Turtle origins: insights from phylogenetic retrofitting and molecular scaffolds

Area of Science:

• * Paleontology
• * Evolutionary Biology
• * Phylogenetics

Background:

• * Adding new taxa to morphological phylogenetic analyses is common but can lead to character undersampling.
• * Morphological analyses have traditionally placed turtles (Testudines) with parareptiles like Eunotosaurus.
• * Genomic data robustly indicate turtles are nested within diapsids, as the sister group to extant archosaurs (birds and crocodilians).

Purpose of the Study:

• * To investigate the conflicting phylogenetic signals between morphological and genomic data for turtle (Testudines) evolutionary history.
• * To assess the compatibility of morphological data with a turtle-archosaur clade derived from genomic evidence.
• * To explore the phylogenetic position of Eunotosaurus in relation to turtles and archosaurs.

Main Methods:

• * Retrofitting turtles and other taxa onto existing reptile phylogenies using morphological data.
• * Conducting Bayesian and parsimony analyses of morphological data.
• * Enforcing a molecular scaffold (turtle-archosaur clade) onto morphological datasets to evaluate tree length and likelihood.

Main Results:

• * Morphological analyses consistently group turtles with parareptiles (Eunotosaurus, pareiasauromorphs).
• * Morphological data are highly consistent with a turtle-archosaur clade, with minimal increase in tree length or decrease in likelihood.
• * Under specific analytical conditions, Eunotosaurus groups with turtles within the turtle-archosaur clade.

Conclusions:

• * Morphological and genomic data, while seemingly contradictory, can be reconciled to support a turtle-archosaur evolutionary relationship.
• * The traditional placement of turtles with parareptiles based on morphology may be an artifact of analysis or undersampling.
• * Eunotosaurus may represent a basal member of the turtle-archosaur clade, complicating traditional parareptile classifications.