The correct answer is - D) covered by warm shallow seas.
The fact that the crinoids are have an abundance in the fossil records in Pennsylvania in the Mississippian Period, tells us that this area was covered with shallow and warm seas. The reason why we can get that conclusion is that the crinoids live only in that kind of environment, so it simply a logical conclusion.
The geological data is also confirming this, as it is easily noticeable in the layers that during this period of the geologic past, what is now Pennsylvania, was covered with shallow sea waters. Also, this waters were warm too, as the climate was warm and humid and that period, so it was a perfect environment for the crinoids to flourish.
Answer: Explanation:
Sickle hemoglobin differs from normal hemoglobin by a single amino acid: valine replaces glutamate at position 6 on the surface of the beta chain. Therefore the red blood cell bends differently giving it a sickle shape
Chloroplasts are only found in plant cells because it is the organelle that makes photosynthesis possible and it makes food for the plant cells as in it makes its own food and animal cells dont need them because animals eat other animals for that food
Answer: Directional selection occurs when individuals with traits on one side of the mean in their population survive better or reproduce more than those on the other. ... Directional selection does the “heavy lifting” of evolution by tending to move the trait mean toward the optimum for the environment.
