Assembly histories of two typical compact ETGs in TNG50. Left: A merger-free galaxy TNG50 475619, the total accreted stellar mass of the satellite comprises less than 1% of its current stellar mass. From top to bottom, the first panel shows the dark matter (black dots), gas (blue dots), and stellar mass (red dots) of the main progenitor galaxy, along with the stellar mass assembly history of accreted satellites (red lines) prior to merging into the main progenitor. The second panel presents the SFR (black) and sSFR (red) as functions of cosmic time. The third panel displays the evolution of the circularity distribution for stellar particles in the main progenitor galaxy, within the radius r < 2.5 kpc, while the fourth panel shows the same for stellar particles at r > 2.5 kpc. The bottom panel illustrates the stellar mass of the disk, bulge, and hot inner stellar halo of the main progenitor galaxy. Right: Similar figures for a strongly stripped ETG, TNG50 184937, which has experienced two massive mergers: a 1:1 major merger at z ∼ 0.9 (marked by the red vertical dashed line) and a 1:10 merger at z ∼ 0.5 (marked by the magenta vertical dashed line) along with several other minor mergers.