Somewhat resembling an ammonite; having characteristics suggestive of ammonites or their fossils.
From ammonite plus -ish (forming adjectives meaning 'somewhat' or 'like'). This is an older or informal descriptive term used in paleontological literature.
The suffix '-ish' is a wonderfully casual way to say 'sort of like'—calling something 'ammonitish' is how a paleontologist might describe a fossil that looks ammonite-like but isn't quite classified as one.
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