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新西兰代写essay:哺乳动物

新西兰代写essay:哺乳动物

哺乳动物也出现在中生代,体积小,小于33lbs直到新生代被称为“哺乳动物时代的黎明。新生代被称为哺乳动物的时代,因为灭绝的群体,给了哺乳动物繁荣和多样化的机会。首先对哺乳动物演变而来的时候,有therapsidsby三叠纪是到达终点。
哺乳动物的起源与进化
哺乳动物的第一次出现是在石炭纪末synapsids形式。合弓类开始像在中三叠纪哺乳动物。最初的哺乳动物–像–爬行动物真小,例如dicynodots少数例外(兽)在形状像gorgonopsians是食肉牛,和尖牙的形状,tritylodonts小食虫类哺乳动物。在三叠纪时期的单弓组演变成最初的哺乳动物中。
哺乳动物的形态是由今天哺乳动物共享的某些特征所识别的.。这包括功能,僵化的根本功能,不要僵化的。例如:温血、毛皮、汗腺、乳腺。特征,并帮助我们识别哺乳动物一样的生物包括:只有两套牙齿,牙齿冠像专业切牙,尖牙,磨牙和前磨牙,下颌由单一的齿骨和骨,包括呼吸用隔膜(大英百科全书,2014)。
一些侏罗纪和白垩纪的哺乳动物主要类群是:
原兽亚纲:又名Australosphenida。他们是最早从monotromes早白垩世。独特的特征包括粗短的腿和尾巴,庞大的姿势和繁殖产卵。他们不是一个占主导地位的群体,但适度存在于特定领域的行星。
Eutriconodonta:繁殖方式仍不清楚这属。大小介于小负鼠獾大小。他们在侏罗纪和白垩纪时期是杂食动物,食肉动物是很常见的。该属在白垩纪后灭绝。
后兽亚纲:一个中生代时期常见的属,一些哺乳动物很小但有些是獾的大小和代表当时最大的哺乳动物。最古老的化石可以追溯到早白垩世后兽亚纲。

新西兰代写essay:哺乳动物

Mammals also appeared during Mesozoic era and were small in size, less than 33lbs until the dawn of Cenozoic which is termed as the “Age of mammals’. Cenozoic is termed as age of mammals because extinction of groups, gave a chance to mammals to flourish and diversify. First of the mammals got evolved from Therapsidsby the time when Triassic period was reaching its end.
Origin and Evolution Of mammals
First appearance of mammals was in the form of Synapsids in the late Carboniferous period. Synapsids started looking like mammals in the mid-Triassic period. Initial mammal –like – reptiles were really small with a few exceptions for e.g. Dicynodots (Lystrosaurus) were cow like in shape, Gorgonopsians were carnivorous and fanged in shape, Tritylodonts were tiny insectivorous mammals. By the middle of Triassic period one of the Synapsid group evolved into the very first mammals.
Mammalian forms are identified by some features which are shared by the mammals of today. This includes features that fossilize and the ones which don’t. Examples of features that don’t fossilize include: Warm blooded, covered with fur, sweat glands, and mammary glands. Features that do fossilizes to help us to identify the mammalian like creatures include: Only two sets of teeth, specialized teeth and development of crown like incisors, canines, molars and premolars, lower jaw made up of single bone and comprising of dentary and respiration using diaphragm(Encyclopedia Britannica, 2014).
Some major groups of mammals in Jurassic and Cretaceous period identified are:
Prototheria: Also known as Australosphenida. They were the earliest from of Monotromes from early Cretaceous period. Unique features include stumpy legs and tail, sprawling posture and reproduction by laying eggs. They were not a dominant group but moderately present in specific areas of the planet.
Eutriconodonta: Mode of reproduction is still unknown for this genera. Size ranged from tiny to opossum to badger sized. They were common in Jurassic and cretaceous period and were omnivores and carnivores. This genera got extinct after the cretaceous period.
Metatheria: One of the common genera of Mesozoic period, some mammals were really small in size but some were badger sized and represented the largest mammals of that time. Oldest fossil dates back to early cretaceous for Metatheria.