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, 8 (5), e63423

An Unusual Basal Therizinosaur Dinosaur With an Ornithischian Dental Arrangement From Northeastern China

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An Unusual Basal Therizinosaur Dinosaur With an Ornithischian Dental Arrangement From Northeastern China

Hanyong Pu et al. PLoS One.

Abstract

Therizinosauria are an unusual group of theropod dinosaurs, found mostly in the Cretaceous deposits in Mongolia, China and western USA. The basal forms of this group are represented by incomplete or disarticulated material. Here, we report a nearly complete, articulated skeleton of a new basal therizinosaur from the Early Cretaceous Yixian Formation of Jianchang County, western part of Liaoning Province, which sheds light on our understanding of anatomy of basal therizinosaurs. This new dinosaur shows some typical therizinosaur features, such as neural spines of the anterior caudal vertebrae that possess anterior and posterior alae, a rectangular buttress on the ventrolateral side of the proximal end of metacarpal I, and appressed metatarsal shafts. Our phylogenetic analysis suggests that it is a basal therizinosaur (sister taxon to Therizinosauroidea) because it bears many basal therizinosaur characters in the dentition, pelvis and hind limbs. The new therizinosaur described here has unique tooth and jaw characters such as the offsetting of the tooth row by a shelf and dentary teeth with labially concave and lingually convex dentary teeth, similar to ornithopods and ceratopsians.

