Therefore fundamental ontology, from which alone all other ontologies can take their rise, must be sought in the existential analytic of Dasein.
Dasein accordingly takes priority over all other entities in several ways. The first priority is an ontical one: Dasein is an entity whose Being has the determinate character of existence. The second priority is an ontological one: Dasein is in itself 'ontological', because existence is thus determinative for it. But with equal primordiality Dasein also possesses—as constitutive for its understanding of existence—an understanding of the Being of all entities of a character other than its own. Dasein has therefore a third priority as providing the ontico-ontological condition for the possibility of any ontologies. Thus Dasein has turned out to be, more than any other entity, the one which must first be interrogated ontologically.
But the roots of the existential analytic, on its part, are ultimately existentiell, that is, ontical. Only if the inquiry of philosophical research is itself seized upon in an existentiell manner as a possibility of the Being of each existing Dasein, does it become at all possible to disclose the existentiality of existence and to undertake an adequately founded ontological  problematic. But with this, the ontical priority of the question of being has also become plain
Dasein's ontico-ontological priority was seen quite early, though Dasein itself was not grasped in its genuine ontological structure, and did not even become a problem in which this structure was sought. Aristotle says: ἡ ψυχὴ τὰ ὄντα πώς ἐστιν.VI "Man's soul is, in a certain way, entities." The 'soul' which makes up the Being of man has αἴσθησις and νόησις among its ways of Being, and in these it discovers all entities, both in the fact that they are, and in their Being as they are—that is, always in their Being. Aristotle's principle, which points back to the ontological thesis of Parmenides, is one which Thomas Aquinas has taken up in a characteristic discussion. Thomas is engaged in the task of deriving the 'transcendentia'—those characters of Being which lie beyond every possible way in which an entity may be classified as coming under some generic kind of subject-matter (every modus specialis entis), and which belong necessarily to anything, whatever it may be. Thomas has to demonstrate that the verum is such a transcendens. He does this by invoking an entity which, in accordance with its very manner of Being, is properly suited to 'come together with' entities of any sort whatever. This distinctive entity, the ens quod natum est convenire cum omni ente, is the soul (anima).VII Here the priority of 'Dasein' over all other entities emerges, although it has not been ontologically clarified. This priority has obviously nothing in common with a vicious subjectivizing of the totality of entities.
By indicating Dasein's ontico-ontological priority in this provisional manner, we have grounded our demonstration that the question of Being is ontico-ontologically distinctive.
Sein und Zeit p. 13
GA 2 p. 17