Rise of the (nearly) Live-bearing Bird

25 Million Years PE

As the Tempuscenic Era progresses, Serina continues to cool. By 25 million years post-establishment, the moon's polar regions have developed the first of their permanent ice caps and tundra has spread across the poles. The planet is largely a savannah world, with widespread grasslands covering the middles of every major landmass. Dense bamboo forest thrives on wet coasts and on the rainy sides of mountains and in isolated pockets worldwide while sunflower forests radiate widely across all of the world's continents. Serinan ecosystems throughout the Tempuscenic are well-established and diverse; the canaries have diversified into more than 20,000 distinct species, covering virtually the whole range of Earthly avian morphology and countless forms like the Earth has never before seen. From the smallest seed-eater to the largest terrestrial predator, thriving in the driest deserts, the coldest tundras, the wettest of jungles and even thousands of miles out at sea, the canaries continue to rule their new home world.

Birds

Aardgeese

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One of the most competitive orders to evolve upon Serina so far, which have radiated enormously by the middle Tempuescenic, are the Aardgeese, Aardanserinae, now comprising a distinct suborder within the Dromaeoserina. Originating from a lineage of flightless, running herbivores, they are mainly a group of large, herbivorous to omnivorous canaries which still retain vestigial barbed wings despite many generations out of the air, with proportionately long legs and necks, and large stomachs able to ferment plant matter efficiently. They all exhibit large cropping bills equipped with tiny serrations for trimming grass and tough browse and rough and flexible tongues which can be scraped against the roof of the bill to crudely break up mouthfuls of coarse vegetation before swallowing it, improving their digestion and making them the first birds to have evolved, in some respect, to chew their food. They are running animals, adapted for long-distance travel, often at high speed. Aardgeese have especially well-developed synsacrum bones and an elongated pygostle that together provide support to an elongated portion of the body set behind the legs, providing extra room to accommodate this large gut and subsequently shifting their center of gravity and altering the posture of their legs to compensate - particularly their thighs - which are more vertical than in other birds. Uniquely among birds, many aardgeese can stand close to fully-erect, like human beings, with the knees highly flexed and stretched completely downwards.

With some primitive exceptions, Aardgeese exhibit a unique variation of plumage; with the exception of the wings and the rump, the development of advanced adult feathering no longer occurs in most members of the lineage and instead the animals retain only their soft, single-stranded down feathers as adults. This plumage is unbarbed and likely very similar to the inferred appearance of the most primitive feathers. As it occurs on the aardgoose it is extremely dense, each feather follicle almost directly adjacent to another, and no longer grows from tracts in the skin but sporadically across the skin, like hair but in clumps of three fibers each attached at the base. Each three-tufted feather is extremely thin and grows rapidly - if plucked, it can completely regenerate within a single day. The feathers in the body plumage are individually so small that they use extremely little blood when developing, meaning that they do not cause heavy bleeding if damaged while immature as large barbed feathers may. Aardgoose plumage is short, soft, and downy, generally just an inch or two thick on the trunk of the body, but extremely dense and insulating and fits more tightly to the body than is expected in a bird, closely following the curvature of the body similarly to fur rather than masking it in thick feathers. Where adult feathering still emerges on the aardgoose's body - the rump and the wings and occasionally the crown of the head - it does so from almost vestigial feather tracts and rises through the thick downy "fur" that covers the bird's body. The neotenic loss of most adult plumage in most aardgeese seems to have occurred in the common ancestor of most living Aardgeese within 10 million years PE. A scarce number of extremely basal surviving representatives of the clade which split before this time still develop adult plumage over their bodies.

Aardgeese by this time occur on every major continent, with a total diversity topping more than 450 species. Aardgeese have come to all but completely stake claim on megafaunal grazing and browsing niches as a result of their efficient grazing adaptations, precocial offspring which can run almost from birth, and cursorial nature that allowed their earliest representatives to escape early predators as the Skykes, Tyrannoserinae, that have since hunted such less adaptable animals as the enormous, defenseless womblers to complete extinction. The smallest Aardgeese of the Tempuscenic are not much larger than a rooster while the largest representatives may stand more than twelve feet tall at the head and weigh very near to one thousand pounds, making them among the most diverse in size of all canaries of their time.

