Modern turtle origins: the oldest known cryptodire

Area of Science:

• Paleontology
• Evolutionary Biology
• Herpetology

Background:

• Modern turtles are divided into two main groups: pleurodires and cryptodires.
• The evolutionary history and origins of these groups are not fully understood.
• Fossil evidence is crucial for reconstructing the early evolution of turtles.

Purpose of the Study:

• To describe a new turtle fossil discovered in the Early Jurassic Kayenta Formation.
• To determine the phylogenetic position of this new taxon within turtles.
• To understand the early evolution of cryptodires and aquatic adaptations in turtles.

Main Methods:

• Fossil excavation and preparation.
• Comparative anatomical analysis of skeletal features, particularly the jaw mechanism.
• Phylogenetic analysis to determine evolutionary relationships.

Main Results:

• Discovery of Kayentachelys, a new turtle taxon from the Early Jurassic (~185 million years ago).
• Kayentachelys exhibits primitive features relevant to the common ancestor of pleurodires and cryptodires.
• The fossil displays a unique cryptodiran jaw mechanism (trochlea over otic chamber), identifying it as the oldest known cryptodire.
• Evidence suggests early development of aquatic habits in turtle evolution.

Conclusions:

• Kayentachelys represents the earliest known cryptodire, significantly extending their fossil record by at least 45 million years.
• This discovery provides critical insights into the early diversification and evolution of modern turtles.
• The findings support the early emergence of aquatic lifestyles in the lineage leading to modern turtles.