In my native language, Russian, coronal stops and approximants are normally dentals. However, when they are "iotated", in addition to palatalization, it also changes their place of articulation to alveolar:
- t̪ → tʲ
- d̪ → dʲ
- n̪ → nʲ
- l̪ → lʲ
These also tend to be somewhat velarized when they are not palatalized. Wikipedia has this to say on velarization in the context of dentals:
For many languages, such as Albanian, Irish and Russian, velarization is generally associated with more dental articulations of coronal consonants.
My understanding is that velarization and palatalization is sort of mutually exclusive, because e.g. a palatalized velar consonant is practically indistinguishable from the corresponding palatal.
OTOH when looking at this table, dentals are in the same column as apical retroflex. Again, my understanding is that retroflex consonants also cannot be palatalized.
Looking for palatalized dentals in PHOIBLE, I only found entries for d̪ʲ|dʲ, t̪ʲ|tʲ, and t̪ʲʰ|tʲʰ. I'm not entirely sure what this notation actually means, but it's interesting that there's no "pure" d̪ʲ or t̪ʲ to be seen.
So, are palatalized dentals impossible in principle? And if so, what is the anatomical reason for that?