Chordate and Vertebrate Evolution Vocabulary

Vocabulary flashcards covering the evolutionary timeline of chordates, vertebrates, and mammals, as well as fundamental cladogram terminology.

Chordates

A branch of organisms defined by the presence of a spinal cord that diverged approximately $\sim 505\,Ma$, starting with Pikaia.

Vertebrates

A branch of organisms defined by bony vertebrae that diverged approximately $\sim 460\,Ma$.

Bony Fish

A group defined by bony skeletons that diverged approximately $\sim 430\,Ma$, starting with the organism Guiyu.

Lobe-finned Fish

A group defined by arm bones, specifically the humerus, radius, and ulna, which diverged approximately $\sim 420\,Ma$ starting with Coelacanth.

Tetrapods

Organisms defined by four weight-bearing limbs that diverged approximately $\sim 340\,Ma$ with the organism Eryops.

Amniotes

A group defined by the shared trait of a sternum that diverged approximately $\sim 320\,Ma$ starting with Mesosaurus.

Mammals

Organisms defined by three inner-ear bones that diverged approximately $\sim 180\,Ma$ starting with the Echidna and Platypus.

Evolutionary Divergence Sequence

Spinal cord ($\sim 505\,Ma$) -> bony vertebrae ($\sim 460\,Ma$) -> bony skeletons ($\sim 430\,Ma$) -> arm bones ($\sim 420\,Ma$) -> four limbs ($\sim 340\,Ma$) -> sternum ($\sim 320\,Ma$) -> inner-ear bones ($\sim 180\,Ma$).

Node

A representation on a cladogram of a common ancestor shared by two or more leaves.

Leaf

A representation on a cladogram of an individual species.

Outgroup

The leaf on a cladogram sharing the fewest nodes with the rest of the tree, representing the most distantly related organism.

Most Recent Common Ancestor (MRCA)

The lowest or most recent node shared by two leaves on a cladogram.

Cladogram Node Significance

Indicates that two organisms share the specific trait that evolved at that particular common ancestor point.