Friday, September 23, 2016

Pycnonemosaurus nevesi is the new King Abelisauroid Theropod


Grillo et al


Abelisauroid dinosaurs normally reached an average body length (BL) of 5–9 m, but there are controversies due to the incomplete or fragmentary nature of most specimens. For Ekrixinatosaurus, for example, BL was estimated as 10–11 m or 7–8 m; for Pycnonemosaurus it was proposed 7–8 m, however its preserved bones are larger than any other described abelisauroid. The lack of a consistent methodology complicates comparisons of estimated BL, so we reevaluated the estimative for the seven most complete specimens of abelisauroids and compared the values against 40 measurements from the skull, vertebrae and appendicular elements using bivariate equations. It allowed estimating the BL of other 30, less complete, specimens of abelisauroids and to evaluate the allometric scaling of the skeletal parts. Strong correlations (R2 > 0.96) were obtained for all vertebrae and hindlimb measurements, as well as skull height, and length of skull roof, lacrimal–squamosal, scapulocoracoid and humerus; other skull and forelimb measurements present weak correlation due to extreme morphological transformations observed in Abelisauridae and were not adequate for BL estimation. Abelisauroids gradually increased in size during evolution: the mean BL was 3.3 ± 2.5 m for basal abelisauroids and Noasauridae, 5.4 ± 1.8 m for basal Brachyrostra and Majungasauridae, and 7.1 ± 2.1 m for Furileusaura. Despite this variation, diversity of BL on each geographic region and stratigraphic epoch was relatively constant (BL usually varied from 4 to 8 m). The smallest noasaurid and abelisaurid are, respectively, Velocisaurus (1.5 ± 0.1 m) and Genusaurus (3.6 ± 0.0 m). The largest abelisaurids is Pycnonemosaurus nevesi (8.9 ± 0.3 m) followed by Carnotaurus (7.8 ± 0.3 m), Abelisaurus (7.4 ± 0.7 m) and Ekrixinatosaurus (7.4 ± 0.8 m). Skull measurement scale negatively at a similar rate but the height scales almost isometrically and the skull roof length scales more negatively; this probably caused a bending on the skull that may explain the upward orientation of the snout in large taxa.

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