The true birds are (and most likely, always were) the only avians in Australia. Here, as in the rest of the Southern Hemisphere, the evolution of clade Aves has, in many ways, precisely mirrored that of Home Earth. Many avian clades, including the ciconiiforms (storks), psittaciforms (parrots), and sphenisciformes (penguins) are little different from each other in their respective worlds. However, in some cases, avian evolution in the two worlds has proceeded along very different lines.
Some of the differences between Specworld's biota and Arel's are shatteringly apparent. Others, like the twitiavians ("tweety birds"), are of a far more subtle nature.
The first Specworld explorers, once the novelty of walking with dinosaurs had worn off, were astounded (or disappointed) by the many similarities between the biota of our two timelines, in particular amongst the birds. Both our worlds possess penguins, petrels, small heron, waterfowl, charadriiform waders, storks and parrots. But looks can be deceiving!
During the initial surveys of Specworld's fauna, the "little brown jobs"n seen merrily singing in the bushes were assumed to be passerine birds. Similarly, Melanesian birds with huge, curved beaks were written off as "hornbills". More detailed anatomical analyses of these forms flushed these assumptions down the proverbial toilet with a loud, embarassing gurgle.
The startling truth soon became apparent: THERE WERE NO PASSERINES ON SPEC!!!
Unlike our world, where a single bird clade (Passerines) excercised near-total dominance over the small-bodied insectivorous and seed-eating guilds, similar niches on Specworld were divided between 2 avian orders (Twitiaviformes and Allospiziformes), neither of which is present on Home Earth.
One of these clades are the tweety birds, so named because of the twittering cacophany that fills the forests and woodlands of Australia, Asia and South America thanks to these creatures' vocalizations.
With exceptions, tweeties are externally quite unremarkable looking birds. The majority are insectivores, others take seeds, fruit and nectar. About half of the twitiavian species, including all the seed and nectar feeders, have clusters of bristles on their tongues to assist in feeding. The clade has entered niches not occupied by the passerines, including large hornbill and toucan-like forms.
The anatomy of the tweety birds immediately sets them apart from all other avians, with skeletons that declare that they are non-neognathous birds. Their palatal configuration is unique amongst birds. Twitiavians possess large pterygoids with dual moveable joints to both the palatine and the large basiopterygoid process. The vomers have been reduced though not to the same extent as in most neognaths. This configuration allows for greater palatial mobility than paleognaths but less so than in neognaths which was the probably reason why this clade has produced few finch-like seed-crackers - that niche being filled by the allospiziforms.
Additionally, the ascending process of the ankle originates on the astragalus (as in paleognaths, enantiornithines and theropods) rather than the calcaneum (as in neognaths). Save for a few insular forms, tweeties are strong fliers with well-developed keeled sterna. Surprisingly, about one quarter of all male twitiavian species have a rudimentary penis.
A more remarkable aspect of twitiavian biology has recently come to light which may hold the key to their success - the majority of twitiavians are poisonous for at least part of their life-cycle.
In Arel's avifauna, the presence of poison in birds is restricted to a handful of passerines from New Guinea whose feathers and skin are laced batrachotoxins - in even here the toxins are apparently not produced by the bird but rather sequestered from another source.
On Spec, the use of secreted chemical toxins has become a common defence amongst a major bird clade. Special glands on the chest produce and secrete a mild hemotoxin that makes the act of biting into a live bird both distasteful and, should the poison make contact with an abrasion in the mouth or gut, very painful. I should know, I've tried it on many occasions. The birds appear to be totally immune to the effects of their secretions and are often seen laboriously applying over their body with their beaks.
In the majority of species, the toxins are present from about half-way through the incubation period and soon permeates most of the egg. The poison is retained in hatchlings and young birds, providing vital protection during this precarious stage of life. After the bird gets its adult plumage, the secretions usually stop. In only a handful of species is the poison retained in adulthood; these are usually very small, spectacularly coloured rainforest denizens. In some species, particularly insular forms, the ability to generate poison is lost altogether.
Thus the twitiavians possess a potent defence against any nest-raiding predator that does not possess specific physiological (immunity to the poison as in certain snakes) or behavioural adaptations (biting a poison-free part of the body like the head or legs; carefully butchering the carcass or leaving it to let the poison denature = behaviour witnessed in several pokemus species). To a lesser extent, the poison may also provide some protection against parasites.
Probably because of their toxic offspring, twitiavian parents generally have a much easier and stress-free life than a comparable Arel passerine couple. They produce small clutches, some species investing in only one or two large eggs per season. As the eggs are usually toxic in the days prior to hatching, less effort is put into concealing and protecting the clutch from predators. In fact, the eggs of some twitiavians are the most beautiful in the animal kingdom and are adorned with bold, colourful warning patterns (as can be expected, many species with non-toxic eggs practice egg mimicry). Expectant tweety-parents are often quite lazy when it comes to nest protection, some seem to actively goad potential nest-predators into sampling their distasteful clutch (on the other hand,
this behaviour tends to open them up to interspecific brood parasitism).
The hatchlings are large and become fully mobile within a day or two, capable of hopping amongst the branches or foraging on the ground. They still stay close to the nest with the parents bringing food to their young to supplement their diet. However, this activity is noticeably less hectic than with other birds.
