With the exception of (one) phenomenon, (many) phenomena, hopefully?
Also, now that I think of it: pegasus/pegasi, prolegomenon/ prolegomena, lemma/ lemmata, schema/ schemata, etc etc. There's one ending in -omenon that I keep forgetting...
For example, Samurai and Kimono are both loan words - but we import the pluralisation of Samurai (Seven Samurai) [1] whereas Kimono pluralises with an s on the end (Seven Kimonos) [2].
[1] https://www.merriam-webster.com/dictionary/samurai [2] https://www.merriam-webster.com/dictionary/kimono
This site lets you search for English words by suffix, and the only words it can find ending in "-omenon" are "phenomenon" and... "superphenomon". What a phenomenal result.
Though Australia is in the antipodes (to the UK), not the antipuses.