What are the oldest and youngest modern species?

[Gecko08]

Whenever I see people talk about Coelacanths or really any animal that looks prehistoric, it's always called a "living fossil" that hasn't changed for millions of years, but actually doing research has led to the revelation that these animals actually appeared in the last few thousand years, and are prehistoric only in regards to their ancestry. Like for example, an ancestor of the West Indian Coelacanth lived 65 million years ago, but it wasn't actually a West Indian Coelacanth, just a relative. In that respect, what are the oldest and youngest modern species?

[Isidro]

I believe that that's absolutely impossible to know. Only is possible to know the oldest and youngest species within certain taxonomic groups, but not in the whole animal kingdom.

Maybe some of the Triops species could be the winner, but really no way of be sure.

[GojiraGuy1954]

Domestic animals could be some of the youngest

[Isidro]

Rarely domestic animals are considered as species, but some taxonomic points of view does that for some of the species (Felis catus, Equus caballus, Bos taurus). At least this is the opinion that I want to follow, as isolation from wild ancestors is bigger than in dogs, chicken and camels for example.

[bmathison1972]

The newest are probably all invertebrates, insects which can speciate at a rapid rate or possibly new parasitic helminths adapting to a novel host. There are things that evolve and then become extinct without us even knowing they existed...

[FossilDiscovery]

Probably the horshoe crab.

[Isidro]

Probably the horshoe crab.

Which of the four living species do you think?

[stargatedalek]

I'm skeptical of horseshoe crabs being the oldest living species, while not changed significantly, invertebrates as already mentioned speciate faster than vertebrates do.

Orcas date back surprisingly far, iirc pushing 7 million years?

*edit*

Nope, Orcinus but it was a different species.

[Isidro]

I'm skeptical of horseshoe crabs being the oldest living species, while not changed significantly, invertebrates as already mentioned speciate faster than vertebrates do.

That's not exactly accurate, it would be more correct to say that species with shorter generational succession period and r-strategists have a more rapid evolution than species with longer generational succesion period and K-strategists. A killifish evolves much more quickly than a lobster.