Figure 2 Ontogram of Tyrannosaurus rex showing growth stages, synontomorphies, individual variation, individual specimens, and chronological ages. Arrowhead points to the most mature specimen and the direction of the entire ontogenetic axis; that is, the least mature specimen is at the lower left whereas the most mature specimen is at the upper right. Asterisk indicates the type specimen. Individual variation occurs as progressions until young adulthood, where reversals are first seen. The maximum amount of change occurs at growth stages 5 and 6, which corresponds to the transition from a long and low skull and jaws to a deep and stout skull frame; this event, marked by the concentration of an extreme number of changes, is evidence that the ontogeny of T. rex is metamorphic (sensu Rose & Reiss, 1993). Each circle represents a numbered growth stage; these numbers do not correspond to those seen in Fig. 12. The star at growth stage 7 marks the ~3,000 kg threshold that separates T. rex from its closest, but smaller, relatives. Color key: red, small juveniles; orange, large juveniles; yellow, subadults; green, young adults; blue, adults; violet, senescent adults. See text for definition of growth categories. Skulls are to scale; AMNH FARB 5027 is scaled to a premaxilla to quadrate length of 1.3 m. Full-size DOI: 10.7717/peerj.9192/fig-2

Published as part of Carr, Thomas D., 2020, A high-resolution growth series of Tyrannosaurus rex obtained from multiple lines of evidence, pp. e9192 in PeerJ 8 on page 14, DOI: 10.7717/peerj.9192, http://zenodo.org/record/5824972