Сообщество, посвящённое ра

Сообщество, посвящённое ра - Compsognathus

[Recent Entries][Archive][Friends][User Info]

August 7th, 2012

01:23 pm
[industrialterro]

[Link]

Compsognathus

Компсогнат (Compsognathus; буквально — «изящная челюсть») — вид динозавра, живший 145 миллионов лет назад. Найден на юге Германии, в Баварии, в таком же известняке, что и скелет археоптерикса. Отличался развитыми органами чувств и быстрыми ногами. Компсогнат имел 68 острых, слегка изогнутых зубов. Благодаря двум длинным задним ногам с четырёхпалыми стопами компсогнат легко догонял юрких ящериц и быстрых насекомых.

Были обнаружены три хорошо сохранившиеся окаменелости, одна в Германии в 1850, вторая во Франции в 1972, а третья в России, в Забайкалье. Внутри одного экземпляра найдены кости мелкой ящерицы баваризавра — остатки последней пищи динозавра.

Судя по найденным скелетам, в длину этот ящер достигал 60-100 см, самые крупные особи до 140 см и, учитывая его размеры и легкие кости, вес хищника был примерно 2,5 кг.

Компсогнат был небольшим двуногим тероподом. Длинная узкая голова животного была посажена на длинную изогнутою шею. Череп и нижняя челюсть были тонкими и изящными, а значит, довольно хрупкими. На челюстях находились маленькие и острые зубы. Шея, судя по всему, была довольна подвижной и позволяла ловко вращать голову во все стороны, что, возможно, помогало ему хватать добычу.

Компсогнат обладал длинными задними конечностями и ещё более длинным хвостом, который он использовал для балансирования во время движения. На передних конечностях имелось по три пальца с острыми когтями, с помощью которых можно было схватить добычу. Тонкий череп был узким и длинным, оканчивался клиновидной мордой. В черепе было пять различных отверстий, наибольшими из которых являлись глазные орбиты.

Компсогнаты достигали около 74 см. Благодаря своей «компактности» эти динозавры вымерли последними.

The genus Compsognathus gives its name to the family Compsognathidae, a group composed mostly of small dinosaurs from the late Jurassic and early Cretaceous periods of China, Europe and South America. For many years it was the only member known; however in recent decades paleontologists have discovered several related genera. The clade includes Aristosuchus, Huaxiagnathus, Mirischia, Sinosauropteryx, and perhaps Juravenator and Scipionyx. At one time, Mononykus was proposed as a member of the family, but this was rejected by Chen and coauthors in a 1998 paper; they considered the similarities between Mononykus and the compsognathids to be an example of convergent evolution. The position of Compsognathus and its relatives within the coelurosaur group is uncertain. Some, such as theropod expert Thomas Holtz Jr. and co-authors Ralph Molnar and Phil Currie in the landmark 2004 text Dinosauria, hold the family as the most basal of the coelurosaurs, while others as part of the Maniraptora.

During the late Jurassic, Europe was a dry, tropical archipelago at the edge of the Tethys Sea. The fine limestone in which the skeletons of Compsognathus have been found originated in calcite from the shells of marine organisms. Both the Solnhofen and Canjuers areas where Compsognathus specimens have been preserved were lagoons situated between the beaches and coral reefs of the Jurassic European islands in the Tethys Sea. Contemporaries of Compsognathus longipes include the early bird Archaeopteryx lithographica and the pterosaurs Rhamphorhynchus muensteri and Pterodactylus antiquus. The same sediments in which Compsognathus have been preserved also contain fossils of a number of marine animals such as fish, crustaceans, echinoderms and marine mollusks, confirming the coastal habitat of this theropod. No other dinosaur has been found in association with Compsognathus, indicating that these little dinosaurs might in fact have been the top land predator in these islands.

In a 2001 study conducted by Bruce Rothschild and other paleontologists, nine foot bones referred to Compsognathus were examined for signs of stress fracture, but none were found.

The Compsognathus specimen discovered in Germany in the 19th century featured only two digits on each forelimb, leading scientists to conclude that this was how the creature appeared in life. However, the fossil discovered later in France revealed the manus (hands) to have had three digits, similar to other members of compsognathid genera. The fossilization of the German Compsognathus had simply failed to preserve the specimen's forefeet completely. Bidar supposed that the French specimen had webbed forefeet, which would look like flippers in life. In the 1975 book The Evolution and Ecology of the Dinosaurs, L. B. Halstead depicts the animal as an amphibious dinosaur capable of feeding on aquatic prey and swimming out of reach of larger predators. Ostrom debunked this hypothesis by showing conclusively that the French specimen was nearly identical to the German specimen in every aspect but its size. Peyer confirmed these conclusions.

The remains of a lizard in the German specimen's thoracic cavity show that Compsognathus preyed on small vertebrates. Marsh, who examined the specimen in 1881, thought that this small skeleton inside Compsognathus belly was an embryo, but in 1903, Franz Nopcsa concluded that it was a lizard. Ostrom identified the remains as belonging to a lizard of the genus Bavarisaurus, which he concluded was a fast and agile runner owing to its long tail and limb proportions. This in turn led to the conclusion that its predators, Compsognathus, must have had sharp vision and the ability to rapidly accelerate and outrun the lizard. The Bavarisaurus is in a single piece, indicating that the Compsognathus must have swallowed its prey whole. The French specimen's gastric contents consist of unidentified lizards or sphenodontids.

