Geomorphometric analysis of Azygograptus species (Graptolithina) from the Central Andean Basin

HERRERA S., NEXXYS C; LO VALVO, G.; DEGRANGE, F. J. ; TORO, BLANCA AZUCENA

Puerto Madryn

Congreso; Reunión de Comunicaciones de la Asociación Paleontológica Argentina 2018; 2018

Asociación Paleontologica Argentina

The single-stiped morphology and simple thecal form make the genus Azygograptus easily recognizable, but the identification at species levelresults complicated by subtle differences, the scarcity of detailed descriptions, intraspecific variations and deformation. Here, an elliptic Fourier analysis is carried out in the proximal end of individuals to test the systematic classification at species level. The resulting coordinates weresubjected to an exploration using principal components and cluster analysis to examine groupings. We include 22 individuals from two speciescharacterized by the absence of adpressed growth of theca1 along the sicula: Azygograptus lapworthi Nicholson and A. eivinonicus Elles.The contour analysis showed that the first three components explain 79.21% ofthe total variation in the shape of the specimens. PC1 represented the stipe width at theca1 and the differences in the sicular morphology: narrowstipes at theca1 and large-elongated siculas (negative) vs. wide stipes at theca1 and short-stouter siculas (positive). Meanwhile, PC2 explained thevariation in the stipe divergence angle: close to 90º (negative) vs. greater than 90º (positive). Moreover, dendrograms illustrated that individualsfrom different species are related and grouped together. Thus, the resulting morphospaces and clusterings allow inferring that the specimenspreviously assigned as two different species are geomorphometrically indistinguishable. Therefore, we can conclude that all the material couldcorrespond to a unique species (A. lapworthi) with intraspecific variations.