The Ovovivavians

The (Nearly) Live-bearing Bird

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The most successful new branch of Aardgeese 25 million years PE is the Ovovivavia, a suborder endemic to the eastern landmass of the moon, from Striata through Wahlteria and down as far as Karii and the southern pole (see world map for reference), but in particular the temperate seasonal environments. The many varied members of this clade have all evolved towards the shortest external incubation period of any bird and surely the shortest that is physically possible - most eggs hatch within minutes of being laid by the female! This remarkable fact, almost unbelievable at first, comes as a direct result of the Ovovivavanians having developed the most advanced reproductive process so far evolved in known archosaurs. Instead of laying clutches of multiple eggs and then incubating them for a prolonged period on the ground where countless predators are always eager to snatch a meal, Ovovivavians produce only one single egg which is retained in the oviduct until it is ready to be laid, effectively being the only birds which truly become pregnant. This manner of reproduction allows an egg which would be too large for the mother to incubate properly outside her body, and subsequently aardgoose eggs are truly enormous. In the smallest species, they may weigh as much as one-sixth that of the mother, and while proportionately smaller in larger species, a 200 pound aardgoose can easily produce a 17 pound egg and that of a truly giant species may weigh as much as 30 pounds, nearly a third again larger than an elephant birds' egg, the largest known on Earth. The egg develops in a uterus-like swelling in the reproductive tract toward the hind end of the animal, behind its legs and pressing near to the stomach, making full use of the elongated body unique to the aardgoose family, which provides not only room for the over-sized stomach but also the enormous egg as it incubates.

Pseudo-ovoviviparity: How does it work?

The term "ovovivavian" is a slight misnomer; these aardgeese are not truly live-bearing, for their eggs hatch externally. However, they are likely as close as a fundamentally modern bird can conceivably evolve towards true ovoviviparity. In most species the entire incubation is done internally.

While other birds produce many eggs, laying one at a time until a whole clutch is complete, the mother aardgeese of this clade stop at a single egg and retain it in their body for a prolonged amount of time. The egg takes up almost the entire oviduct, which prohibits clutches of more than this single embryo in a season, and in the event two eggs are fertilized, the second is given priority and the first voided, laid and abandoned. The successor egg, however, may then remain in the mother's body for more than 50 days before itself being laid - in the very largest of aardgeese as long as 75 days - and is incubated through its most tender days internally at the perfect temperature for its development - the perfect natural body temperature of its species. Among other benefits, this permits the mother to reproduce much earlier in the season in temperate climates than other birds and gives her a strong competitive edge in cold regions where eggs incubated on the ground would freeze. Protected inside her body by its relatively large size and subsequent durability compared to a smaller egg, it is cradled by the mother's abdomen throughout its entire incubation. The muscles of the mother's reproductive tract exert upon the egg at all times a gentle, even level of pressure that prevents any one weak spot of the eggshell from succumbing to stress and cracking as the mother goes about her business, but this works only because the aardgooses' egg is so immense. Much smaller and the shell would be too weak to withstand the pressures it would find itself in as the mother runs and moves - the aardgoose's reproductive strategy is extremely ingenious but limited: it is truly only possible in a relatively large and flightless bird, or perhaps one extremely sedentary while carrying her egg. However, this would defeat the purpose of the adaptation, which is to free the mother from having to sit and expose herself and her young while incubating.

The egg receives the regular gas exchange it requires in the reproductive canal through the periodic reflexive contraction and expansion of the abdominal muscles as they press against the egg with each of the mother's breaths, keeping it stable and additionally ventilating the pseudo-womb with each contraction. Each inhalation of the mother causes the muscles to momentarily pull away from the egg, allowing it to rotate slightly to keep the embryo from sticking to one side of the eggshell, and pulling in a pulse of fresh air through the cloaca which is quickly warmed inside the relatively hot interior of the mother's body. In effect her reproductive tract becomes a second lung of sorts during her pregnancy, not for herself, but for her offspring.