The plate of the German Compsognathus shows several circular irregularities 10 mm in diameter near the skeletal remains. Peter Griffiths interpreted them as immature eggs in 1993. However, later researchers have doubted their connection to the genus because they were found outside the body cavity of the animal. A well-preserved fossil of a Sinosauropteryx, a genus related to Compsognathus, shows two oviducts bearing two unlaid eggs. These proportionally larger and less numerous eggs of Sinosauropteryx cast further doubt on the original identification of the purported Compsognathus eggs. In 1964 German geologist Karl Werner Barthel had explained the discs as gas bubbles formed in the sediment because of the putrefaction of the carcass.

For almost a century, Compsognathus longipes was the only well-known small theropod species. This led to comparisons with Archaeopteryx and to suggestions of an especially close relationship with birds. In fact, Compsognathus, rather than Archaeopteryx, piqued Huxley's interest in the origin of birds. The two animals share similarities in shape and proportions, so many in fact that two specimens of Archaeopteryx, the "Eichstätt" and the "Solnhofen", were for a time misidentified as those of Compsognathus. Many other types of dinosaur, including Deinonychus, Oviraptor and Segnosaurus, are now known to have been more closely related to birds.

Some relatives of Compsognathus, namely Sinosauropteryx and Sinocalliopteryx, have been preserved with the remains of simple feathers covering the body like fur, promoting some scientists to suggest that Compsognathus might have been feathered in a similar way. Consequently, many depictions of Compsognathus show them with coverings of downy proto-feathers. However, no feathers or feather-like covering have been preserved with Compsognathus fossils, in contrast to Archaeopteryx, which are found in the same sediments. Karin Peyer, in 2006, reported skin impressions preserved on the side of the tail starting at the 13th tail vertebra. The impressions showed small bumpy tubercles, similar to the scales found on the tail and hind legs of Juravenator. Additional scales had in 1901 been reported by Von Huene, in the abdominal region of the German Compsognathus, but Ostrom subsequently disproved this interpretation; in 2012 they were by Achim Reisdorf seen as plaques of adipocere, corpse wax.

Like Compsognathus, and unlike Sinosauropteryx, a patch of fossilized skin from the tail and hindlimb of the possible relative Juravenator starki shows mainly scales, though there is some indication that simple feathers were also present in the preserved areas. This may mean that a feather covering was not ubiquitous in this group of dinosaurs.

Известно, что компсогнат питался ящерицами, а также насекомыми и другими мелкими животными. Самого компсогната трудно отличить от первоптицы археоптерикса. И действительно, один из скелетов, обнаруженный в 1951 году в Золенгофене, рассматривался как останки компсогната до 1973 года, когда доказали, что он, на самом деле, принадлежал археоптериксу. Такое сходство является одним из важнейших доказательств того факта, что птицы являются прямыми потомками динозавров.

Возможно, компсогнаты рождались очень маленькими, не больше мыши, и поэтому часто становились жертвами хищников, не доживая до взрослого возраста. Но когда они вырастали, то становились ухищренней, проворнее многих гигантов и легко приспосабливались к суровым условиям юрского периода. В более раннем триасском периоде обитали предки компсогнатов — прокомпсогнаты. В 1909 году их останки были обнаружены в каменном карьере в Германии. В поздний триасский период динозавры только-только появлялись, поэтому эта находка была особенно ценной для ученых. Очень любопытно, что у этих мелких динозавров было по пять пальцев на передних и задних ногах, причем два из них были короче и выполняли ту же роль, что и большой палец у нас, т.е для захвата. Бегал прокомпсогнат, как и его потомок, на двух задних ногах, а передние хоть и были короче, но ничуть не слабее: с их помощью этот ящер расправлялся со своими жертвами.

C. corallestris (1972), обнаружен в киммеридгианских - титонских отложениях (поздняя юра, 152-144 млн. л. н.). в Германии (Европа). Был найден почти полный скелет 1,4 м длиной. Есть лишь несколько отличий (помимо размера) от основного вида, но эти отличия могут также объясняться половым диморфизмом может. C.sp (1998), обнаружен в киммеридгианских отложениях (поздняя юра, 154-148 млн. л. н.), в Португалия (Европа). Было обнаружено 49 зубов (1 зуб на один экземпляр) из нескольких районов. Отличается от C. longipes, в котором каждый последующий зуб имеет зазубренности на среднем carinae.

Compsognathidae is a family of small carnivorous dinosaurs, generally conservative in form, from the Jurassic and Cretaceous Periods. Compsognathids lie at or near the origin of feathers—skin impressions are known from four genera, Compsognathus, Sinosauropteryx, Sinocalliopteryx, and Juravenator. While Juravenator, Sinosauropteryx, and Sinocalliopteryx show evidence of a covering of simple, primitive feathers, Juravenator and Compsognathus also show evidence of scales on the tail or hind legs.

The position of the Compsognathidae within the coelurosaur group is uncertain; some hold the family as the basalmost of the coelurosaurs, while others as part of the Maniraptora.

In 2003, O.W.M. Rauhut redefined the family Coeluridae to include Coelurus (Late Jurassic, North America), Compsognathus (Late Jurassic, Europe), Sinosauropteryx (Early Cretaceous, Asia) and an unnamed Compsognathus-like form (Early Cretaceous, South America; this dinosaur has since been placed in the new genus Mirischia). However, this taxonomy has not been widely adopted. Sereno (2005) points out that Compsognathidae has priority of name, even if dinosaurs such as Coelurus or Ornitholestes belong in the same family as Compsognathus.