Answer:
Interbreeding, morphological similarity, genetic similarity, shared ecology, and fossil records.
Step-by-step explanation:
An animal is any member of the kingdom of Animalia, comprising multicellular organisms that have well-defined shape and usually limited growth, can move voluntarily, actively acquire food and digest it internally, and have sensory and nervous systems that allow them to respond rapidly to stimuli: some classification schemes also include protozoa and certain other single-celled eukaryotes that have motility and animal like nutritional modes.
Species, on the other hand, is one of the classes of things included with other classes of a genus.
Animals that can successfully reproduce and produce fertile offspring are generally classified as the same species. The ability to interbreed indicates a shared gene pool and evolutionary path.
Animals with very similar physical forms, anatomies and characteristics are often considered the same species. This includes features like body shape, body covering, number of limbs, sense organs, etc.
Animals with highly similar DNA sequences, especially in their protein-coding genes, are often classified as the same species. A threshold of around 97-99% genetic similarity is typically used.
Animals that occupy the same ecological niche and have similar basic life functions (feeding, breathing, reproducing) tend to be grouped in the same species. They often depend on the same resources.
Paleontologists study fossilized remains to trace how animal forms have changed over time. Animals that show continuity in morphology and range over successive fossil layers are often classified as the same evolving species.