Hatching The Young

The mother Aardgoose relies on auditory cues from her unborn offspring to determine when is the best time to lay the enormous egg, neither so soon that it will require further incubation out of the body (which the mother has usually lost any instinct to do) or so late that it might rupture internally and fills her body with lacerating chunks of eggshell, infecting and likely killing her. Between forty-five and seventy-five days after the egg is formed in the reproductive tract, longer in larger species and less in the smaller, the embryo inside begins to chirp. At first the calling is faint, but it grows stronger by the day until it is almost constant, nearly frantic. When the embryo within the egg is nearing hatching, typically three to five days after peeping begins, the sound is significantly loud that that the mother can hear it within her own body cavity. The calls of her offspring initiate a rapid flood of her maternal hormones, which serve not only to alter her behavior in a motherly way but to relax the muscles in her reproductive tract and release the egg. From here she knows instinctively that she has a job to do - the aardgoose's eggshell, in its evolutionary process, has become so thick, in order to stay intact inside the mother's body, that the infant usually cannot hatch without the assistance of its mother carefully pipping the egg to assist it. The hen excitedly nestles over the egg, surrounding it in the long, soft plumage of her degraded wings, and gingerly cracks the air pocket in the top of it to free her baby. She works diligently but with extreme care to break the eggshell and let the infant out into the world, pulling the shell apart with her flexible tongue and strong bill until the chick is loose and finally able to see the mother it has called for so long.

A new mother sits tightly over her new baby, keeping it warm and sheltered and grooming its plumage dry in a distinctly un-bird-like manner - more like a mammal would be expected to do - before giving it its first meal - a frothy, highly nutritious crop secretion similar in consistency to cow's milk. Unlike its ancestors, it will have all but used up its egg yolk in the days before hatching. As the infant does not have to exert itself in this process, however, like most birds do, it finds energy and begins to stand and walk around extremely quickly, often within an hour. At birth the chick is extremely well-developed, large and alert, and can run and follow its mother and its herd that same day, unlike the highly dependent and vulnerable young of earlier ancestors. The mother aardgoose is an exceptionally devoted parent to her young and to other's young; living in herds, mothers will readily tend to any young which beg for food, not only their own, and all serve to protect each other's chicks from danger, though it doesn't seem this is because they confuse their young with those of other females, for specific mother-offspring bonds are very strong and mothers will strongly favor their own offspring when resources are limited. Rather, it simply seems to be an instinct to protect all of the young around when conditions are sufficient for everyone - as long as resources allow, when everyone chips in success is improved for all. A young Aardgoose is fed on richly nutritive crop milk for a number of months after its birth before fully weaning around one year of age, but it begins to feed itself a little by two months of age. It is completely independent by its first birthday.

If the offspring dies in its shell, or if it was infertile to begin with, a female aardgoose will eventually void the egg within two weeks of the anticipated incubation time, knowing instinctively that it has proven inviable. Without chirping from within, she will ignore the egg as she would an accidental second offspring at the beginning of her breeding cycle, leaving it for the scavengers. In such an event, the hen has wasted time carrying the lifeless egg, but has not expended significant resources in doing so beyond those used to produce the egg in the first place itself over a month ago, and can become impregnated again immediately, hopefully more successfully. Infertile pregnancies are relatively common in first-time mothers and become less so with maturity.

Evolution

The first Ovovivavian is thought to have evolved roughly eight million years ago, from an ancestor which gradually delayed laying further and further along in order to protect the offspring from predators and get an edge on competition in cold climates. Originally external incubation would be delayed only for a few days and then would commence normally, but through the process of natural selection those individuals which proved able to do so for longer and longer periods and adapted ways to make the process work more efficiently found greater success than their competitors. These adaptations include not only the gradual thickening of the eggshell to resist internal breakage and the subsequently necessary instinct to assist in hatching their own offspring but the advanced state of the muscles within the birds' body itself, which have become sufficiently mobile to manipulate the egg internally and cradle it without either losing it and laying it prematurely or getting it stuck in place, seemingly in response to the habit of the female intentionally delaying laying for short periods of time when conditions may not have been favorable. Other aardgeese can occasionally do this already, even postponing the development of further eggs in the clutch to avoid a waste of energy if conditions are not safe to lay eggs, suggesting it's probable that the original evolution of the modern condition originated in this way. Gradually, it became the norm to abort all but the first egg in a clutch and to retain it for a very long time before laying it, the muscles in the oviduct becoming stronger and better able to support it safely. The instinctive pushing reflex of a female bird with an egg in the oviduct remained, now becoming the driving force for the oxygenation of the oviduct to allow the egg to breathe. The process would quickly void the egg were it not for the support of additional muscles further towards the cloaca which constrict the tract to keep the egg in place. These muscles contract just tight enough to keep the egg from sliding too far southwards and leaving the body during incubation, letting the egg finally slide past only the mother voluntarily relaxes them when the egg is ready to hatch. Once the cloacal muscles retract, the "breathing" movements quickly become pushing movements and release the egg from the oviduct and into the world in the usual manner.

