I believe it would be a fossil of a reptile but I'm not a 100% sure about it.
Was there supposed to be an image?
Cephalochordata is the subphylum that retains all chordate characteristics, even in the adult forms.
Answer:
Population
Explanation:
A population may be defined as the group of organism of the same species. The main dynamics of population ecology are population density, immigration, emigration, birth rate and death rate.
A population should belong to a particular species that occupy the same area. The population can interbreed among themselves. Population ecology refers to the dynamics of population species.
Thus, the correct answer is option (3).