JANE (Nanotyrannus)

Nanotyrannus was named in 1988 by Bakker and Currie, it lived at same period with T-rex.
They thought Nanotyrannus was a small group-hunting tyrannosaurus that occupied a different ecological niche than T. rex.
Until 2001, a specimen “Jane” was found, it helped scientists to verify that Nanotyrannus is Juvenile T-rex.
It's interesting thing that now we know different age of T-rex had different ecological niche and they body shape varies greatly.