Social Behavior and the Benefits of Pseudo-Ovoviviparity

Ovovivavian aardgeese are interestingly not monogamous like most of their near relatives - instead, single males guard harems of females and fight aggressively between themselves for mating rights. The males are much larger than the females and highly ornamented with bold coloration and bill casques while females are plain. More basal Cursoserinans notably are still monogamous but are also gender dimorphic. In these species, males use their brawn to defend and care for their smaller, camouflaged partners whilst they incubate their clutches of eggs. The male in these species does not sit on the eggs, but feeds the female while she does, allowing her to remain on them for the entire long incubation period, and he drives off predators that threaten her in her vulnerable position. When the chicks hatch, the male and female both feed the young crop milk. Both aardgoose clades have precocial offspring, but the Ovovivanian chick is larger and stronger at birth as it does not have to fight a race against time to develop and hatch in the dangerous world outside its mother's body. The Ovovivavian aardgoose hatches only a single chick at once while others may rear as many as six, but its young is born larger and cared for for longer. While the basal aardgoose will likely lose as many as half of its young before they are mature, the single chick has a higher rate of survival as a result of the extra safety net its mother's derived reproductive behavior. The basal aardgoose must also wait to nest until the climate is right, putting her at a disadvantage in those not-too-uncommon springs when the weather takes a long time to warm. Able to start as much as a month earlier, the Ovovivavian female can be onto her second "eggnancy" by the time her competitor has laid her first clutch. She can continually become pregnant and hatch offspring as long as the weather allows, readily producing three clutches in a good summer. By autumn she may lead three chicks of different ages all at once which will all remain with her until the following spring when they are all independent and the weather is mild. By then, food is abundant again for the youngsters as they set out on their own in the herd. Siblings will remain together for most of their second season, the oldest often taking over partial mothering duties for the youngest. The younger siblings may still occasionally be fed small feedings of crop milk by their older brothers and sisters until they are close to one year old. At this time, as they reach their own adolescence, their older siblings their siblings have reached full sexual maturity and move on to start their own families, already having had some advance practice in childcare. The youngest birds, born late in their first year, will not reproduce their second season but will wait until the following spring when they are approaching three years of age.

With a diversity broadly equivalent to all of Earth's ungulates and filling an equivalent series of niches, adaptable bodyplans and revolutionary evolutionary advancements, Aardgeese by the middle Tempuscenic already hold excellent prospects in the coming millennia upon the true world of the birds.

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The White-browed Viva, Cervanser cervanser, is a mid-sized, browsing representative of the Ovovivavian clade. The most widespread member of the Cervanser genus - the "deer-goose" group - it is native to the open woodlands and tall grass prairies across most of Striata in the middle Tempuscenic era, 25 million years PE. Aardgeese of these genus, which comprises about twenty species, are mostly specialized as browsers. They are less sexually dimorphic than some other genera, particularly those which live on the open plains, and the males of this genus are most often only slightly larger and more colored than their female counterparts. Vivas, like some other Ovovivavians, exhibit large, keratin-covered bone spurs on their wrists. These are used by the hen in defense and the male in intra-specific combat. These are not to be confused with true claws, which all Serinan birds, as passerines, ancestrally lost.

Pictured is a day-old chick alongside an expectant mother and adult male. The swollen oviduct of the hen is clearly visible through her feathers as she carries her 15 pound egg. As an Ovovivavian aardgoose can carry only a single offspring per breeding cycle, the infant present in this group must belong to a different mother, either not visible outside the shot or perhaps deceased, the chick subsequently adopted by the expectant mother as her maternal instincts kick in strongly in the days before her own young is born. Vivas live in smaller herds than savannah aardgeese, rarely more than six or seven females to a single dominant male.