..between a crocodile and an alligator and a cayman?
The major visible difference is that crocodile teeth are visible when the mouth is closed. Alligator teeth fit inside. Crocodiles can tolerate saltwater, alligators cannot. Caimans are closely related to alligators. Both are more distantly related to crocodiles.
Seals, sea lions and walruses are
pinnipeds. Sea lions are often called seals; the major difference is that sea lions have external ear flaps.
A blackbird, a crow, a magpie, a raven, and a grackle?
Crows, grackles and ravens are
corvids, a taxonomic group that also includes the jays. Many species rank among the most intelligent birds on earth, rivaling the psittacines--the parrots, including macaws, cockatoos, lories, budgies, etc.
"Blackbird" is a rather generic term applied loosely to quite a few avian species that have nothing in common except coloration. It is not used in science.
A pine tree and a fir tree?
There are about 250 different species of pine. These include approximately 50 species of fir trees.
A cricket and a grasshopper?
There are quite a few species of crickets, and the same is true of grasshoppers. The two families are very closely related. I suppose the most easily seen difference is that crickets are nocturnal and lack wings, while grasshoppers have wings and most are diurnal or crepuscular.
A dolphin and a porpoise?
Porpoises have shorter beaks and flattened, spade-shaped teeth. Dolphins have longer beaks and conical teeth.
Having been an aviculturist for may years, I knew the answer to your question about the corvids. The rest took about ten minutes in Wikipedia.
So I probably learned more from this than you did!
