07:24 pm [industrialterro]
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Champsosaurus
Хампсозавры (Champsosaurus) — род вымерших рептилий группы диапсид отряда
Choristodera.
В длину хампсозавр был
примерно 1,5 метра, хотя C. gigas, самый
крупный вид рода, достигал длины 3—3,5 м.
Считается, что хампсозавр
внешне напоминал гавиала
и, подобно гавиалу, охотился в реках и болотах, ловя рыбу своими длинными
челюстями с большим количеством зубов. Он, вероятно, плавал с помощью боковых движений
тела, зафиксировав свои конечности возле туловища с целью увеличения своей
подвижности, как современные крокодилы и морские игуаны. Мышцы челюстей хампсозавра были
очень широкими и мощными.
Ископаемые останки хампсозавров
были найдены в Северной Америке (Альберта, Саскачеван, Монтана, Нью-Мексико,
Техас, Вайоминг) и Европе (Бельгия и Франция), в отложениях, начиная с верхнего мела и до середины эоцена. Его название означает
«ящерокрокодил»; корень «Champso-» был взят из утверждений древнегреческих
авторов, что «египтяне называют крокодилов χαμψαι [champsae]». Choristodera is
an order of
semi-aquatic diapsid reptiles which ranged from the Middle Jurassic, or possibly Late Triassic, to at least the early Miocene. Choristoderes have been found in North America, Asia, and Europe. The most common fossils are typically found from the Late Cretaceous to the lower Eocene. Cladists have placed them between
basal diapsids and basal archosauromorphs but
the phylogenetic position of Choristodera is still
uncertain. It has also been proposed that they represent basal lepidosauromorphs.
Most recently, workers have placed Choristodera within Archosauromorpha. Champsosauridae is the
best-known family of the Choristodera and typifies the group. Champsosaurus was first described from Late
Cretaceous strata of Montana by Cope in 1876. Champsosaurs resembled modern
gharials (gavials) or false gharials. The skull of these animals have a long, thin
snout filled with small, sharp conical teeth. This is due to champsosaurs and
gharials occupying similar niches: hunting small aquatic prey in rivers and swamps. This is a classic
example of convergent evolution. More primitive
choristoderes have shorter, broader snouts. There are major
differences seen between choristoderes and gharials and other crocodilians, however, particularly
in the skull. The orbits are found well forward on the skull, and the rear of
the skull is bulbous, hugely expanded and consists of complex bony arches
surrounding empty space. These spaces probably contained massive jaw muscles.
Other hypotheses for the spaces, such as an otic sensory organ housing, have been
tossed around with little support. The external nares are found on the tip of the rostrum. This indicates
that champsosaurs breathed while submerged by extending their rostrum through
the water surface while their body rested on the bed of the lake or stream.
Crocodylians and phytosaurs have
their nares located dorsally on their rostrum or skull respectively. This
position allows them to rest submerged just below the surface.
Champsosaur skulls are
actually very similar to lizard skulls,
though heavily modified. This has led some researchers to consider
champsosaurids as lepidosauromorphs. However, champsosaurs lack the complex quadrate of lepidosaurians. With features
of both diapsid groups, the phylogenetic position of Choristodera is highly
confused. Other features found in
choristoderes include heavily ossified gastralia and modified distal limbs, not just the
manus and pes, used as paddles. In addition, champsosaur ribs are short and
massive, as in other aquatic reptiles. The thorax is dorso-ventrally flattened,
and the tail is laterally compressed to aid in swimming. Skin
impressions found with champsosaur fossils show non-overlapping scales of
very small size and the skin containing no scutes like those found in crocodilians (see crocodile exoskeleton). Репродукции (1, 2, 3, 4):     Ископаемые останки и реплики (1, 2, 3, 4, 5, 6):      
Tags: Вымершие рептилии, Мел, диапсиды, хористодеры
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08:16 pm [industrialterro]
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Hyphalosaurus
Hyphalosaurus (meaning
"submerged lizard") is a genus of freshwater aquatic reptiles which represent a major part of the Jehol Biota. They lived during
the early Cretaceous period (Aptian age), about 122 million years ago.
The genus contains two species, H. lingyuanensis and H.
baitaigouensis, both from the Yixian Formation of Liaoning Province, China. They are among the best-known animals from the
Jehol Biota, with thousands of fossil
specimens representing all growth stages in scientific and private
collections. Hyphalosaurus fossils are relatively widespread in the Jehol beds, which
represent a series of freshwater lakes. Several specimens of H.
lingyuanensis and thousands of H. baitaigouensis specimens are known
from the Yixian Formation, including entire growth series from embryos in eggs
to fully grown adults. H.
baitaigouensis was originally reported from the younger Jiufotang
Formation, though subsequent study showed that the fossil beds it was found
in probably also belong to the Yixian, though from younger rocks and a different
region than H. lingyuanensis.
H. lingyuanensis and H. baitaigouensis were largely similar in
anatomy, both achieved a maximum adult body size of about 0.8 meters. They had
small heads with numerous needle-like teeth, and extremely long tails with more
than 55 vertebrae. The primary difference between the two species is the number
of vertebrae in the neck. H. lingyuanensis had 19 neck vertebrae, while
H. baitaigouensis had 26. Two specimens of
Hyphalosaurus have been described with clear impressions of the skin. One
specimen represents H. lingyuanensis, and the other (with clearer
impressions) cannot be assigned to a species because part of the neck (the
length of which is a key indicator of species) was destroyed when fossil dealers
grafted a skull from a different specimen onto the slab. However, both specimens
show nearly identical patterns of scales.
Hyphalosaurus was
covered mostly in small, irregularly patterned polygonal scales, though these
varied across the body. The scales of the hind legs were smaller, finer and more
irregular than those of the torso, while the scales of the tail were nearly
square and arranged in more regular rows. In addition to the small scales, two
rows of large, round scutes with shallow keels ran along the animals sides. One
row ran directly along the flank, with the other either slightly higher or lower
and composed of scutes only 1/4 the size of the flank scutes. The flank row of
larger scutes extended all the way to the base of the tail, and remained uniform
in size across the entire row.
The tail itself has
preserved soft tissue extending well beyond the margins of the skeleton. This,
combined with the already flattened appearance of the tail vertebrae, suggests
that a ridge of skin may have extended from the top and bottom of the tail
creating a small fin. The feet and hands also appear to have been webbed. ( Read more ) Репродукции (1, 2, 3, 4):     Размеры тела в сравнении с человеком:  Ископаемые останки (1, 2, 3, 4, 5, 6, 7, 8):     ( Read More )
Tags: Вымершие рептилии, Мел, диапсиды, хористодеры
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