Morphometric analysis of the conodont Chiosella timorensis (Nogami) from the early Anisian of Romania and China, and its significance for the definition of the Olenekian-Anisian Boundary

The conodont Chiosella timorensis (Nogami) has long been proposed as a biotic proxy for identifying the Olenekian-Anisian Boundary (OAB). However, uncertainty regarding the relationship between this species and its presumed ancestor, Ch. gondolelloides (Bender) and its stratigraphic range have cast doubt on its suitability as a proxy. Morphometric analysis of large populations of Chiosella from the Global Stratotype Section and Point candidate at Deşli Caira, as well as other OAB sections in south China, demonstrate that most morphological variation in this genus is caused by variability in the position of the cusp, not the length of the mid-lateral rib (traditionally used to separate the species Ch. gondoelloides and Ch. timorensis). Furthermore, there is little to no stratigraphic separation between the two species, and no obvious trend in any of the investigated sections of a morphological shift from one species to the other with increasing stratigraphic height. Finally, when investigating the size variation of the population, it becomes apparent that in general, specimens assigned to Ch. gondolelloides are much smaller than those Ch. timorensis. Taken together, the results of this study imply that most specimens of Ch. gondolelloides should be considered to be juvenile forms of Ch. timorensis. If Ch. timorensis is used as the biotic proxy for the OAB, then the results of this morphometric analysis necessitate the base of the Anisian be moved down in several OAB sections, including Deşli Caira. Despite this, the study provides greater taxonomic stability, enhancing the utility of Ch. timorensis for future stratigraphic correlation.

Methods
A total of 168 specimens of Chiosella from Desli Caira, Guandao and Mingtang were utilized for the morphometric analysis. 

Specimens were first photographed in lateral view, and the JPEG file were converted ro TPS files using the software TpsUtil, before the positions of all landmarks were identified per specimen in the software TpsDig. Eleven landmarks were utilized, in an attempt to capture the morphology of the specimens. 

Morphometric analyses were subsequently conducted using the software MorphoJ. First, a generalized Procrustes analysis was conducted on each species dataset, which minimizes all variation in specimen position, size, and rotation, in order to conserve only variation in specimen shape. Then, a wireframe model was created for each species, where landmark points are linked in a consistent manner to better facilitate visualization of form changes. Finally, eigenanalyses were carried out, both Principal Components Analysis (PCA) and Canonical Variate Analysis (CVA). Both analyses generate eigenvectors that represent axes that maximize separation of sets in multivariate space; however, CVA utilizes sets that are externally predefined by classifiers. In the present study, the predefined classifiers were stratigraphic section (either Desli Caira, Guandao, or Mingtang) in one analysis, and stratigraphic height (i. e. sample number in each section, with 1 being the lowest sample) for another analysis.

Both PCA and CVA have strengths and weaknesses; therefore, it is advisable to use both techniques in tandem, and to use them to answer different questions. 

In order to compare the size of specimens of Chiosella, measurements of height and length were made directly off of the same, scaled SEM photographs that were used to conduct the landmark analysis, as well as other proviously published images from South China and Nevada.