Are humans considered fish in cladistics?

In strict cladistics, all descendants of a common ancestor remain part of that ancestor's clade. Because land-dwelling tetrapods—including humans—evolved from lobe-finned fishes, treating fish as a strictly monophyletic group would mean humans are technically classified within the fish clade. However, traditional taxonomic terms like fish are often used paraphyletically to exclude land vertebrates.

What we know

• In strict cladistics, a last common ancestor and all its descendants constitute a clade, and all descendants stay in their overarching ancestral clade. [3]
• If terms like fishes were used within a strict cladistic framework, they would include humans. [3]
• Sarcopterygii is a clade that includes a group of bony fishes and all four-legged land animals, including humans. [2]
• Tetrapods are descended from fish, leading modern phylogenetics to view traditional fish as a paraphyletic group that excludes tetrapods unless tetrapods are treated as a specialized fish subgroup. [4]

Still open

• Whether terms like fish should be abandoned or redefined to keep only valid monophyletic clades remains a difficulty for traditional taxonomy when ranks become inconsistent.

Where to go next

• the bigger pictureWhat are lobe-finned fishes?
• how it workedHow do cladistics classify organisms?
• what caused itWhy are traditional fish a paraphyletic group?
• a case in pointWhat are some examples of living non-tetrapod sarcopterygians?
• compared withHow do early modern humans relate to the human lineage?
• an unexpected connectionHow did fish fins turn into human limbs?Lobe-finned fishes evolved muscular limb buds supported by appendicular skeletons, which eventually transformed into the limbs of land-dwelling tetrapods like humans.

Sources

• [1]Sarcopterygii (Wikidata Q160830) · CC0 1.0
• [2]Sarcopterygii · CC BY-SA 4.0
• [3]Cladistics · CC BY-SA 4.0
• [4]Fish · CC BY-SA 4.0
• [5]Early modern human · CC BY-SA 4.0

Your path

1. What is seismic tomography of the deep Earth mantle?
2. /What is orthostatic hypotension?
3. /Are humans considered fish in cladistics?