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18.12.2015 19:41 - Largest prehistoric animals Vol.1 Vertebrates part2 Birds ch.7 Terror birds from around the world
Автор: valentint Категория: Забавление   
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Последна промяна: 03.12.2016 02:25


Titanis, which is about 2.5m. tall, as tall as a forest elephant.

It lived approximately 5-2 million years ago (early Pliocene to early Pleistocene) in North America. Fossil evidence has been found in Gilchrist County, Florida dating from 3.0 to 2.9 million years.
From circumstantial evidence (i.e., bone fractures), it has been suggested that the species did not become extinct until 15,000 years ago,but more precise dating by McFadden and colleagues refutes such a late date; all known Titanis fossils appear to be at least 2 million years old.Titanis was part of the group of giant flightless birds called the Phorusrhacidae, which are nicknamed "terror birds", and has been thought to represent the youngest species of the lineage (recently, a significantly younger South American example has been reported. The Phorusrhacidae originated in South America; Titanis is the only known member of the branch of the group that migrated out of that continent during the Great American Interchange.
It was 2.5 metres (8 ft 2 in) tall and weighed approximately 150 kilograms (330 lb), but with large variance (perhaps indicating strong sexual dimorphism).Though its skull has not been found, it most probably would have been large, with a huge, axe-like beak, like its relatives.
It is estimated that Titanis could run at speeds of 65 km/h.
The wings were small and could not have been used for flight. The wing bones articulated in an unusual joint-like structure, suggesting the digits could flex to some degree. It also had a relatively rigid wrist, which would not have allowed the hand to fold back against the arm to the same degree as other birds. This led R.M. Chandler to suggest that the wings may have supported some type of clawed, mobile hand similar to the hands of non-avian theropoddinosaurs, such as the deinonychosaurs (also popularly known as "raptors").However, it was later pointed out that this wing joint is not in fact unique, and is present in seriemas (extant members of the same order, Cariamae, to which Titanis and other phorusrhacids belonged), which do not have any specialized grasping hands.
Overall, Titanis was very similar to the South American Phorusrhacos and Devincenzia, its closest relatives. However, it differs from these in having a shorter, thicker neck, a bulkier head, and an overall more heavily built bodily structure. Little is known of its body structure, but it seems to have been less wide-footed than Devincenzia, with a proportionally much stronger middle toe.(Onactornis is now considered a junior synonym of Devincenzia).

Diatrymas (Gastornithiformes)
The largest diatryma was Gastornis 1.75 metres (5.7 feet) tall, with large individuals up to 2 m (6.6 ft) tall.

Gastornis is known from a large amount of fossil remains, but the clearest picture of the bird comes from a few nearly complete specimens of the species G. giganteus. These were generally very large birds, with huge beaks and massive skulls superficially similar to the carnivorous South American "terror birds" (phorusrhacids). The largest known species, G. giganteus could grow to the size of the largest moas, and reached about 2 m (6.6 ft) in maximum height.

