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, 7 (8), e43911

Martharaptor Greenriverensis, a New Theropod Dinosaur From the Lower Cretaceous of Utah

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Martharaptor Greenriverensis, a New Theropod Dinosaur From the Lower Cretaceous of Utah

Phil Senter et al. PLoS One.

Abstract

Background: The Yellow Cat Member of the Cedar Mountain Formation (Early Cretaceous, Barremian?) of Utah has yielded a rich dinosaur fauna, including the basal therizinosauroid theropod Falcarius utahensis at its base. Recent excavation uncovered a new possible therizinosauroid taxon from a higher stratigraphic level in the Cedar Mountain Formation than F. utahensis.

Methodology/principal findings: Here we describe a fragmentary skeleton of the new theropod and perform a phylogenetic analysis to determine its phylogenetic position. The skeleton includes fragments of vertebrae, a scapula, forelimb and hindlimb bones, and an ischium. It also includes several well-preserved manual unguals. Manual and pedal morphology show that the specimen is distinct from other theropods from the Cedar Mountain Formation and from previously described therizinosauroids. It is here named as the holotype of a new genus and species, Martharaptor greenriverensis. Phylogenetic analysis places M. greenriverensis within Therizinosauroidea as the sister taxon to Alxasaurus + Therizinosauridae, although support for this placement is weak.

Conclusions/significance: The new specimen adds to the known dinosaurian fauna of the Yellow Cat Member of the Cedar Mountain Formation. If the phylogenetic placement is correct, it also adds to the known diversity of Therizinosauroidea.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Stratigraphy of the Hayden-Corbett Site (Gr287v).
Stratigraphic section of the basal Cedar Mountain Formation of eastern Utah, showing that Martharaptor is from a bed stratigraphically higher than those yielding Falcarius.
Figure 2
Figure 2. Outlines of manual unguals I (left), II (middle), and III (right) of Martharaptor greenriverensis and two other basal therizinosauroids.
(A)–Martharaptor greenriverensis. (B)–Falcarius utahensis, after Zanno (C)–Beipiaosaurus inexpectus, drawn from photos by the senior author from a cast of IVPP (Institute of Vertebrate Paleontology and Paleoanthropology, Beijing, China) V 11559. Outlines are to scale within sub-figure A and within sub-figure C but not within sub-figure B or between sub-figures. Note that M. greenriverensis differs from F. utahensis and B. inexpectus in overall ungual shape and flexor tubercle morphology, and differs from B. inexpectus in the relative size of the ungual of digit III. The size of the ungual of digit III relative to the others cannot be determined for F. utahensis, because no known specimen preserves all three unguals.
Figure 3
Figure 3. Vertebrae, scapula, forelimb bones, and pelvic bones of Martharaptor greenriverensis (UMNH VP 21400).
(A)–Partial cervical neural arch, dorsal view. (B–E)–Cranial dorsal centrum in cranial (B), caudal (C), right lateral (D), and left lateral (E) views. (F–G)–Distal caudal centrum in lateral (F) and ventral (G) views. (H)–Possible ulna. (I)–Possible radius. (J–K)–Left scapula in lateral (J) and medial (K) views. (L)–Proximal end of ischium. (M)–Possible distal end of pubis Scale bar = 50 mm. acr  =  acromium process, ar  =  acetabular rim, gl  =  glenoid, hyp  =  hypapophysis, poz  =  postzygapophysis, pnp  =  pneumatopore, prz  =  prezygapophysis.
Figure 4
Figure 4. Manual bones of Martharaptor greenriverensis (UMNH VP 21400).
(A)–Presumed metacarpal I. (B)–Presumed phalanx I-1. (C)–Penultimate phalanx. (D) Penultimate phalanx. (E)–Unidentified phalanx. (F)–Unidentified phalanx. (G)–Ungual of digit I. (H)–Ungual of digit I. (I)–Ungual of digit II. (J)–Ungual of digit II. (K)–Ungual of digit III. (L)–Ungual of digit III. Scale bar = 50 mm. Numbers on sub-figures refer to proximal (1), distal (2), dorsal (3), palmar (4), and side (5) views; for side views, whether the side is medial or lateral cannot be determined.
Figure 5
Figure 5. Metatarsals of Martharaptor greenriverensis (UMNH VP 21400).
(A)–Left metatarsal I. (B)–Left metatarsal II. (C)–Presumed left metatarsal III. (D)–Right metatarsal II. (E)–Right metatarsal IV. Scale bar = 50 mm. Numbers on sub-figures refer to proximal (1), distal (2), dorsal (3), plantar (4), medial (5), and lateral (6) views.
Figure 6
Figure 6. Pedal phalanges of Martharaptor greenriverensis (UMNH VP 21400).
(A–K)–Unidentified phalanges. (L)–Ungual of digit I. (M)–Ungual of unidentified digit (II, III, or IV). Scale bar = 50 mm. Numbers on sub-figures refer to proximal (1), distal (2), dorsal (3), plantar (4), and side (5) views; for side views, whether the side is medial or lateral cannot be determined. Phalanx H articulates well with phalanx J, and phalanx G articulates well with phalanx I.
Figure 7
Figure 7. Phylogenetic position of Martharaptor greenriverensis within Coelurosauria, as found by this study.
Genus names in green are Asian therizinosauroids, and those in red are North American therizinosauroids. Numbers at therizinosauroid clades indicate decay indices (Bremer values).

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