The fourth trochanter is a shared characteristic common to archosaurs. It is a knob-like feature on the medial side of the femur that serves as a muscle attachment.
The fourth trochanter first appeared in the Erythrosuchidae, large basal archosaurian predators of the early Triassic period.
This seemingly insignificant detail may have made the evolution of dinosaurs possible (all early dinosaurs and many later ones were bipeds), and may also be connected with the ability of the archosaurs or their immediate ancestors to survive the catastrophic Permian-Triassic extinction event.
Famous quotes containing the word fourth:
“For the Lord thy God is a jealous God among you.”
—Bible: Hebrew Deuteronomy, 6:15.
The words are also found in Exodus 20:5, referring to the second commandment: “Thou shalt not make unto thee any graven image ... for I the Lord thy God am a jealous God, visiting the iniquity of the fathers upon the children unto the third and fourth generation of them that hate me.”