Elevated Extinction Rates as a Trigger for Diversification Rate Shifts: Early Amniotes as a Case Study

Area of Science:

• Evolutionary biology
• Paleontology
• Phylogenetics

Background:

• Tree shape analyses are common for identifying diversification rate shifts.
• Previous studies suggested a link between diversification shifts and key evolutionary innovations.
• Evidence for this link has been largely circumstantial.

Purpose of the Study:

• To investigate diversification patterns in early amniotes (Carboniferous to Triassic).
• To determine if diversification shifts align with the evolution of key innovations.
• To explore the roles of origination and extinction rates in diversification shifts.

Main Methods:

• Analysis of tree balance on a new amniote supertree.
• Examination of diversification patterns across geological time.
• Case studies on herbivory and aquatic lifestyles to assess links with novelties.

Main Results:

• Diversification shifts in amniotes predominantly occurred during periods of high extinction.
• Mass extinctions correlated with numerous and significant diversification shifts.
• Shifts in clades with innovations were delayed until extinction events, not coinciding with innovation emergence.

Conclusions:

• Key innovations may not directly drive cladogenesis rates but enhance clade survival during extinctions.
• Diversification shifts are strongly influenced by extinction events.
• General diversification patterns should be analyzed before interpreting specific shifts related to innovations.