quarta-feira, 3 de dezembro de 2008

Extinct Xenornithes

This a [horrible] essay about extinct xenornithes.


Modern xenornithes are all classified in two orders: Xenorniformes (bunglebirds and nerds-of-paradise), and Pithecaviformes (carpos and paradise carpos). The origins of this group seem to steam from early Cretaceous †Confuciusornidae, which are very similar to modern bunglebirds; for about 65 million years, however, there was a huge gap in Xenornithe fossil record, though at least two jaws from the Maastrichian and some fragmentary remains from the Paleocene might belong to early Xenornithes. What is clear, though, is that violently reappear in the Eocene; in a space of merely 50,000 years, the Xenornithe fossil record passes from a few near fragmentary remains to thousands of nearly complete (and complete) skeletons; Messel was the site that revealed the larger quantity of Xenornithes so far. Because of the large diversity of Eocene Xenornithes, it very often assumed that the forerunners of the known clades made their first appearence in the late Cretaceous or at least in the Paleocene, but right after the thermal maximum there was literally an explosion on these birds' diversity. Such event is blamed on the effects of the thermal maximum: the expansion of the tropical rainforests, as well as a decline in Enantiornithe diversity (all post-Cretaceous opposite-birds trace their origin to merely 6 different ancestors from the Maastrichian; probably 5 or even 4, if the tweetie birds and specworld finches and parrots turn out as sister taxa, or if that such thing happens with ebergs and euavisaurs, which seem to have diverged from a single seagull/shorebird like ancestor) seemed to have been responsible for the "Eocene Explosion".

Modern Xenornithes, as obvious, made their first appearence in this epoch; the earliest bunglebird, †Eoxenavis, was already present, and the distinction between carpos and paradise carpos had already been made at the Eocene. Some extinct Xenornithes were indeed very closely related to modern carpos.


Many of the Eocene's Xenornithes are very similar to the Cretaceous Confuciusornids. Many Eocene "Confuciusornids" are often mistaken for early bunglebirds, and might in fact belong to Xenorniformes. Such genera include Aristotelornis, Awen and Messelavis.


Perhaps the most notable of Spec's Xenornithes, dead or alive, these birds are classified in two families, Thanatids and Tyrannavids. As the crown genus' name, Thanatos (literally "death" in latin), suggests, these birds are assumed to be predatory: their feet strongly resemble those of euavisaurs and those of HE's Falconiformes and Acciptriformes, and they also possess hooked beaks, sometimes with teeth-like serrations akin to those of HE's falcons. Because of their ear asymmetry, they are thought to had been nocturnal, leaving the diurnal predator niches to the first euavisaurs. Their disappearence is consistent with the disappearence of the global forests and the appearence of the first scowls, all in the beginning of the Neogene.


Known mainly from Europe and North America sites, some other thanatid taxa might be synonymous with it. It life, this falcon sized bird would had resembled HE's strigid owls (only with wing claws and a non-zydactyl feet), though more accurate reconstructions depict it with the facial disc of feathers in the head, which Thanatiformes appearently lacked. It has also well defined canine-like serrations on the beak. Three species are known, though only T. adamaste has been well described.


A close relative of Thanatos, this bird is known mainly from North America and Europe, with fossils in South America as well. It has longer legs than its european relative, probably hinting towards a cursorial lifestyle akin to that of HE's borrowing owls, though it was more likely like HE's barn owls.


Possibly a synonym of Thanatos, it is mainly known from Mongolia. It is almost identical to its european relative, though it lacks the canine-like serrations. Some yet to be described australian forms might belong to this genus, if it is valid.


Known exclusively from South America, it differs from other thanatids in the way it might have had a feathered facial disc like HE's owls and Spec's jungle demon. Its name (literally "opposite eater") is a refference to fossiliazed baby enantiornithes (appearently early specworld finches) found in one specimen's stomach; presumably it died before regurgitating the prey's bones in a pellet, as other thanatiformes are known to had done (we have fossil pellets).

Tyrannavis piscivora

The single specie of a single genus of a single family (all other thanatiformes belong to Thanatidae), this bird differs from its closest relatives due to the absence of the typical ear asymmetry (which suggests that it might had been diurnal), and due to its longer, more powerfull beak; in life, it would had been like a HE's osprey with wing claws. It seems to had been a fish eater, as fish scales were found on its stomach.


This clade only includes, as far as it is known, only two genera: Enarornis and Pekkalavis. The first fossil uncovered (a metatarsus) came from Finland ("Enare" means lake in sweedish, and this very first fossil was found roughly 2 miles south of lake Inari), though since then more complete remains came from other parts of Eurasia and North America. Both species are turkey sized (Pekkalavis mainly differs from having a hooked beak and a smaller hallux digit in the feet), have big, round wings, and gastroliths in the stomach; it has therefore been asumed that they occupied a niche roughly similar to the Early Cretaceous Omnivoropteryx and Sapeornis (which are unrelated to Xenornithes), as soaring omnivores.


While obviously not extinct, carpos have some extinct relatives.


A crow sized Pithecaviforme from Europe, this bird resembles the earliest known carpo, Paleocarpo, though it is still capable of flight; however, it is phylogenetically the most basal known Pithecaviforme (and perhaps the oldest, since fragmentary remains from the late Paleocene might belong to this genus; certainly, the possible xenorthitian owners of the parrot like jaws from the late Cretaceous are related to it). Because it already had a quite parrot like beak, it seems that the less powerfull beak of the paradise carpos isn't an ancestral characteristic of this clade.


Probably a synonym of Germanocarpo. Known from the Americas.


An early genus of paradise carpos, appearently still able to fly (though modern paradise carpos might had lost their ability to fly multiple times, as opposed to the true carpos, already flightless in the Eocene); fossils occur in Eurasia and North Africa, thus showing that paradise carpos weren't always restricted to Africa (some undescribed fossils also came from South America).

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