Convergent evolution is quite common among mammals of HE's and Spec's timelines. Spec's spelks, for example, resemble a lot cervids and other small artidactyls, while xenos resemble muroid rodents to such an extent that only molecular data and some morphological features place them as lagomorphs. Thus, it probably wouldn't be a surprise if the small mammalian fliers that can be seen in Spec's nightime weren't, in fact, bats, but a complete different linage of mammals that took the sky. Perhaps remarkable is what they are however; most "parallel mammals" of Spec are therians, like their real world equivelents (a possible exception being walducks, though they are only analogous to HE's beaked whales), which are the most common mammals in both timelines. However, specbats not only aren't within Theria, they also belong to a somewhat poorly understood clade of Mesozoic mammals, which are mostly known from [s]crappy remains, mostly teeth. They are volaticotheres.
Volaticotheria first appeared in the fossil record as the Early Cretaceous critter Volaticotherium antiquum, a gliding mammal quite similar to the eutherian batweasels. Since then, the Mesozoic volaticothere fossil record is limited to some teeth in Africa and South America; because of the (presumed) laurasian origin of the clade, plus the fact that both landmasses were already seperated in the Cretaceous, it is possible that flight could already had evolved by then, though it is just as likely that they simply island jumped from place to place. It was only in the Eocene that volaticotheres reappear in a decent way in the fossil record, as fliers not very different from modern genera. The Eocene fossil record is particularly interesting because it shows both basal forms akin to HE's bat Onychonycteris as well as forms already quite advanced, which suggests that they either evolved flight at least by the Paleocene or that they evolved it remarkably quickly. Either way, specbats didn't change that much since then.
Specbats converged strongly upon chiropterans in their adaptations to flight. The wings are pratically identical; they consist of a membrane (patagium) supported by four of their fingers, with the second digit being smaller than the others and acting like the avian allula, while the thumb is a claw. Also like in bats, the wing membrane has special fibers ("batten ribs") to strenghen it, though they are nowhere as rigid as pterosaurian actinofibrils, as well as specialised Merkel cells with hair which allows them a higher sensivity towards air currents. Unlike bats (other than flying foxes), specbats have underfur, and have a breathing system that, while not as complex as that of ornithodires, is nonetheless the closest mammalian analogue to it (if we ignore elphabas). Both HE's bats and Spec's analogues have a sprawling posture; while in bats this was a result from flight and the development of the patagium, this gait was already ancestral to volaticotheres, as therians seem to be the only mammals that have an upright leg gait (though the reason why other mammals didn't might very well be because they didn't had the chance). Like bats, specbats have an uropatagium, but some don't have a carpal.
Specbats, like HE's bats, use echolocation. The result was a total convergence on ear and vocal chord systems. In HE's bats, only one species can see ultraviolet, but pratically all volaticotheres seem to be able to see in ultraviolet frequencies. If it is a remaining feature from the early mammals (all mammals but monotremates and some placentals can see ultraviolet) or if it aids specbats somehow (they don't seem to be particularly colourfull like metatherians and multies, which makes sense, since they are nocturnal, though there are some excpetions; see below) is unknown. Unlike other basal mammals, they lack venemous spurs, though some species might give poisonous bites.
Volaticotheres, like most mammals, have a cloaca. Like metatherians and eutherians, though, male genital organs are external. As a twisted answer to anseriformes, male specbats have the biggest penises in comparation to the body size in all mammals; in at least one genera (see below), it is slightly bigger than the length on the owner's own body. The reason why specbats have such long genitalia is mostly because they mate on the air (or at least the male does, as the females of some species prefer to hang on a branch during intercourse). Because hovering wastes a lot of energy, the mating is also one of the shortest among mammals, which basically consists of a quick thrust that releases sperm; because chances are that one release won't make the partner pregnant, the male might have to try a couple more times. Because this leaves the male very tired only the strongest males can successfully make babies, which is how females ensure they have a strong offspring (if the male tires too quickly the female can remove the sperm, usually by licking [they also have remarkably long tongues]). Large specbats prefer to mate landed like HE's bats and pretty much every other mammal, and have smaller penises. If everything works fine, the female will then proceed to lay soft shelled eggs like most non-therian mammals do. They then are incubated by both parents (unless the female has a pouch), and the poorly developed offspring that hacthes later is dependent on the mother for quite a long time. It is fairly rare for specbats to form crèches, though they might form flocks like bats do.
