1. Hagfish and lamprey are considered ancestors of fish with jaws. If a node were placed before the hagfish or lamprey, what would be a possible derived character?

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Feb 1, 2018


Answer is vertebral column.


  • The illustration that comes with the question presents evolution of vertebrates in very simplified order.
  • It begins with hagfish, a jaw less vertebrate (Agnatha) related to evolutionary ancestors of vertebrates with jaws.
  • First jawed vertebrates (Gnathostomata) were members of aquatic extinct group Placodermi. The jawed vertebrates are primarily of two types: superclass Pisces and superclass Tetrapoda.(Relatives of lung fishes acted as connecting link between the two.)
  • Four classes under Tetrapoda are Amphibia, Reptilia, Aves and Mammalia. Human and his ancestors are included in order Primata.


Now when we place another node in the beginning, it will represent a branching towards early chordate. Here an organism with permanent notochord in its body has been selected: e.g. Lancelet.

Evolutionary picture suggests that, a line of early chordates must have given rise to early jaw less vertebrates like Ostracodermi, another extinct group of aquatic organisms.

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