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. 2018 Oct 9:6:e5749.
doi: 10.7717/peerj.5749. eCollection 2018.

A new tyrannosaurid (Dinosauria: Theropoda) from the Upper Cretaceous Menefee Formation of New Mexico

Affiliations

A new tyrannosaurid (Dinosauria: Theropoda) from the Upper Cretaceous Menefee Formation of New Mexico

Andrew T McDonald et al. PeerJ. .

Abstract

The giant tyrannosaurids were the apex predators of western North America and Asia during the close of the Cretaceous Period. Although many tyrannosaurid species are known from numerous skeletons representing multiple growth stages, the early evolution of Tyrannosauridae remains poorly known, with the well-known species temporally restricted to the middle Campanian-latest Maastrichtian (∼77-66 Ma). The recent discovery of a new tyrannosaurid, Lythronax argestes, from the Wahweap Formation of Utah provided new data on early Campanian (∼80 Ma) tyrannosaurids. Nevertheless, the early evolution of Tyrannosauridae is still largely unsampled. We report a new tyrannosaurid represented by an associated skeleton from the lower Campanian Allison Member of the Menefee Formation of New Mexico. Despite fragmentation of much of the axial and appendicular skeleton prior to discovery, the frontals, a metacarpal, and two pedal phalanges are well-preserved. The frontals exhibit an unambiguous autapomorphy and a second potential autapomorphy that distinguish this specimen from all other tyrannosaurids. Therefore, the specimen is made the holotype of the new genus and species Dynamoterror dynastes. A phylogenetic analysis places Dynamoterror dynastes in the tyrannosaurid subclade Tyrannosaurinae. Laser-scanning the frontals and creation of a composite 3-D digital model allows the frontal region of the skull roof of Dynamoterror to be reconstructed.

Keywords: Allison member; Dynamoterror dynastes; Menefee formation; Tyrannosauridae.

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Conflict of interest statement

The authors declare that they have no competing interests. Andrew T. McDonald and Alton C. Dooley Jr. are employed by Western Science Center, Hemet, California, and Douglas G. Wolfe is employed by Zuni Dinosaur Institute for Geosciences, Springerville, Arizona.

