Seeing how you gave us the link, I assume you are trying to be as faithful to the intended pronunciation as possible

With the IPA spelling [ˈ'ptɛ.rʊs], it implies that the 'p' is pronounced. If it weren't pronounced, it wouldn't be in the IPA spelling. Of course this could be a mistake, but if it isn't it should be pronounced the same as the 'pt' in 'adapt', 'accept', and 'script'. I do know that in English, we used to pronounce the 'k' in words like "knight" and "knee", but we then dropped it later. It is possible that this is the same case with 'pt'. 

[ɛ] (corresponding to 'e' in "pterus") is pronounced like the 'e' in "bed" if you speak General American, Northern English, and Scottish English, the 'a' in "fat" in Cockney, Singapore, and New Zealand English, the 'ay' in "days" in Belfast English, and the 'a' in "mate" in Zulu English. This sound may or may not exist in other versions of English.

Here the first syllable ends and the second begins. For the record, the first syllable is stressed, the second is unstressed. 

the 'r' is trilled, like the 'rr' in the Spanish word "perro", or the stereotyped 'r' in Scottish English. 

[ʊ] (corresponding to 'u') is pronounced like 'oo' in "hook" in most dialects of English, or the 'o' in "go" in Scottish English. 

's' is just like the 's' in English. 'nuff said. 

The pronunciation you gave in the previous post on the subject would be a good way to map the word to General American pronunciation. The other way I would anglicize it is as you recommended, except the "e" is pronounced like the 'ai' in "air" in General American English instead of the 'i' in "rip".