Discovery and Classification

It is unknown when Manta rays were first dicovered as they seem to have fossile records that date back as far as prehistoric era so essentially they have always been around. This makes it even stranger that they remain a mysterious animal and there is so little research about them.

The first person to accredit the Mantas with an official name was Gerard Krefft in 1798, who was a well renowned Australian zoolologist and palientologist. He published a lot of books about animals native to Australia and worked at the Australian Museum for a period of his life. The naming is often miscredited to Johaan Julius Walbaum who was a German physician, naturalist and taxonamist of the same era.
The official name given to the Manta was Manta Birostris.

The scietific classification of the Manta puts it under:

Kingdom - Animalia
Phylum - Chordata
Class - Chrodirichthyes
Subclass - Elasmobranchii
Order - Myliobatiformes
Family - Mobulidae
Genus - Manta
Species - Manta Birostris

That looks complex but it basically means that it is an animal, it lives in the water, it has a jaw and is related to sharks and other rays and that it evolved from skates.
There is a lot more technical information but it is a bit above me.
Basically they are old.