Data from: Extreme neck elongation evolved despite strong developmental constraints in bizarre Triassic reptiles – implication for neck modularity in archosaurs

The Triassic radiation of vertebrates saw the emergence of the modern
vertebrate groups, as well as numerous extinct animals exhibiting
conspicuous, unique anatomical characteristics. Among these, members of
Tanystropheidae (Reptilia: Archosauromorpha) displayed cervical vertebral
elongation to an extent unparalleled in any other vertebrate.
Tanystropheids were exceptionally ecologically diverse and had a wide
spatial and temporal distribution. This may have been related to their
neck anatomy, yet its evolution and functional properties remain poorly
understood. We used geometric morphometrics to capture the intraspecific
variation between the vertebrae comprising the cervical column among early
archosauromorphs, to trace the evolutionary history of neck elongation in
these animals. Our results show that the cervical series of these reptiles
can be divided into modules corresponding to those of extant animals.
Tanystropheids achieved neck elongation through somite elongation and a
shift between cervical and thoracic regions, without presacral vertebrae
count increase - contrary to crown archosaurs. This suggests a peculiar
developmental constraint that strongly affected the evolution of
tanystropheids. The data obtained just at the base of the archosauromorph
phylogenetic tree is crucial for further studies on the modularity of
vertebral columns of not only Triassic reptile groups but extant and other
extinct animals as well.