The skull of G. giganteus was huge compared to the body and powerfully built. The beak was extremely tall and compressed (flattened from side to side). Unlike other species of Gastornis, G. giganteus lacked characteristic grooves and pits on the underlying bone. The 'lip' of the beak was straight, without a raptorial hook as found in the predatory phorusrhacids. The nostrils were small and positioned close to the front of the eyes about midway up the skull. The vertebrae were short and massive, even in the neck. The neck was relatively short, consisting of at least 13 massive vertebrae. The torso was relatively short. The wings were vestigial, with the upper wings bones small and highly reduced, similar in proportion to the wings of the cassowary.
Gastornis and its close relatives are classified together in the family Gastornithidae, and were long considered to be members of the order Gruiformes. However, the traditional concept of Gruiformes has since been shown to be an unnatural grouping. Beginning in the late 1980s with the first phylogenetic analysis of gastornithid relationships, consensus began to grow that they were close relatives of the lineage that includes waterfowl and screamers, the Anseriformes.A 2007 study showed that gastornithids were a very early-branching group of anseriformes, and formed the sister group to all other members of that lineage.
Recognizing the apparent close relationship between gastornithids and waterfowl, some researchers classify gastornithids within the anseriform group itself.Others restrict the name Anseriformes only to the crown group formed by all modern species, and label the larger group including extinct relatives of anseriformes, like the gastornithids, with the name Anserimorphae. Gastornithids are therefore sometimes placed in their own order, Gastornithiformes.
Gastornis giganteus (Cope, 1876), formerly Diatryma, dates from the middle Eocene of western North America. Its junior synonyms include Barornis regens (Marsh, 1894) and Omorhamphus storchii (Sinclair, 1928). O. storchii was described based on fossils from lower Eocene rocks of Wyoming. The species was named in honor of T. C. von Storch, who found the fossils remains in Princeton 1927 Expedition. The fossil bones originally described as Omorhamphus storchii are now considered to be the remains of a juvenile Gastornis giganteus.Specimen YPM PU 13258 from lower Eocene Willwood Formation rocks of Park County, Wyoming also seems to be a juvenile – perhaps also of G. giganteus, in which case it would be an even younger individual.
Gastornis xichuanensis, from the early Eocene of Henan, China, is known only from a tibiotarsus (upper foot bone). It was originally described in 1980 as the only species in the distinct genus Zhongyuanus.However, a re-evaluation of the fossil published in 2013 concluded that the differences between this specimen and the same bone in Gastornis species were minor, and that it should be considered an asian species of Gastornis.
A long-standing debate surrounding Gastornis is the interpretation of its diet. It has often been depicted as a predator of contemporary small mammals, which famously included the early horse Eohippus.However, with the size of Gastornis legs, the bird would have had to have been more agile to catch fast-moving prey than the fossils suggest it to have been. Consequently, Gastornis has been suspected to have been an ambush hunter and/or used pack hunting techniques to pursue or ambush prey; if Gastornis were a predator, it would have certainly needed some other means of hunting prey through the dense forest. It could have also used its strong beak for eating large or strong vegetation.
The skull of Gastornis is massive in comparison to those of living ratites of similar body size. Biomechanical analysis of the skull suggests the jaw-closing musculature was enormous. The lower jaw is very deep, resulting in a lengthened moment arm of the jaw muscles. Both of these features strongly suggest Gastornis could generate a powerful bite.Some scientists have proposed that the skull of Gastornis was ‘overbuilt’ for a herbivorous diet and support the traditional interpretation of Gastornis as a carnivore, which used its powerfully constructed beak to subdue struggling prey and crack open bones to extract marrow.Others have noted the apparent lack of predatory features in the skull, such as a prominently hooked beak, as evidence that Gastornis was a specialized herbivore of some sort, perhaps having instead used its large beak to crack hard foods like nuts and seeds.Footprints attributed to gastornithids (possibly a species of Gastornis itself), described in 2012, showed these birds lacked strongly hooked talons on the hind legs, another line of evidence suggesting they did not have a predatory lifestyle.
Recent evidence suggests Gastornis was likely a true herbivore.Studies of the calcium isotopes in the bones of specimens of Gastornis by Thomas Tutken and colleagues showed no evidence it had meat in its diet. The geochemical analysis further revealed its dietary habits were similar to those of both herbivorous dinosaurs and mammals when it was compared to known fossil carnivores such as Tyrannosaurus rex, leaving phorusrhacids as the only major carnivorous flightless birds.
In Late Paleocene deposits of Spain and early Eocene deposits of France, shell fragments of huge eggs have turned up, namely in Provence.These were described as the ootaxon Ornitholithus and are presumably from Gastornis. While no direct association exists between Ornitholithus and Gastornis fossils, no other birds of sufficient size are known from that time and place; while the large Diogenornis and Eremopezus are known from the Eocene, the former lived in South America (still separated from North America by the Tethys Ocean then) and the latter is only known from the Late Eocene of North Africa, which also was separated by an (albeit less wide) stretch of the Tethys Ocean from Europe.
Some of these fragments were complete enough to reconstruct a size of 24 by 10 cm (about 9.5 by 4 inches) with shells 2.3–2.5 mm (0.09–0.1 in) thick,roughly half again as large as an ostrich egg and very different in shape from the more rounded ratite eggs. If Remiornis is indeed correctly identified as a ratite (which is quite doubtful, however, Gastornis remains as the only known animal that could have laid these eggs. At least one species of Remiornis is known to have been smaller than the Gastornis, and was initially described as Gastornis minor by Mlíkovský in 2002. This would nicely match the remains of eggs a bit smaller than those of the living ostrich which have also been found in Paleogene deposits of Provence, were it not for the fact that these eggshell fossils also date from the Eocene, but no Remiornis bones are known from that time yet.
The plumage of Gastornis has generally been depicted in art as a hair-like covering similar to some ratites. This has been based in part on some fibrous strands recovered from a Green River Formation deposit at Roan Creek, Colorado, which were initially believed to represent Gastornis feathers and named Diatryma filifera.Subsequent examination has shown the supposed feathers were actually not feathers at all, but plant fibers.
However, a second possible Gastornis feather has since been identified, also from the Green River Formation. Unlike the filamentous plant material, this single isolated feather resembles the body feathers of flighted birds, being broad and vaned. It was tentatively identified as a possible Gastornis feather based on its size; the feather measured 240 mm (9.4 in) long and must have belonged to a gigantic bird.
Gastornis fossils are known from across western Europe, the western United States, and central China. The earliest (Paleocene) fossils all come from Europe, and it is likely that the genus originated there. All other fossil remains are from the Eocene; however, it is not currently known how Gastornis dispersed out of Europe and into North America and Asia. Given the presence of Gastornis fossils in the early Eocene of western China, these birds may have spread east from Europe and crossed into North America via the Bering land bridge. Gastornis also may have spread both east and west, arriving separately in eastern Asia and in North America across the Turgai Strait.


