The phylogenetic origin of turtles.

Area of Science:

• Paleontology
• Evolutionary Biology
• Comparative Anatomy

Background:

• The evolutionary origins of turtles are debated, with conflicting hypotheses from molecular and morphological data.
• Eunotosaurus africanus, a Permian reptile, has been considered the oldest stem turtle, crucial for understanding turtle anatomy evolution.

Purpose of the Study:

• To evaluate phylogenetic hypotheses of turtle origins using anatomical data.
• To reassess the relationship of Eunotosaurus africanus to turtles and other reptiles.

Main Methods:

• Analysis of anatomical observations from X-ray computed microtomography (μCT) scans.
• Comprehensive phylogenetic analysis of Eunotosaurus and candidate stem turtles.

Main Results:

• Eunotosaurus africanus lacks key reptile features and is identified as a millerettid, not a stem turtle.
• Shared traits between Eunotosaurus and turtles, like broadened ribs, evolved convergently due to similar ecological pressures (fossoriality).
• Phylogenetic analysis strongly supports turtles as sister to Archosauria, aligning morphological and molecular data.

Conclusions:

• Eunotosaurus is reclassified, revising our understanding of early turtle evolution.
• Turtle origins are placed among early archosauromorphs, providing insights into the evolution of the turtle body plan.
• Convergent evolution explains similarities between Eunotosaurus and turtles, not shared ancestry.