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Age of dinosaurs

30 Sep

German specialists found almost entirely ichthyosaur skeleton, which is probably 175 million years (middle Jurassic). It is a sensation, as ichthyosaur, found near Brandenburg, may be much younger than previous finds of dinosaurs.
“It’s a sensation! – He exclaims. – This is the fifth instance of the ichthyosaur was found over the past century in northern Germany. Maybe the younger skeleton – in which case it will be even more sensational. “Paleontologists have been surprised by the fact that the four-meter skeleton of ichthyosaur was only two feet above the ground.
Must pass at least a week, so fossils can be safely preserved for study in the laboratory. Prior to the final result will be more than one month. You will need to try to determine the sex, age, and the species of this reptile. Because ichthyosaurs were very diverse and thriving group of Mesozoic marine reptiles. However, they still know very very little.

It is believed that ichthyosaurs appeared in the early Triassic period, ie 250 million years ago. Greatest prosperity and diversity of the group reaches the next, the Jurassic, the period of which there are about six families of reptiles, with more than a dozen species known to science. But already in the next, the Cretaceous, the period of abundance and diversity of ichthyosaurs are sharply reduced, and the Late Cretaceous to survive only by representatives of one genus, the most recent remains of which are between 90 million years. It turns out that ichthyosaurs disappeared from the planet 25 million years before dinosaurs, which, incidentally, they are not entirely irrelevant.
First of all, typical ichthyosaur skull completely different structure than the “terrible lizards.” In the latter, on the sides of the skull were two holes, called temporal windows (so-called diapason skull of the living reptiles, it is common to all groups, except for turtles, as well as close relatives of the reptile – bird), and in ichthyosaurs – only one (skull , in living vertebrates this is not observed). It should be noted that we are, that is, mammals also have a skull with a single temporal window). However, this does not make us relatives ichthyosaurs – that temporal window is located in another place and appear in the process of ontogenesis as a result of differences at all other cranial bones.
In addition, the ichthyosaurs were different from dinosaurs and even the structure of the pelvis – it was their in modern lizards, but not “compressed” as a dinosaur (it was thanks to him the past and could exactly walking on two legs, not rolling in This from side to side). There are also differences in the structure of the limbs (eg, ichthyosaurs legs were always more than five fingers of the dinosaurs has never been observed), chest and spine. They all indicate that these reptiles evolved from some more primitive creatures, the ancestors of the dinosaurs than, and the first ichthyosaurs, were furrowing the sea much earlier than smaller dinosaurs pioneers made their first tentative steps on the land.
What were these active predators of the Mesozoic oceans? As we know, from vertebrates best swimming fish. Perhaps that is why ichthyosaurs “got” fish-body form. Even their spine was what is called a type of fish – swimming in it curved in the horizontal plane. Accordingly, the paddle blade on the tail of these lizards has worked in a vertical plane, like a fish, and not, as in whales and dolphins. By the way, so they probably could not jump out of the water, as do whales, though this ability to almost always give illustrators of popular books and science fiction movie directors.
Limbs ichthyosaurs, as the front and rear, were the flippers, and, as mentioned above, the fingers on them, there are not five, and much more – up to eight or ten, and the fingers themselves consisted of a set of phalanges. In addition, these reptiles have the dorsal fin (like dolphins).
Ichthyosaur head ends with a long snout, formed by the upper and lower jaw. Jaw bones themselves were heavy, which probably helped this dinosaur crush stronger shells and shells of marine invertebrates, as well as holding a big fish, which they swallow without chewing. His teeth were replaced ichthyosaurs throughout life, presumably every year, but not in sync (like crocodiles). Everyone ichthyosaurs had large eyes (up to 20 inches in diameter) that are protected by a bony ring. This suggests that these reptiles were nocturnal predators.
Skin ichthyosaurs, in contrast to that of other reptiles, were not at all covered with scales (which would create additional friction with the water and prevented them to swim quickly). Perhaps it is better to slip was covered with slime (like fish). Even at her, apparently, had some skin receptors, such as the lateral line in fish (a body with which they feel electric shocks and thus determine the chemical composition of water depth and the presence of a number of “neighbors”), to that show signs of nerves and blood vessels in the skull.
Many believe that ichthyosaurs were Ovoviviparous (ie young hatch from eggs while it was still in the womb). Indeed, the skeletons were found of such mothers with young lizards inside. However, the cub was placed in the body of her that a strange way – closer to the head and not the tail. However, it is possible that this is just a result of strains already disposed of the remains.
Also, it is not clear whether ichthyosaurs warm-blooded (that dinosaurs were such, read the article “Scientists have” paint “the dinosaurs”). Imprints on the bones of these reptiles suggest that the most likely, these reptiles dominated the white muscle, which is peculiar to cold-blooded. But at the same time, the spongy bone structure and traces of an extensive network of capillaries, which were found in ichthyosaurs, it is characterized by warm-blooded. Therefore, most paleontologists are inclined to think that ichthyosaurs were a “medium variant” like modern bats – they could maintain a constant body temperature, but in a very wide range of vibration, it could change them within 10 degrees.
Dimensions ichthyosaurs were very different. The largest of these, shonizavr, reaching a length of 23 meters (the skeleton was found in Canada in 2003). But those were only a whopper Triassic ichthyosaurs, in the Jurassic they were “crushed” to 10-15 meters (so that the individual was found, probably a teenager), and Cretaceous ichthyosaurs last only grows to eight or nine feet. The reduction in size suggests that in the Late Jurassic – early Cretaceous group, apparently suffered the effects of some other animals. This is evidenced by a sharp change in the last ichthyosaur habitat: in Triassic and Jurassic they live in open waters, it has been in the middle Cretaceous go out and crammed into coastal waters.
It is not excluded that this crisis was associated with a “change of dominants” from the middle Jurassic in the open waters penetrate distant relatives of the ichthyosaurs, plesiosaurs. This group came later, at the end of the Triassic, but a long time these were the inhabitants of coastal lizards. However, in the Middle Jurassic of them appear maneuvering large creature with a huge (up to two meters in length), skull, which were quite capable of eating ichthyosaur (incidentally, the latter since the Middle Jurassic is often found injuries inflicted by the teeth of these giants.)
Fleeing from them, ichthyosaurs were grow shallow (to go for the lower boundary of the optimal size of the prey and predator to become the very small change, which time and a waste not worth it), but after all cleared out of the dangerous open waters in the quiet coastal waters. However, 95-89 million years ago and it has ceased to be quiet – then begins an evolutionary blossoming in a group of sharks, there are predators, similar to the modern white shark that ichthyosaurs could not fight on equal terms. Sharks are more agile and mobile than reptiles (because their skeleton is not composed of heavy bone and cartilage of the lung). So, most likely, ichthyosaurs have finished this shark, and in the same way as mammals have plagued the dinosaurs (for details, see the article “Who killed the dinosaurs?”) – They are attacked mainly by small cubs, which adults do not possess the collective skills of the dolphin’s defense (since they were much more “blunt”), simply could not defend. So, unable to cope with the new predator, ichthyosaurs disappeared from the face of the earth, leaving only a memory in the form of fossilized skeletons (no descendants of this group is not left). One of these, and found recently by German paleontologists. It is interesting that the skeleton is the most well-preserved remains of dinosaurs in the grave are present in virtually all of the bones. Perhaps it was this skeleton and shed light on many dark moments in the history of these marine reptiles.

 
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Posted by on September 30, 2011 in Dinosaurs

 

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