Bullockornis planei
, nicknamed the Demon-Duck of Doom or Thunderbird, is an extinct flightless bird that lived in the Middle Miocene, approximately 15 million years ago, in what is now Australia.


Bullockornis stood approximately 2.5 metres (8 ft 2 in) tall. It may have weighed up to 250 kg (550 lb). Features of Bullockornis's skull, including a very large beak suited to shearing, indicate that the bird may have been carnivorous. The bird's skull is larger than that of many small horses.

Many paleontologists, including Peter Murray of the Central Australian Museum, believe that Bullockornis was related to geese and ducks.This, in addition to the bird's tremendous size and possible carnivorous habits, gave rise to its colourful nickname. The bird's generic name is improperly translated as "ox-bird",and was named instead for the type locality for the genus at Bullock Creek, Australia.
Although the name actually means 'ox bird', Bullockornis is better known in popular culture as the 'Demon duck of doom'. This is in part because Bullockornis is thought to be more closely related to ducks and geese than any other group of birds. Although Bullockornis was without doubt a large bird, it was not named for being the size of an ox but instead for being discovered in Bullock Creek.
Bullockornis is thought to have been a carnivore, an idea that is based upon the sharp beak that could have easily sliced through flesh. No one is certain what kind of animals Bullockornis preferred, but its large size meant that only the largest of animals could avoid being off the menu. Conversely however the group that Bullockornis belongs too, the Dromornithidae, all have sharp shearing beaks, but may have actually used these beaks for cropping vegetation. Another depiction of the group is that they may have been opportunistic omnivores that had no preference for either meat or plants.

Bullockornis is a good example of the Australian megafauna of the Miocene period, but it was not the only large bird from Australia with Dromornis and Genyornis also being quite well known.


Genyornis newtoni was a large, flightless bird that lived in Australia.