Specbats, like chiropterans, are a cosmopolitian group, often being the only terrestrial mammals present on distant oceanic islands (when elphabas and xenos are absent, obviously). However, they are somewhat less diverse than HE's bats; for instance, there's no large frugivore volaticotheres in the Old World, for elphabas took their niche there. And, although specbats don't usually compete with anurognathids (which are basically pterosaurian nightjars), there are large nocturnal predatory forms in Australasia and Southeast Eurasia, thus preventing the evolution of predatory specbats there. Nonetheless, there are about 900 species, distributed in three clades and more niches than those occupied by HE's bats.
The "american specbats", they actually seem to be of Eurasian or at least African origin, as forms similar to modern paremballonurids. While Old World forms were gone by the Miocene, a south american radiation of the clade diversified, and later members of this group expanded into North America during the interchange. Some also invaded the Old World once more.
This clade consists of 300 or more species of winged insectivores convergent on HE's emballonurid bats. American in origin, several species recolonised Africa and Eurasia. They are brooding specbats, forming monogamous pairs that incubate the eggs and take care of the young. Via muscular contraction, they can control the size and shape of the uropatagium. Like their HE analogues, they have a short tail that ends in the middle of the uropatagium.
Colombian Sac-Wing (Pseudoemballonura dendropterus)
A typical representative of this clade, this small flier occurs in the montane cloud forests of the northern Andes. With a wingspan of ten centimeters, this small flier nests in holes in old trees, often creating the holes themselves with the claws and teeth. Unlike other brooding specbats, which nest in groups, this one prefers a more solitary existence, and rather than choosing a new mate in each mating season it may be monogamous for a lifetime (although couples might "divorce" if they don't have healthy offspring for too long). The older offspring usually also stay for a while to raise their younger brothers and sisters like some birds do, until they go away to raise their own families. The family fiercely defends the nest from predators such as necobaatarids; often, the predatory multies might go away once the specbats start attacking, since they don't want to risk their lifes due to the sac-wing's lethal poisonous bites (a single bite doesn't kill the predator, but several might cause a lot of agony to the multie). Sac-winged bats, as the name implies, have sac-like glands in their wings, which usually produce pheromones that attract mates. In this species however, they produce foul smelling chemicals used to scare off predators.
Indian Tomb Specbat (Kalipteryx mogli)
Part of a radiation of specbats that recolonised the Old World, these volaticotheres are a perfect example of a typical brooding specbat. Nesting in huge groups in caves or dead trees, few predators dare attacking the colonies during the mating season, as the animals attack any intruder in huge flocks. In the rest of the year, or when they go out to prey on insects, their agressivity is smaller, since they don't have the need to protect their young, and they indeed become fairly vulnerable to predators like scowls, so their gather in flocks for protection. If an adult dies, the pups would have less chances of surviving, since they are dependent on both parents for at least the first weeks. Thus, brooding bats that form colonies have an interesting form of solving this problem; closely related individuals often take care of each other's young, thus helping to spread their genes without wasting time on unrelated pups. The individuals most likely to aid their baby relatives are younger cousins who didn't yet had their first litter, thus gaining practice to raise their own families.
The closest Spec has ever managed to produce to Spec's flying foxes, they are a New World radiation of frugivore bats that evolved in the absence of elphabas. Like their HE analogues, they don't use echolocation but sight and the sense of smell to guide themselves, and they are quite more crepuscular than other specbats. Unlike paremballonurids, they have pouches, so they are free to move around while their eggs still haven't hacthed. Because of their size, they can't afford mating on the air like other specbats.
