In this sentence, the comparison is between dinosaur bones in Alberta, and dinosaur bones of South American predecessors. As old as is an equal comparison - Martha is as tall as Mary. We are not looking for an equal comparison because the bones found in Alberta are not the same age as those found in South America, thus choices C, D, and E are eliminated. Older than correctly compares the older Albertan dinosaur bones with the younger South American dinosaur bones. Supposedly is an adverb and cannot modify a noun (predecessors' bones). Supposed is an adjective, making choice A the correct answer.
"Start By Doing What Is Necessary ,Then What Is Possible & Suddenly You Will Realise That You Are Doing The Impossible"