RainbowUnion wrote:
DarthMetaKnight wrote:
Humans and tunicates belong to the same phylum - chordata.
Yes they do. Criteria, possessed by any chordate at some time in its development (this can include traits in an embryo or immature phase not possessed by the adult):
1. Pharyngeal gill slits.
2. A notochord.
3. A dorsal tubular nerve chord.
4. A post anal tail (yes, humans do have one, but its so small and atrophied that the bones don't make it out of the body in most people. Some people ARE in fact born with a tail that does, but the majority have it surgically removed even though it poses no medical risk).
One and two are present in the embryo in humans. Tunicates (Urochordates) possess three and four in their free swimming larval stage.
Theyre also called "sea squirts".
Imagine your pet goldfish -with its pouting lips and gills. Then imagine JUST the pouting mouth and gills (actually just one gill on one side)...and NOTHING else on the animal! No brain, no eyes, no fins, not tail, nada. Just two openings pumping water. And imagine that stuck to a rock on the sea floor. That's a sea squirt. Simple sessile critter. Sucking in water in one hole, and pumping out of another hole on the side.
Hard to believe it could be related to the ancestors of humans.
But in its larval form it swims around, and thus has a tail and a "notochord" (rudimentary spinal chord) so it can find its own home away from mom and dad. It then glues it head to a rock, and the rest of the critter disappears, and it grows up to be that big pair of pulsating holes stuck to a rock.
Apparently at some point half of billion years ago one of the larval forms (maybe it was a deviant aspie sea squirt) failed to grow up, and stayed in its larval form, and kept on free swimming , and became the first fish. And the fish gave rise to four classes of fish, and to amphibians, reptiles, birds, mammals, primates, and to us.