Cerrado Fying Tree Fox (Megalapatochiropterus brasilensis)
A typical member of this family, this critter has a wingspan of one meter and occurs in the savanna that extends across the south and western margins of the Amazon rainforest. Resting in tall trees like palms, they fly long distances in search of fruit trees; like all frugivore fliers, they are very important for these trees, because their seeds travel in the mammals stomach and are relaese in their droppings quite frequently miles away from the mother tree. Cerrado tree foxes breed during the wet season; males form large harems that they fiercely guard with teeth and claw. During this season, they also developed bright purple wing membranes, which reflect ultraviolet frequencies and their ability to see them. Due to their size they have few natural predators, and may live up to 30 years.
Patagonian Flying Tree Fox (Megalapatochiropterus ginkgophagus)
Similar in size and appearence to the cerrado species, this one occurs in the patagonian forests along the southern Andes. As its name implies, it feeds mostly on the fruits of gingkos, which are usually eaten by multies; because there are pratically no ginkgotheres this south, the patagonian flying tree fox is the main carrier of gingko seeds in this area, as few animals feed on the acid filled seeds of these plants. Besides gingko fruits, they also target podocarp and angiosperm fruits, as well as small animals up to the size of a xeno.
It is from within this speciose New World group, which is very similar to Home-Earth's Phyllostomidae, that one of the most interesting spec lineages has been derived: the nosferatus. In our timeline, there are currently only three species of vampire bats, in three genera. The past diversity was greater, with several more species in existence during the Pleistocene, when large hosts (the mammalian megafauna) were prevalent. Some of these extinct species also derived larger body sizes, most likely in response to the availability of especially large hosts. The largest, the Kinski nosferatu (Nosferatus gigas), can obtain a total wingspan of 30 cm, and consume 40 ml of blood in a sitting. It feeds entirely on large, diurnal dinosaurs such as hmungos.
The nosferatus move quickly on the ground, much the same as the vampires of our timeline (and in contrast to most other bats). They can fling themselves into the air with their arms, hopping about the feet of prey and launching themselves into the air when they are weighed down with a blood meal. The Nosferatus species are all relatively stocky, and can jump and run with amazing power and speed. They are fair flyers, but are not very maneuverable in flight. They usually fly low and straight, a cruising height of 1.5 metres is average. They will either land away from a host and walk over to feed, or land on top of an intended host, scampering across its back delicately to find a good place to take a meal of blood.
Nosferatus have robust jaws and massive slicing incisors and canines. These teeth are the same ones used by Home-Earth vampires to make feeding wounds, but those of the Kinski nosferatu, which must pierce the thick hides of dinosaur prey, are 1.5 2.5 times as large, proportionally.
It is as yet unknown how the high diversity of nosferatus affects the ecology (including disease transmission) of the Specworld.
The rival clade of the Apatochiroptera, they are an Old World radiation, though it is now cosmopolitian. They differ from the apatochiropterans by the presence of a carpal.
Known informally as "flying rats", they are the most common clade of insectivore volaticotheres, different from sac-winged specbats by the lack of wing membrane glands and the presence of carpal, as well as longer tails; in some species, the uropatagium is reduced, thus having rodentish tails like HE free tailed bats.
Merry Jesters (Pterattus spp.)
One of the most widespread clade of volaticotheres, this genus has species in every landmass but the most isolated islands. Brood nesters, they gather in large groups in vertical surfaces like cave walls or coastoal cliffs; in most cases, their nests are inside of tunnels that the animal made, sorta like HE's bee catchers. They often share their nesting grounds with birds like tweeties, which make use of the safety that a colony of specbats offers against predators. However, the specbats themselves might very eat the eggs and the chicks, so the birds often hide the nest or attack the mammals that get to close. Merry jesters are fairly more intelligent than sac-winged specbats, and in areas where their competitors are too common they resort to other food stuffs, from lizards to berries.
Flower Kisser (Anthophilus cuvieri)
A denizen from Madagascar's rain forests, this is one of the many specbats that feed on nectar. Living in pairs, they nest in holes in trees, and are susprisingly diurnal for specbats. They are the specbats with the longest tongue in proportion to the body size (the body is 9 cm long, the tongue reaches a length of 5 cm). They are also the specbats with the longest penis, reaching an amazing 10 cm of length. Being more diurnal than other pterattids, they have bright blue wing membranes and red and yellow colour patterns on the fur, warnings against the powerfull venemous bite (uniquely among volaticotheres, they don't produce their own venom, but steal it from the nectar of the plants it ingests).
