Pterodactyl opens with pt-, which English silences to a plain t. The cluster is Greek: pteron, "wing," the same element in helicopter, plus a Latinised form of daktylos, "finger." A pterodactyl is a wing-finger, which is an accurate description of the animal's anatomy — the wing membrane was carried on one enormously elongated digit.
The word is entirely modern. Cuvier coined the French ptérodactyle in 1809 from the Modern Latin genus name Pterodactylus, and English took it in 1826. Nothing about it is ancient except the raw material. This is the standard pattern for scientific naming since the 1700s: the parts are Greek, the compound is nineteenth-century, and the spelling records a set of conventions for transliterating Greek rather than any history of the word itself.
pterodactyl (n.) extinct flying reptile, 1826, from French ptérodactyle (Cuvier, 1809), from Modern Latin genus name Pterodactylus , from Greek pteron "wing" (from PIE root *pet- "to rush, to fly") + Latinized form of daktylos "finger" (see dactyl ). also from 1826
pterodactyl came in through Greek, and its spelling follows that family's conventions.
How that family writes these sounds
| a bare /n/, /t/, /s/, /z/ at the start | put the silent letter back on the front: pn-, pt-, ps-, mn-, x-pneumonia, pterodactyl, psalm, mnemonic, xylophone |
What gives it away on the page
| ps-, pn-, pt-, mn-, x- | Initial clusters English can't actually pronounce, so it silences the first letter.psalm, pneumonia, pterodactyl, mnemonic, xylophone |
Placing it without the spelling
| a medical or technical word starting with a bare /n/, /t/, /s/, or /z/ | Greek — the letter you can't hear comes firstpneumonia, pterodactyl, psalm, xylophone |