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. 2011;6(6):e21376.
doi: 10.1371/journal.pone.0021376. Epub 2011 Jun 29.

Reanalysis of "Raptorex Kriegsteini": A Juvenile Tyrannosaurid Dinosaur From Mongolia

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Free PMC article

Reanalysis of "Raptorex Kriegsteini": A Juvenile Tyrannosaurid Dinosaur From Mongolia

Denver W Fowler et al. PLoS One. .
Free PMC article

Abstract

The carnivorous Tyrannosauridae are among the most iconic dinosaurs: typified by large body size, tiny forelimbs, and massive robust skulls with laterally thickened teeth. The recently described small-bodied tyrannosaurid Raptorex kreigsteini is exceptional as its discovery proposes that many of the distinctive anatomical traits of derived tyrannosaurids were acquired in the Early Cretaceous, before the evolution of large body size. This inference depends on two core interpretations: that the holotype (LH PV18) derives from the Lower Cretaceous of China, and that despite its small size, it is a subadult or young adult. Here we show that the published data is equivocal regarding stratigraphic position and that ontogenetic reanalysis shows there is no reason to conclude that LH PV18 has reached this level of maturity. The probable juvenile status of LH PV18 makes its use as a holotype unreliable, since diagnostic features of Raptorex may be symptomatic of its immature status, rather than its actual phylogenetic position. These findings are consistent with the original sale description of LH PV18 as a juvenile Tarbosaurus from the Upper Cretaceous of Mongolia. Consequently, we suggest that there is currently no evidence to support the conclusion that tyrannosaurid skeletal design first evolved in the Early Cretaceous at small body size.

Conflict of interest statement

Competing Interests: We have the following competing interest: Peter L. Larson is an employee of Black Hills Institute of Geological Research Inc. There are no patents, products in development or marketed products to declare. This does not alter our adherence to all the PLoS ONE policies on sharing data and materials, as detailed online in the guide for authors.

Figures

Figure 1
Figure 1. Comparison of the LH PV18 fish centrum (D) to an ellimmichthyiform centrum (A–C) (Horseshoeichthyes) from the Dinosaur Park Formation (Campanian) of Alberta.
The notochordal foramen (NF) in the LH PV18 fish centrum (D) is so small that it cannot be seen from the angle of the photograph. The exact number and positions of mid-dorsal fossae (MDF) and laterodorsal fossae (LDF) are variable within the same taxon . Photos (A–C) have been rotated to align with the general orientation of the obliquely figured LH PV18 fish centrum. Picture (A) was also flipped horizontally to simulate the right lateral view. Additional abbreviations: NA: neural arch articular pit. (A–C) adapted from Newbrey et al. (, Figure 9h). (D) adapted from Sereno et al. (, Figure S8B).
Figure 2
Figure 2. Osteohistological features of LH PV18 and a near adult Tyrannosaurus rex for comparison.
(A) Femur cross section of LH PV18 modified from Sereno et al. (, Figure S7A). Only two small clusters of secondary osteons (arrows) are visible, associated with adductor muscle attachment sites. The width of cortical bone from the edge of the medullary cavity to LAG 1 (green bar labeled 1) is nearly the same as the width of cortical bone from LAG 2 to the outer surface (green bar labeled 3). (B) Mid to outer cortex of a femur cross section from a Tyrannosaurus rex (MOR 1198; Museum of the Rockies, Bozeman, Montana) described as approaching adult length. The bone surface is located to the right of the picture. Several generations of secondary osteons nearly obliterate primary tissue within the deeper cortex and become scattered close to the surface. This pattern is typical of dinosaurs approaching asymptotic size. Scale bar = 5 mm.

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