IS A STRANGE HEAD CONSEQUENCE OF ITS EVOLUTIONARY HISTORY? THE USE OF GEOMETRIC MORPHOMETRIC AND PHYLOGENETIC COMPARATIVE METHODS TO ASSESS THE EVOLUTION OF THE ABELISAURIDS SKULL

SECULI PEREYRA, EMANUEL; MÉNDEZ, ARIEL; PASCHETTA, CAROLINA

Malargüe

Jornada; IV Jornadas de Palentología de la Cuenca Neuquina; 2023

Abelisauridae represent the best‐known clade of theropod dinosaurs for the UpperCretaceous of Gondwana. In recent decades, the increase of abelisaurid records has allowedus to have a better knowledge of the morphological diversity within this clade. This grouphas been mostly studied in a classic descriptive way without incorporating a quantitativeapproach. Here, we used scientific illustrations to quantify the shape of the skull of differentspecies of abelisaurids using 2D geometric morphometric technique and PrincipalComponent Analysis (PCA) to assess how the skull shape changes when it is compared withcloser taxa like noasaurids and basal taxa like Ceratosaurus. Additionally, we tested if theshape of the skull correlates with the phylogeny using phylogenetic signal test andphylogenetic graphical ordinations methods (Phylomorphospace, Phylo‐PCA, andPhylogenetic Aligned Component Analysis ‐PACA‐) to assess different trends in abelisauridsevolution, following a Brownian motion model. The PC1 explains 32.21% of the variance indata, and it was related to the height and length of the skull, showing taxa like Carnotaurusin the extreme positive of this component with a height and short skull and Herrerasauruswith a long and low skull in the extreme negative of this component. The PC2 explains 18.88% of the variance in data, and it was related to the form of the orbit and the bones thatdefine it (postorbital, lacrimal, and jugal); the taxa that were in the negative extreme of thisPC exhibit expanded and circular orbits (lacrimal and postorbital broad at their bases andslender in contact with the jugal) like noasaurids while the other taxa were closer of themean shape. The phylogenetic signal test was significant with a Kmult=0.59714. When thephylogeny is taken into account, a Phylomorphospace was built; the species that were morerelated in the phylogenetic tree were closer and, in the same way, when a PACA fixed allthe variance due to phylogeny in the first component. These results are consistent with thephylogenetic signal test. The different trends detected in the phylogenetic ordinationmethods suggest that the abelisaurids and noasaurids when we compare them with basaltaxa (Ceratosaurus, Herrerasaurus), are divergent clades due to they occupy different partsof the phylogenetic morphospace. More studies are needed to understand the evolution ofthe abelisaurid skull as a whole, which incorporates different evolutionary models and 3Dgeometric morphometrics of the skull.