Mesosaurus
Skeletal limestone in the Irati Formation ( Paraná Basin, Brazil) in the Geological Museum of Copenhagen
- Mesosaurus tenuidens GERVAIS 1865
Mesosaurus ( "middle lizard" ) is an extinct genus of reptiles from the time of the early Permian ( Artinskian, before 290-279 million years ago). Mesosaurus was aquatic and could not likely to be particularly good move on land. He lived on and in a vast lake or inland sea, or of which covered present-day southern Africa and eastern South America.
The reptile family, is provided in which Mesosaurus that Mesosauriden, are based on current knowledge, the first amniotic, that is, of waters in principle independent fertile land vertebrates, who returned to an almost purely aquatic life - a development direction in the further course of the earth's many other lines of amniotes smashing ( and Others Sauropterygier, Thalattosaurier, penguins, seals ). In addition, they are the only secondarily aquatic amniotes of the Permian. Only in the early Triassic occur geologically next younger representatives in the fossil record with the ichthyosaurs.
- 2.1 nutrition
- 2.2 Reproduction
Features
Mesosaurus was a relatively small, lean reptile, which reached a length of up to one meter. However, most of the specimens found to have a length of only about 40 centimeters. The jaws are very narrow and much elongated, about the way in today's gavials. They are equipped with a variety of needle-shaped and partly very long teeth fitted, the tips of which were addressed during his lifetime relatively strong outward, so that the teeth were slanted in the jaw. The neck has 12 vertebrae and is extended, which probably increased the freedom of head movement.
As an adaptation to the aquatic lifestyle they had a flattened tail rudders for propulsion in the water, similar to own it today's crocodiles. Since the limbs not to carry the hull ashore as rural dwellers, mainly served to the bones are slightly reduced in the hand and the tarsi Mesosauriden. In addition, hands and feet are constructed paddle -like, and the feet are relatively large and probably served also the propulsion. Probably stretched between the fingers and toes webbed, made maybe the soft tissues of the hand and foot even downright " fin ", similar to today's sea lions.
The ribs are thickened in comparison to similarly sized terrestrial reptiles - a modification which is referred to as Pachyostose. Pachyostose occurs as a characteristic element in many other secondary aquatic vertebrates (eg particularly evident in today's sea cows ). The thicker and therefore heavier bones provide a reduced buoyancy in the water.
Temporal window
Many extinct and living reptiles groups are distinguished by characteristic holes in the rear upper and lateral aspects of the skull from so-called temporal or temporal window. Even with Mesosaurus such temporal windows were already described in the first half of the 20th century. However, in subsequent studies it has been found that the skull bones of Mesosaurus are very thin and fragile in this area, and that previous observations of pace Ralf star it was based, that these thin-walled skull parts were damaged during fossilization, Mesosaurus therefore possessed no tempo Ralf Rochester. However, single - Mesosaurus copies were recently re- described, which should have a tempo Ralf Rochester.
Way of life
Nutrition
Mesosaurus was a hunter who actively stalked his prey in the open water, similar to the behavior of today's hunting seals and toothed whales. The needle-like teeth were but probably not the skewering of prey, but as Reuse apparatus for trapping single small free-swimming crustaceans and fish that were held in the mouth when the animal closed the jaw and through pressing the water between the meshing teeth out of the mouth. The main food of Mesosaurus was likely composed of krill -like small crustaceans of the extinct family Notocarididae.
Reproduction
The discovery of a Mesosaurus embryos with largely ossified skeleton in the body cavity of an adult animal suggests that Mesosaurus as some marine reptiles of the Mesozoic era, could have been viviparous. Not less likely it is that he took eggs on the beach, much as do today's sea turtles. Unlike the turtles Mesosaurus the embryo, however, was already developed at the time of oviposition relatively far, so angebrütet was already in mother animal. Since these eggs were quite large compared to the adult animal, a female could carry only one or two eggs in it, so from a reproductive cycle resulted in only a few offspring. Therefore, it is possible that Mesosaurus something like brood care operation to improve the chances of survival of these few offspring.
System
Due to different interpretations of the skull building for the presence of temporal windows Mesosaurus was in the 20th century, first as Diapside and thus as a relative of most living reptiles and dinosaurs, then as Synapside and thus as a distant relative of mammals, and more recently as " Anapside " (see classical concept of Anapsida by Caroll, 1988 ) is considered. However latter group and the structure underlying concept form the actual course of evolution, and thus the actual relationships of amniotes do not correctly or has the meaning of the non - present one of temporal openings decreased for the classification of amniotes. More recent cladistic studies showed that Mesosaurus is apparently related to a number of other, mainly Permian and now entirely extinct reptiles, which are referred to as para Mesosauriden including reptiles. The similarities in physique, the Mesosaurus due to its aquatic life with both extinct as a living today aquatic reptiles, such as the Thalattosauriern or crocodiles, which is the result of convergent evolution.
The closest relatives of Mesosaurus are the other genera in the family Mesosauridae: Brazilosaurus and Stereosternum. From Mesosaurus even two species have been described: M. tenuidens and M. brasiliensis. A third type, M. capensis, was originally a representative of a separate class ( Ditrochosaurus ) described. Today, M. ( = " Ditrochosaurus " ) capensis, and M. brasiliensis regarded as junior synonyms of M. tenuidens. The time may also Stereosternum tumidum, the only species of this genus, regarded as Mesosaurus type.
The holotype of the species Mesosaurus tenuidens, which in turn is type species of the genus Mesosaurus, was in the 1840s in the " Griqualand " (very likely, these were to the Griqualand West - now part of the Northern Cape Province of South Africa ) by the brother of a French trader discovered in a Griqua hut. The rock plate with the Fossil served the inhabitants as a cover for their cooking pot.
Deposits and fossil preservation
Mesosaurus fossils occur in southern Africa in the Permian Whitehill Formation of the Karoo Basin and in Brazil and Uruguay in the Permian Irati also or Mangrullo formation of the Paraná Basin ago. They occur in these layers z.T. en masse, mostly in the form of whole or partial, flattened skeletons.
Whitehill, Irati and Mangrullo lineup consist of dark shales. The skeletons of Mesosaurus have been transformed into these shales to a very soft material and are often already largely weathered out, leaving only footprints in the rock remain. Some sections of the Irati Formation ( Assistência - Subformation ) consist of yellowish- white limestone. In these limestones, the fossil record of the bone is much better.
The sound and limestones of the White Hill, Irati and Mangrullo lineup is the deposits of a vast lake or inland sea ( " Mesosaurus Sea " ), where the limestone coastal, shallow waters and the mudstones coast farther, deeper waters represent.
Mesosaurus and plate tectonics
The distribution of the genus in the Mesosaurus located on both sides of the South Atlantic regions of eastern South America and southern Africa, which are separated by thousands of miles of open ocean today from one another, the German scientist Alfred Wegener was already known. She served him as an important argument in support of the 1915 drawn up by him theory of continental drift. The spread of Mesosaurus fossils on both sides of the Atlantic and the similarity of the rocks that contain them, are a clear indication that were united in life by Mesosaurus Africa and South America in the supercontinent Gondwana. Gondwana broke only after the extinction of the Mesosaurier apart due to the mechanisms of plate tectonics caused by the movements of the lithospheric plates and Africa and South America since then drift away from each other.