The false-nosferatus are a clade of specbats that took false-vampire niches in South America and Africa, with more frugivorous species in Asia due to the presence of the tengu pterosaurs. Like nosferatus and cucas they have pouches; if pouches evolved multiple times in specbats, or if they were lost multiple times, is unknown.
White False Nosferatu (Laviamimus alba)
A typical member of this clade, they occur in southern Eurasia; being winged omnivores, asian populations prefer to feed on fruits (specially figs), while european populations prey on vertebrates more often. The european population is also migratory, while most other populations are either sedentary or nomadic. Practising polyandry, a single female mates with several males, before settling with a single male to help her raising the pups; the purpose of this is to have pups from several males in a single litter, thus the mate, incapable of telling if the pups are his or not, won't attack. Males, however, sometimes backfire by gathering in brother/cousin flocks, thus increasing the chances of the offspring carrying their genes. However, the females can and do remove sperm, if males come in groups or pairs (which is how relatives gather together).
Brownie (Laviamimus africanus)
One of the many african false-nosferatus, this animal occursin wetlands and mangrove forests. It is notorious for preying on aquatic prey, grabing fish and amphibians with their powerfull jaws. They often use an interesting trick to attract prey: they often drop a stick or a leaf in the water. As a fish comes to investigate (as it might look like an invertebrate to its eyes), the specbat quick strikes and kills the unfortunate prey. False-nosferatus are among the most intelligent specbats, so they learn new tricks if the situation demands it.
An autralasian clade, they are probably the most basal of the three specbat clades, even having a claw on the second finger. Aside from a few aerial insect eaters (not shown here), they are mostly terrestrial, having a strongly reduced uropatagium and tail and a semi-erect gait, which HE's bats never developed.
Akin to HE's short tailed bats, they still occur outside of New Zealand, with species present in Australia and New Guinea. Having a pouch, they are the volaticotheres with the longest parental caring period, which lasts for at least 3 months (when in other specbats it doesn't go behind 2 and a half).
Australian Rat Bat (Paramysticina robusta)
Present in the forests of eastern Australia, this solitary omnivore rests in trees or borrows during the day, and crawls in the ground in search of food at night. Using flight only as means of protection, it spends most of its life on the undergrowth, and little is known about it. It is believed tasmanian populations hibernate in the winter.
Hedgehog Bat (Paramysticina erinaceus)
If there is something specbats achieved that bats didn't, was a flightless form. The hedgehog bat, while capable of gliding, is completly incapable of powered flight, and it uses its hedgehog like spikes to defend itself against predatory birds; should it fail, it has the most venemous bite of all volaticotheres and a strong wing claw. The largest of the paramysticinids, it weights as much as two kilos, and it feeds on both small vertebrates and fruit. The hedgehog bat has a single pup per litter, a response to a predator free environment.
A bizarre linage of paramysticiniformes became specialised to a fishing lifestyle in the Miocene, and the ending resulting was a clade that spread across the tropics, with a few species in colder zones in the southern hemisphere like New Zealand. With their semi-erect gaits and a long neck and snout, these mammals resemble to older reconstuctions of pterosaurs as flying marsupials, ence the main genus name (Pterodactylotherium) and their vernacular name, ptero-bats.
Silverwing (Pterodactylotherium opeli)
A denizen from the Caribean, this specbat has a dark fur colouraion with silvery wing membranes. Like most ptero-bats, it walks along shorelines and wetlands in search of small animals that it catches with its powerfull jaws. Living in an archipelago, this species is more terrestrial than most of its relatives, thus being like little nocturnal azhdarchid in habits. Fairly social, they rest in caves during the day time; males form pairs that wacth over a large harem that is often targeted by neighboring males. Battles usually are more like bizarre dances with hisses and growls, rarely needing serious physical violence. Having few predators on the islands, they are often the apex predators in smaller islands like the Bahamas.