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15.01.2016 22:28 - Largest prehistoric animals Vol.1 Vertebrates part9 Reptiles ch.3 Crocodylomorpha
Автор: valentint Категория: Забавление   
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Последна промяна: 05.12.2016 19:35


Crocodiles and relatives (Crocodylomorpha) 
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Giant  prehistoric crocodiles size

Name Time/Location Size (meters)
Deinosuchus‭ (‬alligator-like crocodile‭). Cretaceous/USA. 10-12
Gryposuchus‭ (‬gharial-like crocodile‭). Miocene/S.‭ ‬America. 10
Mourasuchus‭ (‬alligator-like crocodile‭). Miocene/Peru. 12
Purussaurus‭ (‬caiman-like crocodile‭). Miocene/S.‭ ‬America. 11-13
Rhamphosuchus‭ (‬gharial-like crocodile‭). Miocene/India‭. 8-11
Sarcosuchus‭ (‬crocodile‭). Cretaceous/Africa. 11-12
Smilosuchus‭ (‬phytosaur *not a croc‭). Triassic/USA. 12
Stomatosuchus‭ (‬crocodile‭). Cretaceous/Egypt. 10

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Often argue who is the biggest crocodile ever lived. Everyone has a contender for the title between the four almost equal-sized giants - Sarcosuchus imperator, Purussaurus, Deinosuchus, and Rhamphosuchus.In fact , none of those listed in the table is not our main contender for the title of largest crocodile. There is reason to believe that we should start the review with a little-known species:


Aegisuchus

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It is becoming increasingly clear that the dinosaurs were not the only large reptiles that were around in the Mesozoic, and the discovery of the partial skull of Aegisuchus is a further example of this. Although incomplete, the partial remains are from a huge skull, but at the time of writing it is not known exactly what form this skull took. Because of this, Aegisuchus has been envisioned as both a more standard crocodyloform, and a gharial-like crocodile with a longer, slender snout.
This also leads to a lot of speculation about just how big Aegisuchus was. If like a standard crocodile, it may have been between sixteen and twenty-two metres long, if gharial-like, then fifteen to twenty-one metres long. Unfortunately the only way we could be certain to the size of Aegisuchus is if elements of the post cranial skeleton were found, the more complete the better. Unfortunately again the odds are stacked against this happening as the more solid parts of crocodiles such as the skull, teeth and scutes (bony armour) are usually all that remain (though exceptions are known). If the estimates of Aegisuchus are correct however, then it will certainly have been one of the largest crocodiles of all time, and a serious contender for the largest crocodile ever. At 40 cubic centimetres, the braincase of Aegisuchus is much larger in volume than that of any other crocodyliform. Based on the ratio of braincase to skull length in other crocodilians, the total skull length of Aegisuchus is estimated to have been 2.08 to 2.86 metres (6.8 to 9.4 ft) in length. A similar ratio between braincase and body length puts Aegisuchus at 15 to 21 metres (49 to 69 ft) long when based on the proportions of long-snouted gharials, or 16 to 22 metres (52 to 72 ft) long when based on the proportions of short-snouted crocodiles.

Aegisuchus was chosen as the name of the genus because of the presence of a bony boss of bone that was on top of the skull. This is similar to designs of the Aegis shield from Ancient Greece which was a circular shield with a smaller boss (like half a sphere) in the centre. The boss on these ancient shields was often stylised into the head of the Medusa and were often seen carried by Ancient Greek gods such as Zeus, Apollo and Athena, though often it would be a breastplate instead of a shield.
The actual skull of Aegisuchus is believed to have been flat with eyes that pointed up instead of forward. If correct then Aegisuchus may have lain just below the surface of the water, while the surface glare masked its approach from any animals that may have been drinking on the shore. This would allow Aegisuchus to close in unseen until the moment it struck. Alternatively, Aegisuchus may have lain at the bottom of water systems and ambushed creatures like fish or swimming dinosaurs from below.
We do not yet know for certain what kind of animals Aegisuchus showed a preference towards hunting, if any. Future discoveries of teeth, maxilla’s and mandibles may help to determine this but these of course need to be made. Dinosaurs were certainly a viable option as many different kinds are known from the Kem Kem Beds of Morocco. If however Aegisuchus were a fish hunting species, then the large size might denote a preference for preying upon larger fish genera such as the giant sawfish Onchopristis which is also known from the Cenomanian of Morocco.


