关 键 词： 小学四年级 2100字
字 数： 2100字作文
本文适合： 小学四年级
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本作文是关于小学四年级2100字的作文，题目为：《Primamalario Picis》，欢迎大家踊跃投稿。
这是近期的科学作业。科学知识我们已经学过石头的分类，石头的产生，生物演变，地形变化，地表变化，化石种类，地震以及火山的形成和规律，放射性物质考古，石头绝对年龄（用于岩石），石头的像对年龄（适合沉积石），海底板块运动，考古各种定理。 <----> 而这项作业则综合了上述所有知识。题目是：给你的一个时间段，那么自己想象出一种生物，一定是现在不存在的，而且考古历史中没有被发现的。假设你就是发现这个生物的化石的考古学家，写一篇新闻报告，阐述你是如何找到化石，什么样的化石（大概描述），化石的地理位置（这方面要查很多资料），你发现的生物有什么特征（要符合当时的时间段普遍特征），长什么样子，多大，吃什么，被什么吃，何时灭绝的（查大量资料）。 <----> 而我的时间段恰好是是古生代的志留纪，很远古，资料少，难度系数更大。查了两周资料左拼又凑才写得新闻报告。我打算发现的生物是：一条叫做primamalario picis的鱼（名字瞎起的，越接近拉丁文越好），这条鱼是第一个由下颌的鱼，也是早期的肉食动物。 -Sun times evening news- <---->PRESS RELEASE <---->A discovery of Primamalaio Picis in North America <----> ——World’s first jawed fish appeared in Silurian period <----> <----> March, 14, 2008. Jinglu Sun, a former member of Ligon middle school, now a paleontologist, has recently discovered a fossil of an unknown fish in the Mojave Desert of Las Vegas. According to the age of this fossil, this fish was determined to be in Silurian period. This was the oldest jawed fish ever found. <----> <---->Dr. Sun was going into the desert for a trip and looking for traces of ancient animals at the same time when this fossil came into view. It was decided that this new specie will be named the Primamalaio Picis (meaning the world’s first known jawed fish). It is known as the Jawzish today. <----> <---->During the Silurian period, Supercontinent Gondwana continues heading towards South Pole. Siberia, Laurentia, Baltica stay at the equator. At this time, the planet was in greenhouse phase, temperature was suitable. Deglaciation caused rise in sea level so that North America was still covered in shallow sea, the Impetus Ocean, and was rich in marine. Brachiopods and crinoids was wide spread in the ocean, mollusk and other jawless fish was also common. And this contributes to the existence of Primamalaio Picis, because with its jaws, it can tear flesh of its prey. <----> <----> This fossil aged around 440 million years ago, during the Paleozoic era, Silurian period. This cast fossil was composed of limestones that was deposited in the Mojave Desert later on. Fortunately, 80% percent of the fossil material was found. The fossil measured 24.9cm from its snout to its upper trunk and 13.7 cm wide, including the fish’s head, spine, bones, the fins and even the teeth! But its lower jaw was missing and the part where its tail originally should be was completely sliced off. “Because we could tell from the upper jaw and the two long sharp teeth that there must have been a lower jaw and two more lower teeth as well, Primamalaio Picis is one of the world’s earliest carnivals.” Says Dr. Sun. “And even without its tail in the fossil, we could still tell the fish would size around 30 cm long, relatively the size of a carp.” <----> <---->Primamalaio Picis had a rather large, bullet-shaped bony head, long roundish reptile-like body and chubby tail. Despite its large body, it had very small eyes and only four sharp teeth. There are fins at both sides and up the where the spine is. The fish is quite long so that it can be as flexible to circle its tail, forming this wavy line. Since no skin was preserved, we could not be sure how its coloration was. But since it was not a tropical fish, nor a small one, so it’s most likely to be silverfish- grayish in color, perhaps with stripes too, so it could blend into the background, making it hard to notice. Despite the fact that it was a pretty large and strong fish, and no other fish was big or strong enough to eat it, it still must also have had lots of rows of scale in order to protect itself from the natural environment such as hard objects and reefs. Over all, Primamalaio Picis has the structure of a bone fish but an appearance/ figure of a shark. <----> <---->As mentioned earlier, Primamalaio Picis lived in shallow seas with a variety of other marine while the planet was in green house phase. The climate is warm and suitable for all the fishes, sunlight was plentiful for algae and weed plants to grow, and this provides food for small phytophagous fishes such as birkenia. And all those small fishes provide food for jawed fish like Primamalaio Picis. Of course, it is not the only living thing during the Silurian period; other organisms such as brachiopods, crinoids and mollusks all share this habitat. <----> <---->There was a mass extinction at the end of Devonian period caused by Glaciations and meteorite impact that wiped out 30% percent of the animals. Plants couldn’t get enough sunlight, small fishes died out and Primamalaio Picis eventually disappear due to lack of prey. <----> <---->“We’re not sure how this all ends, but Primamalaio Picis can actually be ancestors to modern shark.” Says Dr. Sun <----> <----> ### <---->If you’d like more information about this topic, or to schedule an interview with Dr. Sun, please email her at jinglu-sun@hotmail.com