ProtoIndoEuropean Dative Element -o

Accusative>Lative, Instrumental>Ablative

	Accusative-Dative			Instrumental-Ablative
	Sing.	Du.	Plur.	Sing.	Du.	Plur.
No Lative Element Acc-Ins	-m	-meh	-ns (<ms)	-bhi	-bhih	-bhis
Lative Element -o Lat-Abl	-mo -ei	-moh	-mos	-bio	-bioh	-bhios

*Note: -ei would have been derived from the Locative form, and the -e- element may not have been -o- for whatever reason. Anatolian evidence, especially with regards to Hittite, is that the dative and locative endings were the same, though they had -a for the Allative (which may have been the origin of the Dative case elsewhere).

For Hittites Allative -a, its hard to tell whether or not this represents an -he element or an -o element, as it underwent the o>a shift. At least as far as we can tell from its transcription into cuneiform.

Hittite also as:

Ablative -az (-ats)

Instrumental -it

It's hard for me to say the origin of the Ablative ending, though its definitely not from the Genitive -as ending. The /ts/ element is often a result of ti>ts, like in -anti>-anza. Not sure if this is the result of the same change or not.

*Note: Accusative dual forms merged with Nominative dual forms, this may have always been this way; though the above postulation for a seperate accusative dual form is based on the dative dual forms, and is entirely speculation. As is the Ablative dual/plural forms (though Instrumental singular -mi forms are attested from Baltic and Slavic evidence).