Потребителски вход

Запомни ме | Регистрация
Постинг
18.12.2015 19:10 - Largest prehistoric animals Vol.1 Vertebrates part2 Birds ch.5 Euornithes,Hesperornithines-large birds from the era of dinosaurs
Автор: valentint Категория: Забавление   
Прочетен: 215 Коментари: 0 Гласове:
0

Последна промяна: 03.12.2016 02:23


Gargantuavis

Gargantuavis is a genus of extinct avialan stem-birds containing the single species Gargantuavis philoinos. G. philoinos lived during the late Cretaceous period in what is now southern France. Its fossils were discovered in the Marnes Rouges Inferieures Formation, which has been dated to roughly 70 million years old. A large avialan, Gargantuavis was flightless, occupying an ecological niche somewhat similar to that of modern ratites or more primitive theropods. It is possible that some of the fossil eggs found in the region, usually attributed to non-avialan dinosaurs, actually belong to this bird.

The first Gargantuavis fossil was found in 1995 in Var, France. This first specimen, a partial set of pelvic vertebrae (synsacrum), was uncovered in the village of Fox-Amphoux during construction at a winery. Several other specimens were later found further west, in the villages of Villespassans, Cruzy, and Campagne-sur-Aude, providing enough fossil material to describe and name the species in 1998. The species name G. philoinos, meaning "wine lover", was chosen because several of these first Gargantuavis bones were found in and around vineyards and wineries.

Though Gargantuavis is only known from a few isolated fossil bones, some information about its life appearance and ecology have been inferred by studying their details. Gargantuavis is known from several specimens representing a few limited parts of the skeleton: synsacra (the fused vertebrae above the hip) illia (hip bones), and at least one partial femur (upper leg bone), which was referred to the species based on the fact that it seems to fit well with the hip. A neck vertebra has also been referred to Gargantuavis.

Other than its large size, the most unusual feature of Gargantuavis was its pelvis. The pelvis of Gargantuavis was originally reported to be extremely wide, like that of a moa, though a better preserved specimen described in 2015 showed that this interpretation was due to crushing in the original. The hips of Gargantuavis, while still broad, were narrower and more bird-like than originally thought. In addition to their unusual width, which prevented the two ilia from meeting at the front of the pelvis, the acetabulum, or hip socket, of Gargantuavis was set close to the front, rather than closer to the middle of the pelvis.

Some researchers have suggested that Gargantuavis was not a stem-bird at all, but rather a giant pterosaur. However, when this idea was tested by studying the form and internal structure of the bones, its identity as an avialan was supported.

During the time period in which Gargantuavis lived, the region of southern France were its fossils are found was part of a large island in the prehistoric Tethys Sea. The rock formations that have yielded Gargantuavis fossils have also produced abundant remains of fish, turtles, crocodylomorphs, pterosaurs, sauropods, ankylosaurians, ornithopods, and theropods, including other early avialans, like enantiornithes. Abundant fossils of the ornithopod Rhabdodon, and the lack of any hadrosaurid fossils, have been used as index fossils to roughly date these formations to the early Maastrichtian age. Gargantuavis seems to have been an uncommon part of the fauna in its region. Despite numerous digs at sites where its bones have been found since its discovery, most have yielded only single specimens.


Hesperornithines (Hesperornithes)

The largest of the hesperornithines was Canadaga arctica at 8 ft long.

Canadaga (meaning "Canadian bird") is a flitless bird genus from the Late Cretaceous. The single known sghpecies is Canadaga arctica. It lived in the shallow seas around what today is Bylot Island in Nunavut, Canada. Its fossils were found in rocks dated to the mid-Maastrichtian age, about 67 million years ago.

It was a member of the Hesperornithes, flightless toothed seabirds of the Cretaceous. Among these, it belonged to the Hesperornithidae, along with Hesperornis, the well-known namesake genus.

C. arctica is the largest known member of the Hesperornithes, reaching a length of 2.5 metres (8.2 ft). It also represents one of the last known members of the lineage.Unlike its relatives which are mainly known from subtropical or tropical waters, this species seems to have ranged in temperate or even subarctic areas

 

 

Hesperornis

Hesperornis (meaning "western bird") is a genus of flightless aquatic birds that spanned the first half of the Campanian age of the Late Cretaceous period (83.5–78 mya). One of the lesser-known discoveries of the paleontologist O. C. Marsh in the late 19th century Bone Wars, it was an early find in the history of avian paleontology. Locations for Hesperornis fossils include the Late Cretaceous marine limestones from Kansas and the marine shales from Canada. Nine species are recognised, eight of which have been recovered from rocks in North America and one from Russia.

Hesperornis was a large bird, reaching up to 1.8 metres (5.9 ft) in length. It had virtually no wings, and swam with its powerful hind legs. Fossil evidence shows that the toes were probably lobed, as in today's grebes, rather than webbed as in those of loons.

Like many other Mesozoic birds such as Ichthyornis, Hesperornis had teeth as well as a beak, which were used to hold prey. In the hesperornithiform lineage they were of a different arrangement than in any other known bird (or in non-avian theropod dinosaurs), with the teeth sitting in a longitudinal groove rather than in individual sockets, in a notable case of convergent evolution with mosasaurs. The teeth of Hesperornis were present along nearly the entire lower jaw (dentary) and the back of the upper jaw (maxilla). The front portion of the upper jaw (premaxilla) and tip of the lower jaw (predentary) lacked teeth and were probably covered in a beak. Studies of the bone surface show that at least the tips of the jaws supported a hard, keratinous beak similar to that found in modern birds. The palate (mouth roof) contained small pits that allowed the lower teeth to lock into place when the jaws were closed. They also retained a dinosaur-like joint between the lower jaw bones. It is believed that this allowed them to rotate the back portion of the mandible independently of the front, thus allowing the lower teeth to disengage.










 

 

 





Гласувай:
0
0



Няма коментари
Търсене

За този блог
Автор: valentint
Категория: Политика
Прочетен: 86095
Постинги: 146
Коментари: 24
Гласове: 11
Архив
Календар
«  Юни, 2017  
ПВСЧПСН
1234
567891011
12131415161718
19202122232425
2627282930