The tale of the headless turtle.

Area of Science:

• Paleontology
• Systematics
• Evolutionary Biology

Background:

• Pelomedusoides is the most diverse clade of side-necked turtles with an extensive fossil record dating back to the Lower Cretaceous.
• Phylogenetic hypotheses for this clade primarily rely on cranial characters due to the phenotypic plasticity of shell characters in fossil species.
• Describing new species based on poorly informative, shell-only fossil material is generally not scientifically justified.

Purpose of the Study:

• To correct an unfounded nomenclatural act describing a new bothremydid turtle species from the Early Paleocene of Brazil.
• To provide guidance to taxonomists regarding the description of new fossil species based on shell-only material.

Main Methods:

• Comparative analysis of fossil turtle remains, focusing on cranial versus shell characters.
• Review of existing literature and phylogenetic matrices for Pelomedusoides.
• Evaluation of diagnostic criteria for fossil turtle species identification.

Main Results:

• The recently described bothremydid turtle species from Brazil is based on poorly diagnostic remains and its description is considered unfounded.
• Shell-only material often exhibits significant phenotypic plasticity, making it unreliable for species-level diagnosis.
• A significant number of fossil morphotypes are reported in the literature without formal species description due to insufficient diagnostic evidence.

Conclusions:

• The recent description of a new bothremydid turtle species from Brazil requires correction due to inadequate fossil evidence.
• Taxonomic descriptions of fossil turtles should prioritize cranial material over shell-only remains due to plasticity.
• This study aims to curb the practice of describing poorly preserved fossil specimens as new species, promoting more rigorous taxonomic standards.