Here the comparison is Mary's work and her contribution and not her work with Mary; hence you need Leakey's contribution to be followed after the modifier "In addition.....record" - this eliminated option A,B and C.

Between D and E, the only difference is "discovery of the evidence" and "discovering the evidence"
E - changes the meaning of the sentence - discovering the evidence means contributions included her discovering the evidence and not what she discovered (i mean the content).

In sentence correction, the objective is to use correct grammar without chnaging the original meaning of the sentence.

Hope this helps!

yup that does make sense.

Thanks