Fig 1.
Dorsal vertebrae showing evidence of metaplastic rugosities on the neural spine.
(A) Dorsal vertebra from a Troodon (MOR 553–8.20.92.305), a small-bodied theropod. (B) A dorsal vertebra from an Allosaurus (MOR 693), a large bodied theropod. Note the expanded metaplastic rugosities in Allosaurus (highlighted by 50% transparency) compared with Troodon. of the mature individual compared with the smaller rugosities of the immature animal. Both dorsal vertebrae in left lateral view. Scale bars = 10 cm.
Table 1.
Femur length and the presence or absence of rugose projections that extend from the anterior and posterior blades of the neural spines in the dorsal region.
Fig 2.
Histological section of the interspinous ligament enthesis in a dorsal vertebra in Alligator and Tyrannosaurus.
(A) The enthesis in Alligator (H&E staining, 40x) exhibiting an undulating interface surface between the lighter ligament (marked “En.” on the left of the panel) and bone of the neural spine (marked “N.S.”). (B) The enthesis in Tyrannosaurus (100x) shows rough-bundled metaplastic tissue in the area of the enthesis, which deeply interdigitates with the neural spine.
Fig 3.
(A) Phylogenetic tree onto which femur length (Ln cm) is mapped using maximum likelihood. Species with metaplastic rugosities on neural spines are bolded. Note that Spinosaurus is large-bodied, but lacks rugose neural spines, most likely owing to its elongate neural spines. (B) Distribution of femur length (Ln cm) in theropods grouped by the absence (top quartile plot) or presence (bottom quartile plot) of rugose neural spines. Quantiles are shown in gray boxes with the minimum, 25%, median, 75%, and maximum values shown for each group. The color code of data matches the gradient from the phylogenetic mapping in panel A, which correspond to natural log femur length with red representing the longest and purple representing the shortest. A phylogenetic t-test supports a substantial difference in average body size between species that exhibit or lack neural spine rugosities (n = 56, p-value < 1.0e-10).