An Ottsel is a creature combination of an otter and a weasel. They have reddish-orange fur with golden yellow bellies. Those seen in the series are even capable of speech and a respectable level of intelligence. Although the Precursors are in fact ottsels, it is unknown if all ottsels are Precursors. They appear in every Jak game to date, though in Jak and Daxter: The Precursor Legacy, Jak II, Daxter (game) and Jak and Daxter: The Lost Frontier Daxter is the only ottsel to make an appearance.
There are only six ottsels seen in the Jak universe. They are Daxter, Tess, Veger and the three Precursors. Daxter was possibly the only known ottsel until Jak 3. In Jak 3 it is revealed that the Precursors are Ottsels. Daxter was transformed when he fell into a vat of Dark Eco in Jak and Daxter: The Precursor Legacy located on Misty Island. According to the Precursors in Jak 3, this is because all Eco contains 'the source of their essence', which is capable of blessing anyone who touches it with the form of a Precursor instead of causing the Eco's usual effects. Given how much Eco is used in the world, however, it is unusual that Daxter is the only known case of this happening. When the Precursors are discovered they are the ones to change Veger and Tess into ottsels.
It is unlikely that ottsels are simply every day wild creatures. The most common reactions to Daxter is mild surprise or no reaction. He is often referred to as Jak's "pet". Daxter has also been referred to as a "rat". This similarity to rats, rodents, and other pests sometimes causes people to react to Daxter as a pest himself. In both Jak and Daxter: The Precursor Legacy and Jak 3, the Yellow Sage and Kleiver respectively expresses a desire to want to cook and eat Daxter, possibly from living a hard life in the swamp/desert.
The term "Precursor" in itself is a very vague word and it is unknown if it is used in the sense of a species or simply a group of individuals. They could potentially be a group of individuals that have a certain reaction to Dark Eco. If they are a species, then ottsel and precursor become interchangeable. This doesn't play out in the games, since the Precursors are still referred to as Precursors and the rest of the ottsels are referred to as ottsels. They could potentially be both. There is a theory that in order for Ottsels to achieve the precursor status they have to undergo a procedure similar to that of Young Samos in Jak II to become a sage. The Precursors have not been seen since Jak 3, largely because of their departure from the planet.
Ottsels appear to be very embarrassed of their considerably adorable looks. Daxter often complains about his bad luck with "the ladies" and will blame it on several animal related aspects such as his tail or smell. The Precursors attempted to conceal their image all together originally appeared to be blue, glowing sprites. This was a hologram projected by the Precursors themselves to conceal their true form. Their real form was revealed by accident. Veger appeared to fall into a state of depression when he was changed into an ottsel, his character model that was shown during the credits of Jak 3 showed Veger with his head hung low and his shoulders slumped. Tess seems to be the only ottsel content with her furry form, she "volunteered" to be turned into an ottsel to be with Daxter.
In The Lost Frontier, Daxter once again comes into contact with Dark Eco, however, instead of killing him he gains Dark powers just like Jak did. It is unknown why this happens, and is presumably just that when someone comes into contact, the results are unpredictable. Some fans believe that Daxter should have turned into a Dark Maker after coming into contact with the Eco, because of Daxter being a Precursor, so these fans accuse High Impact Games for not making this happen. But, as said earlier, the effects of Dark Eco are unpredictable.