I would generally aruge that "originally there were no Pitakas", because it appears that the term Pitaka may have been a slightly later usage. It seemed to come about the same time as the nine-limbs (navanga) classification system, and then the twelve-limb.
Can you please say a bit more why do you think this? I mean, I think I read somewhere that navanga is mentioned around 40 times in the sutta pitaka, while pitaka calssification is not, so I'm wondering what does "about the same time" mean - within the last few years of the Buddha's life, within his death and the first council, within 100 years between the first two councils, etc?
We can get back to the nine / twelve limbs in a moment, but for now, it is perhaps more useful to point out the twelve limb system is going to be more helpful than the nine limb system, because the relationship between vedalla and upadesa to the abhidhamma is much stronger.
Can you please say a bit more about the 12-limb system, its difference from the nine-limb system, time and a source?
The Sariputra Abhidharma Sastra structurally is very, very close to the Theravada Vibhanga (and a bit of the Dhammasangani) and also the Sarvastivada Dharmaskandhapada Sastra.
I'd also like to add that the Vatsiputriyas had several Abhidhammic texts, such as the Lokapannatti Sastra, and the Tikkhandhaka. They may have also used the Sariputra Abhidharma Sastra, too.
Are any of these available in English yet? If not, then where can one find the originals? (I assume these sastras have a particualr classification within Chinese or Sanskrit collections of texts, but I'm not familiar with these)
We have a couple of Sthaviravada schools say that there was an Abhidharma early on. Namely: Vatsiputriya, Theravada, Sarvastivada, Dharmagupta and Kasyapiya. This is also kind of the order in which they split off from the original schism Sthaviras.
One very good argument to explain all this is: Between the first schism (second council) and the time of Asoka (third council), there was a large group of Sthaviras around the area from Mathura - Avanti, east of the old heart of the dispensation, and slightly south too. While they were here, they developed possibly a couple of forms of "abhidharma", which are "about the dharma", and basically forms that were very similar to the Vedallas, and Vibhanga suttas, and also the newer Upadesas. These actual suttas were taught by people like Sariputra, Mahakatyayana, Ananda, etc.
Now, during Asoka's time, when the various groups spread out across India, these Sthavira groups took the proto-type Sariputra Abhidharma with them. Because the Theravada ended up so far away, and likewise the Sarvastivada in Kasmir, they developed rather independently, and bear less similarity over time. In central India, the groups like the Vatsiputriyas and Dharmaguptas maintained more commonality, hence their Sariputra Abhidharma Sastra was used by a couple of schools.
Interesting. Can you recommend some literature on this in English?
Also, Vibhajjavada is often mentioned to refer to Sthaviras that are closer to what later became Theravada, than to Sarvastivadins which were also Sthaviras. And then Vibhajjavada later splits into Theravada and Dharmaguptas and others. Any particular reason why you don't mention Vibhajjavada above? Thanks.