Evolutionary adaptations have allowed mammals to survive in places like the cold polar zones and alpine mountain habitats where few other vertebrate animals can live. The success of mammals in colonizing the earth is perhaps best illustrated by one particular species capable of altering its environment on a global scale: the human. The remainder of this unit will focus on marine mammals —mammals that live in or near the ocean.
There are known species of marine mammals. Marine mammals include whales, sirenians, pinnipeds, the marine otter, the sea otter, and the polar bear. There are also several groups of marine mammals that have gone extinct.
These include marine sloths, marine bears, and an entire order of hippo-like mammals called desmostylians.
This document may be freely reproduced and distributed for non-profit educational purposes. Skip to main content. Search form Search. Join The Community Request new password. Main menu About this Site Table of Contents. Home Biological Mammals What is a Mammal? What is a Mammal? They live in nearly every available habitat on Earth—including deep seas, tropical rainforests, and deserts—and they range in size from one-ounce shrews to ton whales.
What exactly is it that makes a mammal a mammal, and not a reptile, a bird or a fish? There are eight main mammal characteristics, ranging from having hair to four-chambered hearts, that set mammals apart from all other vertebrates.
All mammals have hair growing from some parts of their bodies during at least some stage of their life cycle. Mammalian hair can take on several different forms, including thick fur, long whiskers, defensive quills, and even horns. Hair serves a variety of functions: insulation against the cold, protection for delicate skin, camouflage against predators as in zebras and giraffes , and sensory feedback as with the sensitive whiskers the everyday house cat.
Generally speaking, the presence of hair goes hand-in-hand with a warm-blooded metabolism. What about mammals that don't have any visible body hair, such as whales? Unlike other vertebrates , mammals nurse their young with milk produced by mammary glands, which are modified and enlarged sweat glands consisting of ducts and glandular tissues that secrete milk through nipples.
This milk provides young with much-needed proteins, sugars, fats, vitamins, and salts. Not all mammals have nipples, however.
Monotremes such as the platypus, which diverged from other mammals early in evolutionary history, secrete milk through ducts located in their abdomens. Though present in both males and females, in most mammal species, mammary glands fully develop only in females, hence the presence of smaller nipples on males including human males. The exceptions to this rule are the Dayak fruit bat and the Bismarck masked flying fox.
Males of these species have the ability to lactate, and they sometimes help to nurse infants. The lower jawbone of mammals is composed of a single piece that attaches directly to the skull. This bone is called the dentary because it holds the teeth of the lower jaw.
In other vertebrates, the dentary is only one of several bones in the lower jaw and does not attach directly to the skull. Why is this important? The single-pieced lower jaw and the muscles that control it endows mammals with a powerful bite.
It also allows them to use their teeth to either cut and chew their prey like wolves and lions , or grind down tough vegetable matter like elephants and gazelles. Diphyodonty is a trait common to most mammals in which teeth are replaced only once throughout an animal's lifetime.
The teeth of newborn and young mammals are smaller and weaker than those of adults. We are undergoing some spring clearing site maintenance and need to temporarily disable the commenting feature.
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Follow Twitter Instagram Facebook. What makes an animal a mammal? Are human beings mammals? Do all mammals give birth to live young? Wonder What's Next? Try It Out Want to learn eve more about mammals? Check out the following activities with a friend or family member: Visit National Geographic's Mammals video page to see all sorts of different videos featuring mammals!
Choose one or two of your favorite videos to share with a friend. What do they think? Do they like mammals as much as you do? What facts about mammals do you learn from the videos you watch? What is the Oldest Mammal Fossil? Find out when you visit sciencechannel. Can you imagine being the scientist to make such a discovery? Do you think you would ever want to be a paleontologist? Why or why not? Up for a challenge?
Write a story about your favorite mammal. First, choose a mammal. It can be any mammal! Do you have a favorite animal that also happens to be a mammal? If so, perfect! Do some Internet research to learn at least five facts about your chosen mammal, and then write a short story that somehow weaves those five facts into the storyline.
Be sure to share your story with a friend or family member! Did you get it? Test your knowledge. What are you wondering? Wonder Words fish bone ear hair milk egg munch young mammal birth common gland flabbergasted mammary vertebrate characteristic monotreme platypus Take the Wonder Word Challenge. Join the Discussion. Dec 4, Madisoan Nov 15, If a whale or any sea creature are mammal then why do they not have hair. Nov 19, Oct 22, I am learning about mammals in class.
May 15, Dimitris May 10, What is the smallest and cutest mammals in the world? Just asking:. May 10, Hasan May 9, Why do some mammals lay eggs instead of having live young? Jan 27, Why do all mammals have hair? Just wondering! Jan 30, Avalon Nov 17, Nov 18, Sep 14,
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