A Walk Through Time

Reverberating Chords

505 Million Years Ago

Human beings belong to the phylum Chordata, all members of which have notochords (cartilage rods down the middle of the back) at some time during their life history. Chordata include all vertebrates (mammals, birds, amphibians, reptiles, and fish) along with several groups of lesser known marine animals. Details of the path in the evolution from notochords in sea-squirts to those in jawless fish to whose in bony fish remain obscure.

Whatever the precise path, the backbone that enables us to stand speaks to the wonder of evolution: branches, truncations, mergers, as evolutionary continuity spans nearly 4,000 million years.

Top-left:Sea Star. (Photograph courtesy Marine Biological Laboratory, Woods Hole)

Top-right and middle: Squids have nervous systems very similar to our own. (Photograph courtesy Marine Biological Laboratory, Woods Hole,top-right; and Jean Cyril Lecomte, C.N.R.S., middle)

Bottom: Sand Shark (Photograph courtesy Royal British Columbia Museum)

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