Genyornis newtoni was the last of the large, flightless mihirungs ('thunder birds') endemic to Australia. It was a heavily built bird over 2 metres tall, with tiny wings and massive hind legs. Fossils of Genyornis have been found in association with human artifacts, including cave paintings and carved footprints, and Genyornis must have co-existed with humans for a considerable amount of time (at least 15,000 years).
Mihirungs were large, flightless birds with deep lower jaws, a distinctly shaped quadrate bone (connecting upper and lower jaws), stubby wings, massive hind legs and hoof-like toes. They lacked a keeled sternum (breastbone), a specialization related to the reduction of flight muscles.
Genyornis was heavily built, but not the largest dromornithid; that distinction goes to the late Miocene Dromornis stirtoni, one of the largest birds known. Although a complete, undamaged skull of Genyornis is yet to be found, it did not have the extreme development of the beak of Dromornis or Bullockornis (the latter known from a complete skull with massive, curved beak). Its wedge-shaped head may have resembled that of a giant Magpie Goose (dromornithids are probably part of the duck/goose group, Anseriformes). The lower jaw of Genyornis was exceptionally deep and heavily ossified, a condition unusual in birds. This suggests that Genyornis required great force along the jaw and tip of the beak in order to break up its food. Genyornis was over two metres tall and would have weighed from 220-240 kilograms.
Eggshell fragments have been recovered in sand dune deposits. The eggs of Genyornis were large (up to 1.6 kg, almost twice the volume of emu eggs), smooth in texture and less elongate than emu eggs.
Genyornis fossils are known from Lake Callabonna, Baldina Creek, Mt. Gambier, Salt Creek and Naracoorte Caves in South Australia, and from Wellington Caves and Cuddie Springs in New South Wales. Eggshell fragments have been found in dune deposits in South Australia and footprints, possibly those of Genyornis, have been found in Pleistocene dunes in southern Victoria.
Genyornis had a wide distribution in a variety of habitats, but seems to have preferred open forest and savannah-grasslands to more the more closed forest habitats preferred by earlier mihirungs. Eggshell fragments have been found in sand dunes, and Genyornis may have used these dunes as nesting sites.
A shift to grasslands and increasing aridification in some areas may have favoured the emu in some regions (e.g., Cuddie Springs), which may then have replaced Genyornis in local faunas.
The diet of dromornithids has been the subject of much debate. Many palaeontologists are convinced that dromornithids were mainly if not exclusively herbivorous. Dromornithids lack a hooked beak, as in raptors, and have hoof-like rather than recurved claws on their feet. Analysis of eggshells (amino acid analysis) supports an herbivorous diet. Dromornithids are also found in large numbers in some deposits, unlike carnivores which, at the top of the food chain, are generally very rare. A minority view holds that dromornithids were to some degree carnivorous, citing the huge size of the beak ('a case of overdesign').
The diet of Genyornis has not been determined by any direct evidence although it appears to have been herbivorous. Fossils of Genyornis have been found with pebbles (gastroliths) in the gizzard region, which are unknown in carnivores. Gastroliths would have been used to help break up its food, as they do in other herbivorous birds. It is quite possible, given its anatomy and discovery of gastroliths, that Genyornis was herbivorous but the larger Bullockornis and Dromornis had a more varied diet.
Genyornis has sometimes found in large numbers at fossil sites, suggesting that it may have lived in flocks.
Biomechanical studies suggest that dromornithids may have been relatively fast runners. Their massive legs were well muscled, providing the necessary power in spite of their bulk. The eggs of Genyornis have been found in sand dune deposits, which have also preserved the eggshells of emus. These dunes may have served as breeding grounds for both species. Holes similar to those made by mammalian canine teeth have been found in some Genyornis eggshell fragments. The size of these holes suggests that the predators were either Tasmanian devils or eastern quolls, both of which are known from the dune deposits. Skulls and complete skeletons of Genyornis are known, although unbroken/uncrushed skull material is yet to be recovered. The best material comes from Lake Callabonna in South Australia. Gizzard stones and eggshells have also been recovered.
Once thought to be ratites (the group to which emus, cassowaries, rheas and ostriches belong), dromornithids are now believed to be either within Anseriformes (the duck/goose group) or just basal to it. Recent revisions of the taxonomy of other large, flightless birds place these taxa (Gastornithidae, the family to which Diatryma belongs, and the Miocene Brontornis from Patagonia) within Anseriformes. All of these large birds, including the dromornithids, have a short dentary symphysis and a dorsally directed pterygoid process on the quadrate, unusual features not related to flightlessness. This revision is still debated, although many feel that the general placement of at least dromornithids somewhere near the base of the anseriform radiation has merit.












 

 

 




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Автор: valentint
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