Not so fast. There is no fossil evidence for a single trunk. As Stephen Jay Gould explains, the evidence points in the opposite direction:
The history of most fossil species include two features particularly inconsistent with gradualism:
1) Stasis - most species exhibit no directional change during their tenure on earth. They appear in the fossil record looking much the same as when they disappear; morphological change is usually limited and directionless;
2) Sudden appearance - in any local area, a species does not arise gradually by the steady transformation of its ancestors; it appears all at once and ‘fully formed’.
Gould, S.J. (1977)
“Evolution’s Erratic Pace”
Natural History, vol. 86, May