Sarcosuchus imperator

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The largest well-known crocodylomorph is likely Sarcosuchus imperator at 12 metres (39 ft) long and weighing 8 tonnes. Sarcosuchus ( meaning "flesh crocodile") is an extinctgenus of crocodyliform and distant relative of the crocodile that lived 112 million years ago. It dates from the early CretaceousPeriod of what is now Africa and South America and is one of the largest crocodile-like reptiles that ever lived. It was almost twice as long as the modern saltwater crocodile and weighed up to 8 tonnes.

The first remains were discovered during several expeditions led by the French paleontologist Albert-Félix de Lapparent, spanning from 1946 to 1959, in the Sahara Desert. These remains were fragments of the skull, vertebrae, teeth and scutes. In 1964, an almost complete skull was found in Niger by the French CEA, but it was not until 1997 and 2000 that most of its anatomy became known to science, when an expedition led by the American paleontologistPaul Sereno discovered 6 new specimens, including one with about half the skeleton intact and most of the spine.

Sarcosuchus was a giant relative of crocodiles, with fully grown individuals estimated up to have reached up to 11–12 metres (36–39 feet) in total length. It had somewhat telescoped eyes and a long snout compromising 75% of the length of the skull, there were 35 teeth in each side of the upper jaw while in the lower jaw there were 31 teeth in each side, the upper jaw was also noticiably longer than the lower one leaving a gap between them when the jaws were shut, creating an overbite. In young individuals the shape of the snout resembled that of the living gharial but in fully grown individuals it became considerably broader.

At the end of its snout, Sarcosuchus presented an expansion, called bulla, it has been compared to the ghara seen in gharials but unlike the ghara, though, which is only found in male gharial, the bulla is present in all Sarcosuchus skulls that have been found so far, suggesting that it was not a sexually dimorphic trait. The purpose of this structure remains enigmatic. Sereno and others asked various reptile researchers what their thoughts on this bulla were. Opinions ranged from it being an olfactory enhancer to being connected to a vocalization device.

The osteoderms, also known as dermal scutes, of Sarcosuchus were similar to those goniopholodids like Sunosuchus and Goniopholis, they formed an uninterrupted surface that started in the posterior part of the neck up to the middle of the tail like is seen in Araripesuchus and other basal crocodyliforms, different from the pattern seen in living crocodiles, which present discontinuity between the osteoderms of the neck and body.

A common method to estimate the size of crocodiles and crocodile-like reptiles is the use of the length of the skull measured in the midline from the tip of the snout to the back of the skull table, since in living crocodilians there is a strong correlation between skull length and total body length in subadult and adult individuals irrespective of their sex, this method is preferred for Sarcosuchus due to the absence of a complete enough skeleton.

Two regression equations were used to estimate the size of S. imperator, they were created based on measurements gathered from 17 captive gharial individuals from northern India and from 28 wild saltwater crocodile individuals from northern Australia, both datasets supplemented by available measurements of individuals over 1.5 metres (4.9 ft) in length found in the literature.The largest known skull of S. imperator (the type specimen) is 1.6 m (5.2 ft) long, and it was estimated that the individual it belonged to had a total body length of 11.65 m (38.2 ft), its snout-vent length of 5.7 m (19 ft) was estimated using linear equations for the saltwater crocodile and in turn this measurement was used to estimate its body weight at 8 tonnes (8.8 short tons).This shows that Sarcosuchus was able to reach a maximum body size not only greater than previously estimated but also greater than that of the MioceneRhamphosuchus, only the Late CretaceousDeinosuchus and the MiocenePurussaurus may have achieved a comparable maximum body size.

Sarcosuchus is commonly classified as part of the clade Pholidosauridae, a group of crocodile-like reptiles (Crocodyliformes) related but outside Crocodylia (the clade containing living crocodiles, alligators and gharials).Within this group it is most closely related to the North American genus Terminonaris.Most members of Pholidosauridae had long, slender snouts and they all were aquatic, inhabiting several different environments, some forms are interpreted as marine, capable of tolerating saltwater while others, like Sarcosuchus, were freshwater forms, the most primitive members of the clade, however, were found in coastal settings, zones of mixing of freshwater and marine waters.Sarcosuchus stands out among pholidosaurids for being considered a generalist predator, different from most known members of the clade which were specialized piscivores.

