Latin tendere, -fendere

Andrew Sihler is fond of the idea that Latin tendere and -fendere (defendere, offendere) reflect IE *tnje- and *gwhnje- and are therefore correspondent to Greek tein� and thein�.  This is very attractive, but what is the likelihood that /nj/ would become /nd/?  It would seem to be a development unique to Latin and phonologically unlikely.  But then why do these verbs have the -d-?  Are there similar verbs or nouns with *-d- as an extension?  Perhaps the Germanic strong verbs with extensions, e.g. *geutan, are examples of such verbs?  Does Latin have other examples after consonants or vowels other than n?

 

Andrew