To explore the relationship between morphological change and species diversification, we reconstructed the evolutionary changes in skull size, skull shape, and body elongation in a monophyletic group of eight species that make up salamander genus Triturus. Their well-studied phylogenetic relationships and the marked difference in ecological preferences among five species groups makes this genus an excellent model system for the study of morphological evolution. The study involved three-dimensional imagery of the skull and the number of trunk vertebrae, in material that represents the morphological, spatial, and molecular diversity of the genus. Morphological change largely followed the pattern of descent. The reconstruction of ancestral skull shape indicated that morphological change was mostly confined to two episodes, corresponding to the ancestral lineage that all crested newts have in common and the Triturus dobrogicus lineage. When corrected for common descent, evolution of skull shape was correlated to change in skull size. Also, skull size and shape, as well as body shape, as inferred from the number of trunk vertebrae, were correlated, indicating a marked impact of species' ecological preferences on morphological evolution, accompanied by a series of niche shifts, with the most pronounced one in the T. dobrogicus lineage. The presence of phylogenetic signal and correlated evolutionary changes in skull and body shape suggested complex interplay of niche shifts, natural selection, and constraints by a common developmental system
Triturus and Calotriton landmark coordinates
Three-dimensional (3D) models of Triturus skulls were obtained from 177 specimens (121 cleared and stained skeletons from the Institute of Biological Research “Siniša Stanković“, Belgrade and 56 alcohol preserved at the Naturalis Biodiversity Center, Leiden). Specimens vaucher numbers are presented in the file. The specimens were scanned with a Skyscan 1172 100 kV computed microtomograph (micro CT-scanner; Skyscan, Aartselaar, Belgium) under settings that were optimized for the material (aluminium filter Al 0.5 mm, 74 kV, 0.8 rotation step, 515 ms exposure time, four frame averaging). The 3D surface models of newt skulls were produced using SkyScan CT Analyser® 1.10 software, under a marching cube algorithm and a resolution of 26.1 µm. Forty-eight landmarks were defined. A key to the landmarks, brief anatomical descriptions are presented in the file. The landmark coordinates were recorded from the surface models with the software Landmark IDAV 3.0. at http://graphics.idav.ucdavis.edu/research/EvoMorph). Dataset consisting of raw landmark coordinates is presented.
Landmarks numbers and positioning
48 landmarks (22 bilaterally symmetric and four medial landmarks) and wireframe on the dorsal and lateral side of a Triturus skull.
Lateral dorsal and ventral skull of specimen 2C30
The image of the skull is derived from a CT scan with a spatial resolution of 26.1 µm. a) lateral, b) dorsal and d) ventral side of Triturus macedonicus (number 2C30) is presented
video presentation of Triturus and Calotriton skulls
Video representation of Calotriton asper (ZMA.RenA.44640), Triturus carnifex (IBISS.5c35), Triturus cristatus (IBISS.20052), Triturus dobrogicus (IBISS.14C10), Triturus ivanbureschi (IBISS.22444), Triturus karelinii (IBISS 22242), Triturus macedonicus (IBISS.15c30), Triturus marmoratus (ZMA.RenA.7614_165) and Triturus pygmaeus (IBISS.22576) skulls. MP4 files for each species separately are zipped together.
