p then e then t would be acceptable if they appeared in that order in 'reptilian', even if separated by other letters, but as they don't then a second anagram indicator is indeed required, as neatly explained by Azed back in 1980:
"No one, I think, would question a clue constructed on the lines of x + y + anagram indicator = z, where x and y consist of one or more words or letters (such as abbreviations, etc.) each, possibly separated by intervening verbiage which indicates that they are to be dealt with together. It is a relatively small step from that construction to one which goes: x is that which + y + anagram indicator would/could give z, or alternatively x is that which z – y + anagram indicator(s) give, where x is the answer to the clue. The first of these two variants (which involves addition rather than subtraction) is both neater and easier to manipulate since I would maintain that in the second the clue-writer should include anagram indicators for both z and y before the subtraction process occurs except in the rare cases when the letters in y may be subtracted from z in their natural order."