Given the task definition, example input & output, solve the new input case.
In this task, you are given two sentences in the English language (Sentence 1 and Sentence 2). Your task is to identify the connecting word between the two sentences.
Example: Sentence 1:A suicide car bomber detonated his bomb as he attempted to drive an SUV into a Somali military camp . Sentence 2:However the vehicle exploded at the entrance when police guards opened fire on the insurgent driving the vehicle .
Output: however
The above sentence is connected by the word 'however'.

New input case for you: Sentence 1:Subsequent descriptions and redescriptions have ensured that the phylogeny of the clade is rather robust at the genus level . Sentence 2:Yet , a comprehensive species - level phylogenetic analysis has proven impossible due to the large amount of species based on scant and fragmentary fossilised material .
Output:
yet