Heterochrony and Evolutionary Processes

Recognising Heterochrony




Historical Antecedants

Recognising Heterochrony

Modern examples: Sexual Dimorphism

Cambrian trilobites

Cope's Rule

K- and r- selection: Tertiary echinoids

Consequences for debates on adaptation, constraints and evolutionary dynamics


In certain Cambrian trilobite groups, glabellar development has been identified as a proxy for developmental stage. Glabellar development occurs as a five stage process. Trilobites species who only go through three of the stages represent paedomorphs. Maturation occured precociously and truncated glabellar development (though early maturation affected more than just the glabella, of course).

From McNamara (1986).