DNA hybridization studies of these birds have shown no close relationship to any other extant clade but they are closer to paleognaths than to neognaths. In the early days of specornithological research, three competing hypotheses were proposed as to their evolutionary relationships.
1) Twitiavians are "proto-neognaths" that retain old-style ankles and large basipterygoid processes.
2) Twitiavians are highly derived paleognaths that have convergently evolved neognath-like features of the palate.
3) Twitiavians represent a hithero unknown lineage of Neornithes.
New fossil finds may shed some light on the matter and reveal some surprising aspects of their history. Firstly, well preserved fossil avian assemblages from Eocene deposits in Australia display no identifiable twitiavian remains. What is just as startling are the presence in these deposits of small neornithine forms, apparently very close to Arel's passerines. On the other hand, Eocene fossil sites in Europe, most notably the Messel Shales, have recently turned up beautifully preserved twitiavian specimens.
In fact, fossil tweeties do not appear in the Australian record until the Oligocene, which corresponds with a marked decline in the diversity there of small perching neornithines. Similarly, undoubted twitiavian fossils do not appear in South America until about this time as well. This new information strongly suggests that the twitiaviformes originated in Late Cretaceous or Paleocene Laurasia from a paleognath-like ancestor, spreading into the southern landmasses at the expense of similar endemic neognathous clades (such as the passerines) during the Oligocene.
This hypothesis neatly explains the lack of passerines on Spec. It also suggests that twitiavians may have once existed in Arel's Laurasia but were eliminated by the Chicxulub impact. However the fossils that would confirm this idea have yet to be identified.
The Twitiaviformes are distributed worldwide with about 2000 living species in 17 families. It is surprising that today the tweeties are much more diverse in the Australasian and Neotropical regions than in their Eurasian cradle. The rigors of the ice ages and the lack of natural barriers in the Holarctic has led to a poorer degree of speciation in the north.
Twitiaviidae - c.160 spp.
Wagtail Tweety Birds. These archetypal tweetybirds form an almost cosmopolitan family of small-medium sized ground-dwelling birds with slender bills and legs. They are mainly brown in colour although may be boldly marked. The walk has a pronounced swagger that jerks their long tails in a manner similar to our world's passerine wagtails. They run after insects, leaping to pursue them in flight but also take seeds and vegetable matter.
- Black-faced tweety bird
Arborogemmidae - 19 spp.
Treegems, Treeclutchers and their kin. The Treegems or Treeclutchers are small trunk and branch-foraging twitiavians restricted to Australia, Tasmania and New Guinea. They cling to tree trunks with strong, robust legs and use their long, slightly upcurved bills to lever off bark in search of prey - usually insects, their larva and spiders.
- Tasmanian Golden treeclutcher
Balaclavidae - c. 500 spp.
Balaclava Birds and their kin. This huge family includes some of the more bizarre members of the clade. Many members of this group possess a wrinkled sheath of thick leathery skin that covers up to two thirds of the beak which, when combined with the bare faces of some species, creates the illusion that the bird is wearing a balaclava. This sheath reaches it's greatest development in Australian representatives and is often reduced or absent in outlying forms such as on Hawaii.
Balaclava Birds are found throughout Australasia (including New Zealand), Melanesia, Polynesia and Southeast Asia. A few species have reached as far as Hawaii and Japan. All have a club of bristles at the end of their long, extensile tongues. The majority are nectar feeders, collecting the fluid with their brush-like tongues (although some take insects, berries, and sap).
The purpose of the "balaclava" is of some debate and it's use varies between different species. In some forms, the bare sheath is brightly coloured and plays a prominent role in courtship. With the abundance of spines and toxic secretions produced by much of Spec's Australian flora, it has been suggested that the sheath prevents injury to the inside of the bird's mouth while feeding. Similarly, insectivorous balaclava birds find the structure a useful shield against hymenopteran stings.
- Blue-faced balaclava
Pseudoartamidae - 43 spp.
The mistriders are a clade of worldwide distribution. Their rather dull and non-descript appearance is more than made up for by their breathtaking flying skills - they are the only twitiavians that engage in soaring flight. The name "mistrider" was inspired by accounts of these birds in the highlands of Australia and New Guinea, darting in and out of the morning mist.
Mistriders have well developed brush-tipped tongues which they use to glean nectar; however these birds are primarily aerial insectivores.
- Black-collared mistrider
Scythrhynchidae - c. 50 spp.
Channelbills, scytherbills, and sturdybills. These are the giants of the Austro-Asiatic twitiavians with many large and colourful forest forms. Their most distinctive feature is their enormous, lightweight bill, superficially similar to those of our world's toucans (which also exist in Spec's South America) and hornbills.
With a few exceptions, they are denizens of rainforests and tropical woodlands where they feed mainly on fruit and some small animals. They consume hard fruits by mashing them within their beaks whereupon the pulp is collected with their brush-like tongue. Like hornbills and toucans they nest in excavated holes in tree-trunks.
The family reaches it's greatest diversity in Melanesia, New Guinea and the Philippines. They are common in tropical mainland Asia but competition with pithecosaurs limits them to fairly small-bodied forms. The group is poorly represented in Australia with only 5 species, 2 of which are endemic.
(Text by Brian Choo)
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