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All chordates share a suite a shared, derived features (synapomorphies) in common that all must have also been present in their shared common ancestor. These include:
Notochord: A flexible supporting rod that spans much of the length of the body and serves as a structure for muscle attachment (among other features); becomes part of the vertebral column in most vertebrates, though is retained through adulthood in some basal taxa.
Dorsal nerve chord: A nerve chord runs along the dorsal surface of the body (homologous to our backs), rather than the ventral surface (common in some other animal groups).
Post-anal tail: Chordates have a tail that extends beyond the anal opening.
Endostyle: A mucus-covered structure in the pharyx that is used for filter feeding in basal chordates and develops into the thyroid gland in derived chordates.
Pharyngeal slits: Openings into the pharynx (throat region) that are associated with filter feeding in basal chordates and respiration in fishes (in conjunction with gills). Land-dwelling chordates have pharyngeal slits early in embryonic development, but they are subsequently lost. (Note: this feature is also present in hemichordates but is absent in extant members of their sister group, the echinoderms. This means that pharyngeal slits might be a synapomorphy for deuterostomes that was later lost in echinoderms. If true, it means that the character is actually plesiomorphic in chordates. Nevertheless, all chordates have the feature.)
4.0 BYA
LUCA (Last Universal Common Ancestor)
Origin of all life: simple, single-celled, no nucleus. Likely originated from deep sea vents, using chemical gradients (Hydrogen and Hydrogen Sulfide).
3.8 BYA
Split into Domains: Archaea, Bacteria, Eukarya
Salmon lineage continues in Eukarya.
Horzizontal gene transfer from bacterial symbionts to host genomes
2.1 BYA
Asgard archaea posses genes closest to eukaryotes suggesting evolution from ancestor that engulfed bacteria.
Cyanobacteria lead way as first primary producers of oxygen through photsynthesis.
2.0 BYA
Kingdom Eukaryota evolves
Cells with nuclei and organelles (mitochondria from endosymbiosis).
541 MYA
Cambrian Explosion
Rapid diversification of animal life, including first chordates.
Eyes, muscles, nervous systems, segmentation.
500 MYA
Vertebrates
Skull, backbone, cartilage. Originated in marine environments with jawless fish being first.
420 MYA
Gnathostomes
Evolution of jaws from gill arches enabled predation and adaptive radiation.
100–70 MYA
Order Salmoniformes
Streamlined cold-water fish begin to diversify.
Diverged from Laurasia and adapted to both fresh and marine ecosystems.
10 MYA - present
Salmo salar
Diverged from brown trout with precise nasal homing, temperature tolerance, and seasonal spawning.
Domain:
Eukaryota
Kingdom:
Animalia
Phylum:
Chordata
Class:
Actinopterygii
Order:
Salmoniformes
Family:
Salmonidae
Genus:
Salmo
Species:
Salmo salar
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