Groups
Marsupials (Metatheria)
Marsupials are a large group of mammals that have two groups: American marsupials and Australian marsupials. The American marsupials can be found in North, Central, and South America which are the opossums and shrew opossums. Australian marsupials are found in Australia and New Guinea and kangaroos, wallabies, koalas, wombats, bandicoots, and many other animals make up this group. Overall, there are about 334 species of marsupials. Most species (about 235) are found in Australia and New Guinea where no placental mammals exist. Marsupials have a very short gestation period and, like placental mammals, still develop in a placenta but barely rely on it for nutrients unlike placental mammals. Instead, marsupials are born extremely early and spend their time growing inside the pouches of their mothers'. The size of marsupials vary; the long-tailed planigale is the smallest marsupial at 2 to 2.3 inches. Whilst the largest marsupial, the red kangaroo, is about 3 to 5 feet long. Marsupials have two reproductive tracts. Placentals have only one.
Source(s): http://animals.about.com/od/marsupials/a/marsupial-facts.htm, http://www.ferris.edu/card/kids_corner/marsupials.htm, http://www.ucmp.berkeley.edu/mammal/marsupial/marsupial.html
Marsupials are a large group of mammals that have two groups: American marsupials and Australian marsupials. The American marsupials can be found in North, Central, and South America which are the opossums and shrew opossums. Australian marsupials are found in Australia and New Guinea and kangaroos, wallabies, koalas, wombats, bandicoots, and many other animals make up this group. Overall, there are about 334 species of marsupials. Most species (about 235) are found in Australia and New Guinea where no placental mammals exist. Marsupials have a very short gestation period and, like placental mammals, still develop in a placenta but barely rely on it for nutrients unlike placental mammals. Instead, marsupials are born extremely early and spend their time growing inside the pouches of their mothers'. The size of marsupials vary; the long-tailed planigale is the smallest marsupial at 2 to 2.3 inches. Whilst the largest marsupial, the red kangaroo, is about 3 to 5 feet long. Marsupials have two reproductive tracts. Placentals have only one.
Source(s): http://animals.about.com/od/marsupials/a/marsupial-facts.htm, http://www.ferris.edu/card/kids_corner/marsupials.htm, http://www.ucmp.berkeley.edu/mammal/marsupial/marsupial.html
Monotremes (Monotremata)
Monotremes make up six species and there are two "main" animals that are part of this group: the platypus and the echidna. These animals can only be found in New Guinea and Australia. Monotremes are considered "primitive" mammals because they lay eggs, do not have any teeth when they are adults, and have mammary gland openings rather than mammary gland nipples on their bodies. They also have a poison spur but the echidna's is nonfunctional. Monotremes also lack a structure in their brains called the "corpus callosum" which connects the right and left hemispheres of the brain together. Another unusual trait that they have is electroreception, which means they can detect prey via electrical fields generated by their muscle contractions. The platypus has the strongest sense of electroreception compared to the echidna and heavily relies on it to hunt prey. But just like most other mammals, they have a low rate of reproduction, have hair, are warm-blooded, have a fairly high metabolism, and look after their young until they are old enough to live independently. Young monotremes have teeth that is different from placentals and marsupials; it is believed they developed their teeth independently.
Source(s): http://thewebsiteofeverything.com/animals/mammals/Monotremata/, http://www.ucmp.berkeley.edu/mammal/monotreme.html, http://animals.about.com/od/monotremes/p/monotremes.htm
Monotremes make up six species and there are two "main" animals that are part of this group: the platypus and the echidna. These animals can only be found in New Guinea and Australia. Monotremes are considered "primitive" mammals because they lay eggs, do not have any teeth when they are adults, and have mammary gland openings rather than mammary gland nipples on their bodies. They also have a poison spur but the echidna's is nonfunctional. Monotremes also lack a structure in their brains called the "corpus callosum" which connects the right and left hemispheres of the brain together. Another unusual trait that they have is electroreception, which means they can detect prey via electrical fields generated by their muscle contractions. The platypus has the strongest sense of electroreception compared to the echidna and heavily relies on it to hunt prey. But just like most other mammals, they have a low rate of reproduction, have hair, are warm-blooded, have a fairly high metabolism, and look after their young until they are old enough to live independently. Young monotremes have teeth that is different from placentals and marsupials; it is believed they developed their teeth independently.
