You are examining the fossil record and notice that through time a series of fossils exhibits very little change. During the period of time you are studying, this fossil lineage can be described as exhibiting .

Equilibrium

Explanation: Fossil are regarded as decayed remains of plants and animals usually preserved in sedimentary rocks, coal, woods and so on. Records of organism as gathered and traced by the remains of preexisting remains of organisms through geologic time is called Fossil record. There are instances, whereby Fossil record of certain organisms are marked by very little or no changes with the organism's population exhibiting stability and portraying very little change as shown by its Fossil record. Such population of organism are said to exhibit equilibrium due to such stability and lack of wide change in record.

your answer is "the 1950's"