Conflict of interest statement

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

Figures

Figure 1
Figure 1. A photograph of the skeleton of Jianchangosaurus yixianensis gen. et sp. nov. (41HIII-0308A) (A) and line drawing (B).
Abbreviations: at, atlas; ax, axis; cav, caudal vertebra; cv, cervical vertebra; co, coracoid; dc, distal carpal; dv, dorsal vertebra; l., left; f, femur; fi, fibula; fur, furcula; hu, humerus; il, ilium; is, ischium; pu, pubis; ra, radius; sc, scapula; ti, tibia; ul, ulna; mc, metacarpal; mt, metatarsal; mxf, maxillary fenestra; pat, proatlas; r., right; sr, sacral rib; sv, sacral vertebra; ung, ungual. All elements of the skeleton are preserved except the distal half of the caudal vertebrae. Dashed lines of metatarsals indicate areas that have been reconstructed. The middle portion of the neck, from the fourth to ninth cervical vertebrae, and the pedal phalanges have been repositioned. The rest of elements of this specimen are in the original position.
Figure 2
Figure 2. A, Reconstruction the skeleton of Jianchangosaurus yixianensis gen. et sp. nov. The hip height is approximately 1 meter.
It is 1880 mm long from the skull to the eleventh caudal vertebra. B, Reconstruction of the skull. The ventral lacrimal, postorbital, posterior jugal, anterior edge of the quadrate, anterior surangular are missing. A rhamphotheca is reconstructed in grey based on edentulous area and a series of foramina. C, Cross section of the right upper and lower jaws, showing dental arrangement and rhamphotheca. Anterior portion (right) may have been used for plucking food by a rhamphotheca in the upper jaw and anterior dentary teeth with the normal dental morphology (convex labial and concave lingual surfaces). Posterior portion (left) shows the opposite dental morphology (concave labial and convex lingual surfaces) in the dentary, which allows the tips of the upper and lower teeth to abut each other. Abbreviations: an, angular; d, dentary; f, frontal; j, jugal; l, lacrimal; lat, lateral; m, maxilla; med, medial; n, nasal; pf, prefrontal; pm, premaxilla; q, quadrate; rham, rhamphotheca; sa, surangular; sq, squamosal.
Figure 3
Figure 3. Photograph of the skull of Jianchangosaurus yixianensis gen. et sp. nov. (A) and line drawing (B).
The right side of the skull is better exposed than the left side. The braincase and palatal bones are displaced. The seventh cervical vertebra is preserved next to the hyoids. Abbreviations: ect, ectopterygoid; hy, hyoids; mxf, maxillary fenestra; A, a large foramen at the base of the internarial bar of the premaxilla; B, a large foramen within the narial fossa of the premaxilla; C, a maxillary foramen above the eighth maxillary tooth; see captions for figures 1 and 2 for other abbreviations. Scale bars are 3 cm.
Figure 4
Figure 4. Dentition of Jianchangosaurus yixianensis gen. et sp. nov.
A, Teeth in the upper and lower jaws. Labial surfaces of the right maxillary and dentary teeth and lingual surfaces of the left dentary teeth are exposed. The premaxilla and anterior tip of the dentary are edentulous. B, Anterior left dentary teeth (first and second) in lingual view, showing the convex lingual surface. A replacement tooth is exposed at the root of the second dentary tooth. C, Posterior right maxillary teeth (from fourteenth to twentieth) in labial view. The crown size diminishes posteriorly. D, Middle right maxillary and dentary teeth in labial view. The maxillary teeth exhibit the conventional dental morphology (convex labial surfaces), but the dentary teeth show the reversed dental morphology (concave labial surfaces). E, Middle left dentary teeth (from eleventh to thirteenth) in lingual view, showing the reversed dental morphology (convex lingual surfaces). F, Anterior left dentary teeth in labial view, showing a shelf (red arrows; starting between d6 and d7) and a shift from normal (d4 to d6; convex labial surface) to reversed (d7 and posterior; concave labial surface) teeth. Scale bars on A–F are 1 cm.
Figure 5
Figure 5. Cervical and anterior dorsal vertebrae of Jianchangosaurus yixianensis gen. et sp. nov.
A, Atlas, axis and cervical vertebrae 3 and 8 in left lateral view. Cervical 8 is repositioned, but others are in the original position. B, Cervical vertebrae 5 and 6 in right lateral view and cervical vertebra 9 in left lateral view. Cervical 5 and 6 are articulated and repositioned on the opposite side. Cervical 9 is also repositioned. C, Cervical vertebra 10 and dorsal vertebrae 1–3. All are in the original position. See caption of Figure 1 for abbreviations. Scale bar is 5 cm for A–C.
Figure 6
Figure 6. Dorsal vertebrae and cervical vertebra 4 of Jianchangosaurus yixianensis gen. et sp. nov.
All neurocentral sutures are unfused. A, Articulated dorsal vertebrae 2–5 and ribs in left lateral view. B, Cervical vertebra 4 in dorsal view and dorsal vertebra 7 in left lateral view. A partial semilunate carpal can be observed next to dorsal vertebra 7. C, Semi-articulated dorsal vertebrae 8–12, likely displaced post-mortem. Abbreviations: slc, semilunate carpal; see caption of Figure 1 for other abbreviations. Scale bar is 5 cm for A–C.
Figure 7
Figure 7. Sacral and caudal vertebrae of Jianchangosaurus yixianensis gen. et sp. nov.
A, Articulated vertebrae from dorsal 12 to sacral 4. The lateral side of the first and second sacral vertebrae is exposed. The sacral centra are unfused, but the neutral spines of the third and fourth sacral vertebrae are fused into a single plate. B, Articulated caudal vertebrae (from the second to sixth). The distal tips of the neural spines have anterior and posterior alae. C, Articulate caudal vertebrae (from sixth to tenth) in dorsal view. See caption of Figure 1 for abbreviations. Scale bar is 5 cm for A–C.
Figure 8
Figure 8. Pectoral girdle and forelimbs of Jianchangosaurus yixianensis gen. et sp. nov.
A, Left pectoral girdle in lateral view and right humerus in ventral view. The scapula and coracoid are unfused. Scapular blade is straight and narrow. The coracoid is semicircular in shape. B, Left humerus, ulna, radius, and distal carpal (radiale). The forelimb is gracile. C, Disarticulated left metacarpals and manual digits. All metacarpals are preserved but some manual phalanges (II-1, III-1, III-2, and III-4) are missing. D, Right ulna, distal carpals (left, radiale; right, unidentified distal carpal), metacarpals, and manual phalanges. Metacarpal I shows a rectangular buttress for a contact with metacarpal II. Abbreviations: fur, furcula; g, gastralia; see caption of Figure 1 for other abbreviations. Scale bars are 5 cm. The scale bar on D is for panels B–D.
Figure 9
Figure 9. Pelvis and femora of Jianchangosaurus yixianensis gen. et sp. nov.
A, Left ilium in lateral view. The ilium is low and dorsal edge is nearly horizontal in lateral view. B, Left pubis in lateral view and right femur in posterior view. The fourth sacral centrum is preserved next to the right femur. C, Left ischium in lateral view. A triangular obturator process is positioned at the mid-length of the element. See caption of Figure 1 for abbreviations. Scale bar is 5 cm for A–C.
Figure 10
Figure 10. Hind limbs of Jianchangosaurus yixianensis gen. et sp. nov.
A, Right (above) and left (bottom) femora in posterior and anterior views, respectively. B, Both tibiae and right fibula. The distal half of the fibula is missing. C, Metatarsals and pedal unguals. The metatarsals are covered in part by thick coatings, and the distal half of most metatarsals may not be real (reconstructed). The specific identification of most phalanges is not possible because most are crushed. Five bones are identified as pedal phalanges and have been labeled. Abbreviations: lt, lesser trochanter; pph, pedal phalanx; see caption of Figure 1 for abbreviations. Scale bar is 3 cm for A–C.
Figure 11
Figure 11. Feathers of Jianchangosaurus yixianensis gen. et sp. nov.
The distal halves of the feathers are preserved as carbonized impressions, dorsal to the first to fourth dorsal vertebrae. These features are similar to the elongated broad filamentous feathers along the neck of Beipiaosaurus. See caption of Figure 1 for abbreviations. Scale bar is 5 cm.
Figure 12
Figure 12. Strict consensus (A) and 50% Majority-rule consensus (B) of the forty most parsimonious trees recovered in this study.
See Appendix 2 in File S1 for synapomorphies at each node.

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Grant support

This research was supported by JSPS KAKENHI Grant Number 24540494, the Natural Science Foundation of China (90914003; 40872017), and the Basic Outlay of Scientific Research Work from the Ministry of Science and Technology (2011-SYS-02). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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