ENANTIORNITHES In a world where no asteroid struck the Yucatan, the avian tribes of Laurasia where never obliterated. However, millions of years of invasions of true birds from the Gondwana have taken a heavy toll on enantiornithian diversity. The Eurasian opposite birds have fared a little better than their North American cousins, but are quite firmly under the thumb (or, perhaps, the alula) of the euornithians.
LAURASIAVIFORMES
The laurasiavians are a group of enantiornithians that split off from the rest of the opposite birds early in the Tertiary, probably from avisaurid stock. They posses the swept-back sterna, primitive hips, and (most importantly) upside-down metatarsi of all enantiornithians, but have accumulated a series of new developments since their inception. Laurasiavians are distinguishable by their toothless beaks and their unique manual anatomy, with the first digit bearing the flattened aileron that, in these birds, serves the function of the true birds' alulas.In Eurasia, Laurasiaviformes exists as two sub-clades, Terrestriadromidae and Pseudophasianidae. Both are terrestrial (flying and climbing niches being usurped by true birds, mammals, and dinosaurs) and heavily-built.
Terrestriadromidae
The terrestriadromids (or near-chicks) are a cryptic group of groundbirds, and are large and almost flightless. These birds can be found only deep in the jungles of southeast Asia and India, where they eat invertebrates and fallen nuts. Terrestriadromid chicks are precocial, with well-developed wings and teeth, both of which atrophy as the bird ages. This, and other morphological evidence suggests that terrestriadromids split from the other laurasiavians early in their evolution.Pseudophasianidae
The pseudophasianids (skitkins and ballbirds) are the only enantiorn clade that still enjoys a modicum of success. These small ground-dwelling birds range across tropical and temperate Eurasia, with several breeding colonies (though no endemic species) in Mediterranean Africa. They are a diverse group, with dwelling in both deserts and jungles and most are omnivorous with grains their preferred food.Pseudophasianids are distinguished from other laurasiavians by their spur-like hallux claws (used by males in dominance fights) and their long, bony tails, which in some species grow to as long as the body. These tails are composed mostly of a rod-like pygostyle (or parson's nose) of fused vertebrae, and are used as balancing aids when running or flying.
Skitkins and ballbirds, with their rotund builds and terrestrial habits, closely resemble the other laurasiavian clade of Eurasia, the terrestriadromids, but are in fact only distantly related. Genetic studies have yet to be conducted, but their internal anatomy links the pseudophasianids (albeit distantly) with the New World Xenosornidae. Together, the two clades form Xenosornoididea, a super-clade which must once have been widely diversified in Laurasia.
PSEUDORAPTORIFORMES
Few creatures are stranger than the false panha (Pseudoraptor apates), the only member of the pseudoraptoriformes. Being classified first as a glaciotitanid therizinosaur, then as a brevicaudid pithecosaur, and only recently as an aberrant enantiornithian, this creature has gone through as many taxonomic transformations as a troodon.Pseudoraptors are enantiornithians trying very hard to be pithecosaurs. They are flightless, with all three fingers separate and mobile and posses beaks with tiny teeth on the upper mandible. The toes are long and ansiodactyl, with toe 1 opposing the other three to provide a strong grip. The males possess poison glands along the arms which secrete a powerful irritant onto the feathers and claws. Pseudoraptors' pelvises are swept back to accommodate their large bellies and the ischium and pubis are fused in convergence with true birds. These creatures also possess gastralia, or belly ribs, which may serve to protect their stomachs or provide muscle attachments.
The exact taxonomic position of the pseudoraptors is extremely hazy. Scythornis gigantis, only reliable pseudoraptor fossil, dates back only to the Pleistocene, and seems to be simply a scaled-up version of the modern Pseudoraptor apatoides. However, it is clear that the pseudoraptors are widely separated from the rest of the extant enantiornithians. The presence of poison glands in this clade and no other opposite bird suggests a long evolution in isolation from its cousins, while the very similar poison glands of the twitiaviforms, present further taxonomic complication. These factors taken into account, the pseudoraptors must have split off from the laurasiavians at least as early as the Eocene, and probably much earlier. It is entirely possible that, while the laurasiavians are derived from the avisaurs of North America, the pseudoraptors trace their roots back to another progenitor, entirely.
(Text by Daniel Bensen)
SAMPLE TAXA:Back to SpecRecent studies suggest that the twitiaviforms (long regarded as Australian in origin) were, in fact, derived from Laurasian stock. If this is indeed the case, then the anatomical similarities between these birds and the opposite-birds may be more than convergence. If the twitiaviforms are not paleognaths, but trace their origin to Laurasia, then perhaps the fate of the opposite birds has not been so dreary.