the answer is this
hippos and birds were the most common
The most common one was the Egyptian's.
People along several river make that claim. Most common in the U.S. is the Mississippi River. Roads along it are called "Great River Road". See more about the Mississippi River at link below
the poopie plant is the most common plant in Indiana
The Pau-Brasil tree (also known as Brazilwood) was a common plant found along the Atlantic coast of Brazil.
the most common plant grown is the mosses and lichens
the Missouri River
An embankment built along the side of a river to control flooding can be called several things. Probably levee is the most common, but it can be dike or floodbank. It can also be called what you called it, an embankment.
Along the Mississippi River in 1862 and along the Red River in 1864.
New River
Furs were most common along the western frontier.
along the indus river