The global Cenozoic diversification process of tortoises (Testudinidae)

Area of Science:

• Paleontology
• Evolutionary Biology
• Climate Science

Background:

• Testudinidae (tortoises) is the most diverse family of terrestrial chelonians.
• The number of extinct tortoise species exceeds extant ones, prompting investigation into their diversification.
• Environmental changes can significantly impact organism survival and evolutionary trajectories.

Purpose of the Study:

• To investigate the diversification processes within the Testudinidae family.
• To understand the evolutionary history and extinction patterns of tortoises.
• To correlate extinction events with environmental changes.

Main Methods:

• Utilized PyRate software to estimate preservation and diversification rates over time.
• Compiled fossil occurrence data from the Paleobiology Database.
• Used the Catalogue of Life for extant species data to infer ancestral clade probabilities.

Main Results:

• Diversification, extinction, and speciation curves were generated with 95% credibility intervals.
• A notable increase in the extinction rate was observed starting approximately 6 million years ago.
• This extinction surge correlates with a global drop in atmospheric CO2 at the end of the Miocene (8-6 million years ago).

Conclusions:

• The late Miocene environmental shift, marked by decreased CO2 and vegetation changes (C3 to C4 plants, savanna expansion), significantly impacted tortoise evolution.
• Herbivores adapted to grazing were more successful during this period than browsers.
• The study highlights the profound influence of climate and landscape changes on species survival and diversification.