 During the course of several expeditions on the Sahara from 1946 to 1959, lead by the French paleontologist Albert-Félix de Lapparent, several fossils of a crocodyliform of large size were unearthed in the region known as the Continental intercalaire, some of them were found in Foggara Ben Draou, near the town of Aoulef, Algeria (informally named as the Aoulef Crocodile) while others came from Gara Kamboute, in the south of Tunisia, the fossils found were fragments of the skull, teeth, scutes and vertebrae. In 1957, in the region now known as the Elrhaz Formation in the north of Niger several isolated teeth of great size were found by H. Faure. The study of this material by French paleontologist France De Broin helped identify them as coming from a new long snouted crocodile.

Later, in 1964, the research team of the French CEA discovered an almost complete skull in region of Gadoufaoua, in the north of Niger, said skull was shipped to Paris for study and became the holotype of the then new genus and species Sarcosuchus imperator in 1966. The genus name comes from the Greek "sarco" meaning flesh and "suchus" meaning crocodile.

In 1977, a new species of Sarcosuchus was named, S. hartti, from remains found in the late 19th century in the Reconcavo basin of Brazil.In 1867, American naturalist Charles Hartt found two isolated teeth and sent them to the American paleontologist O. C. Marsh who erected a new species of Crocodylus for them, C. hartti,this material, along with other remains were assigned in 1907 to the genus Goniopholis as G. hartti.Now residing in the British Museum of Natural History the fragment of the lower jaw, dorsal scute and two teeth compromising the species G. hartti were reexamined and conclusively placed in the genus Sarcosuchus.

The next major findings occurred during the expeditions lead the American paleontologist Paul Sereno, in 1997 and the follow-up trip in 2000. Partial skeletons, numerous skulls and 20 tons of assorted other fossils were recovered from the deposits of the Elrhaz Formation, which has been dated as late Aptian or early Albianstages of the late Cretaceous. It took about a year to prepare the Sarcosuchus remains.

Additional fossil material was found and described in 2010, from the area of Nalut in northwestern Libya. These fossils are from the Cabao Formation, which is likely to be Hauterivian to Barremian in age.

Sereno took thin sections from trunk osteoderms of an estimated subadult individual (~80% of estimated maximum adult size).Approximately 40 lines of arrested growth (LAG) were counted in these thin sections, suggesting that S. imperator took 50 to 60 years to reach adult size.Given that extant wild crocodylians rarely reach these advanced ages, Sereno suggested that S. imperator achieved its large size by extending its period of rapid, juvenile, growth.A similar growth strategy has been suggested for the equally titanic crocodylian Deinosuchus, based on similar criteria.

Based on the broader snout of fully grown S. imperator when compared to the living gharial and other narrow-snouted crocodiles, along with a lack of interlocking of the smooth and sturdy-crowned teeth when the jaws were closed, Sereno et al. hypothesized that S. imperator had a generalized diet similar to that of the Nile crocodile. A diet that would have included large terrestrial prey such as the abundant dinosaurs that lived in the same region.

However, a 2014 analysis of a biomechanical model of its skull suggested that unlike Deinosuchus, Sarcosuchus would not have been able to perform the "death roll" maneuver used by extant crocodylians to dismember their prey.This suggests that if S. imperator did hunt big game, it probably did not dismember prey in the same fashion as extant crocodylians.

The remains of S. imperator were found in a region of the Ténéré Desert named Gadoufaoua, more specifically in the Elrhaz Formation of the Tegama Group, dating from the late Aptian to the early Albian of the Early Cretaceous, approximately 112 million years ago.The stratigraphy of the region and the aquatic fauna that was found therein indicates that it was an inland fluvial environment, entirely freshwater in nature with a humid tropical climate.S. imperator shared the waters with the holostean fish Lepidotus and the coelacanth Mawsonia.The dinosaur fauna was represented by the iguanodontian Lurdusaurus, which was the most common dinosaur in the region, and its relative Ouranosaurus; there were also two sauropods, Nigersaurus and a currently unnamed sauropod while the theropod fauna included the spinosaurid Suchomimus, the carcharodontosaurid Eocarcharia and the abelisaurid Kryptops.

Meanwhile, S. hartti was found in the Reconcavo basin of Brazil, specifically in the Ilhas Formation of the Bahia series, it was a shallow lacustrine environment dating from the late Aptian, similar in age to the habitat of S. imperator, with similar aquatic fauna, including Lepidotus and two species of Mawsonia. The dinosaur fauna is of a very fragmentary nature and identification does not go beyond indeterminate theropod and iguanodontid remains.












Тагове:   сова,   predators,   prehistoric animals,   giant animals,   crocodile,   reptiles,


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