High-resolution Direct Numerical Simulations (DNS) were carried out to identify the dominant nonlinear mechanisms of three-dimensional wave packets in a Mach 10 boundary layer on a 7◦ half-angle straight (right) cone with a “sharp” nose tip at zero angle of attack. Towards this end, nonlinear wave packets were generated with a short-duration pulse. For these simulations the same cone geometry and flow conditions as in the experiments at the Arnold Engineering Development Complex (AEDC) Hypervelocity Wind Tunnel No. 9 (T9) were used. Wave packet simulations deep into the late nonlinear transition stages were carried out for several cases where the pulse disturbances were introduced in different downstream regions of the cone. The computational domain covered a large extent of the cone in the azimuthal direction to allow for a wide range of azimuthal wavenumbers (kc ). The disturbance spectra obtained from the DNS of nonlinear wave packets provided evidence that the so-called fundamental resonance/breakdown was the dominant nonlinear mechanism. Initiating the wave packet at different downstream locations did not change the dominant nonlinear mechanism but had a significant impact on the dominant frequency and wavenumber range. Furthermore, contours of the time-averaged Stanton number exhibited “hot” streaks on the surface of the cone within the wave packet. Hot streaks have also been observed in the Purdue flared cone experiments using temperature sensitive paint (TSP) and in numerical investigations using DNS.