Crinoids, also known as sea lilies, appear to be sea plants but are not plants at all. Crinoids are an echinoderm species which
uses anchoring structures called holdfasts to attach themselves to the sea floor. Crinoids were most abundant in Pennsylvania during the Mississippian Period, which ranged from 375 to 320 million years ago. Fossils of the crinoids shows that during most of this time Pennsylvania was ________ that provided favorable conditions for crinoid growth. A) glacial terrain B) a dry and sandy plain C) mostly mountain ranges D) covered by warm, shallow seas
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.
Vertebrate paleontology covers everything from the tiny, fish-like creatures, to the salamander-like ancestors of all land vertebrates, to dinosaurs, mammals, flying and swimming reptiles, etc.
Spontaneous recovery is a theory of learning and memory which involves unexpected and recurrence of a conditioned response after a period of reduced response or delay. Spontaneous recovery is associated with classical conditioning and operant conditioning. Extinction will happen quickly after a spontaneous recovery, if the conditioned and unconditioned stimulus is not connected.
