The Evolution of the Arthropod,

Baylee Flynn

Evolution is the process of something changing to adapt to an ever changing lifestyle. The Devonian Period went through changes, and so did the creatures who lived during that age. The Devonian Period is known as ‘The Age of Fishes’ because the dominant part of the living things in the Devonian Period, were fish. There was also a large amount of coral. Three animals that lived in the Devonian were the arthropod, brachiopod, and dunkleosteus. (Oldest to youngest.)

The arthropod was originally a soft-bodied creature that dominated the Devonian Period as well as others. Its name is derived from the Greek words arthros meaning jointed and podes meaning feet. The arthropod was first seen in the early Cambrian Era. (Www.palaeos.com/invertebrates/arthropods/arthropoda.htm, Pamala JW Gore. )It is the oldest animal out of the three. The arthropod has evolved many times throughout its lifetime, and this is one of the reasons that you can tell it is the oldest. Scientists are able to trace the arthropod back to the Cambrian Era because of this. The arthropod originally had many, many legs that each worked individually. Over time the arthropod evolved to have sets of legs that semi-fused together. They worked together to stronger. The arthropod’s body structure is unique to its species. It has a rigid, jointed exoskeleton which supports a muscle layer that protects the body. The arthropod’s exoskeleton sheds in a process called ‘molting’ at regular intervals. The length of the molting process is determined by the size of the arthropod. The larger the arthropod, the longer the molting process. During the molting process the arthropod becomes extremely vulnerable to predators and diseases. This is one major reasons that arthropods evolved to be smaller, and less prone to predators and diseases. They also evolved to have less frequent molting processes. Over time due to the decrease in frequency of molting the arthropod slowly began to turn into a hard bodied creature. They needed some way to protect themselves against the ever-changing climate and predator growth. Their soft bodies became impractical to the world they lived in, so the species of arthropods that could not evolve to gain hard bodies, died out, and the ones that did evolve to hard bodies, such as the trilobite, did survive to flourish the Devonian period. The arthropod differed from the other animals because it is the only one (in this essay) that molted. Also very few animals overall in the Devonian period molted. Unlike the brachiopod and dunkleosteus the arthropods do not have to live in water. As a matter of fact, some arthropods evolved to be able to survive with very little water. Another thing that sets the arthropod away from the others is that they remained very small unlike many of the other animals, which usually grew larger to dominate the Devonian. (http://www.ucmp.berkeley.edu/devonian/devonian.html, Larry Jean)

The brachiopod is another animal type that dominated the Devonian period. This is the middle animal out of my three. This is true, because scientists can calculate about when the brachiopod came about; somewhere around mid-Cambrian time. Some scientists believe that a few of the brachiopod’s ancestors are still alive today. Some may include the clam, and oyster (distant relatives.) The brachiopod looks a lot like modern day shellfish but differs from many of them in several ways. Brachiopod’s shells, unlike the clams, are two different sizes. Clam’s shells seem like a mirror image, while commonly the brachiopod’s shells are one large, and one almost have the size of that. Brachiopods also differ from other shellfish in another way. They feed differently. Brachiopods have tentacles that sweep microscopic food particles from the water, into their mouth. (http://www.palaeos.com/Invertebrates/Brachiopods/brachiopoda.htm, Christian C. Emig)

The final animal is the dunkleosteus. This animal is the youngest. It was first seen by scientist appearing in the mid-Devonian period. That is why, it is a relatively younger animal compared to the arthropod and brachiopod. Also the dunkleosteus had no evolved much during the Devonian, and this is another reason why it is younger. The ancestors before the dunkleosteus were not that much different from him. The dunkleosteus was a heavily armored and primitive fish. The dunkleosteus was not a shark, though some of its attributes led early scientists to believe it was. The dunkleosteus was a strange animal. It had razor-sharp cutting jaws, but no teeth. The dunkleosteus unlike the other two animals was a heavy carnivore. The brachiopod and arthropod ate small microscopic things but the dunkleosteus ate sharks and other large marine life. As well as eating large things, the dunkleosteus could get very large itself. Unlike the other marine life I’ve evaluated, this animal could grow up to 11 ½ feet in length. This armored fish is extremely different from the arthropod and brachiopod, but in some ways similar. Other than the fact that they all lived in the Devonian period, they also all were dominantly marine life. Also the arthropod and dunkleosteus both evolved somewhat in their outer skins. Just like the arthropod becoming a hard-body, the dunkleosteus gained more armored protection on the outside and developed a hinged neck. The hinged neck allowed it to grip on to its prey and slam it back and forth, causing its kills to go by quicker; and not letting the still moving animal turn the dunkleosteus’ head and break its neck. In both scenarios, the dunkleosteus comes out victorious. (Www.enchatedlearning.com/subjects/fish/printouts/Dunkleosteusprintout.shtml, Jeananda Collins)

In conclusion, the Devonian Period was full of marine life that evolved and adapted each day to new and ever-changing environment. The arthropod, brachiopod, and dunkleosteus were no exception to this concept.