# Earliest long-necked sauropterygian Lijiangosaurus yongshengensis and plasticity of vertebral evolution in sauropterygian marine reptiles

## TL;DR

A newly discovered marine reptile fossil shows that long necks evolved earlier than previously thought in a group related to plesiosaurs.

## Contribution

The discovery of Lijiangosaurus yongshengensis reveals that extreme cervical elongation evolved in nothosaurs before plesiosaurs.

## Key findings

- Lijiangosaurus yongshengensis has 42 cervical vertebrae, the longest known in sauropterygians.
- The species shows a unique intervertebral articulation that may reduce body undulation.
- Extreme cervical elongation evolved in nothosaurs prior to plesiosaur ancestors.

## Abstract

A long neck is a morphological innovation in vertebrates, particularly iconic in many plesiosaurs, while the function of these long necks in plesiosaurs remains controversial. Here, we report Lijiangosaurus yongshengensis gen. et sp. nov. from a previously unknown early Middle Triassic locality in southwestern China. This taxon represents the earliest known sauropterygian evolving an exceptionally long neck with 42 cervical vertebrae, and is identified as a nothosaur rather than the immediate ancestors of plesiosaurs. Our discovery demonstrates that extreme cervical elongation developing more than 30 cervical vertebrae emerged in sauropterygians prior to the rise of plesiosaurs and their pistosaur ancestors. Furthermore, Lijiangosaurus possesses a unique type of accessory intervertebral articulation compared with other reptiles, and we attribute this structure to reducing body undulation. This discovery increases the known diversity of accessory intervertebral articulations in reptiles, and underscores the high plasticity of the vertebral column in the early evolution of sauropterygians.

A newly discovered Triassic fossil marine reptile, Lijiangosaurus yongshengensis, reveals that an exceptionally long neck developing more than 40 cervical vertebrae evolved in nothosaurs before the rise of plesiosaurs.