Tyrannosaurid Paleobiology by J. Michael Parrish & Ralph E. Molnar & Philip J. Currie & Eva B. Koppelhus

Author:J. Michael Parrish & Ralph E. Molnar & Philip J. Currie & Eva B. Koppelhus
Language: eng
Format: epub
Publisher: Indiana University Press
Published: 2013-02-05T16:00:00+00:00

Summary

The purpose of this study was assessment of the relative brain and relative cerebrum size of tyrannosaurid dinosaurs (Tyrannosaurus rex, Gorgosaurus, and Nanotyrannus) and comparison of these data to results for allosauroid dinosaurs (Allosaurus and Carcharodontosaurus). To measure relative brain size, EQs (Encephalization Quotients) were calculated using brain-body data for extant non-avian reptile species (N = 62) and extant bird species (N = 174). We compared dinosaur log EQs to the ranges of reptile log REQs and bird log BEQs because these samples were normally distributed, unlike either reptile REQs or bird BEQs. To estimate brain mass (MBr) from dinosaur endocast volume (EV), the MBr:EV ratio was determined in a size series, ranging from the smallest sexually mature to the largest commonly encountered size, of Alligator mississippiensis, an examplar of the extant archosaurian clade Crocodylia. The mean of MBr:EV ratios of the largest male and female was 37 percent, and the ratio was 67 percent in the smallest sexually mature alligators. Dinosaur MBr and MCb (cerebrum mass) were estimated from virtual endocasts produced from CT scans and also from laser scans and double graphic integration. Brain mass was estimated from EV in dinosaurs using the adult ratio and in Nanotyrannus, a possible juvenile, also using the youngest subadult ratio. Estimates were also made using the traditional 50 percent MBr:EV ratio, for comparison to previous studies and because this is the MBr:EV ratio in midrange subadult alligators, appropriate for the Gorgosaurus specimen. Relative brain sizes of small theropods and a wide sample of other dinosaurs were also determined to provide a context for evaluation of these large theropods. The cerebrum mass:brain mass (MCb:MBr) range was compared among dinosaurs and between dinosaurs and each of reptiles and birds.

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