Why are dolphins considered mammals and not as fish? And what are 2 characteristics they share with mammals?

Answer 1

True fish have gills, are cold blooded, lay eggs, and do not have hair.

Mammals are warm blooded, breathe air, give birth to live babies, produce milk for their babies and have hair. Dolphins have all of those characteristics, though the hair is very minimal.

Answer 2

While all mammals do indeed breathe air, that is not a feature that defines the mammalian class - it is shared by all terrestrial vertebrates (i.e. reptiles, birds and mammals).

Live birth is also a feature of most (but not all) mammals - but is not a defining character.

Warm bloodedness is a poorly defined trait, with different degrees of endothermy present in different organisms. It is also not a specifically mammalian trait.

To be defined as a mammal, an organism must possess the following:

- The female produces milk to feed its young (the mammary glands that produce this milk give the group its name: Mammals). This is the main, number one, defining characteristic - shared by all living mammals (including egg-laying platypus and echidna). Unfortunately, it's hard to see in fossil forms.

- The possession of hair. Although some other groups of critters (including some insects) have what appears to be hair, no other animal has hair with the same form and origin. In some groups, such as whales, the hair is highly reduced, perhaps just a few chin whiskers. Again, this trait doesn't show up well in fossils.

- The lower jaw is a single bone on either side. All other groups of vertebrates have more than one bone on each side of the jaw.

- The middle ear contains 3 bones (ossicles). These bones were once part of the lower jaw (in reptiles), but became involved in transferring vibration to the tympanum. This is the absolute defining feature for mammals in skeletal remains. No other group of animals possesses this trait.

- The main artery leaving the heart curves to the left, becoming the aortic arch. In birds it curves to the right, and other groups of vertebrates have more than one main artery leaving the heart.

- Muscular diaphragm that separates the body cavity into two sections. Used in breathing.

Dolphins have all of these traits (even hair), and thus are considered mammals.

Answer 3

a lot of incomplete or slightly inaccurate answers there:
1. Lungs, not gills - yes; big difference, but not a mammal-defining one. Various non-mammals have lungs. Also, lungfish (hence the name).
2. Live birth - not true; there are sharks which produce live young. Some reptiles do, also. Not a defining characteristic for mammals. In fact, there are 2 mammals that lay eggs.
3. Milk; well sort of - mammals produce milk from 'mammary glands' (the primary defining characteristic). Fish don't produce milk at all. Pigeons make a sort of milk to feed their young, but from their crop, not from a mammary gland.
4. Warm-blooded - difference between mammals and fish, but not a defining characteristic of mammals (see birds)
I'd go with hair and mammary glands, myself. And hair is a an 'iffy' one, too.

Answer 4

1) They have lungs, not gills, meaning that they take their oxygen from the air, and not from the water.
2) Young are born live. This occurs underwater, tail-first, and they and must surface immediately to breathe.
3) Dolphin mothers produce milk for the young to feed on.

In short, dolphins are mammals because they have mammaries. ^^ That's where the term comes from.

Dolphins are also credited for having extremely high intelligence, and although that in an of itself does not determine mammalian status, it is a characteristic not shared by the vast majority of non-mammals.

Answer 5

They share many chracteristics with other mammals. The most prominant two would be. 1. Give birth to live young 2. Female produce milk for the nourishment of young

Answer 6

Dolphins are mammals. All mammals bear their young alive and breathe air.

Answer 7

Because they have give birth to live young instead of lay eggs.

Fish lay eggs.

Dolphins are mammals because they have actual intercourse, they bear live young, they breath with lungs, and they are warm blooded.

Answer 8

They have skin instead of scales. The have lungs instead of gills. They have a mammals brain. The females don't lay eggs and they provide milk for their young.

Answer 9

they are mammals because they gibe birth to their young and are not fish because their back fin is horizontal like other mammals in the water and they breathe air.

Answer 10

they are mammals because they give birth, like mammals and the females all have mammary glands