Mammals, birds, reptiles, and amphibians all have two pairs of . They are all tetrapods, or animals. In the fossil record, tetrapods first appeared about million years ago (Ma). Where did they come from?

The closest relatives of tetrapods are . Fish and tetrapods are both vertebrates that have a backbone with a spinal cord. Fish predate (come before) tetrapods, because their appear in rocks that are more than million years old. This observation leads to the hypothesis that tetrapods evolved from .

If tetrapods evolved from fish, as Darwin predicted, you would expect to find fossils with features of both fish and tetrapods. In Darwin’s day, such fossils had not yet been found, but today, there are many such examples.

Fill in the blanks please.

1) limbs

2) Stegocephalia

3) 367.5 million years ago

4) Fishes

5) Fossils

6) 367.5 million years ago

7) Fishes

8) unearthed or preserved

hypoxemia refers to a below usual concentration of oxygen in the blood, mainly in the arteries. hypoxemia is an indication of an issue associated with circulation or breathing and may lead to various symptoms like shortness of breath.  

the condition is identified by determining the level of oxygen in the blood sample obtained from an artery. it can also be predicted by determining the oxygen saturation of the blood with the application of a pulse oximeter.  

the normal arterial oxygen is about 75 to 100 mm hg. the values underneath 60 mm hg is generally considered with the requirement for supplemental oxygen. the normal pulse oximeter readings generally range between 95 to 100 percent. the values under 90 percent are regarded as low.  

in the given case, the oxygen saturation is measured at 93 percent, hence, there is no need to administer oxygen, that is, one should withhold oxygen.