Figures

Figure 1
Figure 1. Frontals of UMNH VP 28348 in rostral view.
Photographs and 3-D models of right (A, B) and left (C, D) frontals of UMNH VP 28348. Abbreviations: bnp, basal of nasal process; cnc, caudal extent of nasal cavity; plp, prefrontolacrimal process; pnp, prefrontonasal process; rpos, rostral part of postorbital suture; vls, ventrolateral part of lacrimal suture. Scale bars equal five cm.
Figure 2
Figure 2. Frontals of UMNH VP 28348 in dorsal view.
Photographs and 3-D models of right (A, B) and left (C, D) frontals of UMNH VP 28348. Abbreviations: bnp, basal of nasal process; mls, medial-most point of lacrimal suture; plp, prefrontolacrimal process; pnp, prefrontonasal process; rpos, rostral part of postorbital suture; scr, sagittal crest; stf, supratemporal fossa. Scale bars equal five cm.
Figure 3
Figure 3. Frontals of UMNH VP 28348 in ventral view.
Photographs and 3-D models of right (A, B) and left (C, D) frontals of UMNH VP 28348. Abbreviations: bnp, basal of nasal process; ccr, crista cranii; cnc, caudal extent of nasal cavity; cpos, caudal part of postorbital suture; es, ethmoid scar; gpos, groove between rostral and caudal parts of postorbital suture; lss, laterosphenoid suture; mls, medial-most point of lacrimal suture; obf, olfactory bulb fossa; oss, orbitosphenoid suture; plp, prefrontolacrimal process; pnp, prefrontonasal process; sog, supraorbital groove; vls, ventrolateral part of lacrimal suture. Scale bars equal five cm.
Figure 4
Figure 4. Frontals of UMNH VP 28348 in medial view.
Photographs and 3-D models of right (A, B) and left (C, D) frontals of UMNH VP 28348. Abbreviations: bnp, basal of nasal process; cnc, caudal extent of nasal cavity; ifs, interfrontal suture; obf, olfactory bulb fossa; oss, orbitosphenoid suture; scr, sagittal crest. Scale bars equal five cm.
Figure 5
Figure 5. Frontals of UMNH VP 28348 in lateral view.
Photographs and 3-D models of right (A, B) and left (C, D) frontals of UMNH VP 28348. Abbreviations: bnp, basal of nasal process; cpos, caudal part of postorbital suture; gpos, groove between rostral and caudal parts of postorbital suture; ow, orbital wall; ps, parietal suture; rpos, rostral part of postorbital suture; scr, sagittal crest; sog, supraorbital groove; stf, supratemporal fossa; vls, ventrolateral part of lacrimal suture. Scale bars equal five cm.
Figure 6
Figure 6. Comparison among derived tyrannosaurine frontals.
Digital models and line drawings of the right (A, B) and left (C, D) frontals of Dynamoterror dynastes, UMNH VP 28348, in lateral view. The postorbital suture is highlighted in purple. Scale bar equals five cm for A–D. BYU 8120/9396, right frontal of Teratophoneus curriei in lateral view, shown as a photograph (E), photograph with the postorbital suture highlighted in purple (F), and a line drawing with the postorbital suture highlighted in purple (G). Photograph of BYU 8120/9396 courtesy of Rod Scheetz (BYU) and is used here with permission. Additional anatomical information from UMNH VP 16690 (Fig. 3E in Loewen et al. (2013)). UMNH VP 20200, right frontal of Lythronax argestes in lateral view, shown as an image with the postorbital suture highlighted in purple (H) (modified from Fig. 2E in Loewen et al. (2013)), and a line drawing with the postorbital suture highlighted in purple (I).
Figure 7
Figure 7. Frontals of UMNH VP 28348 in caudal view.
Photographs and 3-D models of right (A, B) and left (C, D) frontals of UMNH VP 28348. Abbreviations: lss, laterosphenoid suture; ps, parietal suture; scr, sagittal crest; stf, supratemporal fossa. Scale bars equal five cm.
Figure 8
Figure 8. Middle caudal centrum of UMNH VP 28348.
Incomplete middle caudal centrum in left lateral view. Abbreviations: chf, chevron facet. Scale bar equals five cm.
Figure 9
Figure 9. Right metacarpal II of UMNH VP 28348.
Right metacarpal II in (A) dorsal; (B) ventral; (C) lateral; (D) medial; (E) proximal; and (F) distal views. Abbreviations: aMC I, surface for articulation with metacarpal I; lhc, lateral hemicondyle; mhc, medial hemicondyle; tr, trochlea. Scale bar equals five cm.
Figure 10
Figure 10. Supraacetabular crest of the right ilium of UMNH VP 28348.
Supraacetabular crest of the right ilium in lateral view. Abbreviations: acr, rim of the acetabulum. Scale bar equals five cm.
Figure 11
Figure 11. Pedal phalanges of UMNH VP 28348.
Phalanx 2 of left pedal digit IV in (A) proximal; (B) distal; (C) dorsal; (D) ventral; (E) medial; and (F) lateral views. Phalanx 4 of left pedal digit IV in (G) proximal; (H) distal; (I) dorsal; (J) ventral; (K) medial; and (L) lateral views. Abbreviations: fo, fovea; lc, lateral condyle; mc, medial condyle; tr, trochlea. Scale bars equal five cm.
Figure 12
Figure 12. Phylogenetic relationships of Dynamoterror dynastes.
Strict consensus cladogram of 18 most parsimonious trees obtained by TNT. Tree image was prepared in Mesquite. Bremer support values are next to each node.
Figure 13
Figure 13. Reconstructed frontal complex of Dynamoterror dynastes.
Composite, articulated right and left frontals in (A) rostral; (B) caudal; (C) right lateral; (D) dorsal; and (E) ventral views. (F) Reconstructed skull roof in dorsal view. Elements are color-coded as follows: frontals (gray); fused nasals (violet); prefrontals (yellow); lacrimals (red); postorbitals (blue); and parietal (green). Missing elements reconstructed based upon Teratophoneus curriei (UMNH VP 16690) (Loewen et al., 2013). Scale bars equal five cm.

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