  We identify the two dimensional AdS subsupergroup $OSp(16/2,R)$ of the
M-theory supergroup $OSp(1/32,R)$ which captures the dynamics of $n$
$D0$-branes in the large $n$ limit of Matrix theory. The $Sp(2,R)$ factor in
the even subgroup $SO(16) \times Sp(2,R)$ of $OSp(16/2,R)$ corresponds to the
AdS extension of the Poincare symmetry of the longitudinal directions. The
infinite number of $D0$-branes with ever increasing and quantized values of
longitudinal momenta are identified with the Fourier modes of the singleton
supermultiplets of $OSp(16/2,R)$,which consist of 128 bosons and 128 fermions.
The large $n$ limit of N=16 U(n) Yang-Mills quantum mechanics which describes
Matrix theory is a conformally invariant N=16 singleton quantum mechanics
living on the boundary of $AdS_{2}$. We also review some of the earlier results
on the spectra of Kaluza-Klein supergravity theories in relation to the recent
conjecture of Maldacena relating the dynamics of $n$ $Dp$-branes to certain AdS
supergravity theories. We point out the remarkable parallel between the
conjecture of Maldacena and the construction of the spectra of $11-d$ and type
$IIB$ supergravity theories compactified over various spheres in terms of
singleton or doubleton supermultiplets of corresponding AdS supergroups.