Source(s): http://thewebsiteofeverything.com/animals/mammals/Monotremata/, http://www.ucmp.berkeley.edu/mammal/monotreme.html, http://animals.about.com/od/monotremes/p/monotremes.htm
Placentals (Eutheria)
Placentals are the most diverse and dominant group of mammals. There are over 5,000 species, most of them being rodents and bats. Elephants, humans, dolphins, whales, dogs, cats, shrews, armadillos, sheep, horses, and many others all make up this group. The young of placental animals are nourished before birth inside their mother's uterus by an organ attached to the uterus wall, known as the placenta. The placenta plays a massive role in nourishing the young of placental mammals. This organ is derived of the same stuff that surrounds the embryos of reptiles, birds, and monotremes. Placentals are arguably the dominant group of all terrestrial life on earth; some of the most deadliest (lions, bears), largest (elephants), and smartest (humans, dolphins, elephants) animals belong in this group. The body temperature of placentals is slightly higher than that of monotremes and marsupials. But they have hair, are endothermic, and have a cortex. Since placentals are the dominant terrestrial group, they have filled many niches from small scavengers to large and powerful carnivores. The largest placentals became extinct about one million years ago. They included the giant rodents, mammoths, saber-tooth tigers, and several others. The biggest wave of extinction occurred about 50,000 years ago when humans began to spread across the planet and over-hunted many species to their extinction.
Source(s): http://www.ucmp.berkeley.edu/mammal/eutheria/placental.html, http://www.britannica.com/EBchecked/topic/462577/placental-mammal, http://www.wisegeek.com/what-are-placental-mammals.htm
Placentals are the most diverse and dominant group of mammals. There are over 5,000 species, most of them being rodents and bats. Elephants, humans, dolphins, whales, dogs, cats, shrews, armadillos, sheep, horses, and many others all make up this group. The young of placental animals are nourished before birth inside their mother's uterus by an organ attached to the uterus wall, known as the placenta. The placenta plays a massive role in nourishing the young of placental mammals. This organ is derived of the same stuff that surrounds the embryos of reptiles, birds, and monotremes. Placentals are arguably the dominant group of all terrestrial life on earth; some of the most deadliest (lions, bears), largest (elephants), and smartest (humans, dolphins, elephants) animals belong in this group. The body temperature of placentals is slightly higher than that of monotremes and marsupials. But they have hair, are endothermic, and have a cortex. Since placentals are the dominant terrestrial group, they have filled many niches from small scavengers to large and powerful carnivores. The largest placentals became extinct about one million years ago. They included the giant rodents, mammoths, saber-tooth tigers, and several others. The biggest wave of extinction occurred about 50,000 years ago when humans began to spread across the planet and over-hunted many species to their extinction.
Source(s): http://www.ucmp.berkeley.edu/mammal/eutheria/placental.html, http://www.britannica.com/EBchecked/topic/462577/placental-mammal, http://www.wisegeek.com/what-are-placental-mammals.htm
Representative organism: African Elephant
- Scientific name: Loxodonta africana
- Class: Mammalia
- Group: Placental
- They live in various parts of Africa in savannah zones
- Their average lifespan is 70 years
- Their diet mostly consists of grass, leaves, bamboo, bark, and roots
- Female elephants travel in groups called herds usually led by the largest and strongest female, known as the matriarch
- Male elephants usually travel alone and will leave a herd once they are 12-15 years old
- African elephants are the largest land animals on earth
- They are also one of the most intelligent animals on earth, having a memory that spans many years. Elephants also capable of complex emotions
- Habitat loss and poaching has caused the population of elephants to decrease drastically
Source(s): http://www.defenders.org/elephant/basic-facts, http://animals.nationalgeographic.com/animals/mammals/african-elephant/