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Neornithes, the only surviving branch of the dinosaurs, are represented by two major clades, Neognathae and Palaeognathae. The Neognathae are represented by 10,000 species, one of the mosts diverse groups of tetrapods. The Palaeognathae, on the other hand, are represented by only 59 species, and are absent in Eurasia, North America, and Antarctica. This lopsided diversity appears to be a result of the flightlessness or near-flightlessness of all palaeognath species, the ratites convergently evolving flightlessness six or more times, likely due to the near-uselessness of the flight abilities found in the other palaeognaths, tinamous, which the ancestors of ratites likely had.
Strangely enough, Gondwana had already split up long before the first known ratites existed. The most extreme case of this phenomenon may lie in the moas of New Zealand, over three meter tall titanic ratites of the clade Dinornithiformes, which first evolved in the Miocene, 80 million years after the Zealandia continent split from Antarctica. In addition, new evidence suggests a ghost lineage is impossible, as the continent of Zealandia may have completely sunk.
All evidence seems to point towards a conclusion that the tinamous have limited flight powers compared to their ancestors as well, and that at some point in the past, palaeognaths had the same flight capabilities as their sister taxon.
This timeline is different. Sixty million years ago, during the middle Palaeocene, a sudden change in climate turned the Earth into an icehouse world 40 million years premature, and with the icehouse world staying until the present day, Zealandia did as well. This is not only a land of birds, mammals live here as well, mainly odd stem-marsupials present in Antarctica just before Zealandia split. But yet another lineage unknown to the fossil record lives on this continent. In the absence of birds of prey, fully flying aerial palaeognaths rule the skies. These are the Struthioraptoriformes.
The Struthioraptoriformes first evolved 70 million years ago, and were perhaps the first birds of prey. The lineage of predatory theropods continued without a break as the Struthioraptoriformes had evolved before the dawn of the Cenozoic. Apparently basal palaeognaths, this order began as relatively small birds (compared to the palaeognaths of Home Earth) which hunted New Zealand's endemic marsupials, Zelandiadelphia, the likely sister taxon to the more diverse Australodelphia. These marsupials took the niches of rodents and shrews, but more specialised forms never evolved. On Home Earth, the Struthioraptoriformes left no trace of their existence in the bad fossil record of Zealandia, and were forced to become sea birds before dying off around 30 million years ago when Zealandia was near its peak sinking point, perhaps sinking completely soon after.
In this timeline, a sudden, small change in the Earth's orbit led to Miocene-like temperatures occurring when on Home Earth the Palaeocene-Eocene Thermal Maximum was building up. These temperatures remained relatively constant, but the sea levels stayed over 30 metres lower than in our timeline. This difference was enough to stop 80% of the low-lying continent of Zealandia from sinking. Zealandia's endemic fauna diversified, with seven species of tuatara, ten species of lizard (likely coming through a narrower sea passage from Australia), and five species of sea turtle making up the continent's reptilian fauna.
The endemic avian fauna was much larger, including the parrots of Strigopoidea; sleeker, faster basal penguins; and New Zealand wrens; but without a non-endemic group that made it to the islands of New Zealand on Home Earth, the Accipitriformes. For much of Gondwana is partially occupied with fully flying palaeognaths, and Zealandia's most notable group is the Struthioraptoriformes. In response to the icehouse world, the first members of this group evolved a thicker coat; this was no problem in flying, as the early members had thin, kiwi-like coats. In fast, this resistance helped with the later evolution of raptor-like habits. Presently, three families exist, and are perhaps more diverse than the Accipitriformes, which in this timeline mainly inhabit Laurasia, but not without exceptions.
Groups and Description
The first family, and the most basal of the three modern families, is Galliraptoridae. The Galliraptoridae are so-called because of their chicken-like appearance, although they in fact look more like tinamous. While basal members of the order looked similar to the Galliraptoridae, their diet was entirely different, made up mainly of seeds and insects. However, the Galliraptoridae, evolving 58 million years ago, had become carnivorous. Despite their relatively unspecialised flying capabilities, they found a way to hunt small animals, specifically the Zelandiadelphia. This tactic is to jump off of high ground, then to soar down and snatch their prey. This lifestyle still exists, and is compromises between the flying abilities which are average for a palaeognath and the swooping needed to catch prey in the manner of raptors. The Galliraptoridae are now represented by five genera and eighteen species.
The second family is likely the strangest of all. No matter the scenario, palaeognaths always become flightless in one way or another. And here, this has resulted in flightless predators intermediate in size between a kiwi and a lesser rhea. The Sectoavidae ("isolated birds") are like early phorusrhacids. However, their lifestyle is entirely different. Several early members were small flightless predatory birds which could not run. These soon went extinct, but the modern members took many millions of years longer to evolve. While the first members of Sectoavidae had evolved by the middle Eocene, the modern members, all in Sectoavis, finally evolved in the middle Miocene. They had longer legs to compensate for their near inability to run, but their greatest advantage was something no other bird had ever evolved: sharp serrated tooth-like structures for chewing. This finally allowed them to tear flesh off of live prey, and that single genus now contains fourteen species.
The most iconic family of the order is the Struthioraptoridae. They are the only ratite family known to soar, and perhaps do it more efficiently than even albatrosses. While albatrosses and birds of prey rely on wind to allow them to soar for long periods of time, the Struthioraptoridae take advantage of air pressure and lift to allow them to soar for hours without wind and without flapping their wings. All members of the family can bend their wings to some extent, Eversopteryx ("broken wing") can bend its wings to the point where it looks like a seagull from a child's drawing. This creates an updraft which in turn allows it to do a plunge dive maneuver to catch prey. The most diverse family of the order, Struthioraptoridae contains twelve genera and thirty species. However, they are the only family not restricted to Zealandia. Eversopteryx and Deinodites ("fearsome diver") live on both continents. While Australia contains better prey, such as large reptiles and marsupials, New Zealand in the breeding ground for both genera.
Struthioraptoriformes was just one evolutionary experiment out of many on the continent of Zealandia alone. But they had great success, and prove that the Palaeognathae are not birds with no potential other than ratites, and if not for the extinction of much of Gondwana's fauna in the last several million years, it would be hard to tell the difference between a small palaeognath and a passerine. And the story of the Struthioraptoriformes to come has even more potential. They could become some of the top predators of the entire world, but on the other hand, with evolution, there is always extinction. The fate of the Struthioraptoriformes is still to be decided.