Final answer:
The property not characteristic of useful index fossils is that the organisms still exist today; index fossils are used for dating and must have been widespread, abundant, and short-lived geologically.
Step-by-step explanation:
The property that is NOT a characteristic of the organisms that have become useful index fossils is D. The organisms still exist today. Index fossils are indicators of the age of the rocks they are found in because they were widespread, abundant, and only existed for a relatively short period of geologic time, which makes them useful for dating the rocks in which they are found. Fossils often indicate that many organisms from the past are extinct, and it is estimated that 99% of all species that have ever lived are now extinct.
One line of critical thinking pertaining to fossils is that if certain fossils are found in multiple geological layers and then are suddenly not found in the newer layers above, this suggests a mass extinction event. It is also critical to note that index fossils must be unique to a particular geological time frame and not be living organisms today since this would make it difficult to date the strata they are found in accurately.