Thursday, 26 January 2012

DEVONIAN PERIOD

DEVONIAN PARK

By: Uxía Méndez and Raquel Ruda    4ºB


DEVONIAN PARK

It is a geologic period of the Paleozoic era, and it is located between the Silurian period and the Carboniferous period. The word ‘Devon‘comes from England, where it is very common to find rocks which appeared during this period. The Devonian period was the first time in which terrestrial animals appeared (amphibians and reptiles); some new plants came out too. In this era, fish appeared, being the sharks the most predominant and numerous than years before. Birds and mammals didn't existed either.The climate was warm during this period and glaciers didn’t exist.

LIVING ORGANISMS OF THE DEVONIAN PARK

  •  Coccosteus:




 


It was a fish which lived during the Devonian period. Their fossils appeared in Europe and North America in freshwater terrains. Most of them measured around 20 or 24 centimetres long, although the biggest ones reached the 40 centimetres long. They had an internal joint between their neck and the skull which allowed them to open their mouth even wider to help them to catch bigger animals; it was also a way of helping the entrance of water inside the gills to breathe. Normally, they were fed with organic material found in mud which entered through the gills. They belong to a family called coccosteidae.



  • Trilobites:

They are the remaining fossils from a kind of extinct marine arthropods which appeared around the entire planet Earth. They disappeared over 250 million years ago, during the Permian-Triassic. They lived 300 million years ago in the Palaeozoic era. They had a flat body which was divided into three main parts: cephalon (head), thorax (body) and pygidium (tail). They had very evolved eyes in their heads; this was probably one of the reasons they developed in a so successful way. They were the first animals in developing those complex eyes. They lived in the mud at the bottom of marine terrains from which they obtained the aliments.  





  • Acanthostega:

It lived in the marshlands over 370-360 million years ago, at the end of the Devonian. The first remains of this specie were found in Greenland. It was the first tetra pod in the period. It was an animal with similar characteristics to sarcopterygii fish and amphibians. It lived inside the water because it couldn’t support the pressure of their weight due to their lack of articulations in their wrists and ankles. As many tetra pods did at that time, it combined lungs and gills. They measured more than a half meter, they had eight fingers and their feet were fin-size, helping them to move inside the water.





  • Equisetum:

It is also called horsetail. It belongs to the family of vascular plants which reproduces by spores instead of seeds. 

This fossil works for us as a clue know how was the flora million of years ago, because it was the most diverse and significant plant of the Palaeozoic forests. In these plants, leaves are in a less amount and don’t realize the photosynthetic process. 

Most of them grow until they reach 1.5 meters tall, although the giant horsetails could reach 8 meters tall.







  • Ammonites:
 It is an extinct invertebrate mollusc which nowadays is represented as a good guide fossil. These fossil shells used to have the shape of a spiral. They had variable sizes (they could measure meters or centimetres). We don’t have much information about its way of life because it and its relatives are extinct. They used to live in the upper parts of the sea. Their way of protecting themselves was to spread a squirting ink to their predators. That’s the reason why many of them have been found with tooth marks. They had soft bodies and lived inside the shell. In this period they used to be small but they started to grow million years later.


  • Acanthodii:


It was a fish which lived during this period and had bony fins and a cartilaginous skeleton. They were known as “spiny sharks” due to that they had spines in their fins as sharks did. They looked similar to sharks but they were covered by many rhomboid-like scales. They were the earliest known jawed vertebrates. Firstly they lived in marine water, but they started to travel to freshwater. Some of the remains of their skeleton were found in sedimentary rocks. They appeared 50 million years ago before the first shark’s appearance so they were the predecessors of nowadays sharks.

They are classified in three main groups: Climatiiformes, Ischnacanthiformes and Acanthodiformes. 



                                                                                                  

  • Archaeopteris:

It was an extinct giant plant which lived during the end of Devonian and beginning of Carboniferous periods. Their fossils belong to a group of plants called Brogymnospermgoytha. This means that they were one of the first ones on developing seeds. They have similar characteristics with conifers and they are considered the predecessors of modern trees. At the beginning of their appearance, the world was mostly covered by small plants. They started to grow making forests. These produced shadows which protected some zones from the sun. As time passed, small formations of water, where new species lived, were formed. Their leaves served as food for fish. In addition, new seasons appeared too. When leaves fall into the water (because of the change of seasons), bacteria decomposed it and consumed the oxygen contained in the humid terrains. Fish were lack of it, marking the beginning of the first gill-lung animals.




  • Wattieza:

It was a genus of prehistoric trees which appeared during the around 390 million years ago.

Wattieza fossils are the earliest plant ones found, which means that they are the earliest known trees. 
They could be more than eight meters tall and their branches reached 13 cm of diameter. They had fronds rather than leaves and reproduced by spores. 
They lived in what nowadays is called South America, although some of their remains were located in New York.





  • Stethacanthus:



It’s a type of prehistoric shark whose nickname was ‘ironing board shark’. This name was given to it because males had a strong fin on their heads. They probably served as a defence against predators or, due to their lack of presence in females, as a sexual courtship. 

They lived both in saltwater and freshwater; most of their fossils have been found in Europe and North America. They moved quickly under the water and ate fish, although they also were preys of bigger animals such as Dunkleosterus.






                                                                 


  • Dunkleosterus: 

He was also called Dinchthys, which in Latin means ‘the terrible fish’. It was probably the most dangerous predator during the Devonian period. He ate fish animals such as Stethacanthus or Hynerpeton (it was similar to Acanthostega). 
He had a hard non-flexible head, which seemed to be covered by a kind of frame. The rest of their muscular body was covered by scales. Their size varies from more or less 6 to 10 meters long, weighting 1 ton. One of the reasons they were so lethal, were their jaws; instead of teeth, they had sharp blades made of bone which tear their prey to pieces like a scissor cutting a paper. They used to hurt it and kill it before eating it.

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