lunes, 8 de junio de 2015

The extinction of dinosaurs


Sixty-five million years ago the dinsaurs died out along with more 50% of other life forms on the planet. This mass extinction is so dramatic that for many years it was used to mark the boundary between the Cretaceous period, when the last dinosaurs lived, and the Tertiary Period, when no dinosaurs remained.

The Cretaceous period


It's a period of geological  time scale from the late Jurassic period,about 146 million years to the early Paleocene period, about 65,5 billion years ago.




The Cretaceous is usually noted for being the last portion of the "Age of Dinosaurs", but that does not mean that new kinds of dinosaurs did not appear then. It is during the Cretaceous that the first ceratopsian and pachycepalosaurid dinosaurs appeared. Also during this time, we find the first fossils of many insect groups, modern mammal and bird groups, and the first flowering plants.
The breakup of the world-continent Pangea, which began to disperse during the Jurassic, continued. This led to increased regional differences in floras and faunas between the northern and southern continents.
The end of the Cretaceous brought the end of many previously successful and diverse groups of organisms, such as non-avian dinosaurs and ammonites. This laid open the stage for those groups which had previously taken secondary roles to come to the forefront. The Cretaceous was thus the time in which life as it now exists on Earth came together.

The evolution

Here are the three classidications of the types of skull retiles got to have:



The three typesd are called: Anapsid, Sinapsid and Diapsid. Anapsids and Sinapsids are considered authentic reptiles.

The collapse

First they were a small part of the fauna and barely visible until after the collapse of the rainforest. This collapse affectced large groups of animals. Amphibians were particulary affected, while the reptiles, better adaped to dry enviroments could be further developed.




                                    


When did they appear?


Reptiles appeared 310/320 milion years ago in moist land.


The oldest animal that can be considered as the first amniot is the "Casio".

The first unquestionable reptile is the Hylonomus. It is a little animal that looks
like a lizard. It is from 20 to 30 cm long. It had numerous sharp teeth wich tells us that it was insectivorous. Other examples are Westlothiana (currently considered to be closer to amphibians than amniotes) and Paleothyris, both with a constitution similar lifestyle presumably similar.


Què són els rèptils?



Els rèptils són amniotes de sang freda respiradors d'aire que tenen la pell coberta d'escates o closques, en lloc de pèl o plomes. Són tetràpodes i ponen ous amniotes, en què l'embrió està envoltat per la membrana amniòtica.


Són un grau evolutiu dels animals, actualment compren: tortugues, cocodrils, serp, llangardaixos i tuatares. A causa de la seva història evolutiva i la diversitat de les formes extintes, la validesa de la classe no és universalment acceptada en alguns cercles científics, tot i que en la pràctica, continua sent utilitzada per alguns biòlegs més laics, sobretot en els mitjans de comunicació. L'estudi dels rèptils, històricament combinat amb el dels amfibis, es diu herpetologia.