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. 2019 Nov 28;9(1):17801.
doi: 10.1038/s41598-019-53591-7.

Reassessment of a juvenile Daspletosaurus from the Late Cretaceous of Alberta, Canada with implications for the identification of immature tyrannosaurids

Jared T Voris  1 , Darla K Zelenitsky  2 , François Therrien  3 , Philip J Currie  4
Affiliations

Reassessment of a juvenile Daspletosaurus from the Late Cretaceous of Alberta, Canada with implications for the identification of immature tyrannosaurids

Jared T Voris et al. Sci Rep. .

Abstract

Daspletosaurus is a large tyrannosaurine found in upper Campanian deposits of Alberta and Montana. Although several large subadult and adult individuals of this taxon are known, only one juvenile individual, TMP 1994.143.1, has been identified. This specimen has played a key role in the idea that juvenile tyrannosaurid individuals are difficult to differentiate among species. Here the taxonomic affinity of TMP 1994.143.1 is reassessed in light of a juvenile tyrannosaurine postorbital recently discovered in the Dinosaur Park Formation of Alberta. Anatomical comparisons and phylogenetic analyses reveal that TMP 1994.143.1 is referable to the albertosaurine Gorgosaurus libratus, whereas the new postorbital belongs to a small juvenile Daspletosaurus. This taxonomic reassignment of TMP 1994.143.1 results in the juvenile ontogenetic stage of Daspletosaurus being known only from two isolated cranial elements. The new postorbital provides insights into early Daspletosaurus ontogeny, revealing that the cornual process developed earlier or faster than in other tyrannosaurids. Although some ontogenetic changes in the postorbital are found to be unique to Daspletosaurus, overall changes are most consistent with those of other large tyrannosaurines. Our results also show that diagnostic features develop early in ontogeny, such that juveniles of different tyrannosaurid species are easier to differentiate than previously thought.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Skull reconstruction of TMP 1994.143.1. Digital rendering of skull based on CT data in right lateral view (a), left lateral view (b), dorsal view (c) and anterior view (d). Note that not all preserved elements were CT scanned. Skull reconstruction in right lateral view based on combination of preserved right and left elements (e). Digital renderings (c,d) show that the articulated bones of the rostrum (in red) has been mediolaterally widened due to taphonomic deformation, making the temporal region of the skull appear wide. Scale bars equal 100 mm. Institutional abbreviation: TMP, Royal Tyrrell Museum of Palaeontology.
Figure 2
Figure 2
Juvenile Daspletosaurus postorbital TMP 2013.18.11 in lateral (a,c) and medial (b,d) views. Abbreviations: afas, anterior expansion of the frontal sutural surface; ar, anterior ramus; cp, cornual process; dass, anterior end of the dorsal contact for the squamosal; pr, posterior ramus; sr, smooth region separating cornual process from orbit margin; vr, ventral ramus. Scale bars equal 50 mm. Institutional abbreviation: TMP, Royal Tyrrell Museum of Palaeontology.
Figure 3
Figure 3
Left postorbital of TMP 1994.143.1 in lateral (a,c) and medial (b,d) views. Abbreviations as in Fig. 2 in addition to: sop, suborbital process. Scale bar equals 50 mm. Institutional abbreviation: TMP, Royal Tyrrell Museum of Palaeontology.
Figure 4
Figure 4
Growth series of the postorbital in Daspletosaurus (a,d) and Gorgosaurus (b,c,e). Elements shown in lateral view. (a) Small juvenile Daspletosaurus TMP 2013.18.11; (b) Small juvenile Gorgosaurus TMP 1986.144.1; (c) Large juvenile-subadult Gorgosaurus TMP 1994.143.1; (d) Adult Daspletosaurus TMP 2001.36.1; (e) Adult Gorgosaurus UALVP 10. The intermediate large juvenile-subadult Daspletosaurus condition is unknown. Abbreviations as in Figs. 2 and 3. Scale bars equal 50 mm. Institutional abbreviations: TMP, Royal Tyrrell Museum of Palaeontology; UALVP, University of Alberta Laboratory of Vertebrate Paleontology.
Figure 5
Figure 5
Consensus of the cladistic analyses of Tyrannosauroidea, based on the matrix of Carr et al. (2017). (a) Single most parsimonious tree recovered from an analysis of characters pertaining only to the postorbital, which evaluates the positions of TMP 2013.18.11 and TMP 1994.143.1. Tree length = 18 steps, consistency index = 0.778, retention index = 0.949. (b) Single most parsimonious tree recovered from an analysis including cranial and postcranial characters, which evaluates the position of TMP 1994.143.1. Tree length = 833 steps, consistency index = 0.539, retention index = 0.796. Numbers adjacent to nodes constitute Bremer support values (<3) and Bootstrap values (>50). Unsupported nodes are collapsed. Institutional abbreviations: TMP, Royal Tyrrell Museum of Vertebrate Palaeontology.
Figure 6
Figure 6
Ontogenetic series of Daspletosaurus torosus including TMP 2013.18.11 and other key specimens. Specimens are plotted based on percent skull length (SL) relative to the largest known individual (TMP 2001.36.1). Specimens are drawn to scale. Some specimens are listed but not illustrated due to space limitations. Note that this taxon is predominantly known from large individuals (SL > 80%). Institutional abbreviations: CMN, Canadian Museum of Nature; FMNH, Field Museum of Natural History; TMP, Royal Tyrrell Museum of Palaeontology.
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References

    1. Carpenter, K. Tyrannosaurids (Dinosauria) of Asia and North America. In Aspects of Nonmarine Cretaceous Geology (eds Mateer N. J. & Chen, P. J.) 250–268 in (China Ocean Press, 1992).
    1. Carr TD. Craniofacial ontogeny in Tyrannosauridae (Dinosauria, Coelurosauria) J. Vertebr. Paleontol. 1999;19:497–520. doi: 10.1080/02724634.1999.10011161. - DOI
    1. Carr TD. A taxonomic assessment of the type series of Albertosaurus sarcophagus and the identity of Tyrannosauridae (Dinosauria, Coelurosauria) in the Albertosaurus bonebed from the Horseshoe Canyon Formation (Campanian–Maastrichtian, Late Cretaceous) Canadian J. Earth Sci. 2010;47:1213–1226. doi: 10.1139/E10-035. - DOI
    1. Currie PJ. Cranial anatomy of tyrannosaurid dinosaurs from the Late Cretaceous of Alberta, Canada. Acta Palaeontol. Pol. 2003;48:191–226.
    1. Currie PJ. Allometric growth in tyrannosaurids (Dinosauria: Theropoda) from the Upper Cretaceous of North America and Asia. Canadian J. Earth Sci. 2003;40:651–665. doi: 10.1139/e02-083. - DOI

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