The origin of turtles: a paleontological perspective

Area of Science:

• Paleontology
• Evolutionary Biology
• Comparative Anatomy

Background:

• The evolutionary origin and unique body plan of turtles have been debated for centuries.
• Previous molecular studies suggested a close relationship between turtles and archosaurs, but these findings are now questioned due to systematic biases.
• Morphological studies have proposed alternative placements for turtles, but with limited support.

Purpose of the Study:

• To investigate the paleontological hypothesis that Eunotosaurus africanus represents an intermediate stem turtle.
• To resolve questions regarding the origin of the turtle shell and its non-composite, slow, and terrestrial development.
• To extend the known stem lineage of turtles further back into the Permian period.

Main Methods:

• Analysis of morphological characters in Eunotosaurus africanus.
• Comparison of these characters with those previously considered unique to turtles.
• Re-evaluation of paleontological and morphological data in light of new findings.

Main Results:

• Eunotosaurus africanus exhibits numerous characters previously thought to be turtle-specific, indicating an earlier origin.
• These characters originated over millions of years, independent of the turtle shell's final formation.
• The study robustly supports E. africanus as an intermediate stem turtle, extending the lineage to the Permian.

Conclusions:

• Eunotosaurus africanus provides strong evidence for the non-composite and gradual origin of the turtle shell in a terrestrial environment.
• While E. africanus does not definitively place turtles within Amniota, it significantly clarifies the early evolution of turtles.
• The findings resolve key questions about the slow, terrestrial origin of turtles and their shell, pushing their lineage back to the Permian.