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Modern turtle origins: the oldest known cryptodire.

E S Gaffney, J H Hutchison, F A Jenkins

Science (New York, N.Y.)

|July 17, 1987

Summary

A new turtle fossil from the Early Jurassic Kayenta Formation is the oldest known cryptodire, revealing primitive features of modern turtles. This discovery pushes back the record of cryptodires by 45 million years, shedding light on early turtle evolution.

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.

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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.