I didn't know that that p was silent. Unless its not and its a word play like when Douglas Adams compares the flying abilities of ships to those of bricks?
The ships hung in the sky in much the same way that bricks don't
Funny thing, pterodactyl is based on the two Greek words for wing/feather and finger.
I can totally see how it may have started as fftterodacto and over the years the f sound got less and less noticeable! It's my theory/headcannon now at least lol
What actually happened is that these roots were borrowed from Ancient Greek by paleontologists to form the word "pterodactyl", not modern Greek.
In Ancient Greek, they would have pronounced both the "p" and the "t", but "pt" isn't a possible beginning of a word for English speakers, and so borrowed words that start with "pt-" (and "mn-" and a few others) have the first sound deleted as a repair mechanism to allow English speakers to pronounce them.
In modern Greek, "pt" consonant clusters that used to be pronounced as-is have undergone dissimilation - both "p" and "t" are stop consonants, so the "p" has instead become an "f" (which is a fricative, not a stop), to make the cluster easier to pronounce.