullgling, a forearm that is uniquely suited to walking even in the mature animal, and one which retains two finger-clawed clawed appendages - remnants of the spurs and spines common to changeling larvae. Now, these become Serina's second lineage of truly four-legged birds.

The gullglings have come to this sandy spot to engage in a vital act of reproduction. Four females, one with a leucistic plumage, are digging nests into the soft, damp sand which was deposited here during powerful storm surges the previous winter. The sea carried this sediment inland, covering up the vegetation, but now the storms are gone and the seas quiet. This new, vacant land is now warmed by the sun now provides an ideal location for their offspring to develop. Soon, each bird has laid a clutch of as many as eight, and carefully organized them into a ring around her body. She will then carefully scratch the sand back over them, the group of them collectively piling it up to a foot above the shared nesting site. The sand will keep the next generation warm as well as hydrated as they grow, in a manner of egg incubation more alike a sea turtle than that expected of such a bird.

Except that, these are not the bird's eggs at all.

Arguably an even more remarkable change which has occurred in the gullgling, in addition to its use of its wings to stride along, is in the development of its young. Gullglings do not lay eggs; the loss of a calcified eggshell in the metamorph lineage has removed a restrictive pressure on their evolution that has remained since the archosaurs, the birds' earliest relatives, first evolved long before Serina's creation. Because they evolved to lay tiny, soft eggs more like those of frogs than of any other bird, and because their young were born in such a small and undeveloped state, metamorph birds did not need to provide their embryos with calcium through the shell to build their skeletons. The larva, as it grew, would simply find its own minerals and consume them once hatched. A lack of such a shell in the gullgling has allowed this species, though, to simply retain its eggs internally long after they have hatched. This is a viviparous bird, like a bumblet, and is only the second bird lineage to have become so. The miniscule eggs of the gullgling are retained in her body until they hatch, and then the 1 cm long larvae, once hatched, swim and crawl their way to the wall of their mother's oviduct, where they burrow into the tissue and take nutrients directly from her blood. A placental connection is soon formed, a direct line of nutrients that shares the mother's energy with her growing young. The gullging is a placental bird, the very first one, but unlikely to be the last.

What this means is that, like a mother mammal, a gullgling can rear her young inside her body, keeping them much safer than in other birds - ancestral ones which must incubate their hard-shelled eggs in a nest, and metamorphic ones, whose larvae lack any protection from predators or the harsh outside environment. But the gullgling faces a different complicating factor in that she must remain light enough at all times to still fly well enough to find food and escape her own predators. While there are flying mammals, in the form of bats, they compromise by bearing just one small infant at a time, so as not to overburden themselves with too much weight while their young is gestating. Gullglings still bear many young, up to ten surviving embryos in one litter. So they must adopt another intriguing adaptation to make it possible for them to rear their young without compromising their own health too severely. This is where their "eggs" come in.

The gullgling's "eggs" are in fact the pupal cocoons of its larvae, which are spun from mucous internally as the larvae detach from the placenta of the mother and prepare to be born into the outside world. Inside the cocoon, the gullgling will rely on a fatty tail-like organ which it loses entirely by the time it emerges, using this stored energy to fuel its transformation into a juvenile which, though small, is fully independent and closely resembles the adult bird. The female now lays her clutch, selecting a safe, warm and damp site for them to finish their development on their own. She hides them in the soil, and then departs. Around 90 days later, the chicks "hatch" from their sacs and quickly dry off. Their feathers are fully formed, even their wings. Within an hour of emerging, the gullgling chicks, each no bigger than finches, fly off into the wild world and begin their lives, mainly feeding on flying insects until they are larger and less agile, at which time they feed more on seeds and other foods they forage on the ground. In around two years, the luckiest will return to a similar site and repeat the cycle with a new generation. It is not hard to see many possible future descendants of this unassuming little bird. As they become more efficient at their quadrupedal gait, they might become larger. Perhaps some will find flight less necessary, and if so, they may be able to retain their embryos longer during development, perhaps even losing the egg-like sac stage altogether. The Pangeacene is an era still only in its infancy - who can say what even stranger species could yet arise from such early innovators given enough time?