Ancient tropical extinctions at high latitudes contributed to the latitudinal diversity gradient

Area of Science:

• Paleontology
• Macroevolutionary biology
• Biogeography

Background:

• Global biodiversity exhibits a latitudinal diversity gradient (LDG), peaking at the equator and declining towards the poles.
• Fossil evidence suggests this gradient has varied through time, with flatter gradients during past greenhouse periods.
• The mechanisms and timing of high-latitude diversity loss generating the modern LDG remain unclear.

Purpose of the Study:

• To investigate the historical processes that shaped the latitudinal diversity gradient.
• To test the "asymmetric gradient of extinction and dispersal" framework for LDG formation.
• To determine how climate transitions influenced diversity patterns.

Main Methods:

• Phylogenetic analyses of Testudines, Crocodilia, and Lepidosauria.
• Integration of fossil data with phylogenetic information.
• Modeling of extinction and dispersal rates across latitudes under different climate scenarios.

Main Results:

• High-latitude extinctions of tropical-adapted clades during the greenhouse-to-icehouse transition explain the modern hump-shaped LDG.
• Equator-ward dispersal of clades tracked shrinking tropical biomes.
• Equivalent diversification rates across latitudes can explain ancient flat LDGs.

Conclusions:

• The processes generating the LDG differ between greenhouse and icehouse climates.
• Fossil data are crucial for detecting time-dependent extinction rates.
• The "asymmetric gradient of extinction and dispersal" framework effectively explains LDG dynamics.